Windows Forms 中ResizeRedraw 的应用

第一个示例中不启用ResizeRedraw= true;

 1 // C# program to demonstrate the
 2 // DrawLine(Pen, PointF, PointF) Method
 3 using System;
 4 using System.Drawing;
 5 using System.Drawing.Printing;
 6 using System.Windows.Forms;
 7 
 8 namespace GFG
 9 {
10 
11     class PrintableForm : Form
12     {
13 
14         public static void Main()
15         {
16             Application.Run(new PrintableForm());
17         }
18 
19         public PrintableForm()
20         {
21            // ResizeRedraw = true;
22         }
23         protected override void OnPaint(PaintEventArgs pea)
24         {
25             // Defines pen
26             Pen pen = new Pen(ForeColor);
27 
28             // Draws the line
29            // pea.Graphics.DrawLine(pen, 0,0, ClientSize.Width,ClientSize.Height);
30             pea.Graphics.FillEllipse(new SolidBrush(Color.Blue), 2, 2,
31       ClientRectangle.Width - 4, ClientRectangle.Height - 4);
32         }
33     }
34 }

以上示例是用来画椭圆的，并用蓝色填充；运行后的初始呈现结果如下：

拖住windows forms 右下角，迅速向右下扩大，此次的结果如下：

也就是说椭圆并没有随着windows forms框的扩大而自动刷新覆盖。

下面，我们启用ResizeRedraw = true;让控件进行自动刷新并覆盖：

 1 // C# program to demonstrate the
 2 // DrawLine(Pen, PointF, PointF) Method
 3 using System;
 4 using System.Drawing;
 5 using System.Drawing.Printing;
 6 using System.Windows.Forms;
 7 
 8 namespace GFG
 9 {
10 
11     class PrintableForm : Form
12     {
13 
14         public static void Main()
15         {
16             Application.Run(new PrintableForm());
17         }
18 
19         public PrintableForm()
20         {
21             ResizeRedraw = true;
22         }
23         protected override void OnPaint(PaintEventArgs pea)
24         {
25             // Defines pen
26             Pen pen = new Pen(ForeColor);
27 
28             // Draws the line
29            // pea.Graphics.DrawLine(pen, 0,0, ClientSize.Width,ClientSize.Height);
30             pea.Graphics.FillEllipse(new SolidBrush(Color.Blue), 2, 2,
31       ClientRectangle.Width - 4, ClientRectangle.Height - 4);
32         }
33     }
34 }

下面是初始运行的结果：

点住右下角，向右下方拖动并扩大，结果如下：

可见随着控件成倍变大，椭圆进行了刷新并同步扩大；

 1 // C# program to demonstrate the
 2 // DrawLine(Pen, PointF, PointF) Method
 3 using System;
 4 using System.Drawing;
 5 using System.Drawing.Printing;
 6 using System.Windows.Forms;
 7 
 8 namespace GFG
 9 {
10 
11     class PrintableForm : Form
12     {
13 
14         public static void Main()
15         {
16             Application.Run(new PrintableForm());
17         }
18 
19         public PrintableForm()
20         {
21             ResizeRedraw = true;
22         }
23       //  protected override void OnPaint(PaintEventArgs pea)
24       //  {
25       //      // Defines pen
26       //      Pen pen = new Pen(ForeColor);
27 
28       //      // Draws the line
29       //     // pea.Graphics.DrawLine(pen, 0,0, ClientSize.Width,ClientSize.Height);
30       //      pea.Graphics.FillEllipse(new SolidBrush(Color.Blue), 2, 2,
31       //ClientRectangle.Width - 4, ClientRectangle.Height - 4);
32       //  }
33 
34         protected override void OnPaintBackground(PaintEventArgs e)
35         {
36             //base.OnPaintBackground(e);
37             // draw a blue ellipse into the control area
38             e.Graphics.FillEllipse(new SolidBrush(Color.Blue), 2, 2,
39               ClientRectangle.Width - 4, ClientRectangle.Height - 4);
40         }
41     }
42 }