Java SWT：为什么MenuItem侦听器不能在Canvas上执行

Question

为什么MenuItem侦听器不能在Canvas上执行？请参阅下面的测试程序。你会期望“到达这里”被打印到控制台。

import java.util.ArrayList; 

import org.eclipse.jface.resource.ImageDescriptor; 
import org.eclipse.swt.SWT; 
import org.eclipse.swt.events.PaintEvent; 
import org.eclipse.swt.events.PaintListener; 
import org.eclipse.swt.graphics.Image; 
import org.eclipse.swt.graphics.ImageData; 
import org.eclipse.swt.graphics.PaletteData; 
import org.eclipse.swt.layout.FillLayout; 
import org.eclipse.swt.widgets.Canvas; 
import org.eclipse.swt.widgets.Display; 
import org.eclipse.swt.widgets.Event; 
import org.eclipse.swt.widgets.Listener; 
import org.eclipse.swt.widgets.Menu; 
import org.eclipse.swt.widgets.MenuItem; 
import org.eclipse.swt.widgets.Shell; 


public class MenuListenerTest { 
    //BufferedImage bitmapImage = null; 
    Image image = null; 
    Canvas canvas = null; 
      private void createContents(Shell shell) { 

       shell.setLayout(new FillLayout()); 

      // Create a canvas to draw on 
      canvas = new Canvas(shell, SWT.V_SCROLL | SWT.H_SCROLL | SWT.NO_REDRAW_RESIZE | SWT.DOUBLE_BUFFERED); 

      final Menu pixelContextMenu = new Menu(canvas); 
      canvas.setMenu(pixelContextMenu); 

      final MenuItem resetImageItem = new MenuItem(pixelContextMenu, SWT.NONE); 
      resetImageItem.setText("Reset Image"); 
      resetImageItem.addListener(SWT.MenuDetect, new Listener() { 
       @Override 
       public void handleEvent(Event event) { 
        int x = event.x; 
        int y = event.y; 
        System.out.println("Got here"); 
       } 
      }); 

      } 
      public static void main(String[] args) 
      { 
       new MenuListenerTest().run(); 
      } 

      public void run() { 
        Display display = new Display(); 
        Shell shell = new Shell(display); 
        createContents(shell); 
        shell.open(); 
        while (!shell.isDisposed()) { 
         if (!display.readAndDispatch()) { 
         display.sleep(); 
         } 
        } 
        display.dispose(); 
        } 

        /** 
        * Creates the main window's contents 
        * 
        * @param shell the main window 
        */    
} 

Answer 1

您应该使用SelectionListener当按下MenuItem拦截：

resetImageItem.addSelectionListener(new SelectionAdapter() { 

    @Override 
    public void widgetSelected(SelectionEvent event) { 
     System.out.println("menu item pressed"); 
    } 

}); 

事件SWT.MenuDetect取而代之的是当菜单变得可见解雇。拦截它，你将不得不听众直接连接到Canvas：

canvas.addListener(SWT.MenuDetect, new Listener() { 

    @Override 
    public void handleEvent(Event event) { 
     System.out.println("menu visible"); 
    } 

});