WindowBuilder入门:使用swt的canvas类构造显示URL图像

首先如创建一个基于于Canvas的ImageCanvas类，ImageCanvas.java

package net.gdface.ui;import java.net.URL;import org.eclipse.swt.events.PaintEvent;import org.eclipse.swt.events.PaintListener;import org.eclipse.swt.graphics.GC;import org.eclipse.swt.graphics.Image;import org.eclipse.swt.graphics.Point;import org.eclipse.swt.graphics.Rectangle;import org.eclipse.swt.widgets.Canvas;import org.eclipse.swt.widgets.Composite;import org.eclipse.wb.swt.SWTResourceManager;public class ImageCanvas extends Canvas {    // 显示的图像    private Image image;    // 图像缩放比例    private float zoom=1f;    /**     * @param parent     * @param style     * @param image 显示的图像，为null时不显示     */    public ImageCanvas(Composite parent, int style, Image image) {        super(parent, style);        this.image = image;        addPaintListener(new PaintListener() {            @Override            public void paintControl(PaintEvent e) {                // 调用重绘方法                paintImage(e.gc);            }        });    }    /**     * @wbp.parser.constructor     */    public ImageCanvas (Composite parent, int style, URL url){              this(parent,style,SWTResourceManager.getImage( url));    }    /**     * 重绘图像,窗口区域变化时都重新计算适合的显示位置，以保证图像居中完整显示     * @param gc     */    protected void paintImage(GC gc) {        if(null==image)return;        zoom=fitZoom();        Rectangle rect=getPaintRect();        gc.drawImage(image, 0, 0, image.getBounds().width, image                .getBounds().height, rect.x, rect.y, rect.width,                rect.height);    }    /**     * 返回适合当前窗口尺寸完整显示图像的缩放比例,图像长宽都小于显示窗口时，则返回1     * @return      */    private float fitZoom(){        Point size = getSize();        Rectangle imgSize= image.getBounds();        if(imgSize.width<size.x&&imgSize.height<size.y)return 1f;        if(imgSize.width*size.y<imgSize.height*size.x){            return (float)size.y/imgSize.height;        }        return (float)size.x/imgSize.width;    }    /**     * 根据图像缩放比例返回图像在gc中的显示区域(居中显示)     * @return     */    private Rectangle getPaintRect(){        Point size = getSize();        Rectangle imgSize= image.getBounds();        if(zoom>0){            imgSize.width*=zoom;            imgSize.height*=zoom;        }        imgSize.x=(size.x-imgSize.width)/2;        imgSize.y=(size.y-imgSize.height)/2;        return imgSize;    }    @Override    public void dispose() {        super.dispose();        image.dispose();    }}

然后如下图用WindowBuilder创建一个TestDialog类


然后在生成的TestDialog类的createContents中将ImageCanvas对象加入对话框
TestDialog.java

package testwb;import org.eclipse.swt.widgets.Dialog;import org.eclipse.swt.widgets.Display;import org.eclipse.swt.widgets.Shell;import java.net.MalformedURLException;import java.net.URL;import org.eclipse.swt.SWT;import org.eclipse.wb.swt.SWTResourceManager;import net.gdface.ui.ImageCanvas;import org.eclipse.swt.events.PaintListener;import org.eclipse.swt.events.PaintEvent;public class TestDialog extends Dialog {    protected Object result;    protected Shell shell;    private ImageCanvas canvas;    /**     * Create the dialog.     * @param parent     * @param style     */    public TestDialog(Shell parent, int style) {        super(parent, style);    }    /**     * Open the dialog.     * @return the result     */    public Object open() {        createContents();        shell.open();        shell.layout();        Display display = getParent().getDisplay();        while (!shell.isDisposed()) {            if (!display.readAndDispatch()) {                display.sleep();            }        }        return result;    }    /**     * Create contents of the dialog.     */    private void createContents() {        shell = new Shell(getParent(), SWT.NONE);        shell.setSize(450, 300);        shell.setText(getText());        // 将mageCanvas对象加入Dialog        try {            canvas = new ImageCanvas(shell, SWT.NONE,SWTResourceManager.getImage(new URL("http://d.hiphotos.baidu.com/image/pic/item/562c11dfa9ec8a13f075f10cf303918fa1ecc0eb.jpg")));            canvas.setBounds(23, 21, 254, 241);        } catch (MalformedURLException e1) {            // TODO 自动生成的 catch 块            e1.printStackTrace();        }        //    }}

然后在org.eclipse.wb.swt.SWTResourceManager.java中增加支持URL的getImage方法

    public static Image getImage(URL url) {        Image image = m_imageMap.get(url.toString());        if (image == null) {            try {                image = getImage(url.openStream());                m_imageMap.put(url.toString(), image);            } catch (Exception e) {                image = getMissingImage();                m_imageMap.put(url.toString(), image);            }        }        return image;    }

现在，在WindowBuilder的design设计视图中就能看到效果了

JUnit测试代码 TestCanvas.java

package iadbui;import org.eclipse.swt.widgets.Shell;import org.junit.Test;import testwb.AnnDialog;public class TestCanvas {    @Test    public void test() {        new AnnDialog(new Shell(),0).open();    }}