The ControlDesigner Base Class

The `ControlDesigner` Base Class

Just as .NET provides base classes for developing controls, there also exists a set of base classes for implementing designers. In Chapter 5, "Advanced Control Development," the designer base classes are covered in more detail; for now, the ControlDesigner base class is the focus.

The ControlDesigner base class provides the bare-bones functionality for designing a control. Figure 3.1 shows a UML diagram of the ControlDesigner inheritance chain and supported interfaces. UML, or Unified Modeling Language, diagrams are helpful tools for visualizing the various components and classes of any software project.

Figure 3.1. The `ControlDesigner` hierarchy.

figure 3.1. the controldesigner hierarchy.

The base class for ControlDesigner is ComponentDesigner . The ComponentDesigner base class provides support for general component design and is not intended to be used directly for providing design-time support for controls. Its purpose is to provide common functionality for component design-time support.

The ControlDesigner base class serves as a starting point for creating control designers and implements the necessary interfaces for VS .NET. The ControlDesigner base class will serve as the base class for the IconButtonDesigner developed in this chapter. Remember that each control has an associated designer class. This association between the control and its designer class is created by specifying the designer class of a control through the use of an attribute. The DesignerAttribute is used for this purpose.

`DesignerAttribute`

To specify the designer for a control, the System.ComponentMode.Design.DesignerAttribute is used to decorate the control class. The word decorate is used to denote the fact that the DesignerAttribute provides extra information about the control class. The control class itself does not use the specified designer class; however, VS .NET uses this information to locate and create the specified designer. In the case of the IconButton , the DesignerAttribute would be declared as shown here:

1: [
2: System.ComponentModel.Design.Designer (
3:                 typeof( SAMS.ToolKit.Design.IconButtonDesigner )
4:                                        )
5: ]
6: public class IconButton : ... {  //rest of class }

The declaration for the designer assumes that the IconButtonDesigner resides in the namespace SAMS.ToolKit.Design and uses the fully qualified name as the argument for the DesignerAttribute . In C# it's not necessary to include the Attribute part when declaring and using an attribute; the class DesignerAttribute can be referenced as Designer .

The `IconButton` Designer

It's time to create a simple designer for the IconButton control. The designer will be built in two stages. The first stage of the designer will filter properties of the control to remove the BackColor and BackgroundImage properties. The next stage of development will introduce the concept of verbs; verbs are actions that can be associated with a control.

As with any project, the first step involves setting up the development environment. After the VS .NET Solution is created, the process of creating and testing the IconButtonDesigner can begin.

Setting Up the `SAMS.ToolKit` Solution

Before we venture into designer development, now would be a good time to set up a VS .NET Solution that will be used throughout the remainder of the book. In VS .NET a Solution is used to contain one or more related projects. For those of you familiar with Visual Studio 6, a Solution is orthogonal to a workspace.

Start by creating a new C# class library with the name SAMS.ToolKit . This will create a new VS .NET Solution, and the output when compiling the Solution will be SAMS.ToolKit.dll . In addition, the default namespace will also be SAMS.ToolKit .

With the Solution in place, create two folders:

Controls
Design

The new Solution should look similar to what's shown in Figure 3.2.

Figure 3.2. The `SAMS.ToolKit` Solution.

figure 3.2. the sams.toolkit solution.

As with any .NET project, the familiar References folder and the AssemblyInfo.cs source file are automatically created. The folders within the Solution allow for a convenient way to organize code within the project. In addition, any new classes that are created within the folders will have the folder name added to the default namespace.

The Controls folder will need to contain the IconButton.cs file that was created in the preceding chapter. Right-click the Controls folder, select Add Existing Item from the Add menu, and locate the IconButton.cs source file. It is important to note that this operation will copy the source file to the new destination rather than referencing it. This means that there will be two copies of the source and changes to the new source will not be reflected in the original source. Open the IconButton.cs source file and change the namespace to SAMS.ToolKit.Controls .

Filtering Properties

During development of a new custom control, it is sometimes necessary to remove any unwanted or unneeded properties inherited from the base class from which the new custom control derives. The process of adding or removing properties and events is known as filtering. The reason behind filtering, in this case filtering properties, is to alter the available options during the design of the control rather than to provide unnecessary or unused properties/events.

