如何：显示渐变填充
更新：2007 年 11 月
通过显示渐变填充，可将鲜艳动人的图形添加到应用程序。下面的代码示例演示如何在自定义控件中作为窗体背景显示渐变填充。
过程
显示渐变填充
在 Microsoft Visual Studio 2005 中，创建一个智能设备 Pocket PC 项目。
将 Gradientfill 和 GradientFilledButton 类添加到项目中。
NotInheritable Public Class GradientFill ' This method wraps the PInvoke to GradientFill. ' Parmeters: ' gr - The Graphics object we are filling ' rc - The rectangle to fill ' startColor - The starting color for the fill ' endColor - The ending color for the fill ' fillDir - The direction to fill ' ' Returns true if the call to GradientFill succeeded; false ' otherwise. Public Shared Function Fill(ByVal gr As Graphics, ByVal rc As Rectangle, ByVal startColor As Color, _ ByVal endColor As Color, ByVal fillDir As FillDirection) As Boolean ' Initialize the data to be used in the call to GradientFill. Dim tva(1) As Win32Helper.TRIVERTEX tva(0) = New Win32Helper.TRIVERTEX(rc.X, rc.Y, startColor) tva(1) = New Win32Helper.TRIVERTEX(rc.Right, rc.Bottom, endColor) Dim gra() As Win32Helper.GRADIENT_RECT = {New Win32Helper.GRADIENT_RECT(0, 1)} ' Get the hDC from the Graphics object. Dim hdc As IntPtr = gr.GetHdc() ' PInvoke to GradientFill. Dim b As Boolean b = Win32Helper.GradientFill(hdc, tva, CType(tva.Length, System.Int32), gra, CType(gra.Length, System.Int32), CType(fillDir, System.Int32)) System.Diagnostics.Debug.Assert(b, String.Format("GradientFill failed: {0}", System.Runtime.InteropServices.Marshal.GetLastWin32Error())) ' Release the hDC from the Graphics object. gr.ReleaseHdc(hdc) Return b End Function ' The direction to the GradientFill will follow Public Enum FillDirection ' The fill goes horizontally LeftToRight = Win32Helper.GRADIENT_FILL_RECT_H ' The fill goes vertically TopToBottom = Win32Helper.GRADIENT_FILL_RECT_V End Enum End Class ' Extends the standard button control and performs ' custom drawing with a GradientFill background. Public Class GradientFilledButton Inherits Control Private components As System.ComponentModel.IContainer = Nothing Public Sub New() components = New System.ComponentModel.Container() Me.Font = New Font(Me.Font.Name, Me.Font.Size, FontStyle.Bold) End Sub ' Controls the direction in which the button is filled. Public Property FillDirection() As GradientFill.FillDirection Get Return fillDirectionValue End Get Set(ByVal value As GradientFill.FillDirection) fillDirectionValue = value Invalidate() End Set End Property Private fillDirectionValue As GradientFill.FillDirection ' The start color for the GradientFill. This is the color ' at the left or top of the control depeneding on the value ' of the FillDirection property. Public Property StartColor() As Color Get Return startColorValue End Get Set(ByVal value As Color) startColorValue = value Invalidate() End Set End Property Private startColorValue As Color = Color.Red ' The end color for the GradientFill. This is the color ' at the right or bottom of the control depending on the value ' of the FillDirection property Public Property EndColor() As Color Get Return endColorValue End Get Set(ByVal value As Color) endColorValue = value Invalidate() End Set End Property Private endColorValue As Color = Color.Blue ' This is the offset from the left or top edge ' of the button to start the gradient fill. Public Property StartOffset() As Integer Get Return startOffsetValue End Get Set(ByVal value As Integer) startOffsetValue = value Invalidate() End Set End Property Private startOffsetValue As Integer ' This is