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Fix issue with setting SelectedItem on TreeView would crash application #3136

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merged 2 commits into from
Aug 31, 2020
Merged

Fix issue with setting SelectedItem on TreeView would crash application #3136

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2ebd3b9
Fix issue with setting SelectedItem on TreeView would crash application
marcelwgn Aug 15, 2020
f142154
Merge branch 'master' into user/chingucoding/treeview-setselecteditem…
marcelwgn Aug 18, 2020
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20 changes: 20 additions & 0 deletions dev/TreeView/APITests/TreeViewTests.cs
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Original file line number Diff line number Diff line change
Expand Up @@ -736,6 +736,26 @@ public void TreeViewBackgroundTest()
});
}

[TestMethod]
public void VerifySettingSelectionDoesNotCrash()
{
RunOnUIThread.Execute(() =>
{
var treeview = new TreeView();

var items = new ObservableCollection<string>() {
"Item0", "Item1", "Item2"
};

treeview.SelectedItem = items[0];
Verify.AreEqual(treeview.SelectedItem, items[0]);

treeview.ItemsSource = items;
treeview.SelectedItem = items[1];
Verify.AreEqual(treeview.SelectedItem, items[1]);
});
}

private bool IsMultiSelectCheckBoxChecked(TreeView tree, TreeViewNode node)
{
var treeViewItem = tree.ContainerFromNode(node) as TreeViewItem;
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2 changes: 1 addition & 1 deletion dev/TreeView/TreeView.cpp
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Expand Up @@ -264,7 +264,7 @@ void TreeView::OnPropertyChanged(const winrt::DependencyPropertyChangedEventArgs
{

const auto items = SelectedItems();
const auto selected = items.Size() > 0 ? items.GetAt(0) : nullptr;
const auto selected = (items != nullptr && items.Size() > 0) ? items.GetAt(0) : nullptr;
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items != nullptr [](start = 31, length = 16)

Under what circumstances is this null?

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It seems that SelectedItems returns null when TreeView can't resolve it's listcontrol.

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and what causes that to happen?

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SelectedItems returns null if the internal listview can't be found or the listviews ListViewModel can't be found. So in #3129, we probably crashed due to the binding resolving before the template was applied leaving us in a state where we did not have a listview or selectionmodel.

// Checking if new value is different to the currently internally selected item
if (args.NewValue() != selected)
{
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