畫布上的彈出菜單：僅在特定邊界內顯示

Question

我在Canvas上顯示Image。當用戶右鍵單擊畫布時，會顯示一個上下文菜單。

如果用戶在圖像邊界內單擊，我該如何顯示菜單？我可以從事件中獲得x和y的位置，但肯定在這一點上已經太遲了！

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; 
    } 
}); 

Answer 1

使用Event#doit並將其設置爲false如果事件是你的區域之外。下面是會顯示在左半菜單中的例子，但不是Canvas的右半部分：

public static void main(String[] args) 
{ 
    final Display display = new Display(); 
    final Shell shell = new Shell(display); 
    shell.setText("Stackoverflow"); 
    shell.setLayout(new FillLayout()); 

    final Canvas canvas = new Canvas(shell, SWT.NONE); 

    Menu menu = new Menu(canvas); 
    new MenuItem(menu, SWT.NONE).setText("MenuItem"); 
    canvas.setMenu(menu); 

    canvas.addListener(SWT.MenuDetect, new Listener() 
    { 
     @Override 
     public void handleEvent(Event event) 
     { 
      Point location = canvas.toControl(event.x, event.y); 
      if(location.x > canvas.getBounds().width/2f) 
       event.doit = false; 
     } 
    }); 

    shell.pack(); 
    shell.open(); 

    while (!shell.isDisposed()) 
    { 
     if (!display.readAndDispatch()) 
      display.sleep(); 
    } 
    display.dispose(); 
} 

---

如果你想顯示在任何情況下Menu，但禁用基於某些菜單項在活動的位置，然後這樣做：

public static void main(String[] args) { 
    final Display display = new Display(); 
    final Shell shell = new Shell(display); 
    shell.setText("Stackoverflow"); 
    shell.setLayout(new FillLayout()); 

    final Canvas canvas = new Canvas(shell, SWT.NONE); 

    Menu menu = new Menu(canvas); 
    final MenuItem item = new MenuItem(menu, SWT.NONE); 
    item.setText("MenuItem"); 
    canvas.setMenu(menu); 

    canvas.addListener(SWT.MenuDetect, new Listener() 
    { 
     @Override 
     public void handleEvent(Event event) 
     { 
      Point location = canvas.toControl(event.x, event.y); 

      item.setEnabled(location.x <= canvas.getBounds().width/2f); 
     } 
    }); 

    shell.pack(); 
    shell.open(); 

    while (!shell.isDisposed()) 
    { 
     if (!display.readAndDispatch()) 
      display.sleep(); 
    } 
    display.dispose(); 
}