// The final two parameters are the X and Y coordinates of the upper left hand in .NET framework

Encode QR Code ISO/IEC18004 in .NET framework // The final two parameters are the X and Y coordinates of the upper left hand

// The final two parameters are the X and Y coordinates of the upper left hand
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Creating Windows Forms Controls
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// corner of the rendered string.
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g.DrawString(myString, myFont, SystemBrushes.Highlight, 20, 20);
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g.Dispose();
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Rendering Custom Controls by Overriding the OnPaint Method
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You can render the visual interface for a custom control by overriding the OnPaint method. The OnPaint method internally handles the Paint method and contains all of the code required to render the visual appearance of the control. The OnPaint method has a single parameter, an instance of PaintEventArgs. This instance of PaintEventArgs contains two important members. The ClipRectangle parameter contains the rectangle in which painting will take place. The Graphics parameter contains an instance of the Graphics class that represents the drawing sur face of the control being rendered. When a control is drawn or refreshed, only the part of the control that needs to be refreshed is drawn. If the entire control needs to be refreshed, the ClipRectangle will represent the size of the entire control. If only part of the control needs to be refreshed, however, the ClipRectangle object will represent only the region that needs to be redrawn. For the most part, you as the developer will never need to use the ClipRectangle property it is used automatically by the Graphics object. The Graphics object represents the drawing surface of the control. By using the meth ods described in the previous section, you can render the visual appearance of the control. All of the methods that render graphics require coordinates for the location of the graphics. The upper left-hand corner of the control is (0,0), and the control is bounded by the Control.Width and Control.Height properties. The following example demonstrates how to override the OnPaint method and render a filled-in blue rectan gle that fills the entire control.
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' VB Protected Overrides Sub OnPaint(ByVal pe As System.Windows.Forms.PaintEventArgs) MyBase.OnPaint(pe) Dim g As Graphics = pe.Graphics g.FillRectangle(Brushes.Blue, 0, 0, Me.Width, Me.Height) End Sub // C# protected override void OnPaint(PaintEventArgs pe) {
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base.OnPaint(pe);
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Graphics g = pe.Graphics;
g.FillRectangle(Brushes.Blue, 0, 0, this.Width, this.Height);
Lesson 2: Creating Custom Controls
Note the call to MyBase.OnPaint (in Visual Basic) or base.OnPaint (in C#). When over riding a method in an inherited class, you should generally call the method in the base class to call any base implementation.
To create a custom control
1. Add a new class to your project that inherits from the Control class. 2. Override the OnPaint method to provide custom rendering code. 3. Implement other functionality for the control.
Quick Check
1. How is a custom control different from a composite control 2. Briefly describe how the Graphics and ClipRectangle properties of PaintEventArgs are used in the OnPaint method.
Quick Check Answers
1. A composite control provides a designer and a default visual interface and is composed of other Windows Forms controls bound together by com mon functionality and in a common interface. A custom control has no default visual interface and has a limited designer by default. Custom con trols must provide their own rendering code and generally do not incorpo rate other Windows Forms controls. 2. You must override the OnPaint method to create the rendering code for a custom control. The Graphics property of PaintEventArgs represents the drawing surface of the custom control and exposes all of the methods required to render graphics to the user interface. The ClipRectangle is the rectangle that will be drawn or redrawn when the control is rendered. It is used by the Graphics object but generally does not need to be used by the developer.
Lab: Create a Custom Control
In this lab, you will create another digital clock. Like the control you created in the lab from Lesson 1, it will incorporate a Timer component to update the user interface on a regular basis. Unlike the previous lab, however, you will create your own rendering for this control instead of using a Label control to do so.
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