Question

How to override the TextProperty Metadata to set the UpdateSourceTrigger.PropertyChanged
by default while using the functionality from the base TextBox Class

TextBox.OnTextPropertyChanged
TextBox.CoerceText

methods, when both mentioned are private ?

public class MyTextBox : System.Windows.Controls.TextBox
    {
        static MyTextBox()
        {

TextProperty.OverrideMetadata(typeof(TextBox), new FrameworkPropertyMetadata(
                string.Empty, FrameworkPropertyMetadataOptions.Journal | FrameworkPropertyMetadataOptions.BindsTwoWayByDefault, 
                new PropertyChangedCallback(TextBox.OnTextPropertyChanged), 
                new CoerceValueCallback(TextBox.CoerceText), true, UpdateSourceTrigger.PropertyChanged));
...

Answer 1

You should be able to use the GetDefaultMetadata method which will give you access to the callbacks that refer to the private methods.

The following worked for me:

public class MyTextBox : TextBox
{
    static MyTextBox()
    {
        var defaultMetadata = TextBox.TextProperty.GetMetadata(typeof(TextBox));

        TextBox.TextProperty.OverrideMetadata(typeof(MyTextBox), new FrameworkPropertyMetadata(
            string.Empty, FrameworkPropertyMetadataOptions.Journal | FrameworkPropertyMetadataOptions.BindsTwoWayByDefault,
            defaultMetadata.PropertyChangedCallback,
            defaultMetadata.CoerceValueCallback, 
            true, 
            System.Windows.Data.UpdateSourceTrigger.PropertyChanged)); 
    }
}