the offset from the right or bottom edge ' of the button to end the gradient fill. Public Property EndOffset() As Integer Get Return endOffsetValue End Get Set(ByVal value As Integer) endOffsetValue = value Invalidate() End Set End Property Private endOffsetValue As Integer ' Used to double-buffer our drawing to avoid flicker ' between painting the background, border, focus-rect ' and the text of the control. Private Property DoubleBufferImage() As Bitmap Get If bmDoubleBuffer Is Nothing Then bmDoubleBuffer = New Bitmap(Me.ClientSize.Width, Me.ClientSize.Height) End If Return bmDoubleBuffer End Get Set(ByVal value As Bitmap) If Not (bmDoubleBuffer Is Nothing) Then bmDoubleBuffer.Dispose() End If bmDoubleBuffer = value End Set End Property Private bmDoubleBuffer As Bitmap ' Called when the control is resized. When that happens, ' recreate the bitmap used for double-buffering. Protected Overrides Sub OnResize(ByVal e As EventArgs) DoubleBufferImage = New Bitmap(Me.ClientSize.Width, Me.ClientSize.Height) MyBase.OnResize(e) End Sub ' Called when the control gets focus. Need to repaint ' the control to ensure the focus rectangle is drawn correctly. Protected Overrides Sub OnGotFocus(ByVal e As EventArgs) MyBase.OnGotFocus(e) Me.Invalidate() End Sub ' Called when the control loses focus. Need to repaint ' the control to ensure the focus rectangle is removed. Protected Overrides Sub OnLostFocus(ByVal e As EventArgs) MyBase.OnLostFocus(e) Me.Invalidate() End Sub Protected Overrides Sub OnMouseMove(ByVal e As MouseEventArgs) If Me.Capture Then Dim coord As New Point(e.X, e.Y) If Me.ClientRectangle.Contains(coord) <> Me.ClientRectangle.Contains(lastCursorCoordinates) Then DrawButton(Me.ClientRectangle.Contains(coord)) End If lastCursorCoordinates = coord End If MyBase.OnMouseMove(e) End Sub ' The coordinates of the cursor the last time ' there was a MouseUp or MouseDown message. Private lastCursorCoordinates As Point Protected Overrides Sub OnMouseDown(ByVal e As MouseEventArgs) If e.Button = System.Windows.Forms.MouseButtons.Left Then ' Start capturing the mouse input Me.Capture = True ' Get the focus because button is clicked. Me.Focus() ' draw the button DrawButton(True) End If MyBase.OnMouseDown(e) End Sub Protected Overrides Sub OnMouseUp(ByVal e As MouseEventArgs) Me.Capture = False DrawButton(False) MyBase.OnMouseUp(e) End Sub Private bGotKeyDown As Boolean = False Protected Overrides Sub OnKeyDown(ByVal e As KeyEventArgs) bGotKeyDown = True Select Case e.KeyCode Case Keys.Space, Keys.Enter DrawButton(True) Case Keys.Up, Keys.Left Me.Parent.SelectNextControl(Me, False, False, True, True) Case Keys.Down, Keys.Right Me.Parent.SelectNextControl(Me, True, False, True, True) Case Else bGotKeyDown = False MyBase.OnKeyDown(e) End Select End Sub Protected Overrides Sub OnKeyUp(ByVal e As KeyEventArgs) Select Case e.KeyCode Case Keys.Space, Keys.Enter If bGotKeyDown Then DrawButton(False) OnClick(EventArgs.Empty) bGotKeyDown = False End If Case Else MyBase.OnKeyUp(e) End Select End Sub ' Override this method with no code to avoid flicker. Protected Overrides Sub OnPaintBackground(ByVal e As PaintEventArgs) End Sub Protected Overrides Sub OnPaint(ByVal e As PaintEventArgs) DrawButton(e.Graphics, Me.Capture AndAlso Me.ClientRectangle.Contains(lastCursorCoordinates)) End Sub ' Gets a Graphics object for the provided window handle ' and then calls DrawButton(Graphics, bool). ' If pressed is