Fatal crash using TokenizingTextBox with SelectionMode=None (uwp)

[0xNF]

Describe the bug

As the title says:

<tk:TokenizingTextBox  SelectionMode="None" />

and

<tk:TokenizingTextBox  SelectionMode="Single" />

Both of these cause the following failure when pressing backspace:

"System.Exception: Catastrophic failure (Exception from HRESULT: 0x8000FFFF (E_UNEXPECTED))
  at System.Runtime.InteropServices.WindowsRuntime.IVector`1.Append(T value)
  at System.Runtime.InteropServices.WindowsRuntime.VectorToCollectionAdapter.Add[T](T item)
  at Microsoft.Toolkit.Uwp.UI.Controls.TokenizingTextBox.SelectNewItem(TokenizingTextBoxItem item, Int32 increment, Func`2 testFunc)
  at Microsoft.Toolkit.Uwp.UI.Controls.TokenizingTextBox.SelectPreviousItem(TokenizingTextBoxItem item)
  at "

Regression

No response

Reproducible in sample app?

• This bug can be reproduced in the sample app.

Steps to reproduce

1. Clone this repo: https://github.com/0xNF/TokenizingTextBoxCrash
2. Create a new tag by pressing enter with some text in the Text Box
3. Press backspace a few times with the textbox still focused
4. crash

Expected behavior

Not crashing

Screenshots

No response

Windows Build Number

• Windows 10 1809 (Build 17763)
• Windows 10 1903 (Build 18362)
• Windows 10 1909 (Build 18363)
• Windows 10 2004 (Build 19041)
• Windows 10 20H2 (Build 19042)
• Windows 10 21H1 (Build 19043)
• Windows 11 21H2 (Build 22000)
• Other (specify)

Other Windows Build number

No response

App minimum and target SDK version

• Windows 10, version 1809 (Build 17763)
• Windows 10, version 1903 (Build 18362)
• Windows 10, version 1909 (Build 18363)
• Windows 10, version 2004 (Build 19041)
• Other (specify)

Other SDK version

No response

Visual Studio Version

2019

Visual Studio Build Number

Version 16.10.1

Device form factor

Desktop

Nuget packages

Microsoft.Toolkit.Uwp.UI.Controls 7.1.2

Additional context

No response

Help us help you

No.

Hello 0xNF, thank you for opening an issue with us!

I have automatically added a "needs triage" label to help get things started. Our team will analyze and investigate the issue, and escalate it to the relevant team if possible. Other community members may also look into the issue and provide feedback 🙌

[Arlodotexe]

Thanks for reporting this issue @0xNF. Can confirm that this issue is present in 7.1.2 and is reproducible in the current sample app. We'll look into this.

[XAML-Knight]

Can also reproduce the issue by using the left arrow key.

[HEIGE-PCloud]

It may be caused by trying to set SelectedItems while the selection mode is None or Single as only one or no item can be selected.

Changing this

WindowsCommunityToolkit/Microsoft.Toolkit.Uwp.UI.Controls.Input/TokenizingTextBox/TokenizingTextBox.Selection.cs

Line 220 in a39654c

SelectedItems.Add(Items[currentIndex + increment]);

into

if (SelectionMode == ListViewSelectionMode.Single || SelectionMode == ListViewSelectionMode.None)
{
    SelectedItem = Items[currentIndex + increment];
}
else
{
    SelectedItems.Add(Items[currentIndex + increment]);
}

does seem to stop it from crashing.

Notice that there are other places that may contain this bug. For example in this case, trying to use shift + arrow key to select multiple items while the selection is none or single will crash the app as well.

WindowsCommunityToolkit/Microsoft.Toolkit.Uwp.UI.Controls.Input/TokenizingTextBox/TokenizingTextBox.Selection.cs

Lines 86 to 102 in a39654c

	if (IsShiftPressed)
	{
	// What we do here depends on where the selection started
	// if the previous item is between the start and new position then we add the new item to the selected range
	// if the new item is between the start and the previous position then we remove the previous position
	int newDistance = Math.Abs(SelectedIndex - index);
	int oldDistance = Math.Abs(SelectedIndex - previousIndex);
	if (newDistance > oldDistance)
	{
	SelectedItems.Add(Items[index]);
	}
	else
	{
	SelectedItems.Remove(Items[previousIndex]);
	}
	}