XAML for WPF and UWPradar.zhaw.ch/~rege/dnet_fs19/dnet2_3.pdfXAML for WPF and UWP Programming...

XAML forWPF and UWP

■ Programming WPF/UWP application with XAML and C#

■ The structure and purpose of XAML and C# code (behind)

■ Layouts and Styles in XAML

■ Data Binding and Events

■ MVVM and Commands

2 von 171School of Engineering © K. Rege, ZHAW

WPFBasics

Differences between Forms and WPF

Difference of thinking and execution

WinForms

■ The Forms and UI Objects are the

application

WPF/MVVM

■ The application data objects are in the

center

■ The GUI is merely an access layer tothese objects

■ Separation of Presentation and

Logic/Date by design

WPF – Features

■ XAML/WPF has a set of "nice" features

https://www.tutorialspoint.com/wpf/wpf_quick_guide.htm

HelloXAML/WPF

Hello WPF

■ Project Setup with Visual Studio

■ Choose WPF App

… Hello WPF

■ Visual Studio generates a set of filesApp.xaml

App.xaml.cs

MainWindow.xaml

MainWindow.xaml.cs

■ The two App.* files contain the code for

the setup (resources) and start of theapplication

■ The two MainWindow.* files contain the

code for the main window of the

application

Involved Files in Overview and Context

FirstWPF.exeFirstWPF.exe

class Appclass App

App.g.csApp.g.cs MainWindow.Baml

MainWindow.Baml

MainWindow.g.i.cs

App.xamlApp.xaml App.xaml.cs

App.xaml.cs

MainWindow.xaml

MainWindow.xaml.cs

classMainWindow

Content of the App.xaml.* Files

■ The two files App.xaml App.xaml.cs contain the intialization

■ Start-Window (MainWindow.xaml)

</Application.Resources></Application>

namespace WpfApp {

public partial class App : Application {

Content of the generated App.xaml.cs File

■ The Main method is hidden in an also

generated partial class App.xaml.cs

■ should not be modified

class WpfApp : Application {

public static void Main() {

WpfApp.App app = new

WpfApp.App();

app.InitializeComponent();

app.Run();

■ InitializesComponent() Initialize thecontent of the main window

■ Main() start the application

Hello XAML

■ The two files MainWindow.xaml MainWindow.xaml.cd contain the main

Window code: enter the Label Hello Word as shown below

<Grid> <Label> Hallo World

</Label> </Grid></Window>

public partial class MainWindow : Window{public MainWindow (){

InitializeComponent();}

The Application Object

■ Every WPF application is represented by an instance ofWindows.UI.Xaml.Application

orWindows.Application

■ A singleton

■ The static property Application.Current returns that instance

■ The Visual Studio wizard creates a XAML file for the application

■ Useful for application level resources

■ Also can set the StartupUri property to indicate which window to show on

startup

… Application Events

■ Startup■ Called after Application.Run is called before the main window is shown■ Can access command line arguments through the StartupEventArgs.Args property■ Can also be used to create a window explicitly (and calling Window.Show) without relying on the

StartupUri property

■ Exit

■ Application is being shutdown (for whatever reason)■ Can set the exit code that is returned to the OS■ Cannot cancel the shutdown process

■ SessionEnding

■ Windows session is ending (e.g. log off or shutdown)

■ Can cancel the shutdown by setting SessionEndingCancelEventArgs.Cancel to true(otherwise WPF calls Application.Shutdown)

■ Activated

■ Occurs when a top level window in the application is activated when the user switches from anotherapplication

■ Also occurs the first time a window is shown

■ Deactivated

■ Occurs when the user switches to another application

■ DispatcherUnhandledException

■ Occurs when an unhandled exception is about to terminate the application■ Only on the current (UI) thread

■ Can be used to log the error, show a nice dialog to the user, etc.■ Can also “cancel” the exception and continue running by setting the property

DispatcherUnhandledExceptionEventArgs.Handled to true

■ Must be careful – difficult to guarantee the application is in a valid state to continue

Application Shutdown

■ Application shutdown is controlled by the ShutdownMode property■ OnLastWindowClose (default) – application shuts down when the last top level window is closed

■ OnMainWindowClose – application shuts down when the main window closes

■ OnExplicitShutdown – the application does not shut down even if all windows are gone

■ Calling Application.Shutdown must be used

■ This call can be used regardless of the setting of the ShutdownMode property

UI Designer and XAML Fundamentals

■ Visual Studio■ UI Designer

■ Toolbox

■ Document Outline

■ Properties View

■ What is XAML?

