Eclipse Tutorial

Drag and Drop Tutorial

SWT Dnd 功能主要有三部分组成：

• Transfer
• DragSource
• DropTarget

Transfer

Transfer主要用来保存和转换在拖拽过程中的数据。

DragSource

DragSource用来定义拖拽源，它上面会添加一个DragSourceListener的事件监听来完成数据的上传。

// Enable a label as a Drag Source
Label label = new Label(shell, SWT.NONE);
// This example will allow text to be dragged
Transfer[] types = new Transfer[] {TextTransfer.getInstance()};
// This example will allow the text to be copied or moved to the drop target
int operations = DND.DROP_MOVE | DND.DROP_COPY;

DragSource source = new DragSource(label, operations);
source.setTransfer(types);
source.addDragListener(new DragSourceListener() {
    public void dragStart(DragSourceEvent e) {
        // Only start the drag if there is actually text in the
        // label - this text will be what is dropped on the target.
        if (label.getText().length() == 0) {
            event.doit = false;
        }
    };
    public void dragSetData(DragSourceEvent event) {
        // A drop has been performed, so provide the data of the 
        // requested type.
        // (Checking the type of the requested data is only 
        // necessary if the drag source supports more than 
        // one data type but is shown here as an example).
        if (TextTransfer.getInstance().isSupportedType(event.dataType)){
            event.data = label.getText();
        }
    }
    public void dragFinished(DragSourceEvent event) {
        // A Move operation has been performed so remove the data
        // from the source
        if (event.detail == DND.DROP_MOVE)
            label.setText("");
    }
});

DropTarget

DropTarget用来定义Drop目标，它会通过添加DropTargetListener事件监听将Transfer中的数据下载，并应用到当前控件中。

int operations = DND.DROP_MOVE | DND.DROP_COPY | DND.DROP_LINK;
Transfer[] types = new Transfer[] {TextTransfer.getInstance()};
DropTarget target = new DropTarget(label, operations);
target.setTransfer(types);

target.addDropListener (new DropTargetListener() {
    public void dragEnter(DropTargetEvent event) {};
    public void dragOver(DropTargetEvent event) {};
    public void dragLeave(DropTargetEvent event) {};
    public void dragOperationChanged(DropTargetEvent event) {};
    public void dropAccept(DropTargetEvent event) {}
    public void drop(DropTargetEvent event) {
        // A drop has occurred, copy over the data
        if (event.data == null) { // no data to copy, indicate failure in event.detail
            event.detail = DND.DROP_NONE;
            return;
        }
        label.setText ((String) event.data); // data copied to label text
    }
});

参考资料

1. Drag and Drop snippets
2. SWT Example: DNDExample

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