如何向依賴項屬性添加邏輯？

Question

如何將此屬性轉換爲依賴項屬性？至於大家剛纔說的「不要依賴項屬性使用邏輯」，並沒有提出一個補救措施：

public DateTime? SelectedDateGeorgian 
    { 
     get 
     { 
      //choose a control based on this "user control" current mode 
      //and return its value 
     } 


     set 
     { 
      //choose a control based on this "user control" current mode 
      // and set its property after some manipulations on the value 
     } 
    } 

我想將它轉化成這樣：

public static readonly DependencyProperty SelectedDateGeorgianProperty = 
    DependencyProperty.Register("SelectedDateGeorgian", typeof(DateTime?), typeof(MyDatePicker), new PropertyMetadata(default(DateTime?))); 

    public DateTime? SelectedDateGeorgian 
    { 
     get 
     { 
      //Its prohobited to do something here ! So what should I do ? 
      //How should I select a control and return its value here ? 
      //I can't have a simple backing variable because I should do some conversion here     

      return (DateTime?)GetValue(SelectedDateGeorgianProperty); 
     } 
     set 
     { 
      //I want to convert received value here and 
      // and after that update some UI properties in this user control 

      SetValue(SelectedDateMiladiProperty, value); 
     } 
    } 

我想轉換要寫入此依賴項屬性中的值並更新UIElements。

而且我還想從UIElement轉換一個值，並在每次讀取它時返回轉換後的值。

所以你看到我不能有一個簡單的支持變量。

請有人給我一個模式來實現這一點。

感謝您的關注。

Answer 1

是的，你可以。

您必須將您的UIElement property與此DependencyProperty綁定並使用Converter。請參閱How to: Convert Bound Data。

順便說一句：Here你可以找到原因，爲什麼DependencyProperties不應該在屬性包裝中有額外的邏輯。

編輯：

<DatePicker Name="dp1" 
      SelectedDate="{Binding Path=SelectedDateGeorgian, 
            RelativeSource="{RelativeSource AncestorType=UserControl}"}" /> 
<DatePicker Name="dp2" 
      SelectedDate="{Binding Path=SelectedDateGeorgian, 
            RelativeSource="{RelativeSource AncestorType=UserControl}", 
            Converter={StaticResource dateConverter}}" /> 

創建轉換器：

[ValueConversion(typeof(DateTime?), typeof(DateTime?))] 
public class DateConverter : IValueConverter 
{ 
    public object Convert(object value, Type targetType, object parameter, CultureInfo culture) 
    { 
     // your conversions 
    } 

    public object ConvertBack(object value, Type targetType, object parameter, CultureInfo culture) 
    { 
     // your backconversions 
    } 
} 

並將其添加爲一個資源：

<src:DateConverter x:Key="dateConverter"/>