■ Basic XAML

■ Type Converters

■ Markup Extensions

■ Naming Elements

■ XAML Rules

■ Summary

Visual Studio

UI Designer

■ Visual Studio UI Designer provides quick

and easy way to produce rich UI

interface

■ Drag and drop UI controls from thetoolbox into the designer

■ The UI designer provides an easy way to

select, resize, align, transform and more,

using only the mouse

■ The UI designer generates XAML andautomatically updated when XAML

changes

Toolbox

■ The toolbox groups UI controls available

at design time

■ 3rd party and custom controls are also

available from the toolbox

■ Simple drag and drop a control from thetoolbox to the designer canvas

■ Element from the toolbox can be also

drag and drop directly into XAML

■ Controls can be searched within the

search box and can be sorted

■ Additional groups can be created

Document Outline

■ The document outline view displays thelogical tree of UI elements, each elementname or type and an icon of theelement’s type

■ Each element in the hierarchy can bedesign-time locked and hidden

■ The document outline is very useful tonavigate between UI elements,especially in complex XAML files

view other windows Document Outline

Properties View

■ The properties view provides an easy arapid way to:

■ Search for an element’s property by its name■ Set simple property value using plain text■ Set complex property value using designers■ Easily select color brushes, styles, font size,

transformations and more■ Register element’s events■ Arrange properties in groups■ Create data bindings■ Reset to default values

What is XAML

What is XAML?

■ XML based language■ Enable separation of UI and behavior (code)

■ XAML allows■ Creation of objects■ Setting of properties■ Connection to events

■ but XAML cannot be executed or call methods directly■ Code behind in C# is used instead

XAML vs. Code

■ Anything that can be done in XAML can be done in code■ But not vice versa

■ XAML is usually shorter and more concise than the equivalent code■ Thanks to type converters and markup extensions

Natural Separation of XAML and Code

■ XAML should be used for initial UI

■ Code will handle events and change items dynamically

Correspondence of XAML and Code

■ Visual Studio UI designer generates XAML on each control

picked from the toolbox

■ XAML can be visually viewed and modified in the UI designer

<Buttonxmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation" Content="OK" />

Windows.Controls.Button b = newWindows.Controls.Button();()b.Content = "OK";

XAML vs. Code

■ For the GUI specification XAML is usually more readable/shorter than the

corresponding C# code

■ But the result will be the same:

XAML for WPF and UWP

■ The XAML Code looks very similar, but top level element is■ Window for a WPF■ Page for UWP

■ If XAML maps to WPF or UWP classes is defined by the mapping of the XML

Elements to the according library classes

■ For WPF

■ For UWP

using System;using System.Windows;using System.Windows.Controls;

using System;using Windows.ApplicationModel.Activation;using Windows.UI.Xaml;using Windows.UI.Xaml.Controls;

XAML Namespaces

■ The default XAML namespace is assigned a value that is mapped to some of theruntime namespaces contain UI elements

■ The “x” namespace is mapped to a special namespace, contains XAML parserspecific types

■ Other XAML namespaces may be mapped to custom namespaces and otherruntime namespaces

■ XAML namespace can be defined on each element level and other customnamespaces can be included

<Window xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation" xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"

default Namespacedefault Namespace

x Namespace all elementswith x: prefix

Elements and Attributes

■ Elements with type names designate objects, created via the defaultconstructor

■ i.e. Name of the Element correspond to the library class instantiated

■ Attributes indicate property or event values■ Event values are event handlers (methods) names

■ Child elements are used (besides other) for Complex properties using a<Type.Property> notation

Complex PropertyComplex Property

Properties of ButtonProperties of Button

XAML and its Code Behind

■ A root element, usually Page or Window classes, can have code behind file

■ The name of the code behind file is correlated to the XAML file name

■ For example: MainPage.xaml and MainPage.xaml.cs

■ The code behind full class name is specified from XAML using

the x:Class directive

Window for WPFWindow for WPF

Child Elements

Child elements that are not simple Content can be one of

■ A value - often specifiable as Attribute if convertible to String

■ The Complex Content property of the object

■ Collection items

■ The object implements IList or IDictionary

Content Property - A Value

■ A single property that is designated with the ContentProperty attribute on the

type can be specified in different ways

a Value as Childa Value as Child

a Value as Content Attributea Value as Content Attribute

Content Property as ChildContent Property as Child Content Property as ChildContent Property as Child

Collection Items

■ List (IList)

■ Dictionary (IDictionary)

Summary of XAML Rules

■ XML Element – create a new instance

■ XML attribute – set a property (as String) or register an event■ ContentProperty attribute for simple properties that are strings<Button content = "Hallo" />

■ Type.Property – set a “complex” property<Button>

<Button.Content>

</Button.Content>

</Button>

■ Complex Property of type IList or IDictionary

■ Add child elements (XAML calls appropriate Add method)■ Need a x:Key in case of a dictionary

Parsing and Using XAML

■ Visual Studio compiles the XAML file to BAML (Binary XAML) and embeds it as

a resource

■ The BAML is parsed at runtime and the object tree created by the generatedInitializeComponent method

Naming Elements and Code Behind

■ Elements can be named using the x:Name XAML attribute

■ The code-behind file will contain a field with that name

■ e.g. A Label defined with x:Name "label1" can be referenced in the code-

behind as follows

XAML Keywords of x Namespace

Keyword Valid on Meaning

x:Class Root element The code behind class that derivesfrom the element type

x:ClassModifier Root element, must beused with x:Class

The class visibility (public by default)

x:FieldModifier Element, must be usedwith x:Name

Visibility of the field created behindthe element

x:Key Element that its parentimplements IDictionary

Key in a dictionary

x:Name Element The element’s name, used for a fieldname for that element

x:Type Element Give the type of the element e.g. fortests like TargetType = "{x:TypeButton}

