Control EventsC# and the .NET Platform, Second Edition

}

C# and the .NET Platform, Second Edition

}

Apress © 2003 (1200 pages)

When you run thisThisapplication,comprehensiveyou aret xtablestartsto confirmwith a briefthe overviewcoordinatesof theof your Form via the Bounds property. C# language and then quickly moves to key technical and

architectural issues for .NET developers.

Now, let's retrofit your class to override the inherited Dispose() method (this is done automatically when using VS .NET). As you recall from earlier in this chapter, the Application object defines an event named

TableApplicationExitof C ntents. If you configure your Form to intercept this event, you are effectively informed of the C#destructionand the .NETof thePlatform,applicationSecond. AsEditiona (much) simpler alternative, you can achieve the same effect by simply

Introductionoverriding the Dispose() method. Do note that you should call your base class' Dispose() method before

Partexiting:One - Introducing C# and the .NET Platform

Chapter 1 - The Philosophy of .NET

Chapter 2 - Building C# Applications

protected override void Dispose( bool disposing )

Part Two - The C# Programming Language

{

Chapter 3 - C# Language Fundamentals

MessageBox.Show("Disposing this Form");

Chapterif(4 -disposingObject-Oriented) Programming with C#

Chapter{5 - Exceptions and Object Lifetime

Chapter 6 -ifInterfaces(componentsa d Collections!= null)

Chapter 7 -{Callback Interfaces, Delegates, and Events

components.Dispose();

Chapter 8 - Advanced C# Type Construction Techniques

}

Part Three - Programming with .NET Assemblies

Part Four - Leveraging the .NET Libraries

Chapter 12 - Object Serialization and the .NET Remoting Layer

ChapterResponding13 - Bu ldingtoa BetterMouseWindowEvents:(IntroducingTakeWindowsOneForms)

Chapter 14 - A Better Painting Framework (GDI+)

Next, you need to intercept the MouseUp event. The goal is to display the (x,y) position at which the

Chapter 15 - Programming with Windows Forms Controls

MouseUp event occurred. When you wish to respond to events from within a Windows Forms application,

Chapter 16 - The System.IO Namespace

you have two general approaches. The first approach should be familiar to you at this point in the game: Use delegates. The second approach is to override the appropriate base class method. Let's examine each

technique, beginning with standard delegation. Here is the updated MainForm:

Chapter 18 - ASP.NET Web Pages and Web Controls

Chapter 19 - ASP.NET Web Applications

public class MainForm : Form

Chapter 20 - XML Web Services

{

Index

public static int Main(string[] args)

List of Figures

{

List of Tables

Application.Run(new MainForm()); return 0;

}

public MainForm()

{

...

// Listen for the MouseUp event...

this.MouseUp += new MouseEventHandler(OnMouseUp);

}

// Method called in response to the MouseUp event.

public void OnMouseUp(object sender, MouseEventArgs e)

{

this.Text = string.Format("Current Pos: ({0}, {1})", e.X, e.Y);

}

...

}

MouseButtons enumeration. For example:

C# and the .NET Platform, Second Edition

public void OnMouseUp(object sender, MouseEventArgs e)

Apress © 2003 (1200 pages)

{

This comprehensive text starts with a brief overview of the

// Which mouse button was clicked?

C# language and then quickly moves to key technical and

if(e.Button == MouseButtons.Left) architectural issues for .NET developers.

MessageBox.Show("Left click!");

if(e.Button == MouseButtons.Right)

Table of ContentsMessageBox.Show("Right click!");

if (e.Button == MouseButtons.Middle)

C# and the .NET Pla form, Second Edition

Introduction MessageBox.Show("Middle click!");

}

Part One - Introducing C# and the .NET Platform

Chapter 1 - The Philosophy of .NET

Chapter 2 - Building C# Applications

PartRespondingTwo - The C# Programmingto MouseLanguageEvents: Take Two

Chapter 3 - C# Language Fundamentals

The previous mouse event logic followed the standard .NET delegate pattern. The other approach to

Chapter 4 - Object-Oriented Programming with C#

capture events in a Control-derived type is to override the correct base class method, which in this case

Chapter 5 - Exceptions and Object Lifetime

would be OnMouseUp() and OnMouseMove(). The Control type defines a number of protected virtual