true, the button is drawn ' in the depressed state. Overloads Sub DrawButton(ByVal pressed As Boolean) Dim gr As Graphics = Me.CreateGraphics() DrawButton(gr, pressed) gr.Dispose() End Sub ' Draws the button on the specified Grapics ' in the specified state. ' ' Parameters: ' gr - The Graphics object on which to draw the button. ' pressed - If true, the button is drawn in the depressed state. Overloads Sub DrawButton(ByVal gr As Graphics, ByVal pressed As Boolean) ' Get a Graphics object from the background image. Dim gr2 As Graphics = Graphics.FromImage(DoubleBufferImage) ' Fill solid up until where the gradient fill starts. If startOffsetValue > 0 Then If fillDirectionValue = GradientFill.FillDirection.LeftToRight Then If pressed Then gr2.FillRectangle(New SolidBrush(EndColor), 0, 0, startOffsetValue, Height) Else gr2.FillRectangle(New SolidBrush(StartColor), 0, 0, startOffsetValue, Height) End If Else If pressed Then gr2.FillRectangle(New SolidBrush(EndColor), 0, 0, Width, startOffsetValue) Else gr2.FillRectangle(New SolidBrush(StartColor), 0, 0, Width, startOffsetValue) End If End If End If ' Draw the gradient fill. Dim rc As Rectangle = Me.ClientRectangle If fillDirectionValue = GradientFill.FillDirection.LeftToRight Then rc.X = startOffsetValue rc.Width = rc.Width - startOffsetValue - endOffsetValue Else rc.Y = startOffsetValue rc.Height = rc.Height - startOffsetValue - endOffsetValue End If If pressed Then GradientFill.Fill(gr2, rc, endColorValue, startColorValue, fillDirectionValue) Else GradientFill.Fill(gr2, rc, startColorValue, endColorValue, fillDirectionValue) End If ' Fill solid from the end of the gradient fill ' to the edge of the button. If endOffsetValue > 0 Then If fillDirectionValue = GradientFill.FillDirection.LeftToRight Then If pressed Then gr2.FillRectangle(New SolidBrush(StartColor), rc.X + rc.Width, 0, endOffsetValue, Height) Else gr2.FillRectangle(New SolidBrush(EndColor), rc.X + rc.Width, 0, endOffsetValue, Height) End If Else If pressed Then gr2.FillRectangle(New SolidBrush(StartColor), 0, rc.Y + rc.Height, Width, endOffsetValue) Else gr2.FillRectangle(New SolidBrush(StartColor), 0, rc.Y + rc.Height, Width, endOffsetValue) End If End If End If ' Draw the text. Dim sf As New StringFormat() sf.Alignment = StringAlignment.Center sf.LineAlignment = StringAlignment.Center gr2.DrawString(Me.Text, Me.Font, New SolidBrush(Me.ForeColor), Me.ClientRectangle, sf) ' Draw the border. ' Need to shrink the width and height by 1 otherwise ' there will be no border on the right or bottom. rc = Me.ClientRectangle rc.Width -= 1 rc.Height -= 1 Dim pen As New Pen(SystemColors.WindowFrame) gr2.DrawRectangle(pen, rc) ' Draw from the background image onto the screen. gr.DrawImage(DoubleBufferImage, 0, 0) gr2.Dispose() End Sub Protected Overrides Sub Dispose(ByVal disposing As Boolean) If disposing AndAlso Not (components Is Nothing) Then components.Dispose() End If MyBase.Dispose(disposing) End Sub End Classpublic sealed class GradientFill { // This method wraps the PInvoke to GradientFill. // Parmeters: // gr - The Graphics object we are filling // rc - The rectangle to fill // startColor - The starting color for the fill // endColor - The ending color for the fill // fillDir - The direction to fill // // Returns true if the call to GradientFill succeeded; false // otherwise. public static bool Fill( Graphics gr, Rectangle rc, Color startColor, Color endColor, FillDirection