将类型参数传递给附加行为

Question

我正在 WPF 应用程序中实现附加行为。我需要将类型参数传递给行为，因此我可以在SqliteBoundRow 上调用方法void NewRow(Table<T> table)。如果我在 XAML 中实例化一个对象，我会使用 x:TypeArguments 传递一个类型参数，但在设置附加行为时我看不到这样做的方法，因为它使用静态属性。

附加行为的代码如下所示：

public abstract class SqliteBoundRow<T> where T : SqliteBoundRow<T>
{
    public abstract void NewRow(Table<T> table);
}

public class DataGridBehavior<T> where T:SqliteBoundRow<T>
{
    public static readonly DependencyProperty IsEnabledProperty;
    static DataGridBehavior()
    {
        IsEnabledProperty = DependencyProperty.RegisterAttached("IsEnabled",
            typeof(bool), typeof(DataGridBehavior<T>),
            new FrameworkPropertyMetadata(false, OnBehaviorEnabled));
    }
    public static void SetIsEnabled(DependencyObject obj, bool value)
    {
        obj.SetValue(IsEnabledProperty, value);
    }
    public static bool GetIsEnabled(DependencyObject obj)
    {
        return (bool)obj.GetValue(IsEnabledProperty);
    }
    private static void OnBehaviorEnabled(DependencyObject dependencyObject,
        DependencyPropertyChangedEventArgs args)
    {
        var dg = dependencyObject as DataGrid;
        dg.InitializingNewItem += DataGrid_InitializingNewItem;
    }
    private static void DataGrid_InitializingNewItem(object sender,
        InitializingNewItemEventArgs e)
    {
        var table = (sender as DataGrid).ItemsSource as Table<T>;
        (e.NewItem as T).NewRow(table);
    }

}

XAML 如下所示：

<DataGrid DataGridBehavior.IsEnabled="True">
    <!-- DataGridBehavior needs a type parameter -->
</DataGrid>

我目前的解决方案是将 DataGridBehavior 包装在指定类型参数的派生类中。

Answer 1

我不认为 WPF 提供了一种优雅的语法方式来做你想做的事。因此，我正要发布与 Sheridan 的答案类似的答案。也就是说，您可以提供 Type 类型的附加属性来确定泛型类型。然而，谢里登打败了我。下面是一些示例代码，说明如何使用反射来做到这一点：

Xaml

 <DataGrid behaviors:DataGridBehavior.InnerType="namespace:SqliteBoundRow"
      behaviors:DataGridBehavior.IsEnabled="True">
</DataGrid>

后面的代码

public abstract class DataGridBehavior
{
    private static readonly ConcurrentDictionary<Type, DataGridBehavior> Behaviors = new ConcurrentDictionary<Type, DataGridBehavior>();
    public static readonly DependencyProperty IsEnabledProperty;
    public static readonly DependencyProperty InnerTypeProperty;
    static DataGridBehavior()
    {
        IsEnabledProperty = DependencyProperty.RegisterAttached("IsEnabled",
            typeof(bool), typeof(DataGridBehavior),
            new FrameworkPropertyMetadata(false, OnBehaviorEnabled));

        InnerTypeProperty = DependencyProperty.RegisterAttached("InnerType",
            typeof(Type), typeof(DataGridBehavior));
    }
    public static void SetIsEnabled(DependencyObject obj, bool value)
    {
        obj.SetValue(IsEnabledProperty, value);
    }
    public static bool GetIsEnabled(DependencyObject obj)
    {
        return (bool)obj.GetValue(IsEnabledProperty);
    }

    public static void SetInnerType(DependencyObject obj, Type value)
    {
        obj.SetValue(InnerTypeProperty, value);
    }
    public static Type GetInnerType(DependencyObject obj)
    {
        return (Type)obj.GetValue(InnerTypeProperty);
    }

    private static void OnBehaviorEnabled(DependencyObject dependencyObject,
          DependencyPropertyChangedEventArgs args)
    {
        var innerType = GetInnerType(dependencyObject);
        if (innerType == null)
            throw new Exception("Missing inner type");

        var behavior = Behaviors.GetOrAdd(innerType, GetBehavior);
        behavior.OnEnabled(dependencyObject);
    }

    private static DataGridBehavior GetBehavior(Type innerType)
    {
        var behaviorType = typeof(DataGridBehavior<>).MakeGenericType(innerType);
        var behavior = (DataGridBehavior)Activator.CreateInstance(behaviorType);
        return behavior;
    }

    protected abstract void OnEnabled(DependencyObject dependencyObject);

}

public class DataGridBehavior<T> : DataGridBehavior
    where T : SqliteBoundRow
{
    protected override void OnEnabled(DependencyObject dependencyObject)
    {
        //dg.InitializingNewItem += DataGrid_InitializingNewItem;
    }

    private static void DataGrid_InitializingNewItem(object sender,
        InitializingNewItemEventArgs e)
    {
        //var table = (sender as DataGrid).ItemsSource as Table<T>;
        //(e.NewItem as T).NewRow(table);
    }

}

public class SqliteBoundRow
{
}

Answer 2

最简单的解决方案是让您声明另一个Attached Property，但类型为Type 来为您保存参数值。在这种情况下，您可以在 IsEnabled Attached Property 之前设置 Type 属性：

<DataGrid DataGridBehavior.TypeParameter="{x:Type SomePrefix:SomeType}" 
    DataGridBehavior.IsEnabled="True" ... />

再次查看您的代码，似乎您的 IsEnabled 属性除了向您的表中添加新行之外什么都不做......在这种情况下，您没有理由不能用 TypeParameter Attached Property 替换它并使用那个来添加新行。