SWT Image (ImageDescriptor类)

SWT Image (ImageDescriptor类)

Image使用代价昂贵，JFace包提供了一个轻量级的ImageDescriptor类.
An image descriptor is an object that knows how to create an SWT image.It does not hold onto images or cache them, but rather just creates them on demand.
ImageDescriptor类是抽象类，不能用new,有2种常用static方法，createFromFile,createFromURL.

1：ImageDescriptor temp = ImageDescriptor.createFromFile(abc.class,"icons/temp.gif")
   //在类abc目录下的icon目录下的图片temp.gif
   //没有真正加载这个图像

2：//绝对目录
   URL url ＝ new URL("file:\\c:\\icons\\temp.gif");
   ImageDescriptor temp = ImageDescriptor.createFromURL(url)
   //项目主目录
   URL url ＝ new URL("file:icons/temp.gif");
   ImageDescriptor temp = ImageDescriptor.createFromURL(url)

3: Eclipse自带图像调用
   ImageDescriptor temp ＝ WorkbenchImages.getImageDescriptor(IWorkbenchGraphicConstants.IMG_ETOOL_HOME_NAV);

4: 得到image
   Image image = temp.creatImage();

图像注册表ImageRegistry类：高速缓存图像和图像描述符
  ImageRegistry image_registry ＝ new ImageRegistry();

  URL url = new URL("file:icons/folder.gif");
  ImageDescriptor imaged = ImageDescriptor.createFromURL(url);

  image_registry.put("folder",imaged);
 
  //取出image
  Image image = image_registry.get("folder");
  //取出描述符
  ImageDescriptor imageDescriptor = image_registry.getDescriptor("folder");
  //删除图像
  image_registry.remove("folder");

  **项目开发初期，建立一个图像注册表

  **网上教程