自定义WPF绑定 [英] Custom WPF Binding

问题描述

我有一个自定义的MarkupExtension，可以模拟绑定.它在常规分配中效果很好，但在样式设置器"中使用时效果不佳，例如:

I have a custom MarkupExtension that simulates binding. It works well in normal assignments but not when used in Style Setters, for example:

<Setter Property="Content" Value="{local:MyExtension}" />

导致XamlParseException:

results in a XamlParseException:

A 'Binding' cannot be set on the 'Value' property of type 'Setter'.
A 'Binding' can only be set on a DependencyProperty of a DependencyObject.

这是扩展程序的实现:

public class MyExtension : MarkupExtension
{
    public MyExtension()
    {
        Value = 123;
    }

    public object Value
    {
        get;
        set;
    }

    public override object ProvideValue(IServiceProvider serviceProvider)
    {
        var binding = new Binding("Value")
        {
            Source = this,
        };
        return binding.ProvideValue(serviceProvider);
    }
}

出什么问题了?！

推荐答案

有点猜想，但这很可能是因为XAML编译器对 Binding 类具有特殊的内置支持，从而允许将其用于这种情况(和其他情况). Binding 类也是 MarkupExtension ，但不幸的是，它密封了 ProvideValue()的实现.

Kind of guessing, but it's likely because the XAML compiler has special built-in support for the Binding class, allowing its usage in this scenario (and others). The Binding class is also a MarkupExtension, but unfortunately it seals its implementation of ProvideValue().

也就是说，您可能会摆脱这种情况:

That said, you might just get away with this:

public class MyBinding : Binding
{
    private object value;

    public object Value
    {
        get { return this.value; }
        set
        {
            this.value = value;
            this.Source = value;
        }
    }
}

因为 ProvideValue 将始终返回 Binding 实例.

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