QDockWidget::background-color not applied when docked

Question

I have a QDockWidget:

I would like to alert the user to certain events by setting the background color of the title bar.

I have achieved this by setting the style sheet for my DockWidget:

void DockWidget::setCriticalAlert()
{
    setStyleSheet("QDockWidget { background-color:red; }");
}

The result is this:

The problem is that the background-color doesn't get applied when the QDockWidget is docked:

How can I get the background color to be applied when the QDockWidget is docked?

Answer 1

This is a bug in Qt.

Issue 10537

Quoting from the linked issue:

The problem is that in QDockWidget::paintEvent, there is a isFloating() condition before drawing PE_FrameDockWidget. We cannot jsut remove this condition as it would break the other style (that does not whish to draw frame when the dockwidget is docked) We cannot either use PE_Widget to draw the frame as then it goes over the dockwidget's title The solution is maybe to introduce a new PE_FrameDockWidgetDocked primitive element. Or some SH_DockWidget_DrawDockedFrame stylehint to draw the frame in every cases.

Answer 2

a valid workaround seems to be to set the stylesheet of the parent, and use the class-and-id selector. Forgive the python formatted code but the concept is the same - in this case, 'dock' is a QDockWidget which has been given an object name using setObjectName(), and its parent, the QMainWindow, is 'self':

self.setStyleSheet("QDockWidget#"+str(dock.objectName())+"::title {background-color:red}")

In PyQt5.5, this works at runtime, i.e., can be changed on the fly.