无法访问多估计逆变器中的datacontext
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02-10-2019 - |
题
我有一个USERCONTROL,我需要设置特定的DataContext。 USERCONTROL使用多偶联性逆变器。但是,多估计逆变器中的绑定无法使用DataContext。它适用于常规价值转换器。有人知道发生了什么事吗?要澄清,下面的代码与我的真实代码不同,它只是重现我的问题的示例。例如,我的多偶联者会提取多个论点。
XAML:
<Window x:Class="MultConvTest.Window1"
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
xmlns:MultConvTest="clr-namespace:MultConvTest"
Title="Window1" Height="300" Width="300">
<Window.Resources>
<MultConvTest:MyValueConverter x:Key="MyValueConverter" />
<MultConvTest:MyMultiConverter x:Key="MyMultiConverter" />
</Window.Resources>
<StackPanel>
<!--This works, output is Formatted: 7-->
<TextBlock
DataContext="{Binding Path=Data}"
Text="{Binding Path=Length, Converter={StaticResource MyValueConverter}}" />
<!--This works, output is Formatted: 7-->
<TextBlock>
<TextBlock.Text>
<MultiBinding Converter="{StaticResource MyMultiConverter}">
<Binding Path="Data.Length" />
</MultiBinding>
</TextBlock.Text>
</TextBlock>
<!--This fails, the converter never access the DataContext of the textbox-->
<TextBlock
DataContext="{Binding Path=Data}">
<TextBlock.Text>
<MultiBinding Converter="{StaticResource MyMultiConverter}">
<Binding Path="Length" />
</MultiBinding>
</TextBlock.Text>
</TextBlock>
</StackPanel>
</Window>
背后的代码:
using System;
using System.Collections.Generic;
using System.Windows;
using System.Windows.Data;
namespace MultConvTest
{
public partial class Window1 : Window
{
public Window1()
{
InitializeComponent();
DataContext = this;
}
public string Data
{
get { return "My Text"; }
}
}
public class MyValueConverter : IValueConverter
{
public object Convert(object value, Type targetType, object parameter, System.Globalization.CultureInfo culture)
{
int number = (int)value;
return string.Format("Formatted: {0}", number);
}
public object ConvertBack(object value, Type targetTypes, object parameter, System.Globalization.CultureInfo culture)
{
throw new NotImplementedException();
}
}
public class MyMultiConverter : IMultiValueConverter
{
public object Convert(object[] values, Type targetType, object parameter, System.Globalization.CultureInfo culture)
{
// This will fail when DataContext is set. values[0] is of type Ms.Internal.NamedObject
// with value DependencyProperty.UnsetValue.
int number = (int)values[0];
return string.Format("Formatted: {0}", number);
}
public object[] ConvertBack(object value, Type[] targetTypes, object parameter, System.Globalization.CultureInfo culture)
{
throw new NotImplementedException();
}
}
}
解决方案
你不会喜欢这个;-)
简单地放线 DataContext=this
前 InitializeComponent()
似乎在设置全局dataContext之前触发了第三个文本框的多逆变器,因此实际上产生了零参考错误...
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