Vezměte prosím na vědomí, že tento blogový příspěvek byl publikován v lednu 2011, takže v závislosti na době, kdy jej čtete, mohou být některé části zastaralé. Bohužel nemohu tyto příspěvky vždy udržovat plně aktuální, aby informace zůstaly přesné.
Creating a desktop application that allows users to drag and drop files or other data formats to the application is not only cool, but could be really user friendly as well. Implementing this feature in Java is quite easy as well.
This is done by connecting an AWT Component to a DropTargetListener, using a DropTarget. Below is a brief code example on how this could be done.
public class DragDropTestFrame extends JFrame {
private static final long serialVersionUID = 1L;
public static void main(String[] args) {
// Create our frame
new DragDropTestFrame();
}
public DragDropTestFrame() {
// Set the frame title
super("Drag and drop test");
// Set the size
this.setSize(250, 150);
// Create the label
JLabel myLabel = new JLabel("Drag something here!", SwingConstants.CENTER);
// Create the drag and drop listener
MyDragDropListener myDragDropListener = new MyDragDropListener();
// Connect the label with a drag and drop listener
new DropTarget(myLabel, myDragDropListener);
// Add the label to the content
this.getContentPane().add(BorderLayout.CENTER, myLabel);
// Show the frame
this.setVisible(true);
}
}
Secondly we create a new instance of our DropTargetListener, and connect it to our label via DropTarget.
// Create the drag and drop listener
MyDragDropListener myDragDropListener = new MyDragDropListener();
// Connect the label with a drag and drop listener
new DropTarget(myLabel, myDragDropListener);
Afterwards we implement our MyDragDropListener class.
class MyDragDropListener implements DropTargetListener {
@Override
public void drop(DropTargetDropEvent event) {
// Accept copy drops
event.acceptDrop(DnDConstants.ACTION_COPY);
// Get the transfer which can provide the dropped item data
Transferable transferable = event.getTransferable();
// Get the data formats of the dropped item
DataFlavor[] flavors = transferable.getTransferDataFlavors();
// Loop through the flavors
for (DataFlavor flavor : flavors) {
try {
// If the drop items are files
if (flavor.isFlavorJavaFileListType()) {
// Get all of the dropped files
List files = (List) transferable.getTransferData(flavor);
// Loop them through
for (File file : files) {
// Print out the file path
System.out.println("File path is '" + file.getPath() + "'.");
}
}
} catch (Exception e) {
// Print out the error stack
e.printStackTrace();
}
}
// Inform that the drop is complete
event.dropComplete(true);
}
@Override
public void dragEnter(DropTargetDragEvent event) {
}
@Override
public void dragExit(DropTargetEvent event) {
}
@Override
public void dragOver(DropTargetDragEvent event) {
}
@Override
public void dropActionChanged(DropTargetDragEvent event) {
}
}
In the drop method we loop through all the different data formats (since it's possible to drop multiple items on the label).
// Loop through the flavors
for (DataFlavor flavor : flavors) {
// If the drop items are files
if (flavor.isFlavorJavaFileListType()) {
// Get all of the dropped files
List files = (List) transferable.getTransferData(flavor);
// Loop them through
for (File file : files) {
// Print out the file path
System.out.println("File path is '" + file.getPath() + "'.");
}
}
}
Launching the application and dropping files to the JFrame will show the following output.
Pretty easy. This application can of course be extended to support other data flavours, such as text, images and even other Java Components.
More information about drag and dropping in Java can be found in the Introduction to DnD tutorial.
