Question

Using a regular QComboBox populated with items, if currentIndex is set to -1, the widget is empty. It would be very useful to instead have an initial descriptive text visible in the combo box(e.g. "--Select Country--", "--Choose Topic--", etc.) which is not shown in the dropdown list.

我在文件中找不到任何东西,也没有回答以前的任何问题。

Answer 1

在Combo盒式APIC中,似乎没有预料到这种情况。但是,根据基本模式的灵活性,你似乎应当能够将-当选国-<>/em>作为第一个“合法”项目,然后保持其可选择的用途:

QStandardItemModel* model = qobject_cast<QStandardItemModel*>(comboBox->model()); QModelIndex firstIndex = model->index(0, comboBox->modelColumn(), comboBox->rootModelIndex()); QStandardItem* firstItem = model->itemFromIndex(firstIndex); firstItem->setSelectable(false);

视你想要的准确行为而定,你可能希望使用<条码>。或者,如果这只是一个不同的肤色项目,我可以回头来:

Qt, 我如何改变QComboBox一个项目的文字颜色? (C++)

(我不喜欢我点击某件事,然后被困在我可以回去的地方,即使我只举一个没有当选的国家!)。

Answer 2

你们可以采取的一种类似做法是,设置一个地方持有人:

comboBox->setPlaceholderText(QStringLiteral("--Select Country--"));
comboBox->setCurrentIndex(-1);

这样,你就有一个无法选择的缺省。

Answer 3

Leaving my solution here from PyQt5. Create a proxy model and shift all the rows down one, and return a default value at row 0.

class NullRowProxyModel(QAbstractProxyModel):
    """Creates an empty row at the top for null selections on combo boxes
    """

    def __init__(self, src, text= --- , parent=None):
        super(NullRowProxyModel, self).__init__(parent)
        self._text = text
        self.setSourceModel(src)

    def mapToSource(self, proxyIndex: QModelIndex) -> QModelIndex:
        if self.sourceModel():
            return self.sourceModel().index(proxyIndex.row()-1, proxyIndex.column())
        else:
            return QModelIndex()

    def mapFromSource(self, sourceIndex: QModelIndex) -> QModelIndex:
        return self.index(sourceIndex.row()+1, sourceIndex.column())

    def data(self, proxyIndex: QModelIndex, role=Qt.DisplayRole) -> typing.Any:
        if proxyIndex.row() == 0 and role == Qt.DisplayRole:
            return self._text
        elif proxyIndex.row() == 0 and role == Qt.EditRole:
            return None
        else:
            return super(NullRowProxyModel, self).data(proxyIndex, role)

    def index(self, row: int, column: int, parent: QModelIndex = ...) -> QModelIndex:
        return self.createIndex(row, column)

    def parent(self, child: QModelIndex) -> QModelIndex:
        return QModelIndex()

    def rowCount(self, parent: QModelIndex = ...) -> int:
        return self.sourceModel().rowCount()+1 if self.sourceModel() else 0

    def columnCount(self, parent: QModelIndex = ...) -> int:
        return self.sourceModel().columnCount() if self.sourceModel() else 0

    def headerData(self, section: int, orientation: Qt.Orientation, role: int = ...) -> typing.Any:
        if not self.sourceModel():
            return None
        if orientation == Qt.Vertical:
            return self.sourceModel().headerData(section-1, orientation, role)
        else:
            return self.sourceModel().headerData(section, orientation, role)

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