[Android] Combobox dropdown placement can be a bit misaligned vertically

[takla21]

Current behavior

When the app is configured with a shell as a UserControl while also activating translucent, the Combobox dropdown always misaligned itself vertically

Shell.xaml

<UserControl x:Class="Comboboxplacement.Shell"
			 xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
			 xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
			 xmlns:local="using:Comboboxplacement">

	<Frame x:Name="NavigationFrame" />
</UserControl>

Android Style.xml

<?xml version="1.0" encoding="utf-8" ?>
<resources>
	<style name="AppTheme" parent="Theme.AppCompat.Light">

		<!-- This makes the status bar translucent and allows content to be drawn behind -->
		<item name="android:windowTranslucentStatus">true</item>
		
		<!-- This removes the ActionBar -->
		<item name="windowActionBar">false</item>
		<item name="android:windowActionBar">false</item>
		<item name="windowNoTitle">true</item>
		<item name="android:windowNoTitle">true</item>

	</style>
</resources>

Expected behavior

How to reproduce it (as minimally and precisely as possible)

• Download this sample Comboboxplacement.zip
• Deploy on android
• Click on Combobox

Workaround

Setting Uno.UI.FeatureConfiguration.Popup.UseNativePopup to true fix the misalignment issue. Which, this bug was also happening before UseNativePopup was changed to false by default.

Which could also introduce this bug #9004

Works on UWP/WinUI

No response

Environment

Uno.UI / Uno.UI.WebAssembly / Uno.UI.Skia

NuGet package version(s)

4.7.0-dev.60

Affected platforms

Android

IDE

Visual Studio 2022

IDE version

17.3.5

Relevant plugins

No response

Anything else we need to know?

No response

[jeromelaban]

Note for contributor

The positioning of popups is likely not taking Window.VisibleBounds into account, as well as the keyboard position to determine the values.

[MartinZikmund]

I have checked the code, but it seems it is taking VisibleBounds into account correctly - or rather as the status bar is translucent, the visible bounds technically do include its area. And there is specifically a code that shifts the popup by the status bar height in such case. Now the question is what is the correct behavior. As marking the status bar translucent technically means that we want the view to "extend" under it, so popups do get arranged there and that seems to be correct, or not? @jeromelaban I see you added these lines, so maybe you remember what was the main reason:

uno/src/Uno.UI/UI/Xaml/Controls/ComboBox/ComboBox.cs

Lines 857 to 860 in 46b2708

	// Compensate for origin location is some popup providers (Android
	// is one, particularly when the status bar is translucent)
	frame.X -= offset.X;
	frame.Y -= offset.Y;

If the behavior is correct, maybe it should also extend to popups in general, not be ComboBox specific

What is definitely incorrect is that the combo should probably open up down instead of center on top of the box - I need to investigate why it happens this way currently.

[jeromelaban]

@MartinZikmund I don't recall specifically what the reason was at that time, but it may also be a mix of Native vs XAML specific tests. At least, there's a UI test for it :)

uno/src/SamplesApp/SamplesApp.UITests/Windows_UI_Xaml_Controls/ComboBoxTests/UnoSamples_Tests.ComboBoxTests.cs

Line 65 in 1950ce3

public void ComboBoxTests_VisibleBounds()

[jeromelaban]

Now with regards to displaying under the translucent bar, It would make sense for ComboBox popups to not extend under the bar?