Qt mode/view全解七

本章我们讲解MV的选择事件，方法是我们构造一个树状结构，并在标题栏显示我们所选的树状结构的内容和层次。

选择事件也是通过mode实现的，然而他是独立的mode，叫做：QItemSelectionModel，默认每个view都有这样一个mode，可以通过view的selectionModel()获取！selectionModel的selectionChange()信号就是我们要获取的信号！

mainwindows.cpp

#include <QtWidgets/QMainWindow>

QT_BEGIN_NAMESPACE // QT_BEGIN_NAMESPACE / QT_END_NAMESPACE are not needed in Qt user code
class QTreeView; //forward declarations
class QStandardItemModel;
class QItemSelection;
QT_END_NAMESPACE


class MainWindow : public QMainWindow
{
    Q_OBJECT
private:
    QTreeView *treeView;
    QStandardItemModel *standardModel;
private slots:
    void selectionChangedSlot(const QItemSelection & newSelection, const QItemSelection & oldSelection);
public:
    MainWindow(QWidget *parent = 0);
};

selectionChangedSlot()槽函数用来接收selectionChange()信号。

mainwindows.cpp

#include <QTreeView>
#include <QStandardItemModel>
#include <QItemSelectionModel>
#include "mainwindow.h"

MainWindow::MainWindow(QWidget *parent)
    : QMainWindow(parent)
{
    treeView = new QTreeView(this);
    setCentralWidget(treeView);
    standardModel = new QStandardItemModel ;
    QStandardItem *rootNode = standardModel->invisibleRootItem();


    //defining a couple of items
    QStandardItem *americaItem = new QStandardItem("America");
    QStandardItem *mexicoItem =  new QStandardItem("Canada");
    QStandardItem *usaItem =     new QStandardItem("USA");
    QStandardItem *bostonItem =  new QStandardItem("Boston");
    QStandardItem *europeItem =  new QStandardItem("Europe");
    QStandardItem *italyItem =   new QStandardItem("Italy");
    QStandardItem *romeItem =    new QStandardItem("Rome");
    QStandardItem *veronaItem =  new QStandardItem("Verona");

    //building up the hierarchy
    rootNode->    appendRow(americaItem);
    rootNode->    appendRow(europeItem);
    americaItem-> appendRow(mexicoItem);
    americaItem-> appendRow(usaItem);
    usaItem->     appendRow(bostonItem);
    europeItem->  appendRow(italyItem);
    italyItem->   appendRow(romeItem);
    italyItem->   appendRow(veronaItem);

    //register the model
    treeView->setModel(standardModel);
    treeView->expandAll();

    //selection changes shall trigger a slot
    QItemSelectionModel *selectionModel= treeView->selectionModel();
    connect(selectionModel, SIGNAL(selectionChanged (const QItemSelection &, const QItemSelection &)),
            this, SLOT(selectionChangedSlot(const QItemSelection &, const QItemSelection &)));
}
//! [quoting modelview_a]

//------------------------------------------------------------------------------------

//! [quoting modelview_b]
void MainWindow::selectionChangedSlot(const QItemSelection & /*newSelection*/, const QItemSelection & /*oldSelection*/)
{
    //get the text of the selected item
    const QModelIndex index = treeView->selectionModel()->currentIndex();
    QString selectedText = index.data(Qt::DisplayRole).toString();
    //find out the hierarchy level of the selected item
    int hierarchyLevel=1;
    QModelIndex seekRoot = index;
    while(seekRoot.parent() != QModelIndex())
    {
        seekRoot = seekRoot.parent();
        hierarchyLevel++;
    }
    QString showString = QString("%1, Level %2").arg(selectedText)
                         .arg(hierarchyLevel);
    setWindowTitle(showString);
}

构造函数用标准控件构造一棵树，并连接信号和槽，每当我们鼠标进行选择就会触发槽函数。槽函数中取得当前节点的文本信息，并通过QModelIndex的parent()来查询index的层次，现在在标题栏！

运行效果如下：

最后

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