绑定WPF中的一种方法？ [英] Bind to a method in WPF?

问题描述

  public class RootObject 
 {
 public string Name {get; } 
 
 public ObservableCollection< ChildObject> GetChildren（）{...} 
} 
 
 public class ChildObject 
 {
 public string Name {get; } 
} 
  

XAML：

 < TreeView ItemsSource =RootObjects的一些列表> 
< TreeView.Resources> 
< HierarchicalDataTemplate DataType ={x：Type data：RootObject}
 ItemsSource =???> 
< TextBlock Text ={Binding Path = Name}/> 
< / HierarchicalDataTemplate> 
< HierarchicalDataTemplate DataType ={x：Type data：ChildObject}> 
< TextBlock Text ={Binding Path = Name}/> 
< / HierarchicalDataTemplate> 
< /TreeView.Resources> 
< / TreeView> 
  

这里我要绑定到 GetChildren 方法在每个 RootObject 树上。

编辑绑定到 ObjectDataProvider 似乎不起作用，因为我绑定到一个项目列表，而$ code> ObjectDataProvider 需要静态方法，或者它创建它自己的实例并使用它。

例如，使用Matt的答案我得到：

System.Windows.Data错误：33：ObjectDataProvider无法创建对象; Type ='RootObject'; Error ='构造函数的参数错误'。

System.Windows.Data错误：34：ObjectDataProvider：尝试调用类型的方法失败; Method ='GetChildren'; Type ='RootObject'; Error ='指定的成员无法在目标上调用'TargetException：'System.Reflection.TargetException：非静态方法需要一个目标。

解决方案

另一种可能适用于您的方法是创建一个自定义的 IValueConverter ，以便使用如下：

  ItemsSource ={Binding 
 Converter = {StaticResource MethodToValueConverter}，
 ConverterParameter ='GetChildren'}
  

此转换器将使用反射来查找和调用该方法。这需要该方法没有任何参数。

这是一个转换器源代码的示例：

  public sealed class MethodToValueConverter：IValueConverter 
 {
 public object Convert（object value，Type targetType，object parameter，CultureInfo culture）
 {
 var methodName = parameter as string; 
 if（value == null || methodName == null）
返回值; 
 var methodInfo = value.GetType（）。GetMethod（methodName，new Type [0]）; 
 if（methodInfo == null）
返回值; 
 return methodInfo.Invoke（value，new object [0]）; 
} 
 
 public object ConvertBack（object value，Type targetType，object parameter，CultureInfo culture）
 {
 throw new NotSupportedException（MethodToValueConverter只能用于一个方式转换）; 
} 
} 
  

相应的单元测试：

  [测试] 
 public void Convert（）
 {
 var converter =新MethodToValueConverter（）; 
 Assert.AreEqual（1234，converter.Convert（1234，typeof（string），ToString，null））; 
 Assert.AreEqual（ABCD，converter.Convert（ABCD，typeof（string），Trim，null））; 
 
 Assert.IsNull（converter.Convert（null，typeof（string），ToString，null））; 
 
 Assert.AreEqual（Pineapple，converter.Convert（Pineapple，typeof（string），InvalidMethodName，null））; 
} 
  

请注意，此转换器不执行 targetType 参数。

How do you bind to an objects method in this scenario in WPF?

public class RootObject
{
    public string Name { get; }

    public ObservableCollection<ChildObject> GetChildren() {...}
}

public class ChildObject
{
    public string Name { get; }
}

XAML:

<TreeView ItemsSource="some list of RootObjects">
    <TreeView.Resources>
        <HierarchicalDataTemplate DataType="{x:Type data:RootObject}" 
                                  ItemsSource="???">
            <TextBlock Text="{Binding Path=Name}" />
        </HierarchicalDataTemplate>
        <HierarchicalDataTemplate DataType="{x:Type data:ChildObject}">
            <TextBlock Text="{Binding Path=Name}" />
        </HierarchicalDataTemplate>
    </TreeView.Resources>
</TreeView>

Here I want to bind to the GetChildren method on each RootObject of the tree.

EDIT Binding to an ObjectDataProvider doesn't seem to work because I'm binding to a list of items, and the ObjectDataProvider needs either a static method, or it creates it's own instance and uses that.

For example, using Matt's answer I get:

System.Windows.Data Error: 33 : ObjectDataProvider cannot create object; Type='RootObject'; Error='Wrong parameters for constructor.'

System.Windows.Data Error: 34 : ObjectDataProvider: Failure trying to invoke method on type; Method='GetChildren'; Type='RootObject'; Error='The specified member cannot be invoked on target.' TargetException:'System.Reflection.TargetException: Non-static method requires a target.

解决方案

Another approach that might work for you is to create a custom IValueConverter that takes a method name as a parameter, so that it would be used like this:

ItemsSource="{Binding 
    Converter={StaticResource MethodToValueConverter},
    ConverterParameter='GetChildren'}"

This converter would find and invoke the method using reflection. This requires the method to not have any arguments.

Here's an example of such a converter's source:

public sealed class MethodToValueConverter : IValueConverter
{
    public object Convert(object value, Type targetType, object parameter, CultureInfo culture)
    {
        var methodName = parameter as string;
        if (value==null || methodName==null)
            return value;
        var methodInfo = value.GetType().GetMethod(methodName, new Type[0]);
        if (methodInfo==null)
            return value;
        return methodInfo.Invoke(value, new object[0]);
    }

    public object ConvertBack(object value, Type targetType, object parameter, CultureInfo culture)
    {
        throw new NotSupportedException("MethodToValueConverter can only be used for one way conversion.");
    }
}

And a corresponding unit test:

[Test]
public void Convert()
{
    var converter = new MethodToValueConverter();
    Assert.AreEqual("1234", converter.Convert(1234, typeof(string), "ToString", null));
    Assert.AreEqual("ABCD", converter.Convert(" ABCD ", typeof(string), "Trim", null));

    Assert.IsNull(converter.Convert(null, typeof(string), "ToString", null));

    Assert.AreEqual("Pineapple", converter.Convert("Pineapple", typeof(string), "InvalidMethodName", null));
}

Note that this converter does not enforce the targetType parameter.

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