The first designer will be used to remove or filter out two properties from the IconButton : BackColor and BackgroundImage . These properties are inherited from the Control base class and serve no purpose for the IconButton control because neither of these properties has any effect on the control.

The capability to filter properties, events, and attributes comes from implementing the IDesignerFilter interface. Table 3.1 lists the IDesignerFilter interface methods .

Table 3.1. The `IDesignerFilter` Interface Methods

Method	Description
`PostFilterAttributes`	Allows a designer to change or remove attributes.
`PostFilterEvents`	Allows a designer to change or remove events.
`PostFilterProperties`	Allows a designer to change or remove properties.
`PreFilterAttributes`	Allows a designer to add attributes.
`PreFilterEvents`	Allows a designer to add events.
`PreFilterProperties`	Allows a designer to add properties.

Advanced uses of the IDesignerFilter interface are covered in Chapter 5, "Advanced Control Development."

As the first venture into developing a designer, the first pass of the IconButton designer will remove the unused properties BackColor and BackgroundImage . Currently, the IconButton provides both of these properties as they are implemented by the Control base class. The default properties are supplied when the control is created and can be seen in the property grid when the control is selected on the form (see Figure 3.3).

Figure 3.3. The `IconButton` default properties.

figure 3.3. the iconbutton default properties.

Note

The BackgroundImage property has the value of (none) . This means that currently there is no image associated with this property. One of the responsibilities of a Designer class is to provide such feedback to the developer and to the property grid.

Notice the BackColor and BackgroundImage properties displayed in Figure 3.3. To remove these properties, the IconButtonDesigner class will implement the method PostFilterProperties and remove the unwanted properties from the properties collection. Because the ControlDesigner base class implements the IDesignerFilter interface, the IconButtonDesigner class needs to override the implementation of the PostFilterProperties method. Listing 3.1 contains the C# source for the IconButtonDesigner .

Listing 3.1 Designer Stage One

1: ////////////////////////////////////////////////////////////////////////
 2: ///File        :IconButton.cs
 3: ///Author    :Richard L. Weeks
 4: ///
 5: /// Copyright (c) 2001 by Richard L. Weeks
 6: /// This file is provided for instructional purposes only.
 7: /// No warranties.
 8: ////////////////////////////////////////////////////////////////////////
 9:
10: using System;
11: using System.ComponentModel;
12: using System.ComponentModel.Design;
13: using System.Collections;
14: using System.Drawing;
15:
16:
17: namespace SAMS.ToolKit.Design
18: {
19:     /// <summary>
20:     /// Simple Designer for IconButton
21:     /// </summary>
22:     public class IconButtonDesigner : System.Windows.Forms.Design.ControlDesigner {
23:
24:
25:
26:         public IconButtonDesigner()    {
27:         }
28:
29:
30:         //Overrides
31:
32:         /// <summary>
33:         /// Remove some basic properties that are not supported by the IconButton
34:         /// </summary>
35:         /// <param name="Properties"></param>
36:         protected override void PostFilterProperties( IDictionary Properties ) {
37:             Properties.Remove( "BackgroundImage" );
38:             Properties.Remove( "BackColor" );
39:         }
40:
41:
42:
43:  }
44: }

The PostFilterProperties method receives an IDictionary interface to a collection of properties associated with the control being designed. As with any collection, the Remove method is used to remove the specified item from the collection. In the case of the IconButtonDesigner , the code on lines 37 and 38 of Listing 3.1 remove or filter out the unwated properties: BackgroundImage and BackColor .

With the unwanted properties filtered out, they will no longer be displayed within the property grid during the design-time of the IconButton control. However, pragmatic access to the properties is still available to the developer.

To enable the designer for the IconButton control, add the following attribute to the IconButton class:

System.ComponentModel.Designer(typeof(SAMS.ToolKit.Design.IconButtonDesigner))

The IconButton class should now look similar to what's shown in Listing 3.2.

