学步园

Canvas主要用于显示图像，既可以在Canvas上画图，也可以将图片显示于其中。

下面通过一个小程序，来演示Canvas使用的3个主要方面：设置图像、更换图像、清除图像。

其代码如下：

package swt;
import java.io.*;
import org.eclipse.swt.SWT;
import org.eclipse.swt.events.*;
import org.eclipse.swt.graphics.Image;
import org.eclipse.swt.layout.*;
import org.eclipse.swt.widgets.*;

public class HelloWorld {
 public static void main(String[] args) {
  final Display display=Display.getDefault();
  final Shell shell=new Shell();
shell.setLayout(new RowLayout());
final Canvas canvas=new Canvas(shell,SWT.BORDER);
//监听canvas的重绘事件
canvas.addPaintListener(new PaintListener(){
 public void paintControl(final PaintEvent event){
  Image image=(Image)canvas.getData();
  if(image!=null){
   event.gc.drawImage(image,10,10);//定位图像左上角距canvas左上角的距离
  }
 }
});
final Image refreshImage=new Image(display,"E:\\workspace\\canvas\\src\\swt\\1.jpg");
final Image nextIamge=new Image(display,"E:\\workspace\\canvas\\src\\swt\\2.jpg");

Button button1=new Button(shell,SWT.NONE);
button1.setText("大力水手");
button1.addSelectionListener(new SelectionAdapter(){
 public void widgetSelected(SelectionEvent e){
  canvas.setData(nextIamge);
  canvas.redraw();
 }
});
Button button2=new Button(shell,SWT.NONE);
button2.setText("海绵宝宝");
button2.addSelectionListener(new SelectionAdapter(){
 public void widgetSelected(SelectionEvent e){
  canvas.setData(refreshImage);
  canvas.redraw();
 }
});
Button clearButton=new Button(shell,SWT.NONE);
clearButton.setText("清除图像");
clearButton.addSelectionListener(new SelectionAdapter(){
 public void widgetSelected(SelectionEvent e){
  canvas.setData(null);
  canvas.redraw();
 }
});
shell.layout();
shell.open();
shell.setSize(300, 200);
while(!shell.isDisposed()){
 if(!display.readAndDispatch())
  display.sleep();
}
display.dispose();
 }

}