WPF&x2013;转换器作为DependencyObject
无法将值绑定到WPF&x2013;转换器作为DependencyObject,wpf,binding,wpf-controls,converters,Wpf,Binding,Wpf Controls,Converters,无法将值绑定到Binding的ConverterParametr绑定只能在DependencyObject的dependencProperty上设置 我很想把IValueConverter转换器实现为DependencyObject public class AddConverter : DependencyObject, IValueConverter { public static readonly DependencyProperty AddIntegerProperty =
Binding
的ConverterParametr
<代码>绑定只能在DependencyObject
的dependencProperty
上设置
我很想把IValueConverter
转换器实现为DependencyObject
public class AddConverter : DependencyObject, IValueConverter
{
public static readonly DependencyProperty AddIntegerProperty =
DependencyProperty.Register(nameof(AddInteger),
typeof(int),
typeof(AddConverter),
new PropertyMetadata(0));
public int AddInteger
{
get => (int)GetValue(AddIntegerProperty);
set => SetValue(AddIntegerProperty, value);
}
public object Convert(object value, Type targetType, object parameter, CultureInfo culture)
{
if (!(value is int intValue)) return 0;
return intValue + AddInteger;
}
public object ConvertBack(object value, Type targetType, object parameter, CultureInfo culture)
{
int intValue;
try
{
intValue = System.Convert.ToInt32(value);
}
catch (Exception)
{
return 0;
}
return intValue - AddInteger;
}
}
让我们在示例视图中查看它
<TextBox>
<TextBox.Text>
<Binding Path="MyIntegerProperty">
<Binding.Converter>
<local:AddConverter AddInteger="{Binding MyAddIntegerProperty, Mode=OneWay}" />
</Binding.Converter>
</Binding>
</TextBox.Text>
</TextBox>
结果是AddInteger
仍然返回默认值。通过提供的绑定
,没有更改AddInteger
依赖项属性的原因是什么
脚注:
MultiBinding
对我没有帮助,因为ConvertBack
方法仅由控件提供的值组成。这个问题也应该在ViewModel中解决,但我对使用转换器的解决方案感到好奇。问题是,首先,转换器无法继承其所在的DataContext,因此绑定无法工作:如果您对已有的绑定进行跟踪,您将在VS输出中看到“未找到Framework mentor”(见附录a)。这也是为什么您不能仅仅从FrameworkElement派生并使用RelativeSource={RelativeSource AncestorType=Whatever}
:您已经脱离了可视化树。没有祖先。此外,即使有框架指导者,DependencyObject也不能为绑定提供源。消息来源必须明确。只有从FrameworkElement继承的类才能继承DataContext
所以我偷了一个BindingProxy类()并用它来提供绑定的源代码。这有点笨拙,但我想到的另一种选择是从Freezable继承转换器,本质上赋予它BindingProxy的属性,并在参考资料中创建转换器。它起作用了,但我更喜欢它的组织方式
public class BindingProxy : Freezable
{
#region Overrides of Freezable
protected override Freezable CreateInstanceCore()
{
return new BindingProxy();
}
#endregion
#region Data Property
public Object Data
{
get { return (Object)GetValue(DataProperty); }
set { SetValue(DataProperty, value); }
}
public static readonly DependencyProperty DataProperty =
DependencyProperty.Register(nameof(Data), typeof(Object), typeof(BindingProxy),
new PropertyMetadata(null));
#endregion Data Property
}
XAML
System.Windows.Data警告:56:为绑定(哈希=21653700)创建了BindingExpression(哈希=14964341)
System.Windows.Data警告:58:路径:“MyAddIntegerProperty”
System.Windows.Data警告:60:BindingExpression(哈希=14964341):默认模式解析为单向
System.Windows.Data警告:61:BindingExpression(哈希=14964341):默认更新触发器已解析为PropertyChanged
System.Windows.Data警告:62:BindingExpression(哈希值=14964341):附加到WpfApp2.AddConverter2.AddInteger(哈希值=57434139)
System.Windows.Data警告:64:BindingExpression(哈希=14964341):使用Framework mentor
System.Windows.Data警告:67:BindingExpression(哈希=14964341):解析源
System.Windows.Data警告:69:BindingExpression(哈希=14964341):找不到Framework mentor
System.Windows.Data警告:65:BindingExpression(哈希=14964341):解析源延迟
System.Windows.Data警告:67:BindingExpression(哈希=14964341):解析源
System.Windows.Data警告:69:BindingExpression(哈希=14964341):找不到Framework mentor
由于转换器不是框架元素
,因此通过相对资源查找工具查找数据上下文
,
也没有帮助。我懂了。谢谢你的例子。@David正确。此外,即使您继承了FrameworkElement,FindAncestor也不会工作,因为您已经脱离了可视化树——再也没有框架导师了。
<StackPanel.Resources>
<local:BindingProxy
x:Key="VMProxy"
Data="{Binding}"
/>
</StackPanel.Resources>
<TextBlock>
<TextBlock.Text>
<Binding Path="MyIntegerProperty">
<Binding.Converter>
<local:AddConverter
AddInteger="{Binding Data.MyAddIntegerProperty, Source={StaticResource VMProxy}}"
/>
</Binding.Converter>
</Binding>
</TextBlock.Text>
</TextBlock>
AddInteger="{Binding MyAddIntegerProperty, Mode=OneWay,
PresentationTraceSources.TraceLevel=High}"
System.Windows.Data Warning: 56 : Created BindingExpression (hash=14964341) for Binding (hash=21653700)
System.Windows.Data Warning: 58 : Path: 'MyAddIntegerProperty'
System.Windows.Data Warning: 60 : BindingExpression (hash=14964341): Default mode resolved to OneWay
System.Windows.Data Warning: 61 : BindingExpression (hash=14964341): Default update trigger resolved to PropertyChanged
System.Windows.Data Warning: 62 : BindingExpression (hash=14964341): Attach to WpfApp2.AddConverter2.AddInteger (hash=57434139)
System.Windows.Data Warning: 64 : BindingExpression (hash=14964341): Use Framework mentor <null>
System.Windows.Data Warning: 67 : BindingExpression (hash=14964341): Resolving source
System.Windows.Data Warning: 69 : BindingExpression (hash=14964341): Framework mentor not found
System.Windows.Data Warning: 65 : BindingExpression (hash=14964341): Resolve source deferred
System.Windows.Data Warning: 67 : BindingExpression (hash=14964341): Resolving source
System.Windows.Data Warning: 69 : BindingExpression (hash=14964341): Framework mentor not found