Listing 3.2 Updated Attributes for the IconButton

1:[
2:System.ComponentModel.Description( "SAMS IconButton Control" ),
3:System.ComponentModel.Designer( typeof( SAMS.ToolKit.Design.IconButtonDesigner ) )
4:]
5:public class IconButton : System.Windows.Forms.Control {
6: //IconButton implementation
7: }

Rebuild the SAMS.ToolKit Solution to produce the new control library. To test the results of the designer, start a new Windows Forms Solution and add the IconButton to the form. Notice that the BackColor and BackgroundImage properties are no longer displayed in the property grid, as shown in Figure 3.4.

Figure 3.4. The first phase of the `IconButtonDesigner` .

figure 3.4. the first phase of the iconbuttondesigner.

Designer Verbs

Verbs are best described as actions that can be applied to the control being designed. Verbs for a control are linked to an event handler and are added to the context menu for the control, as well as the property window. The best way to understand the role of verbs is to implement them, and that's exactly what the second phase of the IconButtonDesigner is about.

To support adding verbs for a control, the designer needs to implement the Verbs property. The Verbs property returns a DesignerVerbsCollection of DesignerVerbs that the control designer supports. The IconButtonDesigner will be extended to provide verbs for changing the ForeColor property of the control to Red , Green , or Blue . The event handler for custom verbs uses the following EventHandler signature:

void EventHandler( object sender, EventArgs e )

Listing 3.3 shows the updated IconButtonDesigner with the Verbs property implemented.

Listing 3.3 Designer Stage Two

1: ////////////////////////////////////////////////////////////////////////
 2: ///File      :IconButton.cs
 3: ///Author    :Richard L. Weeks
 4: ///
 5: /// Copyright (c) 2001 by Richard L. Weeks
 6: /// This file is provided for instructional purposes only.
 7: /// No warranties.
 8: ////////////////////////////////////////////////////////////////////////
 9:
10: using System;
11: using System.ComponentModel;
12: using System.ComponentModel.Design;
13: using System.Collections;
14: using System.Drawing;
15:
16:
17: namespace SAMS.ToolKit.Design
18: {
19:     /// <summary>
20:     /// Simple Designer for IconButton
21:     /// </summary>
22:     public class IconButtonDesigner : System.Windows.Forms.Design.ControlDesigner {
23:
24:
25:
26:         public IconButtonDesigner()    {
27:         }
28:
29:         public override DesignerVerbCollection Verbs {
30:             get {
31:  DesignerVerb[] verbs = new DesignerVerb[3];
32:                 verbs[0] = new DesignerVerb( "Red", new EventHandler( this.OnRedVerb

) );
33:                 verbs[1] = new DesignerVerb( "Green", new EventHandler(

this.OnGreenVerb ) );
34:                 verbs[2] = new DesignerVerb( "Blue", new EventHandler(

this.OnBlueVerb ) );
35:                 return new DesignerVerbCollection( verbs );
36:             }
37:         }
38:
39:
40:         //Overrides
41:
42:         /// <summary>
43:         /// Remove some basic properties that are not supported by the IconButton
44:         /// </summary>
45:         /// <param name="Properties"></param>
46:         protected override void PostFilterProperties( IDictionary Properties ) {
47:             Properties.Remove( "BackgroundImage" );
48:             Properties.Remove( "BackColor" );
49:         }
50:
51:
52:         //Verb Handlers
53:         protected void OnRedVerb( object sender, EventArgs e ) {
54:             this.Control.ForeColor = System.Drawing.Color.Red;
55:         }
56:         protected void OnGreenVerb( object sender, EventArgs e ) {
57:             this.Control.ForeColor =  System.Drawing.Color.Green;
58:         }
59:         protected void OnBlueVerb( object sender, EventArgs e ) {
60:             this.Control.ForeColor =  System.Drawing.Color.Blue;
61:         }
62:
63:
64:  }
65: }

Line 29 of Listing 3.3 implements the Verbs property. Each verb defines a text string for the menu and an EventHandler to be invoked when the menu handler is selected. Figure 3.5 shows the context menu and property grid of the IconButton using the revised IconButtonDesigner class.

Figure 3.5. Verbs support.

figure 3.5. verbs support.

VS .NET handles the context menu and property grid support for displaying the supported verbs or commands that the current control designer supports. When one of the supported verbs is selected, the designated EventHandler is invoked so that the verb can be executed. In the case of the IconButtonDesigner , the ForeColor property of the IconButton being designed is updated accordingly .

