PyQt4 - 拖放 [英] PyQt4 - Drag and Drop

问题描述

我一直在通过教程了解PyQt4中的拖放方法。但是我不能理解以下几点。如果somepne可以使我更清楚，那将是很好的。

Hey I had been going through this tutorial for understanding drag and drop methods in PyQt4. However I am not able to understand the following points . It would be nice if somepne could make it clearer to me.

 def mouseMoveEvent(self, e): //class Button


    mimeData = QtCore.QMimeData()

    drag = QtGui.QDrag(self)
    drag.setMimeData(mimeData)
    drag.setHotSpot(e.pos() - self.rect().topLeft())

    dropAction = drag.start(QtCore.Qt.MoveAction)

def dropEvent(self, e): //class Example

    position = e.pos()
    self.button.move(position)

    e.setDropAction(QtCore.Qt.MoveAction)
    e.accept()

为什么有一个单独的self.button .move（）和e.setDropAction（）does not self.button.move（）实际上移动按钮本身？还有人可以解释一下drag.setHotSpot和drag.start（）吗？谢谢。

Why is there are a seperate self.button.move() and e.setDropAction() Doesnt self.button.move() actually move the button itself? And could someone explain what drag.setHotSpot and drag.start() do? Thanks.

推荐答案

该教程严重过时。 QDrag.start 自 Qt 4.3 QDrag.exec _ 应该使用。

That tutorial is seriously outdated. QDrag.start is obsolete since Qt 4.3. QDrag.exec_ should be used instead.

从文档中可以看到 exec ，它有一个返回值。 setDropAction 在 dropEvent 中确定此值。它不执行移动。这就是为什么你需要一个 self.button.move（）来做实际的移动。那么， setDropAction 的意思是什么？你可能需要知道你做了什么样的拖动操作。想象一下，您正在两个列表小部件之间实现拖放。如果您进行了移动操作，那意味着您需要从源窗口小部件中删除该项目，并在目标中创建一个。如果是复制操作，您可以离开原件，只需在目标中创建副本。

As you can see from the docs for exec, it has a return value. setDropAction in dropEvent determines this value. It doesn't perform the move. That's why you need a self.button.move() to do the actual moving. So, what's the point of a setDropAction? You might need to know what kind of drag operation you did. Imagine you're implementing drag-drop between two list widgets. If you did a move operation, that means you need to remove the item from the source widget and create one in the target. If it was a copy operation, you can leave the original and just create a copy in the target.

setHotSpot / hotSpot 与 QDrag 的 setPixmap 相关。您可以在拖动项目时显示 QPixmap 。 hotSpot 确定像素图的位置。像素映射将被定位成使得光标相对于像素图的左上角处于 hotSpot 。所以，在这个教程的情况下，它是没有意义的，因为没有pixmap被显示。

setHotSpot/hotSpot is related to the setPixmap of a QDrag. You can display a QPixmap as you drag the item. hotSpot determines the positioning of the pixmap. The pixmap will be positioned such that the cursor will be at hotSpot relative to the top-left corner of the pixmap. So, in the case of that tutorial, it is rather pointless since there is no pixmap to be shown.

这是一个修改和更新版本的教程。希望我已经包含了足够的评论。您可以使用右键单击或复制 右键单击 code>：

Here is a bit modified and updated version of that tutorial. Hopefully, I've included enough comments. You can move with Right-Click or copy with Shift + Right-Click:

#!/usr/bin/python
# -*- coding: utf-8 -*-

import sys
from PyQt4 import QtGui, QtCore


class Button(QtGui.QPushButton):
    def mouseMoveEvent(self, e):
        if e.buttons() != QtCore.Qt.RightButton:
            return

        # write the relative cursor position to mime data
        mimeData = QtCore.QMimeData()
        # simple string with 'x,y'
        mimeData.setText('%d,%d' % (e.x(), e.y()))

        # let's make it fancy. we'll show a "ghost" of the button as we drag
        # grab the button to a pixmap
        pixmap = QtGui.QPixmap.grabWidget(self)

        # below makes the pixmap half transparent
        painter = QtGui.QPainter(pixmap)
        painter.setCompositionMode(painter.CompositionMode_DestinationIn)
        painter.fillRect(pixmap.rect(), QtGui.QColor(0, 0, 0, 127))
        painter.end()

        # make a QDrag
        drag = QtGui.QDrag(self)
        # put our MimeData
        drag.setMimeData(mimeData)
        # set its Pixmap
        drag.setPixmap(pixmap)
        # shift the Pixmap so that it coincides with the cursor position
        drag.setHotSpot(e.pos())

        # start the drag operation
        # exec_ will return the accepted action from dropEvent
        if drag.exec_(QtCore.Qt.CopyAction | QtCore.Qt.MoveAction) == QtCore.Qt.MoveAction:
            print 'moved'
        else:
            print 'copied'


    def mousePressEvent(self, e):
        QtGui.QPushButton.mousePressEvent(self, e)
        if e.button() == QtCore.Qt.LeftButton:
            print 'press'



class Example(QtGui.QWidget):
    def __init__(self):
        super(Example, self).__init__()
        self.initUI()


    def initUI(self):
        self.setAcceptDrops(True)

        button = Button('Button', self)
        button.move(100, 65)

        self.buttons = [button]

        self.setWindowTitle('Copy or Move')
        self.setGeometry(300, 300, 280, 150)


    def dragEnterEvent(self, e):
        e.accept()


    def dropEvent(self, e):
        # get the relative position from the mime data
        mime = e.mimeData().text()
        x, y = map(int, mime.split(','))

        if e.keyboardModifiers() & QtCore.Qt.ShiftModifier:
            # copy
            # so create a new button
            button = Button('Button', self)
            # move it to the position adjusted with the cursor position at drag
            button.move(e.pos()-QtCore.QPoint(x, y))
            # show it
            button.show()
            # store it
            self.buttons.append(button)
            # set the drop action as Copy
            e.setDropAction(QtCore.Qt.CopyAction)
        else:
            # move
            # so move the dragged button (i.e. event.source())
            e.source().move(e.pos()-QtCore.QPoint(x, y))
            # set the drop action as Move
            e.setDropAction(QtCore.Qt.MoveAction)
        # tell the QDrag we accepted it
        e.accept()



if __name__ == '__main__':
    app = QtGui.QApplication(sys.argv)
    ex = Example()
    ex.show()
    app.exec_()  

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