- Qt 6.8
- Qt Widgets
- Tree Model Completer Example
- Qt 6.8.1 Reference Documentation

# Tree Model Completer Example

The Tree Model Completer example shows how to provide completion facilities for a hierarchical model, using a period as the separator to access Child, GrandChild and GrandGrandChild level objects.

Similar to the Completer Example, we provide QComboBox objects to enable selection for completion mode and case sensitivity, as well as a QCheckBox for wrap completions.

#### The Resource File

The contents of the TreeModelCompleter is read from treemodel.txt. This file is embedded within the treemodelcompleter.qrc resource file, which contains the following:

     <!DOCTYPE RCC><RCC version="1.0">
     <qresource prefix="/">
        <file>resources/treemodel.txt</file>
     </qresource>
     </RCC>

#### TreeModelCompleter Class Definition

The `TreeModelCompleter` is a subclass of QCompleter with two constructors - one with parent as an argument and another with parent and model as arguments.

     class TreeModelCompleter : public QCompleter
     {
         Q_OBJECT
         Q_PROPERTY(QString separator READ separator WRITE setSeparator)

     public:
         explicit TreeModelCompleter(QObject *parent = nullptr);
         explicit TreeModelCompleter(QAbstractItemModel *model, QObject *parent = nullptr);

         QString separator() const;
     public slots:
         void setSeparator(const QString &separator);

     protected:
         QStringList splitPath(const QString &path) const override;
         QString pathFromIndex(const QModelIndex &index) const override;

     private:
         QString sep;
     };

The class reimplements the protected functions splitPath() and pathFromIndex() to suit a tree model. For more information on customizing QCompleter to suit tree models, refer to Handling Tree Models.

`TreeModelCompleter` also has a separator property which is declared using the Q_PROPERTY() macro. The separator has READ and WRITE attributes and the corresponding functions `separator()` and `setSeparator()`. For more information on Q_PROPERTY(), refer to Qt's Property System.

#### TreeModelCompleter Class Implementation

The first constructor constructs a `TreeModelCompleter` object with a parent while the second constructor constructs an object with a parent and a QAbstractItemModel, model.

     TreeModelCompleter::TreeModelCompleter(QObject *parent)
         : QCompleter(parent)
     {
     }

     TreeModelCompleter::TreeModelCompleter(QAbstractItemModel *model, QObject *parent)
         : QCompleter(model, parent)
     {
     }

The `separator()` function is a getter function that returns the separator string.

     QString TreeModelCompleter::separator() const
     {
         return sep;
     }

As mentioned earlier, the `splitPath()` function is reimplemented because the default implementation is more suited to QFileSystemModel or list models. In order for QCompleter to split the path into a list of strings that are matched at each level, we split it using QString::split() with `sep` as its separator.

     QStringList TreeModelCompleter::splitPath(const QString &path) const
     {
         return (sep.isNull() ? QCompleter::splitPath(path) : path.split(sep));
     }

The `pathFromIndex()` function returns data for the completionRole() for a tree model. This function is reimplemented as its default implementation is more suitable for list models. If there is no separator, we use QCompleter's default implementation, otherwise we use the prepend() function to navigate upwards and accumulate the data. The function then returns a QStringList, `dataList`, using a separator to join objects of different levels.

     QString TreeModelCompleter::pathFromIndex(const QModelIndex &index) const
     {
         if (sep.isNull())
             return QCompleter::pathFromIndex(index);

         // navigate up and accumulate data
         QStringList dataList;
         for (QModelIndex i = index; i.isValid(); i = i.parent())
             dataList.prepend(model()->data(i, completionRole()).toString());

         return dataList.join(sep);
     }

#### MainWindow Class Definition

The `MainWindow` class is a subclass of QMainWindow and implements five custom slots: `about()`, `changeCase()`, `changeMode()`, `highlight()`, and `updateContentsLabel()`.

     class MainWindow : public QMainWindow
     {
         Q_OBJECT

     public:
         MainWindow(QWidget *parent = nullptr);

     private slots:
         void about();
         void changeCase(int);
         void changeMode(int);
         void highlight(const QModelIndex &index);
         void updateContentsLabel(const QString &sep);

In addition, the class has two private functions, `createMenu()` and `modelFromFile()`, as well as private instances of QTreeView, QComboBox, QLabel, `TreeModelCompleter` and QLineEdit.

     private:
         void createMenu();
         QAbstractItemModel *modelFromFile(const QString &fileName);

         QTreeView *treeView = nullptr;
         QComboBox *caseCombo = nullptr;
         QComboBox *modeCombo = nullptr;
         QLabel *contentsLabel = nullptr;
         TreeModelCompleter *completer = nullptr;
         QLineEdit *lineEdit = nullptr;
     };

#### MainWindow Class Implementation

The `MainWindow`'s constructor creates a `MainWindow` object with a parent and initializes the `completer` and `lineEdit`. The `createMenu()` function is invoked to set up the "File" menu and "Help" menu. The `completer`'s model is set to the QAbstractItemModel obtained from `modelFromFile()`, and the highlighted() signal is connected to `MainWindow`'s `highlight()` slot.

