Question

为什么MenuItem监听器不能在Canvas上执行？请参阅下面的测试程序。您可能希望将“Got Here”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

在按下SelectionListener时，您应使用MenuItem拦截：

resetImageItem.addSelectionListener(new SelectionAdapter() {

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

});

当菜单变得可见时，会触发事件SWT.MenuDetect。要拦截它，您必须将侦听器直接附加到Canvas：

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

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

});

Java SWT：为什么MenuItem监听器不能在Canvas上执行

1 个答案: