WPF自定義控件的工具提示MultiBinding問題

Question

當我設置一個工具提示綁定在WPF自定義控件，這樣它完美的作品：

public override void OnApplyTemplate() 
{ 
    base.OnApplyTemplate(); 
    ... 
    SetBinding(ToolTipProperty, new Binding 
         { 
          Source = this, 
          Path = new PropertyPath("Property1"), 
          StringFormat = "ValueOfProp1: {0}" 
         });   
} 

但是當我嘗試使用MultiBinding在工具提示有幾個特性，不起作用：

public override void OnApplyTemplate() 
{ 
    base.OnApplyTemplate(); 
    ... 
    MultiBinding multiBinding = new MultiBinding(); 
    multiBinding.StringFormat = "ValueOfProp1: {0}\nValueOfProp2: {1}\nValueOfProp3: {2}\n"; 

     multiBinding.Bindings.Add(new Binding 
     { 
      Source = this, 
      Path = new PropertyPath("Property1") 
     }); 
     multiBinding.Bindings.Add(new Binding 
     { 
      Source = this, 
      Path = new PropertyPath("Property2") 
     }); 
     multiBinding.Bindings.Add(new Binding 
     { 
      Source = this, 
      Path = new PropertyPath("Property3") 
     }); 

     this.SetBinding(ToolTipProperty, multiBinding);   
} 

在這種情況下，我根本沒有顯示工具提示。

我在哪裏錯了？

Answer 1

事實證明，StringFormat上MultiBinding僅適用於string類型的屬性，而ToolTip屬性爲object型。在這種情況下，MultiBinding需要定義一個值轉換器。

作爲一種變通方法，你可以設置一個TextBlock爲ToolTip和綁定使用MultiBinding其Text財產（因爲Text是string型的，它會與StringFormat工作）：

TextBlock toolTipText = new TextBlock(); 

MultiBinding multiBinding = new MultiBinding(); 
multiBinding.StringFormat = "ValueOfProp1: {0}\nValueOfProp2: {1}\nValueOfProp3: {2}\n"; 

multiBinding.Bindings.Add(new Binding 
{ 
    Source = this, 
    Path = new PropertyPath("Property1") 
}); 
multiBinding.Bindings.Add(new Binding 
{ 
    Source = this, 
    Path = new PropertyPath("Property2") 
}); 
multiBinding.Bindings.Add(new Binding 
{ 
    Source = this, 
    Path = new PropertyPath("Property3") 
}); 

toolTipText.SetBinding(TextBlock.TextProperty, multiBinding); 

ToolTip = toolTipText;