     MainWindow::MainWindow(QWidget *parent)
         : QMainWindow(parent)
     {
         createMenu();

         completer = new TreeModelCompleter(this);
         completer->setModel(modelFromFile(":/resources/treemodel.txt"));
         completer->setSeparator(QLatin1String("."));
         QObject::connect(completer, QOverload<const QModelIndex &>::of(&TreeModelCompleter::highlighted),
                          this, &MainWindow::highlight);

         QWidget *centralWidget = new QWidget;

         QLabel *modelLabel = new QLabel;
         modelLabel->setText(tr("Tree Model<br>(Double click items to edit)"));

         QLabel *modeLabel = new QLabel;
         modeLabel->setText(tr("Completion Mode"));
         modeCombo = new QComboBox;
         modeCombo->addItem(tr("Inline"));
         modeCombo->addItem(tr("Filtered Popup"));
         modeCombo->addItem(tr("Unfiltered Popup"));
         modeCombo->setCurrentIndex(1);

         QLabel *caseLabel = new QLabel;
         caseLabel->setText(tr("Case Sensitivity"));
         caseCombo = new QComboBox;
         caseCombo->addItem(tr("Case Insensitive"));
         caseCombo->addItem(tr("Case Sensitive"));
         caseCombo->setCurrentIndex(0);

The QLabel objects `modelLabel`, `modeLabel` and `caseLabel` are instantiated. Also, the QComboBox objects, `modeCombo` and `caseCombo`, are instantiated and populated. By default, the `completer`'s mode is "Filtered Popup" and the case is insensitive.

         QLabel *separatorLabel = new QLabel;
         separatorLabel->setText(tr("Tree Separator"));

         QLineEdit *separatorLineEdit = new QLineEdit;
         separatorLineEdit->setText(completer->separator());
         connect(separatorLineEdit, &QLineEdit::textChanged,
                 completer, &TreeModelCompleter::setSeparator);

         QCheckBox *wrapCheckBox = new QCheckBox;
         wrapCheckBox->setText(tr("Wrap around completions"));
         wrapCheckBox->setChecked(completer->wrapAround());
         connect(wrapCheckBox, &QAbstractButton::clicked, completer, &QCompleter::setWrapAround);

         contentsLabel = new QLabel;
         contentsLabel->setSizePolicy(QSizePolicy::Fixed, QSizePolicy::Fixed);
         connect(separatorLineEdit, &QLineEdit::textChanged,
                 this, &MainWindow::updateContentsLabel);

         treeView = new QTreeView;
         treeView->setModel(completer->model());
         treeView->header()->hide();
         treeView->expandAll();

         connect(modeCombo, &QComboBox::activated,
                 this, &MainWindow::changeMode);
         connect(caseCombo, &QComboBox::activated,
                 this, &MainWindow::changeMode);

         lineEdit = new QLineEdit;
         lineEdit->setCompleter(completer);

We use a QGridLayout to place all the objects in the `MainWindow`.

         QGridLayout *layout = new QGridLayout;
         layout->addWidget(modelLabel, 0, 0); layout->addWidget(treeView, 0, 1);
         layout->addWidget(modeLabel, 1, 0);  layout->addWidget(modeCombo, 1, 1);
         layout->addWidget(caseLabel, 2, 0);  layout->addWidget(caseCombo, 2, 1);
         layout->addWidget(separatorLabel, 3, 0); layout->addWidget(separatorLineEdit, 3, 1);
         layout->addWidget(wrapCheckBox, 4, 0);
         layout->addWidget(contentsLabel, 5, 0, 1, 2);
         layout->addWidget(lineEdit, 6, 0, 1, 2);
         centralWidget->setLayout(layout);
         setCentralWidget(centralWidget);

         changeCase(caseCombo->currentIndex());
         changeMode(modeCombo->currentIndex());

         setWindowTitle(tr("Tree Model Completer"));
         lineEdit->setFocus();
     }

The `createMenu()` function sets up the QAction objects required and adds them to the "File" menu and "Help" menu. The triggered() signals from these actions are connected to their respective slots.

     void MainWindow::createMenu()
     {
         QAction *exitAction = new QAction(tr("Exit"), this);
         QAction *aboutAct = new QAction(tr("About"), this);
         QAction *aboutQtAct = new QAction(tr("About Qt"), this);

         connect(exitAction, &QAction::triggered, qApp, &QApplication::quit);
         connect(aboutAct, &QAction::triggered, this, &MainWindow::about);
         connect(aboutQtAct, &QAction::triggered, qApp, &QApplication::aboutQt);

         QMenu *fileMenu = menuBar()->addMenu(tr("File"));
         fileMenu->addAction(exitAction);

         QMenu *helpMenu = menuBar()->addMenu(tr("About"));
         helpMenu->addAction(aboutAct);
         helpMenu->addAction(aboutQtAct);
     }

The `changeMode()` function accepts an index corresponding to the user's choice of completion mode and changes the `completer`'s mode accordingly.

     void MainWindow::changeMode(int index)
     {
         QCompleter::CompletionMode mode;
         if (index == 0)
             mode = QCompleter::InlineCompletion;
         else if (index == 1)
             mode = QCompleter::PopupCompletion;
         else
             mode = QCompleter::UnfilteredPopupCompletion;

         completer->setCompletionMode(mode);
     }

The `about()` function provides a brief description on the Tree Model Completer example.

     void MainWindow::about()
     {
         QMessageBox::about(this, tr("About"), tr("This example demonstrates how "
             "to use a QCompleter with a custom tree model."));
     }

The `changeCase()` function alternates between Case Sensitive and Case Insensitive modes, depending on the value of cs.

     void MainWindow::changeCase(int cs)
     {
         completer->setCaseSensitivity(cs ? Qt::CaseSensitive : Qt::CaseInsensitive);
     }

#### `main()` Function

The `main()` function instantiates `MainWindow` and invokes the show() function to display it.

     int main(int argc, char *argv[])
     {
         QApplication app(argc, argv);
         MainWindow window;
         window.show();
         return app.exec();
     }

Example project @ code.qt.io