Descendant of TextBox not shown

[emayevski]

In TextBox, the TextInput event does not work (TextBox consumes all characters without firing an event). I need to override this behavior, so I have created a simple descendant which overrides the OnTextInput method.

If I use TextBox directly (either in XAML or create one in code), it is shown in the view properly. As soon as I replace the name with the name of my descendant, the control is not shown (although, it is functional - I can type something and when I press Enter, which I also handle in the KeyDown event handler, it works). I checked whether MaskedTextBox (a descendant of TextBox) works when I replace the type of the created control, and it works. I don't see anything in MaskedTextBox that would make it visible where my control is not.
I thought about styles, but MaskedTextBox doesn't have styles too. Is it styled just because it is in the same namespace as TextBox itself?

In all cases, I specify only MinHeight and MinWidth. If I explicitly set Width and Height for my class, its border is shown, but there is no cursor there, and I cannot type in it (so, it must be just a border, not a control itself).

And then, how do I make my custom TextBox visible? Is it some kind of bug?

[emayevski]

...This is weird. I have subclassed my descendant from MaskedTextBox, and it started appearing. So, I am wondering what the trick is.

[maxkatz6]

While inheriting a control with a new control type, you also need to provide styles for this new control type. By default, Avalonia is not reusing styles from the base class.

If you want to keep your new control type using TextBox styles, you should override StyleKeyOverride:

public Type StyleKeyOverride => typeof(TextBox);

See https://docs.avaloniaui.net/docs/basics/user-interface/styling/styles#style-key

[emayevski]

While inheriting a control with a new control type, you also need to provide styles for this new control type. By default, Avalonia is not reusing styles from the base class.

Thank you, I suspected something like this but couldn't find information in the help file. That's why I looked at how MaskedTextBox worked. And it does not seem to use this override approach. Also, why does my workaround by subclassing MaskedTextBox work then? Even if MaskedTextBox does override the styles, my class still doesn't do this and would still not work.

[tobyfirth]

MaskedTextBox overrides the style key here.

Avalonia/src/Avalonia.Controls/MaskedTextBox.cs

Line 184 in 2dc808f

protected override Type StyleKeyOverride => typeof(TextBox);

Because MaskedTextBox overrides it any descendants will inherit that override and will be styled as a TextBox. Whereas TextBox does not override it and so uses the default behaviour which is what is returned by the GetType function that all C# classes have so if you inherit from TextBox, the GetType will now return your class as the type. Hence the behaviour you are seeing.

[emayevski]

MaskedTextBox overrides the style key here.

Thank you very much for the detailed explanation! It really helps a lot.