在Java SWT中创建自定义滑块Widget

Question

我正在为我的项目所需的java swt创建一个自定义滑块小部件。我的目标是创建一个控制3个数量的滑块。我实际上已经设计了GUI，但功能给了我一些问题。滑块包含2个要滑动的按钮，其中的错误是两个按钮不能相互独立工作。 所以请帮助找到纠正我的错误。

       public class Snippet46 {
    public static void main (String [] args) {
        Display display = new Display ();
        final Shell shell = new Shell (display);
        final Canvas canvas = new Canvas(shell, SWT.BORDER);
        canvas.setBounds(84, 70, 56, 195);

        final Composite composite = new Composite (canvas, SWT.BORDER);
        composite.setEnabled (false);
        composite.setLayout (new FillLayout ());
        Button button = new Button (composite, SWT.PUSH);
        button.setText ("1");
        composite.pack ();
        composite.setLocation (0,10);
        System.out.println("com:"+composite.getBounds());
        composite.setSize(52, 19);

        final Composite composite_1 = new Composite(canvas, SWT.BORDER);
        composite_1.setEnabled(false);
        composite_1.setLayout(new FillLayout());
        Button btnNewButton = new Button(composite_1, SWT.PUSH);
        btnNewButton.setText("2");
        composite_1.pack();
        composite_1.setLocation(0, 162);
        composite_1.setSize(52, 19);
        final int default_y_up=10;
        final int default_y_down=162;
        final Point [] offset = new Point [1];

        Listener listener = new Listener () {
            public void handleEvent (Event event) {
                Rectangle rect = canvas.getBounds ();
                Rectangle rect_canvas=composite.getBounds();
                switch (event.type) {
                case SWT.MouseDown:          
                    System.out.println("compo:"+rect_canvas);
                    rect.x=0;
                    rect.y=0;
                    System.out.println("bounds:"+rect+"rec:"+event.x+" "+event.y);
                    if (rect.contains (event.x, event.y)) {
                        Point pt1 = canvas.toDisplay (0, 0);
                        Point pt2 = composite.toDisplay (event.x, event.y); 
                        offset [0] = new Point (0,pt2.y - pt1.y );
                        System.out.println("offset:"+offset[0]);
                    }
                    /*if((rect_canvas.y)<0)//195
              offset[0]=null;
                     */
                    break;
                case SWT.MouseMove:
                    System.out.println("move:"+(rect_canvas.y));
                    if((rect_canvas.y)>0)//195
                        if (offset [0] != null) {
                            Point pt = offset [0];
                            composite.setLocation (pt.x,event.y);
                        }
                    break;
                case SWT.MouseUp:           
                    if((rect_canvas.y)<=canvas.getBounds().height)
                    {               
                        composite.setLocation (0,default_y_up);
                    }
                    offset [0] = null;
                    break;
                }
            }
        };
        canvas.addListener (SWT.MouseDown, listener);
        canvas.addListener (SWT.MouseUp, listener);
        canvas.addListener (SWT.MouseMove, listener);


        //**************************slider 2**************
        final Point [] offset_slider2 = new Point [1];
        Listener listener_slider2 = new Listener () {
            public void handleEvent (Event event) {
                Rectangle rect1 = canvas.getBounds ();
                Rectangle rect_canvas1=composite_1.getBounds();
                switch (event.type) {
                case SWT.MouseDown:


                    System.out.println("compo:"+rect_canvas1);
                    rect1.x=0;
                    rect1.y=0;
                    System.out.println("bounds:"+rect1+"rec:"+event.x+" "+event.y);
                    if (rect1.contains (event.x, event.y)) {
                        Point pt1 = canvas.toDisplay (0, 0);
                        Point pt2 = composite_1.toDisplay (event.x, event.y); 
                        offset_slider2 [0] = new Point (0,pt2.y - pt1.y);
                        System.out.println("offset:"+offset[0]);
                    }
                    if((rect_canvas1.y+rect_canvas1.height)>canvas.getBounds().height)
                        offset_slider2[0]=null;

                    break;
                case SWT.MouseMove:         
                    System.out.println("move:"+(rect_canvas1.y+rect_canvas1.height));
                    if((rect_canvas1.y+rect_canvas1.height)<195)
                        if (offset_slider2 [0] != null) {
                            Point pt = offset_slider2 [0];
                            composite_1.setLocation (pt.x,event.y - pt.y);
                        }
                    break;
                case SWT.MouseUp:           
                    if((rect_canvas1.y+rect_canvas1.height)>=195)
                    {               
                        composite_1.setLocation (0, default_y_down);
                    }
                    offset_slider2 [0] = null;
                    break;
                }
            }
        };
        canvas.addListener (SWT.MouseDown, listener_slider2);
        canvas.addListener (SWT.MouseUp, listener_slider2);
        canvas.addListener (SWT.MouseMove, listener_slider2);

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