依赖属性重写

public class MyTextBox : TextBox
{
public MyTextBox(): base()
    {
    }

static MyTextBox()
    {
//第一种方法，通过OverrideMetadata
FlowDirectionProperty.OverrideMetadata(typeof(MyTextBox), new FrameworkPropertyMetadata(new PropertyChangedCallback(FlowDirectionPropertyChanged)));
    }

private static void FlowDirectionPropertyChanged(DependencyObject sender, DependencyPropertyChangedEventArgs args)
    {
        ((MyTextBox)sender).FontWeight = (((MyTextBox)sender).FlowDirection == FlowDirection.LeftToRight) ? FontWeights.Bold : FontWeights.Normal;

    }
}

private void Window1_Loaded(object sender, RoutedEventArgs e)
 {
//第二种方法，通过OverrideMetadata
DependencyPropertyDescriptor descriptor = DependencyPropertyDescriptor.FromProperty(TextBox.TextProperty, typeof(TextBox));
     descriptor.AddValueChanged(tbxEditMe, tbxEditMe_TextChanged);
 }

private void tbxEditMe_TextChanged(object sender, EventArgs e)
 {
MessageBox.Show("", "Changed");
 }