Summary

■ XAML is used to define a Windows App user interface

■ It declaratively allows object creation, property and event assignment

■ A code-behind file will usually contain the logic

Basic Concepts

Agenda

■ Logical and Visual Trees

■ Dependency Properties

■ Attached Properties

■ Routed Events

■ Attached Events

■ Resources

■ Summary

Logical and Visual Trees

PagePage

StackPanelStackPanel

ButtonButton ListBoxListBox

ListBoxItemListBoxItem ListBoxItemListBoxItem

BorderBorder

TextBlockTextBlock

Logical Tree - Defined Structure

■ A tree of elements/controls making up the user interface;■ the essential structure of your UI.■ closely matches the elements you declare in XAML, and excludes most

visual elements created internally to help render the elements you declared.■ used to determine dependency property value inheritance,

resource resolution, etc.

<Page x:Class="UWPDemo.MainPage"

xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"> <StackPanel> <Button

Content="OK" Background="Red" Margin="6"/> <ListBox Margin="6" > <ListBoxItem Margin="2"> <Border BorderThickness="4"> <TextBlock

Text="Hello" FontSize="20" /> </Border> </ListBoxItem> <ListBoxItem Content="Item 2" /> </ListBox> </StackPanel></Page>

"Live" Visual Tree - Actual Tree

■ The actual visual objects that are making

up a logical tree■ Generated from the control template■ Can be inspected in

■ programmatically■ by a Tool in Debug Mode

■ Live Visual Tree Tool allows to observe

XAML visual tree in runtime

■ review properties of elements

■ change properties in runtime

■ without restarting application itself.

Traversing the Trees at runtime

■ The logical and visual trees can be examined programmatically using the staticclasses System.Windows.LogicalTreeHelper andWindows.Media.VisualTreeHelper

■ VisualTreeHelper■ GetParent, GetChild, GetChildrenCount

■ LogicalTreeHelper■ GetParent, GetChildren, GetChildrenCount

Properties

■ Properties are the values that are stored with the various XAML Elements

■ Each Element may have quite a lot of them

■ A XAML GUI may have hundreds of Elements■ Thousands of Properties■ For each Property (used or not) memory has to be provided

PropertiesPropertiesPropertiesPropertiesPropertiesPropertiesPropertiesProperties

Custom (CLR) Properties in a separate Class

■ For this, first a new Class Library with the class has to be created

■ Then a new Namespace is introduced (reference to Assembly in Project!)

namespace DataLib { public class Person { public string FirstName { get; set; } public string LastName { get; set; } public override string ToString() => $"{FirstName} {LastName}";

<Window x:Class="WpfApp2.MainWindow" ... xmlns:datalib="clr-namespace:DataLib;assembly=DataLib" ... mc:Ignorable="d" Title="MainWindow" Height="450" Width="800"> <StackPanel> <Label>Hello World</Label> <ListBox> <datalib:Person FirstName= "Stephany" LastName = "Nagel" /> <datalib:Person FirstName= "Matthias" LastName = "Nagel" /> </ListBox> </StackPanel></Window>

CLR PropertiesCLR Properties

Disadvantage of CLR Properties

■ The container for the Properties is an Object

■ Thus, for every Property the according memory space has to be provided,

independently of its usage

■ As mentioned, XAML defines thousands of properties■ thus a XAML GUI would waste a considerable amount memory

■ -> For XAML a special type of Properties has been introduced:■ Uses less Memory■ Support Change Notification Events

■ The Dependency Properties

Dependency Properties

■ Dependency properties are the "workhorse" of any XAML based technology

■ Dependency Property can used over a CLR property in the following scenarios■ If you want to set the style■ If you want data binding■ If you want to set with a resource (a static or a dynamic resource)■ If you want to support animation

■ Are be registered by calling the DependencyProperty.Register method

■ Almost all WPF properties are dependency Properties

Advantages of Dependency Properties

■ Dependency Properties vs CLR Properties

■ CLR properties can directly read/write from the private member of a class by

using getter and setter. Thus, for every property used or not, the accordingmemory space has to be provided

■ In contrast, dependency properties are not stored in local objects■ saves memory because it stores the property only when accessed.

■ Dependency properties are stored in a dictionary of key/value pairs instead■ that is provided by the DependencyObject base class.

