StackView: fix crash when attempting to transition null items

Don't attempt to kick off view transitions for stack elements that have
failed to load.

Change-Id: I6e42785a30abc815d14a07e7d16aad5bde66391d
Reviewed-by: Mitch Curtis <mitch.curtis@theqtcompany.com>

2 files changed, 19 insertions, 6 deletions

diff --git a/src/templates/qquickstackview_p.cpp b/src/templates/qquickstackview_p.cpp
index 1a08d349..ffd9934e 100644
--- a/src/templates/qquickstackview_p.cpp
+++ b/src/templates/qquickstackview_p.cpp
@@ -405,13 +405,13 @@ void QQuickStackViewPrivate::popTransition(QQuickStackElement *enter, QQuickStac
     }
 
     if (exit) {
-        if (immediate || !exit->prepareTransition(transitioner, viewBounds))
+        if (immediate || !exit->item || !exit->prepareTransition(transitioner, viewBounds))
             completeTransition(exit, transitioner->removeTransition);
         else
             exit->startTransition(transitioner);
     }
     if (enter) {
-        if (immediate || !enter->prepareTransition(transitioner, QRectF()))
+        if (immediate || !enter->item || !enter->prepareTransition(transitioner, QRectF()))
             completeTransition(enter, transitioner->removeDisplacedTransition);
         else
             enter->startTransition(transitioner);
@@ -437,13 +437,13 @@ void QQuickStackViewPrivate::pushTransition(QQuickStackElement *enter, QQuickSta
     }
 
     if (enter) {
-        if (immediate || !enter->prepareTransition(transitioner, viewBounds))
+        if (immediate || !enter->item || !enter->prepareTransition(transitioner, viewBounds))
             completeTransition(enter, transitioner->addTransition);
         else
             enter->startTransition(transitioner);
     }
     if (exit) {
-        if (immediate || !exit->prepareTransition(transitioner, QRectF()))
+        if (immediate || !exit->item || !exit->prepareTransition(transitioner, QRectF()))
             completeTransition(exit, transitioner->addDisplacedTransition);
         else
             exit->startTransition(transitioner);
@@ -470,13 +470,13 @@ void QQuickStackViewPrivate::replaceTransition(QQuickStackElement *enter, QQuick
     }
 
     if (exit) {
-        if (immediate || !exit->prepareTransition(transitioner, QRectF()))
+        if (immediate || !exit->item || !exit->prepareTransition(transitioner, QRectF()))
             completeTransition(exit, transitioner->moveDisplacedTransition);
         else
             exit->startTransition(transitioner);
     }
     if (enter) {
-        if (immediate || !enter->prepareTransition(transitioner, viewBounds))
+        if (immediate || !enter->item || !enter->prepareTransition(transitioner, viewBounds))
             completeTransition(enter, transitioner->moveTransition);
         else
             enter->startTransition(transitioner);
diff --git a/tests/auto/controls/data/tst_stackview.qml b/tests/auto/controls/data/tst_stackview.qml
index 23eaf317..1cd12af3 100644
--- a/tests/auto/controls/data/tst_stackview.qml
+++ b/tests/auto/controls/data/tst_stackview.qml
@@ -744,4 +744,17 @@ TestCase {
 
         control.destroy()
     }
+
+    function test_failures() {
+        var control = stackView.createObject(testCase, {initialItem: component})
+        verify(control)
+
+        ignoreWarning("QQmlComponent: Component is not ready")
+        control.push("non-existent.qml")
+        ignoreWarning("QQmlComponent: Component is not ready")
+        control.replace("non-existent.qml")
+        control.pop()
+
+        control.destroy()
+    }
 }