Canvas 上的弹出菜单：仅在特定边界内显示

Question

我在Canvas 上显示Image。当用户在画布上单击鼠标右键时，会显示一个上下文菜单。

如果用户在图像范围内单击，我如何只显示菜单？我可以从活动中获得x 和y 的位置，但到那时肯定为时已晚！

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

如果活动不在您的区域，请使用 Event#doit 并将其设置为 false。这是一个示例，它会在左半边显示菜单，而不是在 Canvas 的右半边显示：

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();
}

---

如果您想在任何情况下都显示Menu，但要根据事件位置禁用某些菜单项，请执行以下操作：

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();
}