QMessageBox: Forward helper checkbox state via lambda

There may not be a checkbox when the helper is initialized, and
we want to support the case of a checkbox being added at a later
stage.

Regression from e5c40ec5c117376f401c01069f05780046d07094.

Pick-to: 6.7
Change-Id: I397c3b3a101b249aab17804bd90085cfd4ab7dbb
Reviewed-by: Axel Spoerl <axel.spoerl@qt.io>

1 files changed, 7 insertions, 2 deletions

diff --git a/src/widgets/dialogs/qmessagebox.cpp b/src/widgets/dialogs/qmessagebox.cpp
index e91a2625cf..9ff2b5159b 100644
--- a/src/widgets/dialogs/qmessagebox.cpp
+++ b/src/widgets/dialogs/qmessagebox.cpp
@@ -2782,9 +2782,14 @@ void QMessageBoxPrivate::initHelper(QPlatformDialogHelper *h)
     auto *messageDialogHelper = static_cast<QPlatformMessageDialogHelper *>(h);
     QObjectPrivate::connect(messageDialogHelper, &QPlatformMessageDialogHelper::clicked,
                             this, &QMessageBoxPrivate::helperClicked);
+    // Forward state via lambda, so that we can handle addition and removal
+    // of checkbox via setCheckBox() after initializing helper.
     QObject::connect(messageDialogHelper, &QPlatformMessageDialogHelper::checkBoxStateChanged,
-                     checkbox, &QCheckBox::setCheckState);
-
+        q_ptr, [this](Qt::CheckState state) {
+            if (checkbox)
+                checkbox->setCheckState(state);
+        }
+    );
     messageDialogHelper->setOptions(options);
 }