■ Dependency Properties may generate an Event that is fired when they are

changed (-> Data Binding)

WPF Dependency Properties

■ Sample of some application of Dependency Properties in WPF■ since almost all properties in WPF are Dependency Properties anyway

■ Shows a button and when mouse hovers over it, text turns red

Custom Dependency Properties

■ The Names of the property are defined in the registration, e.g. "Value"

■ The Values itself are stored in a Collection handled by the base class■ The Values are always accessed by the Get/Set Method

■ via a reference to a static DependencyProperty variable■ the redundant CLR "Value" here is merely for convenience in the C# Code

■ With the registration also the type of the property, type of the owner, the initial

value are specified, and when an Event is fired. public class MyDependencyObject : DependencyObject { public int Value { get { return (int)GetValue(ValueProperty); } set { SetValue(ValueProperty, value); } }

public static readonly DependencyProperty ValueProperty = DependencyProperty.Register("Value", typeof(int),

typeof(MyDependencyObject), // owner new PropertyMetadata(0, OnValueChanged)); } }

Attached Properties

■ Special kind of dependency properties

■ May be “attached” to objects of different types than the declaring type■ Declared with the static DependencyProperty.RegisterAttached method

■ Allows “context” properties■ E.g. Canvas.Left for elements that happen to be in a Canvas element

■ Can be set on any object

■ XAML■ An attribute with Type.Property syntax is used

■ In code■ The type exposes a SetXxx and a GetXxx with the element reference

Attached Properties Example

■ XAML

■ Code

Canvas.SetLeft(cmdOK, 30);Canvas.SetTop(cmdOK, 20);

cmdOK.SetValue(Canvas.LeftProperty, 30);cmdOK.SetValue(Canvas.TopProperty, 30);

Layout

■ Layout is the arranging of user interface elements within some container

■ Older technologies (e.g. Windows Forms) exact position and sizes may be

applied■ Limited in flexibility and adaptability■ However:

■ By use of Forms Anchors, etc also flexible layout is feasible■ With the Canvas also absolute positioning is possible

■ XAML provides several layout panels that can control dynamically size and

placement of elements

■ Elements may advertise their size and position needs

Size and Position of Elements

■ Element sizing and positioning is determined by■ the element itself■ its logical parent

■ A child element may request various settings

■ But the parent panel does not have to comply

Element Layout Properties

Margin

ContentContent

Padding

VerticalAlignment

Height

LayoutTransformFlowDirection

Element/ControlHorizontalAlignment

■ XAML Elements define various Properties to give hints to their container for their

sizing and positioning (i.e. Layout)

Element Size

■ Width and Height properties (from Base Class FrameworkElement)

■ Control the exact size of the element

■ Default value is Double.NaN

■ Meaning: be as large as it needs to be

■ usually a bad idea to use these properties

■ Prevents smart resizing by panel

■ Reasonable only in a Canvas

■ Use MinWidth, MinHeight, MaxWidth, MaxHeight instead

■ Defaults are 0 for MinWidth, MinHeight

■ Double.PositiveInfinity for MaxWidth, MaxHeight

“Infinity” in XAML“Infinity” in XAML

More Size Related Properties

Read only properties

■ DesiredSize

■ Set indirectly by elements to report their desired size to their parent

■ Internally used by panels

■ RenderSize

■ The actual size the element is rendered with

■ ActualWidth, ActualHeight

■ Just the components of RenderSize (RenderSize.Width, RenderSize.Height)

Margin and Padding

■ Both of type Thickness (value type)■ Maintains the properties Left, Top, Right, Bottom indicating distance from the corresponding

■ Margin

■ The amount of space to add around the element

■ Padding

■ The amount of space to add around the content of the control

Visibility

■ Visibility of elements is determined by the Visibility property (from

UIElement) of the Windows.Visibility enumeration■ Visible

■ The element is rendered and participates in layout■ Collapsed

■ The element is invisible and does not participate in layout

Element Positioning

■ Finally, element position is determined by the containing panel policy■ Simple X,Y is possible but is not the usual case

■ Elements can indicate their position constraints or preferences to their containingpanel

Layout Panels

■ Layout panels derive from the abstract Windows.Controls.Panel class

■ Each child element can be a panel as well■ Allows creation of complex and adaptive user interfaces

■ WPF provides several built in panels with specific Layout policies

■ Custom layout panels can be created as well

WPF Layout Panels

■ Main layout panels are

■ Canvas

■ Arranges children in a 2D coordinate system

■ StackPanel

■ Arranges children in a horizontal or vertical “stack”

■ DockPanel

■ Arranges children horizontally or vertically to each other towards the edges

■ WrapPanel

■ Arranges children continuously horizontally or vertically, flowing to the next row/column

■ Grid

■ Arranges children in a flexible grid

Canvas

■ Canvas is the most simple layout

■ All the controls are positioned absolutely

■ Cartesian xy-Coordinate are applied

■ Canvas provides the embedded components with attributes Canvas.RightCanvas.Left, Canvas.Top Canvas.Bottom

■ Height and Width are set by the embedded control elements

Canvas Example 1

Canvas Example 2

The StackPanel

■ Stacks its elements in a vertical or horizontal “stack”

■ Orientation property■ Vertical (default) or Horizontal

■ Alignment is ignored in the direction of stacking

Alignment

■ Alignment indicates what should be done with any extra space given to an

element

■ HorizontalAlignment■ Left, Right, Center, Stretch

■ VerticalAlignment■ Top, Bottom, Center, Stretch

<Button HorizontalAlignment="Center" Background="Orange">Center</Button>

<Button HorizontalAlignment="Right" Background="Yellow">Right</Button>

<Button HorizontalAlignment="Stretch" Background="Lime">Stretch</Button>

</StackPanel>

Content Alignment

■ Similar to element alignment

■ What to do with extra space when the content is smaller than its control

■ HorizontalContentAlignment

■ VerticalContentAlignment

<Button HorizontalContentAlignment="Center" Background="Orange">Center</Button>

<Button HorizontalContentAlignment="Right" Background="Yellow">Right</Button>

<Button HorizontalContentAlignment="Stretch" Background="Lime">Stretch</Button>

</StackPanel>

Westboro Baptist Church Kan.Westboro Baptist Church Kan.