Designer verbs also allow for user feedback such as providing a check mark for the current ForeColor selected. To provide this feedback, the Checked property of the DesignerVerb item needs to be set. The current implementation of the IconButtonDesigner merely creates the supported designer verbs within the context of the Verbs property rather than as an implementation member. Listing 3.4 updates the IconButtonDesigner to support providing the DesignerVerbs as members and makes use of the Checked property.

Listing 3.4 The Updated `IconButtonDesigner` Class

1: ////////////////////////////////////////////////////////////////////////
 2: ///File        :IconButton.cs
 3: ///Author    :Richard L. Weeks
 4: ///
 5: /// Copyright (c) 2001 by Richard L. Weeks
 6: /// This file is provided for instructional purposes only.
 7: /// No warranties.
 8: ////////////////////////////////////////////////////////////////////////
 9:
10: using System;
11: using System.ComponentModel;
12: using System.ComponentModel.Design;
13: using System.Collections;
14: using System.Drawing;
15:
16:
17: namespace SAMS.ToolKit.Design
18: {
19:     /// <summary>
20:     /// Simple Designer for IconButton
21:     /// </summary>
22:  public class IconButtonDesigner : System.Windows.Forms.Design.ControlDesigner {
23:
24:         private enum VERBS {
25:             Red,
26:             Green,
27:             Blue
28:         }
29:
30:         private DesignerVerb[]            designerVerbs;
31:
32:         public IconButtonDesigner()    {
33:             designerVerbs = new DesignerVerb[3];
34:             DesignerVerb[] verbs = new DesignerVerb[3];
35:             designerVerbs[(int)VERBS.Red] = new DesignerVerb( "Red", new

EventHandler( this.OnRedVerb ) );
36:             designerVerbs[(int)VERBS.Green] = new DesignerVerb( "Green",  new

EventHandler( this.OnGreenVerb ) );
37:             designerVerbs[(int)VERBS.Blue] = new DesignerVerb( "Blue",  new

EventHandler( this.OnBlueVerb ) );
38:         }
39:
40:  public override DesignerVerbCollection Verbs {
41:             get {
42:                 return new DesignerVerbCollection( designerVerbs );
43:             }
44:         }
45:
46:
47:         //Overrides
48:
49:         /// <summary>
50:         /// Remove some basic properties that are not supported by the IconButton
51:         /// </summary>
52:         /// <param name="Properties"></param>
53:         protected override void PostFilterProperties(  IDictionary Properties ) {
54:             Properties.Remove( "BackgroundImage" );
55:             Properties.Remove( "BackColor" );
56:         }
57:
58:
59:         //Verb Handlers
60:  protected void OnRedVerb( object sender, EventArgs e ) {
61:             this.Control.ForeColor = System.Drawing.Color.Red;
62:             UpdateCheckMarks( VERBS.Red );
63:         }
64:         protected void OnGreenVerb( object sender, EventArgs e ) {
65:             this.Control.ForeColor =  System.Drawing.Color.Green;
66:             UpdateCheckMarks( VERBS.Green );
67:         }
68:         protected void OnBlueVerb( object sender, EventArgs e ) {
69:             this.Control.ForeColor =  System.Drawing.Color.Blue;
70:             UpdateCheckMarks( VERBS.Blue );
71:         }
72:
73:
74:         private void UpdateCheckMarks( VERBS ActiveVerb ) {
75:             foreach( DesignerVerb dv in designerVerbs )
76:                 dv.Checked = false;
77:             designerVerbs[ (int)ActiveVerb ].Checked = true;
78:         }
79:    }
80: }

As a result of the updated IconButtonDesigner , the custom verbs on the context menu will show a check mark next to the currently selected foreground color corresponding to the selected verb (see Figure 3.6).

Figure 3.6. Using the designer verb `Checked` property.

figure 3.6. using the designer verb checked property.

With the addition of verbs, the IconButtonDesigner class is beginning to take shape. In Chapter 5, "Advanced Control Development," the designer will be extended to provide even more features. By now you should have the basic idea of what is involved in developing a designer.

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