- Enabling Drag and Drop
- Supporting Custom Drag Types
- Clipboard Handling
This chapter is from the book
This chapter is from the book
This chapter is from the book
Clipboard Handling
Most applications make use of Qt's built-in clipboard handling in one way or another. For example, the QTextEdit class provides cut(), copy(), and paste() slots as well as keyboard shortcuts, so little or no additional code is required.
When writing our own classes, we can access the clipboard through QApplication::clipboard(), which returns a pointer to the application's QClipboard object. Handling the system clipboard is easy: Call setText(), setImage(), or setPixmap() to put data onto the clipboard, and call text(), image(), or pixmap() to retrieve data from the clipboard. We have already seen examples of clipboard use in the Spreadsheet application from Chapter 4.
For some applications, the built-in functionality might not be sufficient. For example, we might want to provide data that isn't just text or an image, or we might want to provide data in many different formats for maximum interoperability with other applications. The issue is very similar to what we encountered earlier with drag and drop, and the answer is also similar: We can subclass QMimeData and reimplement a few virtual functions.
If our application supports drag and drop through a custom QMimeData subclass, we can simply reuse the QMimeData subclass and put it on the clipboard using the setMimeData() function. To retrieve the data, we can call mimeData() on the clipboard.
On X11, it is usually possible to paste a selection by clicking the middle button of a three-button mouse. This is done using a separate "selection" clipboard. If you want your widgets to support this kind of clipboard as well as the standard one, you must pass QClipboard::Selection as an additional argument to the various clipboard calls. For example, here's how we would reimplement mouseReleaseEvent() in a text editor to support pasting using the middle mouse button:
void MyTextEditor::mouseReleaseEvent(QMouseEvent *event)
{
QClipboard *clipboard = QApplication::clipboard();
if (event->button() == Qt::MidButton
&& clipboard->supportsSelection()) {
QString text = clipboard->text(QClipboard::Selection);
pasteText(text);
}
}
On X11, the supportsSelection() function returns true. On other platforms, it returns false.
If we want to be notified whenever the clipboard's contents change, we can connect the QClipboard::dataChanged() signal to a custom slot.