在PyQT中为QTreeWidgetItem设置边框

Question

我没有找到任何方法可以为特定的QTreeWidgetItem定义样式表，所以我决定尝试用SetBackground或SetForeground来解决我的问题。我想要实现的效果是在树形视图中的一个小部件周围加一个边框，但我不知道怎么用QBrush手动绘制一个边框，如果这样做是对的。有没有什么建议？提前谢谢！

Answer 1

你不能单靠一个 QTreeWidgetItem 来画边框，你需要使用一个代理（delegate）。
你可以在每个想要有边框的项目中存储一个边框样式，使用一个自定义的“角色”来保存这个样式，这样在代理中就可以取出来使用了。

下面是一个完整的、带注释的示例：

import sys
from PyQt4 import QtGui, QtCore

class BorderItemDelegate(QtGui.QStyledItemDelegate):
    def __init__(self, parent, borderRole):
        super(BorderItemDelegate, self).__init__(parent)
        self.borderRole = borderRole

    def sizeHint(self, option, index):        
        size = super(BorderItemDelegate, self).sizeHint(option, index)
        pen = index.data(self.borderRole).toPyObject()
        if pen is not None:        
            # Make some room for the border
            # When width is 0, it is a cosmetic pen which
            # will be 1 pixel anyways, so set it to 1
            width = max(pen.width(), 1)            
            size = size + QtCore.QSize(2 * width, 2 * width)
        return size

    def paint(self, painter, option, index):
        pen = index.data(self.borderRole).toPyObject()
        # copy the rect for later...
        rect = QtCore.QRect(option.rect)
        if pen is not None:
            width = max(pen.width(), 1)
            # ...and remove the extra room we added in sizeHint...
            option.rect.adjust(width, width, -width, -width)      

        # ...before painting with the base class method...
        super(BorderItemDelegate, self).paint(painter, option, index)

        # ...then paint the borders
        if pen is not None:
            painter.save()  
            # The pen is drawn centered on the rectangle lines 
            # with pen.width()/2 width on each side of these lines.
            # So, rather than shifting the drawing of pen.width()/2
            # we double the pen width and clip the part that would 
            # go outside the rect.
            painter.setClipRect(rect, QtCore.Qt.ReplaceClip);          
            pen.setWidth(2 * width)
            painter.setPen(pen)
            painter.drawRect(rect)     
            painter.restore()

if __name__ == "__main__":
    app = QtGui.QApplication(sys.argv)
    mainWindow = QtGui.QMainWindow() 
    mainWindow.resize(300,300); 

    # Define the Qt.ItemDataRole we will be using 
    MyBorderRole = QtCore.Qt.UserRole + 1

    # Create and populate the view
    treeWidget = QtGui.QTreeWidget(mainWindow)
    for i in range(3):
        item = QtGui.QTreeWidgetItem(["Item %d"%(i)])                
        treeWidget.addTopLevelItem(item)        
        treeWidget.expandItem(item);
        for j in range(10):
            subItem = QtGui.QTreeWidgetItem(["SubItem %d %d"%(i,j)])
            pen = QtGui.QPen(QtGui.QColor.fromHsv(j*25, 255, 255))
            pen.setWidth(j)
            # Store the border pen in the item as the role we defined
            subItem.setData(0, MyBorderRole, pen)
            item.addChild(subItem)

    # Pass the role where we stored the border pen to the delegate constructor
    delegate = BorderItemDelegate(treeWidget, MyBorderRole) 
    treeWidget.setItemDelegate(delegate)

    mainWindow.setCentralWidget(treeWidget)
    mainWindow.show()   

    sys.exit(app.exec_())