C#: Introduction for Developers

C#: INTRODUCTION

FOR DEVELOPERS

Neal Stublen

nstublen@jccc.edu

Tonight’s Agenda

Interfaces Generics Code Organization Databases ADO.NET Datasets Q&A

CHAPTER 15

INTERFACES

What’s an interface? It’s like a class with…

No member dataAll methods are publicAll methods are abstract

An interface implies nothing about the implementation behind it

A class can only inherit from one class A class can implement multiple interfaces

Interfaces often represent only a portion of a class’ functionality

Why interfaces? Interfaces are better suited to situations in which

your applications require many unrelated object types to provide certain functionality

Interfaces are more flexible than base classes because you can define a single implementation that can implement multiple interfaces.

Interfaces are better in situations in which you do not want or need to inherit implementation from a base class.

Structures cannot inherit from classes, but they can implement interfaces.

Common .NET Interfaces

IComparableUsed to compare two objectsSorting algorithms

IDisposableFrees unmanaged resources when an

object goes out of scope If your classes implement these

interfaces, they can be used wherever these interfaces are specified

Example Interfacespublic interface IStreamable{ bool Read(FileStream inInput); bool Write(FileStream inOutput);}

public interface IHTMLDisplayable{ void Render(OutputStream inStream);}

Implementing Interfacespublic interface IStreamable{ bool Read(FileStream inInput); bool Write(FileStream inOutput);}

public class MyObject : IStreamable{ public bool Read(FileStream inInput) { } public bool Write(FileStream inOutput) { }}

Implementing ICloneable// Duplicate any cloneable objectpublic List<object> Duplicator(ICloneable src, int count){ List<object> list = new List<object>(); for (int index = 0; index < count; ++index) { list.Add(src.Clone()); } return list;}

Looking at IComparable

Any object that implements IComparable can be sorted with the generic Array.Sort() method

CHAPTER 15, PART 2

GENERICS

What’s a generic class?

A class definition that doesn’t explicitly declare all of the types it uses internally

Allows creation of new types by specifying those internal types later

Using Generic Types

Generic types are declared using <> after the type nameInstead of the general purpose interface:

IComparableUse the type-specific interface:

IComparable<T>

class Temperature : IComparableclass Temperature : IComparable<Temperature>

Generics Exampleclass Average<T>{ public void Include(T inValue);

public T Average { get { ... } }}

Average<int> integerAverage;Average<double> doubleAverage;

Updating IComparable

Instead of comparing generic objects, we can compare Temperature objects

Common Generics

Collection classesList<T>SortedList<K, V>

Enumeration (foreach)IEnumerable<T>IEnumerator<T>

Generic Constraintspublic class MyGeneric<T> where T: class{ // T is a class (can be assigned null)}

public class MyGeneric<T> where T: class, IComparable<T>{ // T implements IComparable interface}

public class MyGeneric<T> where T: struct{ // T is a struct}

public class MyGeneric<T> where T: new(){ // T has a default constructor}

CHAPTER 16

CODE ORGANIZATION

Code Organization

Multiple classes in a single fileClosely related classes (e.g. EventArgs)

Nested classesObjects that only exist within the context of

another type of object

Partial Classes

Split a single class over multiple filesForms split Designer code into separate filePossible to split interface implementations

into separate files Partial classes must have the same

visibility Partial methods split the declaration and

implementation across files

Namespaces

Organize classes into logical groupings Avoid type name collisions using <namespace> <namespace>.<ClassName>

Nested Namespaces

using ns1{ using ns2 { }}

using ns1.ns2{}

CHAPTER 16, PART 2

DOCUMENTING CLASSES

XML Documentation

Standardized documentation format for C# code

Type three slashes “///” before a method implementation or class member

<summary> tag is used by IntelliSense Processed by third party tools

DoxygenSandcastle

CHAPTER 16, PART 3

CLASS LIBRARIES

Class Libraries

Share class across multiple projects Projects “reference” other projects

Move SportsTeam into a class library

CHAPTER 17

DATABASE PROGRAMMING

Databases

Client-server architectureOne server, many clientsServer runs Microsoft SQL ServerClients use ADO.NET 4

Relational databasesSQL (Structured Query Language)

Tables

Tables store data One or more records (rows) A primary key uniquely identifies each

row Indexes provide an efficient way to

access data based on values in specific columns

“Relations” Among Tables Key columns are used to relate tables Foreign keys in one table correspond to

primary keys in another tableOne-to-manyOne-to-oneMany-to-many

Table Columns

Columns are defined by a name and data typebitchar, varchar, textdatetime, smalldatetimedecimal, numericfloat, realbigint, int, smallint, tinyintmoney, smallmoney

