AutoSuggestBox TextChanged reports reason as UserInput when programmatically setting AutoSuggextBox.Text in SuggestionChosen handler in C++ (and in C# as well under certain circumstances)

[roxk]

Describe the bug

AutoSuggestBox's suggestion collection binding and text updating routines do not work well with collection item whose type is not string. AutoSuggestBox has some undocumented usage of ToString and some behavior related to these usage is inconsistent between C# and C++. On top of that, TextChanged would incorrectly report any change to AutoSuggestBox.Text in SuggestionChosen as AutoSuggestionBoxTextChangeReason::UserInput if the ItemsSource's item type is not a string, regardless of whether the type implements IStringable, and regardless of whether the language is C# or C++.

Hideen Usage of ToString

There are two hidden usage of ToString:

1. Binding item to text in suggestion list
2. Setting AutoSuggestBox.Text inside SuggestionChosen

For (1), I could only confirm it when directly looking at the source of xaml control gallery. AutoSuggestBoxPage.xaml in the gallery (both uwp and WinUI3) contains no item template and I was wondering how the suggestion list binds ControlInfoDataItem. It turns out ControlInfoDataItem implements ToString. If I comment out said implementation of ToString, the suggestion lists would show the fully qualified name of ControlInfoDataItem, as shown below:

The doc only mentions:

To control how items are displayed in the suggestion list, you can use DisplayMemberPath or ItemTemplate.

To display the text of a single property of your data item, set the DisplayMemberPath property to choose which property from your object to display in the suggestion list.
To define a custom look for each item in the list, use the ItemTemplate property .

For (2), you can refer to the reproducing steps below. In short, setting a break point in the ToString method of the item of the collection bound to the ItemsSource of AutoSuggestBox, and calling AutoSuggestBox.Text inside SuggestionChosen handler would trigger the break point.

Bugs

There are two bugs, assuming the hidden usage of ToString is intended behavior (I appreciate the automatic conversion, but think more documention would help :)):

1. Even if ToString is implemented for the item of the collection bound to AutoSuggestBox.ItemsSource, suggestion list still shows the fully qualified type name, in C++. This bug does not happen in C#.
2. If ToString is implemented for the item of the collection bound to AutoSuggestBox.ItemsSource, TextChanged would report the reason as UserInput if in SuggestionChosen handler, AutoSuggestBox.Text is assigned a value that is not equal to chosenItem.ToString(); if ToString is not implemented for the item, TextChanged would report the reason as UserInput if AutoSuggestBox.Text is assigned any value.

For C++, unless otherwise specified, "implementing ToString" implies implementing the IStringable interface.

Steps to reproduce bug (1)

1. Clone the minimal reproducible https://github.com/roxk/auto-suggestbox-change-reason-min-repro. Launch either UWP or WinUI app.
2. Enter text in auto suggest box below the title With ToString
3. Observe the list shows fully qualified name of the underlying view model instead of the result of ToString

Expected behavior

The list shows the value of ToString() of the item instead of the fully qualified name of the item type.

Actual behavior

The list shows fully qualified name of the underlying item type. The fact that it works in C# is evident in the officla xaml control gallery.

Screenshots

Steps to reproduce bug (2.1)

With ToString

1. Clone the minimal reproducible https://github.com/roxk/auto-suggestbox-change-reason-min-repro. Launch either UWP or WinUI app.
2. Enter a single character a in auto suggest box below the title With ToString
3. Observe in Output window Updating a is printed.
4. Use arrow down key to move to any suggestion
5. Observe in Output window Updating a A and text set through suggestion chosen is printed.

Optionally, you can set a break point in the ToString method of SuggestionViewModel and see that it is called right after pressing the arrow down key at step (4).

Expected behavior

Output window does not print Updating a A and text set through suggestion chosen. Since the print is guarded in TextChanged handler by checking if the reason is UserInput, it means the expected behavior is that the reason should not be UserInput when setting custom text in SuggestionChosen handler.

Actual behavior

Output window is printing Updating a A and text set through suggestion chosen, i.e. the TextChanged handler reports the reason is UserInput.

Note: Commenting out custom text concantenation would fix it, but this shouldn't be. Setting text in SuggestionChosen handler should not make TextChanged report reason as UserInput.

Screenshot

Steps to reproduce bug (2.2)

Without ToString

1. Clone the minimal reproducible https://github.com/roxk/auto-suggestbox-change-reason-min-repro. Launch either UWP or WinUI app.
2. Enter a single character a in auto suggest box below the title Without ToString
3. Observe in Output window Updating a is printed.
4. Use arrow down key to move to any suggestion
5. Observe in Output window Updating a B is printed.

Expected behavior

Output window does not print Updating a B. Since the print is guarded in TextChanged handler by checking if the reason is UserInput, it means the expected behavior is that the reason should not be UserInput when setting custom text in SuggestionChosen handler.

Actual behavior

Output window is printing Updating a B, i.e. the TextChanged handler reports the reason is UserInput.

Version Info

NuGet package version:

Uwp

N/A

WinUI

WinUI 3.0.0-preview2.200713.0

Windows app type:

UWP	Win32
Yes

Windows 10 version	Saw the problem?
Insider Build (xxxxx)
May 2020 Update (19041)	Yes
November 2019 Update (18363)
May 2019 Update (18362)
October 2018 Update (17763)
April 2018 Update (17134)
Fall Creators Update (16299)
Creators Update (15063)

Device form factor	Saw the problem?
Desktop	Yes
Xbox
Surface Hub
IoT

Additional context

I first encountered this issue without implementing ToString for my item in the collection bound to AutoSuggestBox.ItemsSource, and only realized the hidden behavior with ToString. Having the ToString automatic conversion is great! But IMHO the proper fix should not rely on any assumption of the availabity of ToString as I do not wish to implement a ToString, which should really be domain/debug info specific, but ends up being tied to the display requirement of just one particular AutoSuggestBox. The worse case scenario I could imagine is, if, by only using existing API, there is really no 100% reliable way of checking if the cause of text change is from user input or not, adding a SetText(String, Reason) API seems to be the best compromise in terms of reliability and developer experience (Setting one more flag manually is 100 times better than using an unreliable API).

TL;DR: I wish the fix is that I can set whatever text in SuggestionChosen and without using ToString at all.

P.S. I appreciate the focus on accessbility and ease of use of AutoSuggestBox! :) Wish this bug report could help make it even better.

Note: I included both UWP and WinUI minimal reproducible for your convenience. All issues reported here exist in both UWP and the latest WinUI preview.

[roxk]

Closing it as it's too long to read for the teams (it was a bad idea to mix several bugs into one issue). The incorrect query changed reason bug still exists in 0.8 preview for UWP - I could re-open a more succinct issue.