通過xaml中的依賴屬性公開初始化對象的內部屬性

Question

我有從Control派生的類，它位於UserControl的內部。所以我的UserControl是綁定的連接層，所有事情都在xaml。

代碼看起來這樣：

public partial class CombinedControl: UserControl{} 
public class DerivedControl: MainControl 
{ 
    public int ExampleProp{get; set;} 
} 

我想要做的就是在XAML訪問MainControl性能。我在CombinedControl中有它的實例，我可以通過DependancyProperty公開對象本身。

public DerivedControl Instance 
{ 
    get 
    { 
     return (DerivedControl)GetValue(InstanceProperty); 
    } 
    set 
    { 
     SetValue(InstanceProperty, value); 
    } 
} 

public static readonly DependencyProperty InstanceProperty= 
     DependencyProperty.Register("Instance", typeof(DerivedControl), typeof(CombinedControl)); 

我的目標：<NameSpaceName:CombinedControl Instance.ExampleProp = "10"/>

問題：如何訪問和修改XAML中初始化對象的屬性？

Answer 1

由於您無法使用正常的元素/屬性級語法，因此您可以使用混合行爲來定位CombinedControl上的Instance屬性，並將其屬性ExampleProp設置爲您想要的值。這需要添加對System.Windows.Interactivity的引用，該引用是Blend SDK（隨Visual Studio附帶）的一部分。首先是主要行爲：

using System; 
using System.ComponentModel; 
using System.Reflection; 
using System.Windows; 
using System.Windows.Interactivity; 

// Sets properties on targeted items via XAML. 
public class SetPropertyBehavior : Behavior<FrameworkElement> 
{ 
    // Name of the property we want to set on our target. 
    public static DependencyProperty PropertyNameProperty = 
     DependencyProperty.Register("PropertyName", typeof(string), typeof(SetPropertyBehavior), 
     new PropertyMetadata(OnTargetPropertyOrValueChanged)); 

    public string PropertyName 
    { 
     get { return (string)GetValue(PropertyNameProperty); } 
     set { SetValue(PropertyNameProperty, value); } 
    } 

    // Value of the property we want to set. 
    public static DependencyProperty PropertyValueProperty = 
     DependencyProperty.Register("PropertyValue", typeof(object), typeof(SetPropertyBehavior), 
     new PropertyMetadata(OnTargetPropertyOrValueChanged)); 

    public object PropertyValue 
    { 
     get { return GetValue(PropertyValueProperty); } 
     set { SetValue(PropertyValueProperty, value); } 
    } 

    // Target object that has the property we want to set. If this is null, the behavior's 
    // associated object will be the target instead. 
    public static DependencyProperty TargetProperty = 
     DependencyProperty.Register("Target", typeof(object), typeof(SetPropertyBehavior), 
     new PropertyMetadata(OnTargetPropertyOrValueChanged)); 

    public object Target 
    { 
     get { return GetValue(TargetProperty); } 
     set { SetValue(TargetProperty, value); } 
    } 

    protected override void OnAttached() 
    { 
     UpdateTargetProperty(); 
    } 

    private static void OnTargetPropertyOrValueChanged(DependencyObject d, DependencyPropertyChangedEventArgs e) 
    { 
     var behavior = d as SetPropertyBehavior; 
     if(behavior != null) 
      behavior.UpdateTargetProperty(); 
    } 

    private void UpdateTargetProperty() 
    { 
     // Ensure we have a property name and target to work with. 
     if(string.IsNullOrEmpty(this.PropertyName)) 
      return; 

     var target = this.Target ?? this.AssociatedObject; 
     if(target == null) 
      return; 

     // Make sure our property is actually on our target. 
     var targetType = target.GetType(); 
     PropertyInfo propInfo = targetType.GetProperty(this.PropertyName, 
      BindingFlags.Instance | BindingFlags.Public | BindingFlags.NonPublic); 

     if(propInfo == null) 
      return; 

     // Try to convert the string from the XAML to a value the target property can store. 
     TypeConverter converter = TypeDescriptor.GetConverter(propInfo.PropertyType); 
     object propValue = null; 
     try 
     { 
      if(converter.CanConvertFrom(this.PropertyValue.GetType())) 
       propValue = converter.ConvertFrom(this.PropertyValue); 
      else 
       propValue = converter.ConvertFrom(this.PropertyValue.ToString()); 
     } 
     catch(Exception) 
     { 
      // Do whatever is appropriate in your case. 
      propValue = null; 
     } 

     propInfo.SetValue(target, propValue); 
    } 
} 

然後取決於它讓你最感設定值ExampleProp，您將通過XAML添加的行爲。例如，如果您添加的XAML內的行爲爲您CombinedControl，它可能是這個樣子：

<UserControl x:Class="NameSpaceName.CombinedControl" 
      xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation" 
      xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml" 
      xmlns:local="clr-namespace:NameSpaceName" 
      xmlns:i="http://schemas.microsoft.com/expression/2010/interactivity" 
      x:Name="Root"> 

    <i:Interaction.Behaviors> 
     <local:SetPropertyBehavior Target="{Binding Instance, ElementName=Root}" PropertyName="ExampleProp" PropertyValue="10"/> 
    </i:Interaction.Behaviors> 

    <!-- Rest of control here --> 
</UserControl> 

如果你想從XAML做任何的母公司在託管您CombinedControl，你可以像這個（使用基本的WPF Window作爲例子）：

<Window x:Class="NameSpaceName.MainWindow" 
     xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation" 
     xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml" 
     xmlns:local="clr-namespace:NameSpaceName" 
     xmlns:i="http://schemas.microsoft.com/expression/2010/interactivity" 
     Title="MainWindow" Height="350" Width="525"> 

    <i:Interaction.Behaviors> 
     <local:SetPropertyBehavior Target="{Binding Instance, ElementName=myCombinedControl}" PropertyName="ExampleProp" PropertyValue="10"/> 
    </i:Interaction.Behaviors> 

    <Grid> 
     <local:CombinedControl x:Name="myCombinedControl"/> 
    </Grid> 
</Window>