Chapter 6 - Interfaces and Collections

methods that will be called automatically when the corresponding event is triggered. If you were to update

Chapter 7 - Callback Interfaces, Delegates, and Events

your Form using this technique, you have no need to manually specify a custom event handler (or write the

Chapter 8 - Advanced C# Type Construction Techniques

necessary event handling logic):

Part Three - Programming with .NET Assemblies

protected override void OnMouseMove(/*object sender,*/ MouseEventArgs e) { this.Text = string.Format("Current Pos: ({0}, {1})", e.X, e.Y); }

}

Notice how the signature of each method takes a single parameter of type MouseEventArg, rather than two parameters that conform to the MouseEventHandler delegate. If you run the program again, you see no change whatsoever (which is good).

Recall that these virtual methods defined by your base types are simply the default event handlers that will be called if you do not explicitly handle a given event. Typically you only need to override an "OnXXXX()" method if you have additional work to perform before calling your parent's implementation. The preferred

approach (and the one used by Visual Studio .NET) is to handle the event directly as you did in the first

C# and the .NET Platform, Second Edition

mouse example, and make use of the .NET event syntax. Given this, I will refrain from overriding base class

by Andrew Troelsen ISBN:1590590554

GUI event handlers during the remainder of this text.

Apress © 2003 (1200 pages)

This comprehensive text starts with a brief overview of the C# language and then quickly moves to key technical and architectural issues for .NET developers.

Table of Contents

C# and the .NET Platform, Second Edition

Introduction

Part One - Introducing C# and the .NET Platform

Chapter 1 - The Philosophy of .NET

Chapter 2 - Building C# Applications

Part Two - The C# Programming Language

Chapter 3 - C# Language Fundamentals

Chapter 4 - Object-Oriented Programming with C#

Chapter 5 - Exceptions and Object Lifetime

Chapter 6 - Interfaces and Collections

Chapter 7 - Callback Interfaces, Delegates, and Events

Chapter 8 - Advanced C# Type Construction Techniques

Part Three - Programming with .NET Assemblies

Chapter 9 - Understanding .NET Assemblies

Chapter 10 - Processes, AppDomains, Contexts, and Threads

Chapter 11 - Type Reflection, Late Binding, and Attribute-Based Programming

Part Four - Leveraging the .NET Libraries

Chapter 12 - Object Serialization and the .NET Remoting Layer

Chapter 13 - Building a Better Window (Introducing Windows Forms)

Chapter 14 - A Better Painting Framework (GDI+)

Chapter 15 - Programming with Windows Forms Controls

Chapter 16 - The System.IO Namespace

Chapter 17 - Data Access with ADO.NET

Part Five - Web Applications and XML Web Services

Chapter 18 - ASP.NET Web Pages and Web Controls

Chapter 19 - ASP.NET Web Applications

Chapter 20 - XML Web Services

Index

List of Figures

List of Tables

The ControlC#Classand theRevisited.NET Pla form, Second Edition

The Control class defines further behaviors to configure background and foreground colors, background

Apress © 2003 (1200 pages)

images, font characteristics, drag-and-drop functionality and support for pop-up context menus. This class

This comprehensive text starts with a brief overview of the

provides dockingC#andlanguageanchoringandbehaviorsthen quicklyformovesthe derivedto keytypestechnical(whichandyou examine in Chapter 15). Perhaps the mostarchitecturalimportant dutyissuesof forthe.ControlNET developersclass is. to establish a mechanism to render images, text, and various geometric patterns onto the client area via a registered Paint event handler. To begin, observe these additional properties of the Control class, as seen in Table 13-10.

Table of Contents

Chapter 20 - XML Web Services

The Control class also defines a number of additional methods and events used to configure how the

Index

Control should respond to drag-and-drop operations and respond to painting operations (Table 13-11).

List of Figures

List of Tables

Table 13-11: Additional Control Methods

ChapterOnPaint()3 - C# Language FundamInheritingntals classes should override this method to handle the Paint

event.

Chapter 4 - Object-Oriented Programming with C#

Chapter 5 - Exceptions and Object Lifetime

DragEnter These events are sent in response to drag-and-drop operations.