fillDir) { // Initialize the data to be used in the call to GradientFill. Win32Helper.TRIVERTEX[] tva = new Win32Helper.TRIVERTEX[2]; tva[0] = new Win32Helper.TRIVERTEX(rc.X, rc.Y, startColor); tva[1] = new Win32Helper.TRIVERTEX(rc.Right, rc.Bottom, endColor); Win32Helper.GRADIENT_RECT[] gra = new Win32Helper.GRADIENT_RECT[] { new Win32Helper.GRADIENT_RECT(0, 1)}; // Get the hDC from the Graphics object. IntPtr hdc = gr.GetHdc(); // PInvoke to GradientFill. bool b; b = Win32Helper.GradientFill( hdc, tva, (uint)tva.Length, gra, (uint)gra.Length, (uint)fillDir); System.Diagnostics.Debug.Assert(b, string.Format( "GradientFill failed: {0}", System.Runtime.InteropServices.Marshal.GetLastWin32Error())); // Release the hDC from the Graphics object. gr.ReleaseHdc(hdc); return b; } // The direction to the GradientFill will follow public enum FillDirection { // // The fill goes horizontally // LeftToRight = Win32Helper.GRADIENT_FILL_RECT_H, // // The fill goes vertically // TopToBottom = Win32Helper.GRADIENT_FILL_RECT_V } } // Extends the standard button control and performs // custom drawing with a GradientFill background. public class GradientFilledButton : Control { private System.ComponentModel.IContainer components = null; public GradientFilledButton() { components = new System.ComponentModel.Container(); this.Font = new Font(this.Font.Name, this.Font.Size, FontStyle.Bold); } // Controls the direction in which the button is filled. public GradientFill.FillDirection FillDirection { get { return fillDirectionValue; } set { fillDirectionValue = value; Invalidate(); } } private GradientFill.FillDirection fillDirectionValue; // The start color for the GradientFill. This is the color // at the left or top of the control depeneding on the value // of the FillDirection property. public Color StartColor { get { return startColorValue; } set { startColorValue = value; Invalidate(); } } private Color startColorValue = Color.Red; // The end color for the GradientFill. This is the color // at the right or bottom of the control depending on the value // of the FillDirection property public Color EndColor { get { return endColorValue; } set { endColorValue = value; Invalidate(); } } private Color endColorValue = Color.Blue; // This is the offset from the left or top edge // of the button to start the gradient fill. public int StartOffset { get { return startOffsetValue; } set { startOffsetValue = value; Invalidate(); } } private int startOffsetValue; // This is the offset from the right or bottom edge // of the button to end the gradient fill. public int EndOffset { get { return endOffsetValue; } set { endOffsetValue = value; Invalidate(); } } private int endOffsetValue; // Used to double-buffer our drawing to avoid flicker // between painting the background, border, focus-rect // and the text of the control. private Bitmap DoubleBufferImage { get { if (bmDoubleBuffer == null) bmDoubleBuffer = new Bitmap( this.ClientSize.Width, this.ClientSize.Height); return bmDoubleBuffer; } set { if (bmDoubleBuffer != null) bmDoubleBuffer.Dispose(); bmDoubleBuffer = value; } } private Bitmap bmDoubleBuffer; // Called when the control is resized. When that happens, // recreate the bitmap used for double-buffering. protected override void OnResize(EventArgs e) { DoubleBufferImage = new Bitmap( this.ClientSize.Width, this.ClientSize.Height); base.OnResize(e); } // Called when the control gets focus. Need to