根據選擇的組合框更改元素高度

Question

我有一個用於選擇媒體類型的組合框。當選擇.vmw，.mpeg或.avi文件時，我想要改變mediaelement的高度。我如何用MVVM方法實現這一點？

在此先感謝

Answer 1

一個解決辦法是到ComboBox綁定到自我創造MediaTypeDefinition類的列表。

public class MediaTypeDefinition 
{ 
    public string Name { get; set; } 

    public int Height { get; set; } 
} 

然後，您可以將SelectedItem綁定到媒體元素的高度。

<ComboBox x:Name="mediaTypeList" ItemsSource="{Binding Definitions}" SelectedValuePath="Name" /> 

<MediaElement Height="{Binding SelectedItem.Height, Elementname=mediaTypeList}" /> 

Answer 2

您可以在MediaElement的Width和Height直接綁定到其Source屬性用合適的轉換器，它選擇合適的大小取決於媒體類型：

<MediaElement 
    Width="{Binding Path=Source, RelativeSource={RelativeSource Self}, Converter={StaticResource MediaElementSizeConverter}, ConverterParameter=Width}" 
    Height="{Binding Path=Source, RelativeSource={RelativeSource Self}, Converter={StaticResource MediaElementSizeConverter}, ConverterParameter=Height}"/> 

變換器：

public class MediaElementSizeConverter : IValueConverter 
{ 
    private const double defaultWidth = 320d; 
    private const double defaultHeight = 240d; 
    private const double wmvWidth = 640d; 
    private const double wmvHeight = 480d; 

    public object Convert(object value, Type targetType, object parameter, CultureInfo culture) 
    { 
     Uri source = value as Uri; 

     if (source != null) 
     { 
      if (source.AbsolutePath.EndsWith(".wmv")) 
      { 
       return (parameter as string) == "Width" ? wmvWidth : wmvHeight; 
      } 

      // more media types ... 
     } 

     return (parameter as string) == "Width" ? defaultWidth : defaultHeight; 
    } 

    public object ConvertBack(object value, Type targetType, object parameter, CultureInfo culture) 
    { 
     throw new NotImplementedException(); 
    } 
}