WPF TemplateBinding不适用于每个属性

Question

I have created custom control, but TemplateBinding does not work for every property? Template Binding does start working if I use dummy Converter that just forwards original values. Simplified example that has the same issue:

<Style TargetType="{x:Type controls:ElipticProgressBar}">
    <Setter Property="Template">
        <Setter.Value>
            <ControlTemplate TargetType="{x:Type controls:ElipticProgressBar}">
                <ControlTemplate.Resources>
                    <converters:DebugConverter x:Key="DebugConverter"/>
                </ControlTemplate.Resources>
                <StackPanel>
                    <!--BarColor works always-->
                    <!--BarTickness works-->
                    <Label Background="{TemplateBinding BarColor}" Content="{TemplateBinding BarTickness}"/>
                    <!--BarTickness does not works-->
                    <TextBlock Background="{TemplateBinding BarColor}" Text="{TemplateBinding BarTickness}"/>
                    <!--BarTickness works-->
                    <TextBlock Background="{TemplateBinding BarColor}" Text="{Binding BarTickness, RelativeSource={RelativeSource TemplatedParent}, Mode=OneWay}"/>
                    <!--BarTickness works-->
                    <TextBlock Background="{TemplateBinding BarColor}" Text="{TemplateBinding BarTickness, Converter={StaticResource DebugConverter}}"/>
                </StackPanel>
            </ControlTemplate>
        </Setter.Value>
    </Setter>
</Style>

back code:

public class ElipticProgressBar : Control
{
    static ElipticProgressBar()
    {
        DefaultStyleKeyProperty.OverrideMetadata(typeof(ElipticProgressBar), new FrameworkPropertyMetadata(typeof(ElipticProgressBar)));
    }

    public static readonly DependencyProperty BarTicknessProperty = DependencyProperty.Register(
        "BarTickness", typeof(int), typeof(ElipticProgressBar), new FrameworkPropertyMetadata(default(int)));

    public int BarTickness
    {
        get { return (int)GetValue(BarTicknessProperty); }
        set { SetValue(BarTicknessProperty, value); }
    }

    public static readonly DependencyProperty BarColorProperty = DependencyProperty.Register(
        "BarColor", typeof(Brush), typeof(ElipticProgressBar), new FrameworkPropertyMetadata(default(Brush)));

    public Brush BarColor
    {
        get { return (Brush)GetValue(BarColorProperty); }
        set { SetValue(BarColorProperty, value); }
    }
}

usage:

controls:ElipticProgressBar BarTickness="30" BarColor="Orange"

DebugConverter:

public class DebugConverter : IValueConverter
{
    public object Convert(object value, Type targetType, object parameter, CultureInfo culture)
    {
        return value;
    }

    public object ConvertBack(object value, Type targetType, object parameter, CultureInfo culture)
    {
        return value;
    }
}

Answer 1

{TemplateBinding} is an optimized version of a binding that has some limitations.

In this case you need to change the type of the BarThickness property to string to be able to bind it directly to the Text property of a TextBlock using a {TemplateBinding} .

Answer 2

The docs state that a {TemplateBinding} is

an optimized form of a Binding for template scenarios, analogous to a Binding constructed with {Binding RelativeSource={RelativeSource TemplatedParent}}

with some limitations - most importantly that it works only within the visual tree!

---

What that means for your specific case: while you cannot use

<TextBlock Text="{TemplateBinding BarTickness}" />

you can (and have to) use

<TextBlock Text="{Binding BarTickness, RelativeSource={RelativeSource TemplatedParent}, Mode=OneWay}" />

because TextBlock.Text property is of type string while the BarTickness is not.

{TemplateBinding} does not do that kind of converting; that's why you need to use the more generic {Binding} or a converter, whose both methods

public object Convert(object value, Type targetType, object parameter, CultureInfo culture)
{
    return value;
}

public object ConvertBack(object value, Type targetType, object parameter, CultureInfo culture)
{
    return value;
}

both convert the actual value to an object .