Qt：如何处理 QAbstractItemView 的焦点变化

Question

我想做的就是知道用户何时按下 ctrl + 向上箭头/向下箭头来聚焦列表中的项目。我希望我可以区分用户关注项目和选择项目。

我有一个 QAbstractItemView 的实现，我已经覆盖了它

::selectionChanged(const QItemSelection& selected, const QItemSelection& deselected) 以及

::currentChanged(const QModelIndex& current, const QModelIndex& previous)

阅读https://doc.qt.io/archives/qtjambi-4.5.2_01/com/trolltech/qt/model-view-selection.html 后我的理解是，如果我用ctrl + up arrow 聚焦一个项目，我将得到一个currentChanged 事件。如果我通过up arrow 选择某些内容，我将获得selectionChanged 事件。

但是，事实并非如此。按ctrl + up arrow 会导致selectionChanged 和currentChanged 都被解雇。我不知道为什么一旦我进入这些功能就会被解雇。当我在selectionChanged 时，我不知道我为什么在那里。是因为专注吗？是因为选择吗？

有件事可能应该告诉我QItemSelectionModel.SelectionFlag，但我显然也无权访问这些。

那么发生了什么？这是一个错误吗？同样，我想做的只是列表中的焦点项目。

qt 版本 5.9

Answer 1

我试图重现 OP 描述的问题。

不幸的是，OP 没有提供MCVE。所以，我自己做了一个：

// Qt header:
#include <QtWidgets>

class ListWidget: public QListWidget {

  public:
    ListWidget(QWidget *pQParent = nullptr): QListWidget(pQParent) { }
    virtual ~ListWidget() = default;
    ListWidget(const ListWidget&) = delete;
    ListWidget& operator=(const ListWidget&) = delete;

    virtual void currentChanged(
      const QModelIndex &current, const QModelIndex &previous) override
    {
      qDebug() << "currentChanged():" << previous << "->" << current;
      QListWidget::currentChanged(current, previous);
    }

    virtual void selectionChanged(
      const QItemSelection &selected, const QItemSelection &deselected) override
    {
      qDebug() << "selectionChanged():" << selected << "->" << deselected;
      QListWidget::selectionChanged(selected, deselected);
    }
};

void populate(QListWidget &qLst)
{
  const int n = 10;
  for (int i = 1; i <= n; ++i) {
    new QListWidgetItem(QString("item %1").arg(i), &qLst);
  }
}

// main application
int main(int argc, char **argv)
{
  qDebug() << "Qt Version:" << QT_VERSION_STR;
  QApplication app(argc, argv);
  // setup GUI
  ListWidget qLst;
  qLst.setSelectionMode(QListWidget::ExtendedSelection);
  populate(qLst);
  qLst.show();
  // runtime loop
  return app.exec();
}

在VS2017中用Qt5.13编译：

输出：

Qt Version: 5.13.0
currentChanged(): QModelIndex(-1,-1,0x0,QObject(0x0)) -> QModelIndex(0,0,0x2adc4f38610,QListModel(0x2adc4f3a3a0))

我用 Shift ↓ 选择了前 5 个项目：

currentChanged(): QModelIndex(0,0,0x2adc4f38610,QListModel(0x2adc4f3a3a0)) -> QModelIndex(1,0,0x2adc4f38a00,QListModel(0x2adc4f3a3a0))
selectionChanged(): (QItemSelectionRange(QModelIndex(0,0,0x2adc4f38610,QListModel(0x2adc4f3a3a0)),QModelIndex(0,0,0x2adc4f38610,QListModel(0x2adc4f3a3a0))), QItemSelectionRange(QModelIndex(1,0,0x2adc4f38a00,QListModel(0x2adc4f3a3a0)),QModelIndex(1,0,0x2adc4f38a00,QListModel(0x2adc4f3a3a0)))) -> ()
currentChanged(): QModelIndex(1,0,0x2adc4f38a00,QListModel(0x2adc4f3a3a0)) -> QModelIndex(2,0,0x2adc4f38a70,QListModel(0x2adc4f3a3a0))
selectionChanged(): (QItemSelectionRange(QModelIndex(2,0,0x2adc4f38a70,QListModel(0x2adc4f3a3a0)),QModelIndex(2,0,0x2adc4f38a70,QListModel(0x2adc4f3a3a0)))) -> ()
currentChanged(): QModelIndex(2,0,0x2adc4f38a70,QListModel(0x2adc4f3a3a0)) -> QModelIndex(3,0,0x2adc4f38ae0,QListModel(0x2adc4f3a3a0))
selectionChanged(): (QItemSelectionRange(QModelIndex(3,0,0x2adc4f38ae0,QListModel(0x2adc4f3a3a0)),QModelIndex(3,0,0x2adc4f38ae0,QListModel(0x2adc4f3a3a0)))) -> ()
currentChanged(): QModelIndex(3,0,0x2adc4f38ae0,QListModel(0x2adc4f3a3a0)) -> QModelIndex(4,0,0x2adc4f38f40,QListModel(0x2adc4f3a3a0))
selectionChanged(): (QItemSelectionRange(QModelIndex(4,0,0x2adc4f38f40,QListModel(0x2adc4f3a3a0)),QModelIndex(4,0,0x2adc4f38f40,QListModel(0x2adc4f3a3a0)))) -> ()