Flow Direction

■ The FlowDirection property indicates the flow of layout■ LeftToRight (the default)■ RightToLeft

■ The RightToLeft setting reverses the meaning of “left” and “right”

The Grid

■ The most versatile and useful panel

■ Usually used as the top-level panel■ Visual Studio and Expression Blend windows/user controls start this way

■ Arranges its children in a multi-row and multi-column way■ Their sizes and number can be manipulated in interesting ways■ Somewhat similar to an HTML table

Creating a Grid

■ For rows■ Set the RowDefinitions property■ Add a RowDefinition object for each row

■ Set any special properties

■ For columns■ Set the ColumnDefinitions property■ Add a ColumnDefinition object for each column

■ Set any special properties

■ For each element■ Set the Grid.Row and Grid.Column attached properties (default is 0, 0)

Sizing Rows and Columns

■ By default, all rows are of equal height and all columns are of equal width■ Can change the height of a row using the RowDefinition.Height property

■ Can change the width of a column using the ColumnDefinition.Width property■ Each one of type GridLength■ The unit is controlled by the GridUnitType property

■ Auto – size as required by content

■ Pixel – size is the number specified■ Star – size is a weighted proportional (default)

■ “*”, “2*”, etc. in XAML■ Spanning

■ A row may span more than one column and vice versa■ Can be set by the Grid.RowSpan and Grid.ColumnSpan attached properties

■ Default for both is 1

Example:

■ Example of Form with GridPanel

<Grid.ColumnDefinitions> <ColumnDefinition Width="Auto" /> <ColumnDefinition /> </Grid.ColumnDefinitions>

<Grid.RowDefinitions> <RowDefinition Height = "*" /> <RowDefinition Height = "*" /> <RowDefinition Height = "*" /> </Grid.RowDefinitions>

<TextBox Grid.Row = "0" Grid.Column = "1" Margin = "10"/> <TextBlock Grid.Row="1" Grid.Column="0" Text="ID" Margin="10"

HorizontalAlignment = "Left" VerticalAlignment = "Center" Width = "100"/>

<TextBox Grid.Row = "1" Grid.Column = "1" Margin = "10"/> <TextBlock Grid.Row = "2" Grid.Column = "0" Text = "Age"

Margin = "10" HorizontalAlignment = "Left" VerticalAlignment="Center" Width = "100"/>

</Grid>

as height asthe control

stretchesremaining space

Controls

What is a Control?

■ Controls are elements capable of receiving focus and handling input■ Behavior is the distinction, not looks

■ Many controls are available “out of the box”

■ Also new, individual controls can be created■ User controls that wrap one or more controls and expose higher level properties■ Custom controls that derive from an existing control and extend its functionality

Simple Example: Static Text

■ The TextBlock (Control-)Element■ The Text property■ Font related properties

■ FontSize, FontFamily, etc.■ TextAlignment, TextTrimming, TextDecorations

■ An optional collection of “inlines”■ Replacement for the Text property■ Inheriting from the abstract Inline class

■ Hyperlink, Bold, Run, Span, Underline, Italic, LineBreak

Example: TextBlock

<TextBlock FontSize="16" Margin="4"> <Run Text="Hello" /> <Bold> Hello <Italic>Hello</Italic> </Bold> <LineBreak /> <Hyperlink>Go to my web site</Hyperlink> <LineBreak /><LineBreak /> <Underline>This line is underlined</Underline> <LineBreak /> <Span FontSize="20"> Hello in Bigger Font </Span></TextBlock>

■ A structured Text à la HTML cdn be composed within a TextBlock

Other Controls

https://msdn.microsoft.com/en-us/library/windows/apps/mt185406.aspx

Styles

■ Styles are used to specify the appearance of the Elements itselfs

■ Usually defined as a resource

■ Can be applied to any element with the Style property

■ Any specific property changed by the element that conflicts with the style takesprecedence over the style setting

Style Example

<Page x:Class="Demo.StyleWindow"

xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"

xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"

Title="Style Demo" SizeToContent="WidthAndHeight">

<Window.Resources>

<Setter.Value>

</Setter.Value>

</Setter>

</Style>

</Window.Resources>

</StackPanel>

</Page>

Restricting Style Usage

■ A style may be restricted to work on certain types using the TargetType

property■ And on any derived types

■ In this case, the full property qualification is unnecessary

Implicit Styles

■ With the TargetType property the x:Key attribute may be omitted

■ The style will automatically apply to all elements of the specified type■ The exact type only (not a derived type)

■ Elements can still override properties or use a different style, or clear the style bysetting it to null

Data Binding

What is Data Binding?