Column Values

null (maybe, maybe not – depends on column definition)

Default value Identity column (auto-increment) Constraints

SELECT

Select data from a databaseSELECT column_name,column_name FROM table_name;

SELECT * FROM table_name;SELECT title, publisher FROM books;

INNER JOIN

Select all rows from two table where specified columns have matching valuesSELECT column_name(s)FROM table1INNER JOIN table2ON table1.column_name=table2.column_name;

SELECT column_name(s)FROM table1JOIN table2ON table1.column_name=table2.column_name;

INNER JOIN is the same as JOIN

ADD, UPDATE, DELETE

Add a row to a table INSERT INTO table_nameVALUES (value1,value2,value3,...);

INSERT INTO table_name (column1,column2,column3,...)VALUES (value1,value2,value3,...);

Update a row in a table UPDATE table_nameSET column1=value1,column2=value2,...WHERE some_column=some_value;

Delete a row from a table DELETE FROM table_nameWHERE some_column=some_value;

Online Reference

Tutorials and referenceshttp://w3schools.com/sql

ADO.NET

ADO.NET

Data providers implement a common API to various database serversSQL ServerOLE DBODBCOracle

Third partyMySQLSQLite

Components

Database server .NET data provider

Connection○ Connects to a specific database

Command○ SELECT, UPDATE, etc.

DataReader, DataAdapter○ Help retrieve data from a query

Datasets

Store data in a disconnected cache Data source may be a database, XML

data, local application data Mimics the structure and behavior of a

relational database

Datasets Mimic Relational DB

Dataset contains a collection of tablesNot necessarily the same table from the databaseMay be a subset of columns and rowsMay be joined to another table

Tables contain a collection of columns Tables contain a collection of rows Tables contain a collection of constraints Dataset contains a collection of relations Everything is accessed through object

properties

Alternatives to Datasets

You can use Command and Connection objects directlySelect, Insert, Update, Delete

Database Concurrency Multiple clients accessing data ADO.NET datasets are “disconnected” Pessimistic concurrency

Lock database records to prevent conflicts Optimistic concurrency

Check for data changes before writingThrow an exception if data has changed

“Last in wins”Data is written by last operationData may be lost

Avoid Concurrency Issues Update and refresh datasets frequently Avoid updating large tables in datasets Only reduces risk!

You still must handle the exceptions

CHAPTER 18

CREATING DATASETS

DATABASE CHECK

Populating a Database

SQLExpress should be installed with Visual Studio

The book provides a .sql file for populating the MMABooks database in SQLExpress

Double-click the .bat file on the S: drive We’ll need to repeat this process at the

start of each class session

Confirm Database Access Using Visual Studio to locate the new

database as a Data SourceView > Server ExplorerAdd Connection...Server name: .\SQLEXPRESSDatabase name: MMABooksTest Connection

Using the Data Sources Window

Dataset Summary

Instead of a database, we can pull data from:WCF Data ServicesCustom objectsSharePoint

Entity FrameworkObject-relational mapping framework (ORM)Maps database table data to C# objects

○ Object instance represents a table row

View > Server Explorer

Dataset Summary

Connection strings can be stored in app.config

Allows reuse of the connection string A dataset can be modified in Visual

Studio to add tables, columns, etc. Visual Studio generates .xsd schema

files for the dataset

CHAPTER 18, PART 2

USING DATASETS

DataGridView Control

Bound control Table view of the dataset Multiple objects are added to the form

Other Bound Controls

Change default data control for table in Data Sources

Change default data control for columns in Data Sources

Behind the Scenes…

Load event is updated for the form Save click event is updated for the

binding navigator

Bound TextBox Controls

Formatting and Advanced Binding Select TextBox Open Properties Window Expand DataBindings property Select Advanced option, click “…”

Select new format type Specify representation of null value

Bound ComboBox Controls Populate a ComboBox with values from

a column of a database table SelectedItem is used to specify the

value in a column of another database table

Code Practice Select customer state using dropdown list

ComboBox instead of TextBox

Create StatesDataSet in Data Source window Add DataSet control for StatesDataSet and set

DataSetName property Add BindingSource control for DataSet and set

DataSource/DataMember properties Set State field to use ComboBox Set ComboBox to use data bound controls Clear ComboBox data bindings for Text property