然后我使用 Ctrl ↓ 将焦点移动到item 10：

currentChanged(): QModelIndex(4,0,0x2adc4f38f40,QListModel(0x2adc4f3a3a0)) -> QModelIndex(5,0,0x2adc4f3f990,QListModel(0x2adc4f3a3a0))
currentChanged(): QModelIndex(5,0,0x2adc4f3f990,QListModel(0x2adc4f3a3a0)) -> QModelIndex(6,0,0x2adc4f3f6f0,QListModel(0x2adc4f3a3a0))
currentChanged(): QModelIndex(6,0,0x2adc4f3f6f0,QListModel(0x2adc4f3a3a0)) -> QModelIndex(7,0,0x2adc4f3f1b0,QListModel(0x2adc4f3a3a0))
currentChanged(): QModelIndex(7,0,0x2adc4f3f1b0,QListModel(0x2adc4f3a3a0)) -> QModelIndex(8,0,0x2adc4f3f840,QListModel(0x2adc4f3a3a0))
currentChanged(): QModelIndex(8,0,0x2adc4f3f840,QListModel(0x2adc4f3a3a0)) -> QModelIndex(9,0,0x2adc4f3f7d0,QListModel(0x2adc4f3a3a0))

这在我看来是合理的 - 正如 OP 所报告的那样，没有对 selectionChanged() 的不必要调用。

可以肯定的是，我在cygwin中编译了相同的代码并再次尝试：

$ qmake-qt5 
Info: creating stash file /cygdrive/d/ds32737/Entwicklung/tests/Qt/QAbstractItemViewCurrentChanged/.qmake.stash

$ make && ./testQAbstractItemViewCurrentChanged
g++ -c -fno-keep-inline-dllexport -D_GNU_SOURCE -pipe -O2 -Wall -W -D_REENTRANT -DQT_NO_DEBUG -DQT_WIDGETS_LIB -DQT_GUI_LIB -DQT_CORE_LIB -I. -isystem /usr/include/qt5 -isystem /usr/include/qt5/QtWidgets -isystem /usr/include/qt5/QtGui -isystem /usr/include/qt5/QtCore -I. -I/usr/lib/qt5/mkspecs/cygwin-g++ -o testQAbstractItemViewCurrentChanged.o testQAbstractItemViewCurrentChanged.cc
g++  -o testQAbstractItemViewCurrentChanged.exe testQAbstractItemViewCurrentChanged.o   -lQt5Widgets -lQt5Gui -lQt5Core -lGL -lpthread 
Qt Version: 5.9.4
currentChanged(): QModelIndex(-1,-1,0x0,QObject(0x0)) -> QModelIndex(0,0,0x60014b260,QListModel(0x6000df6b0))
currentChanged(): QModelIndex(0,0,0x60014b260,QListModel(0x6000df6b0)) -> QModelIndex(1,0,0x60014ba60,QListModel(0x6000df6b0))
selectionChanged(): (QItemSelectionRange(QModelIndex(0,0,0x60014b260,QListModel(0x6000df6b0)),QModelIndex(0,0,0x60014b260,QListModel(0x6000df6b0))), QItemSelectionRange(QModelIndex(1,0,0x60014ba60,QListModel(0x6000df6b0)),QModelIndex(1,0,0x60014ba60,QListModel(0x6000df6b0)))) -> ()
currentChanged(): QModelIndex(1,0,0x60014ba60,QListModel(0x6000df6b0)) -> QModelIndex(2,0,0x60014bb20,QListModel(0x6000df6b0))
selectionChanged(): (QItemSelectionRange(QModelIndex(2,0,0x60014bb20,QListModel(0x6000df6b0)),QModelIndex(2,0,0x60014bb20,QListModel(0x6000df6b0)))) -> ()
currentChanged(): QModelIndex(2,0,0x60014bb20,QListModel(0x6000df6b0)) -> QModelIndex(3,0,0x60014bc30,QListModel(0x6000df6b0))
selectionChanged(): (QItemSelectionRange(QModelIndex(3,0,0x60014bc30,QListModel(0x6000df6b0)),QModelIndex(3,0,0x60014bc30,QListModel(0x6000df6b0)))) -> ()
currentChanged(): QModelIndex(3,0,0x60014bc30,QListModel(0x6000df6b0)) -> QModelIndex(4,0,0x60014bd20,QListModel(0x6000df6b0))
selectionChanged(): (QItemSelectionRange(QModelIndex(4,0,0x60014bd20,QListModel(0x6000df6b0)),QModelIndex(4,0,0x60014bd20,QListModel(0x6000df6b0)))) -> ()
currentChanged(): QModelIndex(4,0,0x60014bd20,QListModel(0x6000df6b0)) -> QModelIndex(5,0,0x60014be10,QListModel(0x6000df6b0))
currentChanged(): QModelIndex(5,0,0x60014be10,QListModel(0x6000df6b0)) -> QModelIndex(6,0,0x60014bf00,QListModel(0x6000df6b0))
currentChanged(): QModelIndex(6,0,0x60014bf00,QListModel(0x6000df6b0)) -> QModelIndex(7,0,0x60014bbb0,QListModel(0x6000df6b0))
currentChanged(): QModelIndex(7,0,0x60014bbb0,QListModel(0x6000df6b0)) -> QModelIndex(8,0,0x60014c120,QListModel(0x6000df6b0))
currentChanged(): QModelIndex(8,0,0x60014c120,QListModel(0x6000df6b0)) -> QModelIndex(9,0,0x60014c210,QListModel(0x6000df6b0))

所以，我再次无法复制。报告的事件与我使用 VS2017 得到的事件相当。

请注意，我已经在 cygwin 上安装了 Qt5.9.4——OP 声称拥有的版本。