■ Data in WPF can reference any .NET object

■ Data binding means tying two arbitrary objects

■ Typical scenario is a non-visual object (or collection) to a visual element

■ Any changes to the non-visual object are reflected in the visual element (and

optionally vice versa)

Data Binding Concepts

■ Source■ The data object to bind to

■ Property Path■ The property on the source object to use■ May be a nested property, an array element or an indexer

■ Target■ The target object to modify■ Must be a dependency property

■ Binding Mode■ Typically one way or two way (target update source)

Using Data Binding

■ Typically done in XAML using the {Binding} markup extension■ The Binding class is the workhorse behind the scenes■ Set on the target property

■ Can be done programmatically in code■ Common scenario is when building custom Control

■ Supported by Visual Studio

Example 1: Element Binding Label to TextBox

■ The content of the label should be

dependent of the content of a Textbox

■ In the property window chose the label

and specify the content

■ Click the black rectangle and a pop upwindow appears

… Element Binding Label

■ Choose the line «create data binding»

the window below appears. We choose

for binding type the "ElementName"

■ With «ElementName» anther selection

appears and the Textbox is chosen

… Element Binding Label

■ For «Path» we choose the entry «Text:

(String)» and press ok.

■ The XAML code is generated

accordingly

Result

■ After the start of the application the entered content of the TextBox and the label

are synchronized.

Example 2: Bind Label to a ListBox entry

■ The selected item in the ListBox should be shown in the label

… Bind Label to ListBox entry

■ Proceed as before but choose ListBox this time

Generated Code of the Property Editor

The generated code is not yet completeand has to be fixed in the XAML file

Add "Content" to Fix Code

Or Use C# Code instead

■ Alternatively the data binding can also be specified programmatically

The Binding Class

■ Is used to connect■ a Data Target (usually a WPF-Element) and■ a Data Source (e.g. an arbitrary Data Object, a DataBase, an XML Data Structure)

… The Binding Class

■ A Binding comprises a binding targed (with additional constraints) a bindingsource with additionally the path to the value of the source. This binding can be

specified by XAML or by C# code.

■ In XAML a binding is created by <Binding ….> e.g.

■ In C# the binding object is a instatiation of the binding class

Example 1: Data Binding to a C# Person Object

■ The state of a Model should automatically be synchronized with the View

The Data Source: The Class Person

Instantiate Object and define Data Source

Specify Binding in the XAML Code

Result

■ The state (values) of the Model is synchronized with the view

■ Any Change in the TextBoxes is passed to the Model

Example 2: The Class Inscription

… The Class Inscription

Binding in the XAML Code

The Different Syntaxes of the Binding Element

■ Given a DataContext MyRecord

■ The three binding syntaxes (below) function identically:

https://blogs.msdn.microsoft.com/jerrynixon/2012/10/12/xaml-binding-basics-101/

The Binding Properties

Property Meaning

ElementName Specifies the name of the data source

Path Path ist the Property to which the data are bound: (Content,Value, Text, …)

Mode Define Binding Direction, e.g. One Way etc.

Converter Defines the object that is used for conversion

Source Reference to the source object

UpdateSourceTrigger

Defines when data should be actualized (e.g. every time somedata value has changed)

Binding Mode i.e. Direction

■ The Mode attribute allows specifying how the target / source properties are

updated

■ Mode property (of type enum BindingMode)

Binding Mode Meaning

OneWay The target property is updated by source property changes

TwoWay OneWay + the source property is updated by changes of thetarget property

OneWayToSource Similar to OneWay, but from target to sourceFor source properties that are not dependency properties

OneTime Target is updated by the source the first time they are bound

Default Depends on the target property.TwoWay for user settable properties, OneWay for everythingelse.This is the default value

Update Trigger Modes

■ Updates from the source property to the target property happen immediately

■ In a TwoWay or OneWayToSource bindings, the source is updated by the target

based on the UpdateSourceTrigger property

UpdateSourceTrigger Meaning

PropertyChanged The source is updated whenever the target changes

LostFocus The source is updated when the target property’s element loses focus

Explicit The source is updated only when the methodBindingExpression.UpdateSource is called

Default Depends on the target property(FrameworkPropertyMetadata.DefaultUpdateSourceTrigger property)

Binding to Objects

■ The Object that content is used can be specified

■ Explicitly via Source Property in Binding■ Reference to the source name in the Binding

■ Implicitly by the DataContext■ Used by default if Source or RelativeSource is not specified

■ RelativeSource (not covered here)■ Sets the source based on the “location” of the target in the layout tree■ Useful in data and control templates

Model Change Notifications

■ If data source object properties are changed from e.g. another view

■ An object that act as a data source must notify the view(s) when one of its

properties changes

■ Simple: By defining the property as a dependency property■ The notification mechanism is built in

■ Or by implementing the INotifyPropertyChanged interface■ Raise the PropertyChanged event

■ Will be covered later together with the event handling

EventProcessing

Introduction

■ An Event is fired when the state of the GUI or underlying data (or application)

has changed. Events may indicate:■ A button has been clicked■ The Text of a Textbox has changed■ The Size of a Window or Control has changed■ The Mouse Pointer has moved■ ….

