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用.NET Compact Framework创建图像按钮 |
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时间: 2003-04-28 来自：yesky |
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三、应用规则
在实际的操作中，我们将建立一个自画的图像按钮控件.需要在按钮上面显示一个图片，当用户在按按钮时可以看到效果。
我们开始 Visual Studio .NET中建立一个SmartDevice项目的Windows应用程序.在这个项目中我们加入一个新的ImageButton类。
using System;
using System.Drawing;
using System.Windows.Forms;
public class ImageButton : Control
{
//Private members
private Image image;
//flag to indicate the pressed state
private bool bPushed;
private Bitmap m_bmpOffscreen;
public ImageButton()
{
bPushed = false;
//default minimal size
this.Size = new Size(21, 21);
}
protected override void OnPaint(PaintEventArgs e )
{
//Some drawing logic
}
protected override void OnPaintBackground(PaintEventArgs e )
{
//Do nothing
}
} |
在以上代码中，我们用Control控件中的ImageButton类,和重载OnPaint以及OnPaintBackground事件,在上面提到，ImageButton将要一个图片用来显示，所以我们添加图像属性:
public Image Image
{
get
{
return image;
}
set
{
image = value;
}
} |
当然，还有重载OnPaint事件来绘制按钮
protected override void OnPaint(System.Windows.Forms.PaintEventArgs e )
{
Graphics gxOff; //Offscreen graphics
Rectangle imgRect; //image rectangle
Brush backBrush; //brush for filling a backcolor
if (m_bmpOffscreen == null) //Bitmap for doublebuffering
{
m_bmpOffscreen = new Bitmap(ClientSize.Width, ClientSize.Height);
}
gxOff = Graphics.FromImage(m_bmpOffscreen);
gxOff.Clear(this.BackColor);
if (!bPushed)
backBrush = new SolidBrush(Parent.BackColor);
else //change the background when it's pressed
backBrush = new SolidBrush(Color.LightGray);
gxOff.FillRectangle(backBrush, this.ClientRectangle);
if (image != null)
{
//Center the image relativelly to the control
int imageLeft = (this.Width - image.Width) / 2;
int imageTop = (this.Height - image.Height) / 2;
if (!bPushed)
{
imgRect = new Rectangle(imageLeft, imageTop, image.Width,
image.Height);
}
else //The button was pressed
{
//Shift the image by one pixel
imgRect = new Rectangle(imageLeft + 1, imageTop + 1, image.Width,
image.Height);
}
//Set transparent key
ImageAttributes imageAttr = new ImageAttributes();
imageAttr.SetColorKey(BackgroundImageColor(image),
BackgroundImageColor(image));
//Draw image
gxOff.DrawImage(image, imgRect, 0, 0, image.Width, image.Height,
GraphicsUnit.Pixel, imageAttr);
}
if (bPushed) //The button was pressed
{
//Prepare rectangle
Rectangle rc = this.ClientRectangle;
rc.Width--;
rc.Height--;
//Draw rectangle
gxOff.DrawRectangle(new Pen(Color.Black), rc);
}
//Draw from the memory bitmap
e.Graphics.DrawImage(m_bmpOffscreen, 0, 0);
base.OnPaint(e);
} |
根据上面章节的提要，我们成功的按.NET Compact Framework的画图方法写下了这些代码。我们先建立好绘图对象的缓存，并尽可能的用双缓存来减少图像闪烁。我们用下面的函数来帮助识别背景色，使图像透明:
private Color BackgroundImageColor(Image image)
{
Bitmap bmp = new Bitmap(image);
return bmp.GetPixel(0, 0);
} |
上面的函数返加位图左上角的颜色。当在画按钮时，我们用bPushed标志判断按钮按下否。我们可以很容易重载OnMouseDown和OnMouseUp事件：
protected override void OnMouseDown(System.Windows.Forms.MouseEventArgs e )
{
bPushed = true;
this.Invalidate();
}
protected override void OnMouseUp(System.Windows.Forms.MouseEventArgs e)
{
bPushed = false;
this.Invalidate();
} |
五、用法
可以很容易的新建一个ImageButton控件。把下面的少量代码添加到Form 结构中:
public Form1()
{
InitializeComponent();
imageButton1 = new ImageButton();
imageButton1.Image = new
Bitmap(Assembly.GetExecutingAssembly().GetManifestResourceStream("ImageButtonProject.doorin2.gif"));
imageButton1.Location = new Point(30, 50);
imageButton1.Size = new Size(44, 34);
//Hook up into click event
imageButton1.Click+=new EventHandler(imageButton1_Click);
this.Controls.Add(imageButton1);
} |
我们添加doorin2.gif文件，同样可以在很容易用GetManifestResourceStream方法当前集合在项目的资源中。
图一(程序界面上三个按钮)
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图二（第一个控件按下时）
六、结论
.NET Compact Framework并不像.NET Framework一样提供很多可用的图形和绘图函数。这是由于平台资源限制的缘故。不过，我们可以用一些自画技巧，在用户程序中建立大量丰富和可响应的图形。
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