QStyledItemDelegate的选项未更新

Question

我在使用PyQt5时遇到了一个问题。我有一个用QStyledItemDelegate类绘制它的项目的列表。下面是最小的可重现示例：

import sys
from PyQt5.QtCore import (
    QAbstractListModel,
    Qt,
    QSize,
    QRect,
    QRectF,
)
from PyQt5.QtGui import (
    QPainter,
    QFontMetrics,
    QFont,
    QTextDocument,
    QTextOption,
    QPen,
)
from PyQt5.QtWidgets import (
    QApplication,
    QListView,
    QMainWindow,
    QStyledItemDelegate,
)

window_width = 0

class MessageDelegate(QStyledItemDelegate):
    WINDOW_PADDING = 30
    font = QFont("Times", 14)

    def __init__(self, *args, **kwargs):
        super(MessageDelegate, self).__init__(*args, **kwargs)

    def paint(self, painter, option, index):
        msg = index.model().data(index, Qt.DisplayRole)
        print("paint " + str(index.row()) + " " + str(option.rect.top()))
        field = QRect(option.rect)
        doc = QTextDocument(msg)
        doc.setDocumentMargin(0)
        opt = QTextOption()
        opt.setWrapMode(opt.WrapAtWordBoundaryOrAnywhere)
        doc.setDefaultTextOption(opt)
        doc.setDefaultFont(self.font)
        doc.setTextWidth(field.size().width())
        field.setHeight(int(doc.size().height()))
        field.setWidth(int(doc.idealWidth()))
        painter.setPen(Qt.gray)
        painter.setFont(self.font)
        painter.translate(field.x(), field.y())
        textrectf = QRectF(field)
        textrectf.moveTo(0, 0)
        doc.drawContents(painter, textrectf)
        painter.translate(-field.x(), -field.y())

    def sizeHint(self, option, index):
        global window_width
        msg = index.model().data(index, Qt.DisplayRole)
        doc = QTextDocument(msg)
        doc.setDocumentMargin(0)
        opt = QTextOption()
        opt.setWrapMode(opt.WrapAtWordBoundaryOrAnywhere)
        doc.setDefaultTextOption(opt)
        doc.setDefaultFont(self.font)
        doc.setTextWidth(window_width - self.WINDOW_PADDING)
        print("sizeHint " + str(index.row()) + " " + str(int(doc.size().height())))
        return QSize(0, int(doc.size().height()))


class MessageModel(QAbstractListModel):
    def __init__(self, *args, **kwargs):
        super(MessageModel, self).__init__(*args, **kwargs)
        self.messages = []

    def data(self, index, role):
        if role == Qt.DisplayRole:
            return self.messages[index.row()]

    def rowCount(self, index):
        return len(self.messages)

    def add_message(self, text):
        if text:
            self.messages.append(text)
            self.layoutChanged.emit()


class Dialog(QMainWindow):

    def __init__(self):
        global window_width
        super(Dialog, self).__init__()
        self.setMinimumSize(int(QApplication.primaryScreen().size().width() * 0.1), int(QApplication.primaryScreen().size().height() * 0.2))
        self.resize(int(QApplication.primaryScreen().size().width() * 0.3), int(QApplication.primaryScreen().size().height() * 0.5))
        window_width = int(QApplication.primaryScreen().size().width() * 0.3)
        self.messages = QListView()
        self.messages.setItemDelegate(MessageDelegate())
        self.model = MessageModel()
        self.messages.setModel(self.model)
        self.model.add_message("qwerty qwerty qwerty qwerty qwerty qwerty qwerty qwerty qwerty qwerty qwerty qwerty qwerty qwerty")
        self.model.add_message("abcdef")
        self.setCentralWidget(self.messages)

    def resizeEvent(self, event):
        global window_width
        super(Dialog, self).resizeEvent(event)
        window_width = self.size().width()

app = QApplication(sys.argv)
window = Dialog()
window.show()
app.exec_()

如您所见，在sizeHint中返回每一项的高度之前，我打印了每一项的高度。我还打印了在paint中接收到的option.rect的Y坐标。因为我只有两个项目，所以我希望item1的坐标等于item0的高度。乍一看，这似乎是可行的：

sizeHint 0 23
paint 0 0
sizeHint 1 23
paint 1 23

然而，当我缩小窗口的范围时，sizeHint中的高度开始增长(因为窄窗口无法容纳所有内容)，但option.rect的Y坐标保持不变：

sizeHint 0 46
paint 0 0
sizeHint 1 23
paint 1 23

即使到了第三行，option.rect的位置也没有更新：

sizeHint 0 69
paint 0 0
sizeHint 1 23
paint 1 23

因此，item1与item0重叠而不是向下移动。

​

​

有没有办法在之前某一项的大小发生变化时立即更新option.rect位置？

Answer 1

当索引的大小提示发生变化时，您需要发出MessageDelegate.sizeHintChanged，让条目的布局管理器知道它需要重新分布条目。在这种情况下，只有在调整窗口大小时，项目的高度才会改变，所以您可以在Dialog.resizeEvent中发出(自定义)信号并将其连接到MessageDelegate.sizeHintChanged。对于这个Dialog，需要根据如下所示进行修改

from PyQt5.QtCore import pyqtSignal, QModelIndex

class Dialog(QMainWindow):

    # custom signal for signalling when window is resized
    width_changed = pyqtSignal()

    def __init__(self):
        ... as before ...
        self.messages = QListView()
        delegate = MessageDelegate()
        self.messages.setItemDelegate(delegate)
        # Connect custom signal to delegate.sizeHintChanged. 
        # This signal expects a ModelIndex for which we take the root, i.e. QModelIndex()  
        self.width_changed.connect(lambda : delegate.sizeHintChanged.emit(QModelIndex()))
        .... rest as before ....

    def resizeEvent(self, event):
        global window_width
        super(Dialog, self).resizeEvent(event)
        window_width = self.size().width()
        # emit the custom signal
        self.width_changed.emit()

在上面的代码中，我没有修改代码中的任何其他内容，但是您可以选择删除全局window_width变量，方法是修改自定义信号以发出新的宽度，并在MessageDelegate中创建一个插槽以将新的宽度分配给一个实例变量。

Answer 2

项目内容的包装已经在QListView中实现，并且可以使用self.messages.setWordWrap(True)启用。如果你只使用委托进行文本换行，你根本就不需要它。