■ For every Event the registered Event Listeners are notified

Some Important Events

■ Press of a mouse button results in a Click-Event.

■ A focusable component (Button, Text-Component, Window, …) has been clickedi.e. activated (GotFocus).

■ Another component has been clicked; the formed component lost is focus

(LostFocus)

■ The content of a TextBox has changed (TextChanged)

■ ...

Example 1: Attach a Click-Event to a Button

… Attach a Click-Event to a Button

Example 2: Mouse-Event: MainWindow.xaml

… Mouse-Event: MainWindow.xaml.cs

Example 3: Property Changed Event

… Property Changed Event

… Property Changed Event: Code Behind

… Property Changed Event: Data

… Property Changed Event: Fire Event

… Property Changed Event

The Events Fired

MVVM and Commands

The MVVM Pattern

■ Model – View – ViewModel

■ Based on similar principles of Model View Controller (MVC) and ModelView Presenter (MVP)

■ Natural pattern for XAML based applications■ Data binding is key

■ Enables developer-designer workflow

■ Increases application portability

ModelModel

ViewView ViewModelViewModel

Commands,Properties,Behaviors

Methods,Properties

ModelModelModelModel

Events

While MVC's Control is Modelindependent the ViewModel ismodel specific

MVVM Participants

■ Model - the data container (also persistent data e.g. data base)■ Business logic and data

■ May implement change notification for properties and collections

■ View - the data presenter■ Data display and user interactivity

■ Implemented as a Page or Window or custom control

■ Has little or no code behind

■ ViewModel - the data processor■ UI logic and data for the View

■ Abstracts the Model for View usage

■ Exposes commands (ICommand) to be used by the View

■ Implements change notifications

■ Maintains state for the View (communicates via data binding)

While MVC's Control is Modelindependent the ViewModel isheavily model specific

The View (written mainly in XAML)

■ Provides the user interface and interaction

■ The DataContext property points to the View Model

■ Updated using property changes from the ViewModel

■ Binds to commands (on ICommandSource elements) provided by the

ViewModel

The ViewModel (written in C#)

■ Exposes properties the View binds to

■ Most of the functionality is implemented here

■ Can be an adapter if some functionality missing from Model classes

■ Exposes commands to be invoked by the view

■ Maintains state for the View

■ Notifies View of changes■ Uses Dependency Properties■ Implements change notifications (INotifyPropertyChanged)■ Uses e.g. ObservableCollection<T> that already implements INotifyCollectionChanged

Wiring the View and the View Model

■ The View’s DataContext must be set to its supporting ViewModel

■ Some options■ The View can create an instance of the right VM (even in XAML)■ The ViewModel can be injected using some dependency injection technique (e.g. Unity or MEF)■ Use some global ViewModel locator object■ A Main VM can be set explicitly on the main View, and other VMs can be exposed as properties,

which will be bound by child views

The Model (written in C#)

■ Responsible for data access (storage), e.g.■ Data Transfer Objects (DTO)■ POCOs (Plain Old CLR Objects)■ Generated entity objects■ Generated proxy objects

■ May provide change notifications

■ Provides validation if appropriate

Commands

Introduction to Commands

■ Handling events and executing some code is fine for simple applications

■ Sometimes the same code needs to execute from unrelated events (e.g. mouse

click, keyboard shortcut, menu item, toolbar)

■ Maintaining UI state (e.g. enabled/disabled) becomes difficult

■ Higher level functionality, such as an undo / redo system is not possible

■ Solution: use commands (the “Command” design pattern) with some support

from WPF

The Command

■ A command is an object implementing theSystem.Windows.Input.ICommand interface

public interface ICommand { event EventHandler CanExecuteChanged; bool CanExecute(object parameter); void Execute(object parameter);}

Commands for MVVM

■ MVVM frameworks typically provide a basic ICommand implementation that uses

a delegate■ Class typically call DelegateCommand

■ Using commands in MVVM

■ Some controls expose a Command and CommandParameter properties that can

be bound to a command exposed by the ViewModel■ e.g. ButtonBase, Hyperlink and MenuItem expose these

Some Command are Predefined

■ For TextBoxes are the some Command already implemented

Use of Predefined Commands

■ To Use these Commands only the according Name has to be specified

Write Custom Commands

■ Write the according Commands in the Code Behind File

… Write Custom Commands

■ In the XAML File define the according Command Binding

Summary

■ Commands allow high level segregation of tasks

■ The MVVM pattern is common in WPF to separate logic from UI and increase

testability

Asynchronous Event Processingin WPF

Asynchronous Operations

■ WPF, like other UI technologies, is single threaded (STA)

■ but long operations may freeze the UI

■ < 10 Seconds -> change cursor

■ >10 Seconds, < 5h: provide a Dialog with a progress indicator (also offer cancel option)

■ > 5h Play Video "Lord of the Ring "

