TemplateBinding is not updating value on control in TextBox.Inner***Content

[timunie]

Discussed in https://github.com/AvaloniaUI/Avalonia/discussions/11891

^{Originally posted by **sn4k3** June 25, 2023} I'm trying to extend the NumericUpDown control to add Left content to it TextBox. If I enter static text it will show, however any `TemplateBinding` sees no alterations. Extended NumericUpDown xaml code: ```xml ``` Relevant part: ```xml Text="{TemplateBinding Text}" ToolTip.Tip="Old value" AcceptsReturn="False" TextWrapping="NoWrap" /> ``` Results in `InnerLeftContent` never to update the `Text` with `Text="{TemplateBinding Text}" `  If I set fixed text, ie: `Text="123"` it will show  I believe I'm doing something wrong, but I can't figure out where's the problem Note: Attaching the debugger on `this.GetObservable(TextProperty).Subscribe` fires correctly, just to be sure that `Text` is getting the notification. **EDIT 1:** Found a workaround that works: `Text="{Binding $parent[controls:ResettableNumericUpDown].Text, Mode=OneWay}"` but it looks silly... Actually any binding inside only works with this way, TemplateBinding always null. Why?

[cesarchefinho]

Look material.avalonia, they have InnerLeft on textbox that works with binding

[TomEdwardsEnscape]

The TemplatedParent of the inner control (PART_OldValueTextBox) is not the outer NumericUpDown as expected, but PART_TextBox from within the template.

Looks like a control assigned to InnerLeftContent isn't assigned a templated parent when constructed from a XAML template.