repaint // the control to ensure the focus rectangle is drawn correctly. protected override void OnGotFocus(EventArgs e) { base.OnGotFocus(e); this.Invalidate(); } // // Called when the control loses focus. Need to repaint // the control to ensure the focus rectangle is removed. protected override void OnLostFocus(EventArgs e) { base.OnLostFocus(e); this.Invalidate(); } protected override void OnMouseMove(MouseEventArgs e) { if (this.Capture) { Point coord = new Point(e.X, e.Y); if (this.ClientRectangle.Contains(coord) != this.ClientRectangle.Contains(lastCursorCoordinates)) { DrawButton(this.ClientRectangle.Contains(coord)); } lastCursorCoordinates = coord; } base.OnMouseMove(e); } // The coordinates of the cursor the last time // there was a MouseUp or MouseDown message. Point lastCursorCoordinates; protected override void OnMouseDown(MouseEventArgs e) { if (e.Button == MouseButtons.Left) { // Start capturing the mouse input this.Capture = true; // Get the focus because button is clicked. this.Focus(); // draw the button DrawButton(true); } base.OnMouseDown(e); } protected override void OnMouseUp(MouseEventArgs e) { this.Capture = false; DrawButton(false); base.OnMouseUp(e); } bool bGotKeyDown = false; protected override void OnKeyDown(KeyEventArgs e) { bGotKeyDown = true; switch (e.KeyCode) { case Keys.Space: case Keys.Enter: DrawButton(true); break; case Keys.Up: case Keys.Left: this.Parent.SelectNextControl(this, false, false, true, true); break; case Keys.Down: case Keys.Right: this.Parent.SelectNextControl(this, true, false, true, true); break; default: bGotKeyDown = false; base.OnKeyDown(e); break; } } protected override void OnKeyUp(KeyEventArgs e) { switch (e.KeyCode) { case Keys.Space: case Keys.Enter: if (bGotKeyDown) { DrawButton(false); OnClick(EventArgs.Empty); bGotKeyDown = false; } break; default: base.OnKeyUp(e); break; } } // Override this method with no code to avoid flicker. protected override void OnPaintBackground(PaintEventArgs e) { } protected override void OnPaint(PaintEventArgs e) { DrawButton(e.Graphics, this.Capture && (this.ClientRectangle.Contains(lastCursorCoordinates))); } // // Gets a Graphics object for the provided window handle // and then calls DrawButton(Graphics, bool). // // If pressed is true, the button is drawn // in the depressed state. void DrawButton(bool pressed) { Graphics gr = this.CreateGraphics(); DrawButton(gr, pressed); gr.Dispose(); } // Draws the button on the specified Grapics // in the specified state. // // Parameters: // gr - The Graphics object on which to draw the button. // pressed - If true, the button is drawn in the depressed state. void DrawButton(Graphics gr, bool pressed) { // Get a Graphics object from the background image. Graphics gr2 = Graphics.FromImage(DoubleBufferImage); // Fill solid up until where the gradient fill starts. if (startOffsetValue > 0) { if (fillDirectionValue == GradientFill.FillDirection.LeftToRight) { gr2.FillRectangle( new SolidBrush(pressed ? EndColor : StartColor), 0, 0, startOffsetValue, Height); } else { gr2.FillRectangle( new SolidBrush(pressed ? EndColor : StartColor), 0, 0, Width, startOffsetValue); } } // Draw the gradient fill. Rectangle rc = this.ClientRectangle; if (fillDirectionValue == GradientFill.FillDirection.LeftToRight) { rc.X = startOffsetValue; rc.Width = rc.Width - startOffsetValue - endOffsetValue; } else { rc.Y = startOffsetValue; rc.Height = rc.Height - startOffsetValue - endOffsetValue; } GradientFill.Fill( gr2, rc, pressed ? endColorValue : startColorValue, pressed ? startColorValue : endColorValue, fillDirectionValue); // Fill solid from the end of the gradient fill // to the edge of the button. if (endOffsetValue > 0) { if (fillDirectionValue == GradientFill.FillDirection.LeftToRight) { gr2.FillRectangle( new SolidBrush(pressed ? StartColor : EndColor), rc.X + rc.Width, 0, endOffsetValue, Height); } else { gr2.FillRectangle( new SolidBrush(pressed ? StartColor : EndColor), 0, rc.Y + rc.Height, Width, endOffsetValue); } } // Draw the text. StringFormat sf = new StringFormat(); sf.Alignment = StringAlignment.Center; sf.LineAlignment = StringAlignment.Center; gr2.DrawString(this.Text, this.Font, new SolidBrush(this.ForeColor), this.ClientRectangle, sf); // Draw the border. // Need to shrink the width and height by 1 otherwise // there will be no border on the right or bottom. rc = this.ClientRectangle; rc.Width--; rc.Height--; Pen pen = new Pen(SystemColors.WindowFrame); gr2.DrawRectangle(pen, rc); // Draw from the background image onto the screen. gr.DrawImage(DoubleBufferImage, 0, 0); gr2.Dispose(); } protected override void Dispose(bool disposing) { if (disposing && (components != null)) { components.Dispose(); } base.Dispose(disposing); } }将 Win32Helper 类添加到项目中，该类包含用于本机代码互操作性的平台调用和结构。
Public NotInheritable Class Win32Helper Public Structure TRIVERTEX Public x As Integer Public y As Integer Public Red As System.Int16 Public Green As System.Int16 Public Blue As System.Int16 Public Alpha As System.Int16 Public Sub New(ByVal x As Integer, ByVal y As Integer, ByVal color As Color) MyClass.New(x, y, color.R, color.G, color.B, color.A) End Sub Public Sub New(ByVal x As Integer, ByVal y As Integer, ByVal red As System.Int16, ByVal green As System.Int16, ByVal blue As System.Int16, ByVal alpha As System.Int16) Me.x = x Me.y = y Me.Red = CInt(red << 8) Me.Green = CInt(green << 8) Me.Blue = CInt(blue << 8) Me.Alpha = CInt(alpha << 8) End Sub End Structure Public Structure GRADIENT_RECT Public UpperLeft As System.Int32 Public LowerRight As System.Int32 Public Sub New(ByVal ul As System.Int32, ByVal lr As System.Int32) Me.UpperLeft = ul Me.LowerRight = lr End Sub End Structure Public Declare Function GradientFill Lib "coredll.dll" Alias "GradientFill" (ByVal hdc As IntPtr, _ ByVal pVertex() As TRIVERTEX, ByVal dwNumVertex As Integer, _ ByVal pMesh() As GRADIENT_RECT, ByVal dwNumMesh As Integer, _ ByVal dwMode As Integer) As Boolean Public Const GRADIENT_FILL_RECT_H As Integer = &H0 Public Const GRADIENT_FILL_RECT_V As Integer = &H1 End Classpublic sealed class Win32Helper { public struct TRIVERTEX { public int x; public int y; public ushort Red; public ushort Green; public ushort Blue; public ushort Alpha; public TRIVERTEX(int x, int y, Color color) : this(x, y, color.R, color.G, color.B, color.A) { } public TRIVERTEX( int x, int y, ushort red, ushort green, ushort blue, ushort alpha) { this.x = x; this.y = y; this.Red = (ushort)(red << 8); this.Green = (ushort)(green << 8); this.Blue = (ushort)(blue << 8); this.Alpha = (ushort)(alpha << 8); } } public struct GRADIENT_RECT { public uint UpperLeft; public uint LowerRight; public GRADIENT_RECT(uint ul, uint lr) { this.UpperLeft = ul; this.LowerRight = lr; } } [DllImport("coredll.dll", SetLastError = true, EntryPoint = "GradientFill")] public extern static bool GradientFill( IntPtr hdc, TRIVERTEX[] pVertex, uint dwNumVertex, GRADIENT_RECT[] pMesh, uint dwNumMesh, uint dwMode); public const int GRADIENT_FILL_RECT_H = 0x00000000; public const int GRADIENT_FILL_RECT_V = 0x00000001; }声明一个 GradientFilledButton 类型的名为 gfButton 的窗体变量。