Chapter 6 - Interfaces and Collections

DragLeave

Chapter 7 - Callback Interfaces, Delegates, and Events

DragDrop

Chapter 8 - Advanced C# Type Construction Techniques

To illustrate some of these additional Control members, the following class sets the background color of the Form object to "Tomato" (you just have to love the names of these colors), the opacity to 50 percent

(to generate a semi-transparent main window), and configures the mouse cursor to display an hourglass

Chapter 17 - Data Access with ADO.NET

icon. More important, let's handle the Paint event in order to render a text string into the Form's client area.

Part Five - Web Applications and XML Web Services

Here is the update:

Chapter 18 - ASP.NET Web Pages and Web Controls

Chapter 19 - ASP.NET Web Applications

using System;

Chapter 20 - XML Web Services

using System.Windows.Forms;

Index

using System.Drawing; // Needed for Color, Brush, and Font types.

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public class MainForm : Form

{

...

public MainForm()

{

// Set some properties that we have inherited from Control.

BackColor = Color.Tomato;

Opacity = 0.5d;

this.Cursor = Cursors.WaitCursor;

// Handle the Paint event.

this.Paint += new PaintEventHandler(MainForm_Paint);

}

private void MainForm_Paint(object sender, PaintEventArgs e)

{

Graphics g = e.Graphics; g.DrawString("What a head trip...",

new Font("Times New Roman", 20),

}Apress © 2003 (1200 pages)

This comprehensive text starts with a brief overview of the C# language and then quickly moves to key technical and

architectural issues for .NET developers.

If you run this application you will see that the Form is indeed transparent!

Painting Basics

Table of Contents

C# and the .NET Platform, Second Edition

The most important aspect of this application is the handling of the Paint event. Notice that the delegate

Introduction

defines a method that takes a parameter of type PaintEventArgs. This type defines two properties to help

you configure the current paint session for the Control as seen in Table 13-12.

Chapter 1 - The Philosophy of .NET

Chapter 2 - Building C# Applications

Table 13-12: Additional Control Properties

Part Two - The C# Programming Language

ChapterPaintEventArgs3 - C# LanguagePropertyFundamentals Meaning in Life

Chapter 4 - Object-Oriented Programming with C#

Chapter 5 - Exceptions and Object Lifetime

ChapterGraphics6 - Interfaces and Collections Gets the Graphics object used during a paint session

Chapter 7 - Callback Interfaces, Delegates, and Events

ChapterThe critical8 - propertyAdvancedofC#PaintEventArgsType Constructionis Graphics,Tec niqueswhich is called to retrieve a Graphics object to use

PartduringThreethe-paintingProgrammingsessionwith. You.NETexamineAssembliesthis class (and GDI+ in general) in greater detail in Chapter 14. ChapterFor now,9 do- Understandingunderstand that.NETtheAssembliesGraphics class defines a number of members that allow you to render

text, geometric shapes and images onto a Control-derived type.

Chapter 10 - Processes, AppDomains, Contexts, and Threads

Chapter 11 - Type Reflection, Late Binding, and Attribute-Based Programming

Finally, in this example you also configured the Cursor property to display an hour-glass symbol whenever the mouse cursor is within the bounding rectangle of this Control. The Cursors type can be assigned to

any member of the Cursors enumeration (e.g., Arrow, Cross, UpArrow, Help, and so forth):

Chapter 13 - Building a Better Window (Introducing Windows Forms)

Chapter 14 - A Better Painting Framework (GDI+)

public MainForm()

Chapter 15 - Programming with Windows Forms Controls

{

Chapter 16 - The System.IO Namespace

...

Chapter 17 - Data Access with ADO.NET this.Cursor = Cursors.WaitCursor;

Part Five - Web Applications and XML Web Services

}

Chapter 18 - ASP.NET Web Pages and Web Controls Chapter 19 - ASP.NET Web Applications

Chapter 20 - XML Web Services

IndexSOURCE The MoreControlBehaviors project is included under the Chapter 13 subdirectory.

