无论项目如何，QComboBox都会设置标题文本

Question

我有一个带有QStandardModel的QComboBox，我通过以下方式添加项目：

QStandardItem * item = new QStandardItem();
item->setText("someText");
item->setCheckable(true);

item->setFlags(Qt::ItemIsUserCheckable | Qt::ItemIsEnabled);
item->setData(Qt::Checked, Qt::CheckStateRole);

m_model->appendRow(item);
m_ComboBox->setModel(m_model);

这给了我一个带复选框的组合框，这正是我想要的。现在，当用户取消选择所有项目时，“无”应该是下拉菜单的文本。如果用户选择了一些项目，则“多个”将是文本。

我还没有找到如何设置QComboBox的标题文本的方法。除了子类化和自己做之外没有方便的方法吗？

Answer 1

没有子类化就没有方便的方法。实际上，子类化是最方便的方法。

即使你可以运行你的QComboBox模型并检查哪些项目被检查，一旦项目全部（或部分全部）被检查，你将无法告诉你的组合框自我更新。没有信号或特定功能允许您这样做。

但是将QComboBox子类化为具有此行为并不是非常复杂：您需要重新实现paintEvent（）。

//return a list with all the checked indexes
QModelIndexList MyComboBox::checkedIndexes()const
{
    return model()->match(model()->index(0, 0), Qt::CheckStateRole, Qt::Checked, -1, Qt::MatchRecursive);
}

// returns a list with all the unchecked indexes
QModelIndexList MyComboBox::uncheckedIndexes()const
{
    return model()->match(model()->index(0, 0), Qt::CheckStateRole, Qt::Unchecked, -1, Qt::MatchRecursive);
}

//return true if all the items are checked
bool MyComboBox::allChecked()const
{
    return (uncheckedIndexes().count() == 0);
}

//return true if all the items are unchecked
bool MyComboBox::noneChecked()const
{
    return (checkedIndexes().count() == 0);
}

void MyComboBox::paintEvent(QPaintEvent *)
{
    QStylePainter painter(this);

    // draw the combobox frame, focusrect and selected etc.
    QStyleOptionComboBox opt;
    this->initStyleOption(&opt);

    // all items are checked
    if (allChecked())
        opt.currentText = "All";
    // none are checked
    else if (noneChecked())
        opt.currentText = "None";
    //some are checked, some are not
    else
        opt.currentText = "Multiple";

    painter.drawComplexControl(QStyle::CC_ComboBox, opt);

    // draw the icon and text
    painter.drawControl(QStyle::CE_ComboBoxLabel, opt);
}

Answer 2

万一有人在python中执行什么，使用下面的代码，

class CheckableComboBox(QtGui.QComboBox):
    def __init__(self, parent=None):
        super(CheckableComboBox, self).__init__(parent)
        self.view().pressed.connect(self.handleItemPressed)
        self._changed = False

    def handleItemPressed(self, index):
        item = self.model().itemFromIndex(index)
        if item.checkState() == QtCore.Qt.Checked:
            item.setCheckState(QtCore.Qt.Unchecked)
        else:
            item.setCheckState(QtCore.Qt.Checked)
        self._changed = True

    def hidePopup(self):
        if not self._changed:
            super(CheckableComboBox, self).hidePopup()
        self._changed = False

    def itemChecked(self, index):
        item = self.model().item(index, self.modelColumn())
        return item.checkState() == QtCore.Qt.Checked

    def setItemChecked(self, index, checked=True):
        item = self.model().item(index, self.modelColumn())
        if checked:
            item.setCheckState(QtCore.Qt.Checked)
        else:
            item.setCheckState(QtCore.Qt.Unchecked)

    def checkedIndexes(self):
        return self.model().match(self.model().index(0,0), QtCore.Qt.CheckStateRole, QtCore.Qt.Checked, -1, QtCore.Qt.MatchRecursive)

    def uncheckedIndexes(self):
        return self.model().match(self.model().index(0,0), QtCore.Qt.CheckStateRole, QtCore.Qt.Unchecked, -1, QtCore.Qt.MatchRecursive)

    def allChecked(self):
        return len(self.uncheckedIndexes()) == 0

    def noneChecked(self):
        return len(self.checkedIndexes()) == 0

    def paintEvent(self, event):

        painter = QtGui.QStylePainter(self)
        opt = QtGui.QStyleOptionComboBox()
        self.initStyleOption(opt)

        if self.allChecked():
            opt.currentText = "All"
        elif self.noneChecked():
            opt.currentText = "None"
        else:
            opt.currentText = "Multiple"

        painter.drawComplexControl(QtGui.QStyle.CC_ComboBox, opt)
        painter.drawControl(QtGui.QStyle.CE_ComboBoxLabel, opt)