[Android] Incorrect text measurements

[carldebilly]

Incorrect Android's implementation of TextBlock's .Measure()

The layout engine is relying to the desired size of a control to know if this one should be clipped. That means the control should return its actual desiredSize.

This bug has been identified by the automated visual tests on PR #4178.

Current behavior

Take this XAML:

<Border Width="35" Background="LightBlue">
  <TextBlock FontSize="15">This is a very long text, which should take more than 35px horizontally</TextBlock>
</Border>

The correct result to a call to .Measure() should be something like (510, 20), but the current implementation will cap its measurement to availableSize, giving a result like (35, 20) in this case.

Impact of this bug

This bug will prevent the layout from applying clipping when it's required.

Expect result

(for the XAML provided)

Current result on Android

(for the XAML provided)

Affected platform(s)

• iOS
• Android
• WebAssembly
• WebAssembly renderers for Xamarin.Forms
• macOS
• Skia
  • WPF
  • GTK (Linux)
  • Tizen
• Windows
• Build tasks
• Solution Templates

[robloo]

I discovered another text measurement issue on Android. I have a TextBlock with multi-line content inside a ScrollViewer. All content can be displayed without scrollbars and none are shown. However, horizontally, it is still possible to scroll a small amount left/right causing the text to clip.

Note that if the text is long enough to vertically scroll the same issue still occurs.

Is this the same issue or should I file a new report?

[carldebilly]

@robloo That's another problem, please open a new issue.