在Xaml绑定中切换(选择)语句？

Question

有没有办法在XAML中创建条件绑定？

例:

<Window x:Name="Me" DataContext="{Binding ElementName=Me}">
    <TextBlock>
        <TextBlock.Text>
            <SelectBinding Binding="{Binding MyValue}">
                <Case Value="Value1" Value="value is 1!">                
                <Case Value="Value2" Value="value is 2!">                
                <Case Value="Value3" Value="value is 3!">                
            </SelectBinding >
        </TextBlock.Text>
    </TextBlock>
</Window>

最重要的是,我想根据另一个值来设置TextBlock值,该值Binding可以是每个案例(或案例)被发送到适当的输出/设置器的情况列表.

也许我可以DataTrigger在我的情况下使用,我只是不知道我将如何做到这一点,因为我没有DataTemplate在这里使用任何.

更新
在我的场景中,我有一个UserControl有几个控件.我希望根据UserControl.DataContext数据项中的某个属性,用户控件中的其他控件应该相应地受到影响.基本上与我上面的例子相同,每个案例都会导致一个Setters 列表.

Answer 1

用一个 DataTrigger

(已编辑 - 原版有轻微错误)

<TextBlock>
  <TextBlock.Style>
    <Style>
      <Style.Triggers>
        <DataTrigger Binding="{Binding MyValue}" Value="Value1">
          <Setter Property="TextBlock.Text" Value="value is 1!"/>
        </DataTrigger>
        <DataTrigger Binding="{Binding MyValue}" Value="Value2">
          <Setter Property="TextBlock.Text" Value="value is 2!"/>
        </DataTrigger>
        <DataTrigger Binding="{Binding MyValue}" Value="Value3">
          <Setter Property="TextBlock.Text" Value="value is 3!"/>
        </DataTrigger>
      </Style.Triggers>
    </Style>
  </TextBlock.Style>

Answer 2

你有很多选择......

• 您可以通过在文本块中应用"样式"来使用"DataTrigger"(使用"Style.Triggers").
• 您可以创建一个转换器,将"MyValue"转换为适当的文本.
• 您可以在任何数据源上创建另一个属性(理想情况下,这将是一个ViewModel样式的类),它反映了应该显示的文本.从代码更新属性并直接绑定到它,而不是将逻辑放在XAML中.

真的,我认为这是一种风格/设计选择 - 以上都不是天生好或坏,它们只适合不同的场景.

Answer 3

尝试使用Josh编写的Switch Converter:

SwitchConverter -

XAML的"切换声明" - http://josheinstein.com/blog/index.php/2010/06/switchconverter-a-switch-statement-for-xaml/

编辑:

这是SwitchConverter的代码,因为Josh的网站似乎已经关闭 -

/// <summary>
/// A converter that accepts <see cref="SwitchConverterCase"/>s and converts them to the 
/// Then property of the case.
/// </summary>
[ContentProperty("Cases")]
public class SwitchConverter : IValueConverter
{
    // Converter instances.
    List<SwitchConverterCase> _cases;

    #region Public Properties.
    /// <summary>
    /// Gets or sets an array of <see cref="SwitchConverterCase"/>s that this converter can use to produde values from.
    /// </summary>
    public List<SwitchConverterCase> Cases { get { return _cases; } set { _cases = value; } }
    #endregion
    #region Construction.
    /// <summary>
    /// Initializes a new instance of the <see cref="SwitchConverter"/> class.
    /// </summary>
    public SwitchConverter()
    {
        // Create the cases array.
        _cases = new List<SwitchConverterCase>();
    }
    #endregion

    /// <summary>
    /// Converts a value.
    /// </summary>
    /// <param name="value">The value produced by the binding source.</param>
    /// <param name="targetType">The type of the binding target property.</param>
    /// <param name="parameter">The converter parameter to use.</param>
    /// <param name="culture">The culture to use in the converter.</param>
    /// <returns>
    /// A converted value. If the method returns null, the valid null value is used.
    /// </returns>
    public object Convert(object value, Type targetType, object parameter, System.Globalization.CultureInfo culture)
    {
        // This will be the results of the operation.
        object results = null;

        // I'm only willing to convert SwitchConverterCases in this converter and no nulls!
        if (value == null) throw new ArgumentNullException("value");

        // I need to find out if the case that matches this value actually exists in this converters cases collection.
        if (_cases != null && _cases.Count > 0)
            for (int i = 0; i < _cases.Count; i++)
            {
                // Get a reference to this case.
                SwitchConverterCase targetCase = _cases[i];

                // Check to see if the value is the cases When parameter.
                if (value == targetCase || value.ToString().ToUpper() == targetCase.When.ToString().ToUpper())
                {
                    // We've got what we want, the results can now be set to the Then property
                    // of the case we're on.
                    results = targetCase.Then;

                    // All done, get out of the loop.
                    break;
                }
            }

        // return the results.
        return results;
    }

    /// <summary>
    /// Converts a value.
    /// </summary>
    /// <param name="value">The value that is produced by the binding target.</param>
    /// <param name="targetType">The type to convert to.</param>
    /// <param name="parameter">The converter parameter to use.</param>
    /// <param name="culture">The culture to use in the converter.</param>
    /// <returns>
    /// A converted value. If the method returns null, the valid null value is used.
    /// </returns>
    public object ConvertBack(object value, Type targetType, object parameter, System.Globalization.CultureInfo culture)
    {
        throw new NotImplementedException();
    }
}

/// <summary>
/// Represents a case for a switch converter.
/// </summary>
[ContentProperty("Then")]
public class SwitchConverterCase
{
    // case instances.
    string _when;
    object _then;

    #region Public Properties.
    /// <summary>
    /// Gets or sets the condition of the case.
    /// </summary>
    public string When { get { return _when; } set { _when = value; } }
    /// <summary>
    /// Gets or sets the results of this case when run through a <see cref="SwitchConverter"/>
    /// </summary>
    public object Then { get { return _then; } set { _then = value; } }
    #endregion
    #region Construction.
    /// <summary>
    /// Switches the converter.
    /// </summary>
    public SwitchConverterCase()
    {
    }
    /// <summary>
    /// Initializes a new instance of the <see cref="SwitchConverterCase"/> class.
    /// </summary>
    /// <param name="when">The condition of the case.</param>
    /// <param name="then">The results of this case when run through a <see cref="SwitchConverter"/>.</param>
    public SwitchConverterCase(string when, object then)
    {
        // Hook up the instances.
        this._then = then;
        this._when = when;
    }
    #endregion

    /// <summary>
    /// Returns a <see cref="System.String"/> that represents this instance.
    /// </summary>
    /// <returns>
    /// A <see cref="System.String"/> that represents this instance.
    /// </returns>
    public override string ToString()
    {
        return string.Format("When={0}; Then={1}", When.ToString(), Then.ToString());
    }
}