如何使自定义依赖属性可以在wpf中绑定时实时更改

Question

当我们绑定textblock。长度与文本框长度相同的文本

<TextBox x:Name="txtName" Grid.Row="0" />
<TextBlock Text="{Binding ElementName=txtName, Path=Text.Length}" Grid.Row="1" />

Textblock的文本将随着txtName的文本实时变化。但是当我在WPF用户控件中定义一个新的DependencyProperty时，像这样:

    //MyCustomUC.xaml.cs
    static FrameworkPropertyMetadata propertymetadata = new FrameworkPropertyMetadata("Comes as Default", FrameworkPropertyMetadataOptions.BindsTwoWayByDefault, new PropertyChangedCallback(MyCustom_PropertyChanged), new CoerceValueCallback(MyCustom_CoerceValue), false, UpdateSourceTrigger.PropertyChanged);
    public static readonly DependencyProperty MyCustomProperty = DependencyProperty.Register("MyCustom", typeof(string), typeof(MyCustomUC), propertymetadata, new ValidateValueCallback(MyCustom_Validate));
    public string MyCustom
    {
        get
        {
            return this.GetValue(MyCustomProperty) as string;
        }
        set
        {
            this.SetValue(MyCustomProperty, value);
        }
    }

并将其绑定到文本框

//MyCustomUC.xaml
<UserControl ... x:Name="ucs" ...>
<TextBox Text="{Binding ElementName=ucs, Path=MyCustom}"></TextBox>
</UserControl>
//MainWindow.xaml
<local:MyCustomUC x:Name="ucust" Grid.Row="0" />
<TextBox x:Name="tbChange" Text="{Binding ElementName=ucust, Path=MyCustom}" Grid.Row="1"/>

似乎"MyCustom"将不会改变，直到文本框失去焦点。我怎样才能使它被改变时，文本框中的文本在实时?

Answer 1

<TextBox x:Name="tbChange" Text="{Binding ElementName=ucust, Path=MyCustom, UpdateSourceTrigger=PropertyChanged}" Grid.Row="1"/>