Private gfButton As GradientFilledButtonprivate GradientFilledButton gfButton;将下列代码添加到 Form1 类的构造函数中，该代码初始化渐变填充的按钮自定义控件。应该将该代码放在对 InitializeComponent 方法的调用之后。可以指定渐变填充的起始和结束颜色以及 TopToBottom 或 LeftToRight 填充方向。
InitializeComponent() Me.gfButton = New GradientFilledButton() Me.gfButton.Location = New System.Drawing.Point(71, 24) Me.gfButton.Name = "gfButton" Me.gfButton.Size = New System.Drawing.Size(100, 23) Me.gfButton.TabIndex = 1 Me.gfButton.Text = "Button Test" AddHandler Me.gfButton.Click, AddressOf Me.gfButton_Click ' Select desired start color, end color, and fill direction. Me.gfButton.StartColor = System.Drawing.Color.SlateBlue Me.gfButton.EndColor = System.Drawing.Color.LightCyan gfButton.FillDirection = GradientFill.FillDirection.LeftToRight Me.Controls.Add(gfButton)InitializeComponent(); this.gfButton = new GradientFilledButton(); this.gfButton.Location = new System.Drawing.Point(71, 24); this.gfButton.Name = "gfButton"; this.gfButton.Size = new System.Drawing.Size(100, 23); this.gfButton.TabIndex = 1; this.gfButton.Text = "Button Test"; this.gfButton.Click += new System.EventHandler(this.gfButton_Click); // Select desired start color, end color, and fill direction. this.gfButton.StartColor = System.Drawing.Color.SlateBlue; this.gfButton.EndColor = System.Drawing.Color.LightCyan; gfButton.FillDirection = GradientFill.FillDirection.LeftToRight; this.Controls.Add(gfButton);将处理按钮的 Click 事件的事件处理代码添加到窗体中。
Private Sub gfButton_Click(ByVal sender As Object, ByVal e As System.EventArgs) Dim control As Control = sender System.Diagnostics.Debug.Assert( Not (control Is Nothing)) MessageBox.Show("Clicked", "Click event handler") End Subvoid gfButton_Click(object sender, System.EventArgs e) { Control control = sender as Control; System.Diagnostics.Debug.Assert(control != null); MessageBox.Show("Clicked", "Click event handler"); }重写 OnPaint 方法以渐变填充模式绘制窗体背景。该代码使用 GradientFill 类而不是 GradientFilledButton 类。
' Paints the background of the form with a GradientFill pattern. Protected Overrides Sub OnPaintBackground(ByVal e As PaintEventArgs) ' On Windows Mobile Pocket PC 2003, the call to GradientFill ' fails with GetLastError() returning 87 (ERROR_INVALID_PARAMETER) ' when e.Graphics is used. ' Instead, fill into a bitmap and then draw that onto e.Graphics. Dim bm As New Bitmap(Width, Height) Dim gr As Graphics = System.Drawing.Graphics.FromImage(bm) GradientFill.Fill(gr, Me.ClientRectangle, Color.LightCyan, Color.SlateBlue, GradientFill.FillDirection.TopToBottom) e.Graphics.DrawImage(bm, 0, 0) gr.Dispose() bm.Dispose() End Sub// Paints the background of the form with a GradientFill pattern. protected override void OnPaintBackground(PaintEventArgs e) { // On Windows Mobile Pocket PC 2003, the call to GradientFill // fails with GetLastError() returning 87 (ERROR_INVALID_PARAMETER) // when e.Graphics is used. // Instead, fill into a bitmap and then draw that onto e.Graphics. Bitmap bm = new Bitmap(Width, Height); Graphics gr = System.Drawing.Graphics.FromImage(bm); GradientFill.Fill( gr, this.ClientRectangle, Color.LightCyan, Color.SlateBlue, GradientFill.FillDirection.TopToBottom); e.Graphics.DrawImage(bm, 0, 0); gr.Dispose(); bm.Dispose(); }生成和部署应用程序。