Set parent's status bar text?

design-patterns, qt

Solution

Use signals and slots;

Make `EditorWindow::setStatusBarText` a slot. Give the child a signal when it wants to change status, and connect that to the `setStatusBarText` slot.

// make setStatusBarText a slot...
class EditorWindow : public QWidget {
    Q_OBJECT
    ...
    public slots:
        void setStatusBarText(const QString&);
}

// make a signal to be emitted when status should change:
class SomeChildWidget : public QWidget {
    Q_OBJECT
    ...
    signals:
        void statusEvent(const QString&);
}

// connect them up when appropriate
EditorWindow::EditorWindow()
 : QWidget()
{
    ...
    m_childWidget = new SomeChildWidget(this);
    connect(m_childWidget, SIGNAL(statusEvent(QString)),
            this,          SLOT(setStatusBarText(QString)));
    ...
}

Then the child would `emit statusEvent(somestring)` when the status should be updated.

This scales well, you can have as many child widgets as you like with the ability to change the status text, they don't know anything about their parent widget, and you can implement a policy in the parent widget for accepting or refusing status updates from child widgets.

Problem

I can set the parent's status bar text with this function I wrote ``` void EditorWindow::setStatusBarText(const QString& text) { statusBar()->showMessage(text); } ``` Called like this (from child) ``` ((EditorWindow*) parent())->setStatusBarText(tr("%1, %2").arg(mousePos.x(), 0, 'f', 2).arg(mousePos.y(), 0, 'f', 2)); ``` But I'm pretty sure that breaks a few design principles. For instance, what if `parent()` is not an `EditorWindow*`? So what's the workaround for this? Force the user to pass a reference to an `EditorWindow` upon creation to ensure parent is of the correct type?

Original source