Question

I have custom control:

public class TestTextBox : TextBox
{
    public TestTextBox()
    {
        Text = "ctor text";
    }
}

And xaml that uses this control:

<StackPanel Orientation="Vertical">
    <!-- 1. Use TestTextBox directly -->
    <controls:TestTextBox Text="xaml text"/>

    <!-- 2. Use TestTextBox in DataTemplate -->
    <ItemsControl>
        <ItemsControl.ItemTemplate>
            <DataTemplate>
                <controls:TestTextBox Text="xaml text"/>
            </DataTemplate>
        </ItemsControl.ItemTemplate>
        <System:String>111</System:String>
    </ItemsControl>
<StackPanel>

The result is TestTextBox.Text is different in these cases – “xaml text” in first case, “ctor text” in second case.

Could someone explain why it works this way? I’d expect that TestTextBox.Text will be “xaml text” in both cases.

Answer 1

I think you need to understand Dependency Property Value Precedence.

When you are using Templates, value precedence for dependency properties is different.