List ofCODEFigures

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The ScrollableControlC# and the .NET Platform,Class Second Edition

ScrollableControl is used to define a small number of members that allow your widget to support vertical

Apress © 2003 (1200 pages)

and horizontal scrollbars. The most intriguing members of the ScrollableControl type would have to be the

This comprehensive text starts with a brief overview of the

AutoScroll propertyC#andlanguagethe relatedand thenAutoScrollMinSizequickly moves topropertykey technical. For example,and assume you wish to ensure that if the end usera chitecturalresizes yourissuesForm,forhorizontal.NET developersand vertical. scrollbars are automatically inserted if the size of the client area is less than or equal to 300×300 pixels. Programmatically, your task is simple:

Table of Contents

// Note that you need to reference the System.Drawing namespace

C# and the .NET Platform, Second Edition

// to gain access to the Size type.

Introduction this.AutoScroll = true;

Part One - Introducing C# and the .NET Platform

this.AutoScrollMinSize= new System.Drawing.Size (300, 300);

Chapter 1 - The Philosophy of .NET

Chapter 2 - Building C# Applications

PartTheTwoScrollableControl- The C# Programmingclass takesLanguagecare of the rest. For example, if you had a Form that contained a

Chapternumber3of-childC# Languageobjects (buttons,F ndamentalslabels, or whatnot), you would find that the scrolling logic ensures the ChaptentirerForm4 - Objectreal estate-Ori ntedis viewableProgramming. For thewithcurrentC# example, simply render a large block of text onto a

Label object (see Figure 13-12).

Chapter 5 - Exceptions and Object Lifetime

Chapter 6 - Interfaces and Collections

Chapter

Chapter

Part

Chapter 15 - Programming with Windows Forms Controls

Chapter 16 - The System.IO Namespace

At runtime, the Form will automatically display vertical and horizontal scrollbars when any part of the Label

Chapter 17 - Data Access with ADO.NET

is not visible. The ScrollableControl class does define a number of additional members beyond AutoScroll

Part Five - Web Applications and XML Web Services

and AutoScrollMinSize, but not many. Also be aware that when you wish to take greater control over the

Chapter 18 - ASP.NET Web Pages and Web Controls

scrolling process, you are able to create and manipulate individual ScrollBar types (such as HScrollBar

Chapter 19 - ASP.NET Web Applications

and VScrollBar). I'll leave it to you to check out the remaining members using online Help.

Chapter 20 - XML Web Services

IndexSOURCE The ScrollForm project is included under the Chapter 13 subdirectory.

CODE

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ContainerControlC# and theClass.NET Platform, Second Edition

ContainerControl defines support to manage the focus of a given GUI item. In practice, the behavior

Apress © 2003 (1200 pages)

defined by System.Windows.Forms.ContainerControl is much more useful when you are building a Form

This comprehensive text starts with a brief overview of the

that contains a numberC# languageof childandcontrols,then quicklyand wishmovesto allowto keythetechnicaluser toanduse the Tab key to alternate focus. Using a small setarchitof members,ctural issuesyou canfor .programmaticallyNET developers. obtain the currently selected control, force another to receive focus, and so forth. Table 13-13 gives a rundown of some of the more interesting members.

Table of Contents

On a related note, recall that all descendents of System.Windows.Forms.Control inherit the TabStop and

Chapter 7 - Callback Interfaces, Delegates, and Events

TabIndex properties. As you might be able to guess, these items are used to set the tab order of controls maintained by a parent container, and are used in conjunction with the members supplied by the

ContainerControl class. You revisit the issue of tab order during the discussion of programming controls

Chapter 9 - Understanding .NET Assemblies

(Chapter 15).

Chapter 10 - Processes, AppDomains, Contexts, and Threads

Chapter 11 - Type Reflection, Late Binding, and Attribute-Based Programming

Part Four - Leveraging the .NET Libraries

Chapter 12 - Object Serialization and the .NET Remoting Layer

Chapter 13 - Building a Better Window (Introducing Windows Forms)

Chapter 14 - A Better Painting Framework (GDI+)

Chapter 15 - Programming with Windows Forms Controls

Chapter 16 - The System.IO Namespace

Chapter 17 - Data Access with ADO.NET

Part Five - Web Applications and XML Web Services

Chapter 18 - ASP.NET Web Pages and Web Controls

Chapter 19 - ASP.NET Web Applications

Chapter 20 - XML Web Services

Index

List of Figures

List of Tables