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QML QtQuick `control` property of corresponding Style object is sometimes null

I have some QML code using QtQuick.Controls 1.4 from Qt 5.6.1. I have some wrappers around various controls, such as ComboBox; these make use of Style objects. For instance, MyComboBox is a ComboBox with a custom ComboBoxStyle.

Every so often, when certain components are loaded, the control property in the Style object is null:

In MyComboBox.qml:

...
style: ComboBoxStyle {
    ...
    label: Label {
        text: control.currentText
...

The resulting error output is:

qrc:/MyComboBox.qml:72: TypeError: Cannot read property 'currentText' of null

Restarting the application typically fixes the error.

I have no idea how this could happen or why the error appears non-deterministic. What can I do to investigate?

Solution

  • This appears to have been fixed in release 5.6.1-1; since upgrading, we have not observed this error. Presumably we were simply observing one of the less-critical symptoms of QTBUG-53761.

    Credit to jpnurmi for recognizing the similarity of the symptoms I described to the behavior of the bug, and for notifying me that a release with a fix was available (which, sadly, is not evident on the Qt 5.6 release-series page).