SWT 树的展开事件，懒加载

原文来自：Snippet8

SWT中的树可以利用SWT.Expand事件实现懒加载。

 

public class Snippet8 {

	public static void main (String [] args) {
		final Display display = new Display ();
		final Shell shell = new Shell (display);
		shell.setText ("Lazy Tree");
		shell.setLayout (new FillLayout ());
		
		final Tree tree = new Tree (shell, SWT.BORDER);
		File [] roots = File.listRoots ();
		for (int i=0; i<roots.length; i++) {
			TreeItem root = new TreeItem (tree, 0);
			root.setText(roots[i].toString());
			root.setData(roots[i]);
			
			// display '+' default.
			new TreeItem(root, 0);
		}
		tree.addListener(SWT.Expand, new Listener () {
			public void handleEvent (final Event event) {
				final TreeItem root = (TreeItem) event.item;
				TreeItem[] items = root.getItems ();
				for(int i= 0; i<items.length; i++) {
					// if have added children for the item, just return.
					if(items[i].getData() != null)
						return;
					items[i].dispose();
				}
				
				File file = (File) root.getData();
				File[] files = file.listFiles();
				
				// disc return
				if(files == null) return;
				for(int i= 0; i<files.length; i++) {
					TreeItem item = new TreeItem(root, 0);
					item.setText(files[i].getName());
					item.setData(files[i]);
					if(files[i].isDirectory()) {
						// display '+' only for directory.
						new TreeItem(item, 0);
					}
				}
			}
		});

		Point size = tree.computeSize(300, SWT.DEFAULT);
		int width = Math.max(300, size.x);
		int height = Math.max(300, size.y);
		shell.setSize (shell.computeSize (width, height));
		shell.open ();
		while (!shell.isDisposed ()) {
			if (!display.readAndDispatch ()) display.sleep ();
		}
		display.dispose ();
	}
}

保证根节点的+图像 写道

// display '+' default.
new TreeItem(root, 0);

 

不重复加载 写道

// if have added children for the item, just return.
if(items[i].getData() != null)
return;