绑定使用"new“文本属性的自定义TextBlock的Text属性

public class CustomTextBlock : TextBlock
{
    public static readonly DependencyProperty TextProperty =
        DependencyProperty.Register("Text", typeof(string), typeof(CustomTextBlock), new PropertyMetadata(string.Empty));

    public string Text
    {
        get { return (string)GetValue(TextProperty); }
        set { SetValue(TextProperty, value); }
    }
}

<Window x:Class="YourNamespace.YourWindow"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        xmlns:local="clr-namespace:YourNamespace"
        Title="Your Window" Height="450" Width="800">
    <Grid>
        <local:CustomTextBlock Text="{Binding NewText}" />
    </Grid>
</Window>

public class YourWindow : Window
{
    public string NewText { get; set; } = "new";

    public YourWindow()
    {
        InitializeComponent();
        DataContext = this;
    }
}