■ Use Async Event Handler

https://stackoverflow.com/questions/1568557/how-can-i-make-the-cursor-turn-to-the-wait-cursor

view.OnRefreshClicked += new EventHandler(async (s, e) => await RefreshObjectExplorerAsync());

Using the Dispatcher (see last lecture)

■ Asynchronous operations on the UI thread can be scheduled using the

Dispatcher object responsible for that UI thread

■ Accessible using Dispatcher.CurrentDispatcher static property if on the UI thread

■ Or by calling DispatcherObject.Dispatcher instance property (which is inherited by all WPF

elements)

■ Or use AsyncHelper extension methods (see last lecture)

■ An operation can be scheduled using the Invoke or BeginInvoke methods■ Accept at least a delegate and an optional DispatcherPriority■ .NET 4.5 also adds InvokeAsync variants

■ DispatcherPriority enumeration■ Indicates the priority to process the operation■ Lower priorities can assume higher priority operations have already completed■ Default is DispatcherPriority.Normal

Updating the UI (see last lecture)

■ When doing work on a background thread (either explicitly created or using the

thread pool or task), some result may need to update WPF elements■ Accessing the object directly will cause an exception

■ Need to marshal the required operation to the UI thread using the Dispatcher■ Call Invoke (for synchronous invocation) or BeginInvoke/InvokeAsync (for asynchronous

invocation)■ Specify a priority for the update operation (usually DispatcherPriority.Normal)

Questions?

Uff!Yeep!

Binary Ressources

Binary Resources

■ The resources that can be used by any .NET application■ Usually store bitmaps, icons, etc.

■ Packaging■ Embedded inside an Assembly■ Loose files that are known to the application at compile time■ Loose files that are not known to the application at compile time

■ May be localized

Defining Binary Resources

■ Binary resources can be embedded using Visual Studio by adding theresource and selecting an action type

■ Resource■ Embedded inside the assembly

■ Content■ Remains as a loose file, but an AssemblyAssociatedContentFile attribute is

added with the relative path of the file

■ Don’t use the Embedded Resource■ WPF can’t use such resources

Accessing Binary Resources

■ Binary resources that are added to the project as Content or Resourcecan be referenced easily, even if loose files are involved (as long as they

are in the folder of the executable or a subfolder)

<Button VerticalAlignment="Center" HorizontalAlignment="Center" > <StackPanel Orientation="Horizontal" > <Image Source="apple.png" Width="48" Height="48" Margin="4"/> <TextBlock Text="This is an Apple" FontSize="24"

VerticalAlignment="Center" Margin="4"/> </StackPanel></Button>

Data Templates

■ A data template is a piece of UI that describes how to display a source object

■ Various elements have properties of type DataTemplate just for this■ ContentControl has a ContentTemplate property■ ItemsControl has a ItemTemplate property■ HeaderedContentControl and HeaderedItemsControl have a HeaderTemplate property

■ With data binding, the source object is automatically set to the current object that

is being rendered

public interface IValueConverter {

object Convert(object value, Type targetType, object parameter, CultureInfo culture);

object ConvertBack(object value, Type targetType, object parameter,

CultureInfo culture);

Value Converters

■ A value converter can completely alter the way the source is interpreted into the

target

■ Often used to match source and target that are of incompatible types■ E.g. show a red background when the price of a book is greater than 50

■ A value converter implements the IValueConverter interface

■ Create an instance of the converter as a resource and use in a bindingexpression

public interface IValueConverter {

object Convert(object value, Type targetType, object parameter, CultureInfo culture);

object ConvertBack(object value, Type targetType, object parameter,

CultureInfo culture);

Converter Parameters

■ The “parameter” object is null by default■ Can be set using the ConverterParameter property of the Binding object

■ Not “bindable” in itself!

■ The culture info supplied is by default set to “en-US”■ A type converter exists that can be used via the ConverterCulture property of the Binding object

(e.g. “fr-CA”, “he-IL”)

■ The return value can be Binding.DoNothing, which cancels the binding

operation

Data Template Selectors

■ A way to replace a data template completely■ Cannot be done in XAML alone

■ Derive a class from DataTemplateSelector

■ Override the SelectTemplate method

■ Set the ItemTemplateSelector property on the ItemsControl element to

an instance of the custom template selector

Data Template Selector Example

<Window.Resources>

<local:AlternateTemplateSelector x:Key="tmpselect" EvenTemplate="tmp1" OddTemplate="tmp2" />

</DataTemplate>

</DataTemplate>

</Window.Resources>

<ListBox Name="list" ItemTemplateSelector="{StaticResource tmpselect}"

HorizontalContentAlignment="Stretch"/>

public class AlternateTemplateSelector : DataTemplateSelector { public string OddTemplate { get; set; } public string EvenTemplate { get; set; } public override DataTemplate SelectTemplate(object item, DependencyObject container) { return (DataTemplate)((FrameworkElement)container).FindResource(

(int)item % 2 == 0 ? EvenTemplate : OddTemplate); }}

var data = new List<int>();Random r = new Random();for(int i = 1; i < 100; i++) data.Add(r.Next(1, 100));list.ItemsSource = data;

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