WPF MarkupExtension和RowDefinition导致NotImplementedException

Question

场景: 创建一个MarkupExtension,用Grid.Row ="{namespace:ClassExtension GridRowName}"替换Grid.Row ="0"(列相同)

Xaml代码:

<Grid>
  <Grid.RowDefinitions>
    <RowDefinition Height="Auto" x:Name="TitleRow" />
    <RowDefinition Height="Auto" x:Name="LastNameRow" />
    <RowDefinition Height="Auto" x:Name="FirstNameRow" />
    <RowDefinition Height="Auto" x:Name="EmailRow" />
  </Grid.RowDefinitions>
  <Grid.ColumnDefinitions>
    <ColumnDefinition x:Name="LabelColumn" />
    <ColumnDefinition x:Name="ValueColumn" />
  </Grid.ColumnDefinitions>

    <Label Grid.Row="{me:GridDefinition Name=TitleRow}" Grid.ColumnSpan="2" FontWeight="Bold" FontSize="14" />
    <Label Grid.Row="{me:GridDefinition Name=LastNameRow}" Grid.Column="{me:GridDefinition Name=LabelColumn}" FontWeight="Bold" FontSize="14" />
</Grid>

要求:

• 使用incorrent GridRowName(或columnName)时显示XAML错误
• 使用正确的GridRowName(或columnName)时,不显示XAML错误
• 当Valid ColumnName用于Row声明(和vica verca)时,应显示XAML错误

问题: Grid.Column的一切正常,但Grid.Row总是在设计时抛出"未实现的异常"(grid.row带下划线,grid.column不是).

行和列都命名正确,但行始终显示错误.如果我们指定一个无效的列名,该列会显示一个错误(这是预期的,因此Grid.Column工作正常!)

如您所见,列工作正常,但行不行.问题出在名为GridDefinitionExtension的MarkupExtension中:

[MarkupExtensionReturnType(typeof(int))]
public class GridDefinitionExtension : MarkupExtension
{
    public string Name { private get; set; }

    public override object ProvideValue(IServiceProvider serviceProvider)
    {
        var referenceExt = new Reference(Name);
        var definition = referenceExt.ProvideValue(serviceProvider);

        if (definition is DefinitionBase)
        {
            var grid = (definition as FrameworkContentElement).Parent as Grid;

            if (grid != null && definition is RowDefinition)
                return grid.RowDefinitions.IndexOf(definition as RowDefinition);

            if (grid != null && definition is ColumnDefinition)
                return grid.ColumnDefinitions.IndexOf(definition as ColumnDefinition);
        }

        // This Extension only works for DefinitionBase Elements.
        throw new NotSupportedException();
    }
}

该行上有异常:

var definition = referenceExt.ProvideValue(serviceProvider);

在查看调用此方法的DLL内部后,我发现此ProvideValue方法的主体如下所示:

public override object ProvideValue(IServiceProvider serviceProvider)
{
  if (serviceProvider == null)
    throw new ArgumentNullException("serviceProvider");
  IXamlNameResolver xamlNameResolver = serviceProvider.GetService(typeof (IXamlNameResolver)) as IXamlNameResolver;
  if (xamlNameResolver == null)
    throw new InvalidOperationException(System.Xaml.SR.Get("MissingNameResolver"));
  if (string.IsNullOrEmpty(this.Name))
    throw new InvalidOperationException(System.Xaml.SR.Get("MustHaveName"));
  object obj = xamlNameResolver.Resolve(this.Name);
  if (obj == null)
  {
    string[] strArray = new string[1]
    {
      this.Name
    };
    obj = xamlNameResolver.GetFixupToken((IEnumerable<string>) strArray, true);
  }
  return obj;
}

我已经简化了这个ProvideValue方法,只显示它在我的场景中实际使用的代码:

if (serviceProvider == null)
    throw new ArgumentNullException("serviceProvider");

IXamlNameResolver xamlNameResolver = serviceProvider.GetService(typeof(IXamlNameResolver)) as IXamlNameResolver;

object obj = xamlNameResolver.Resolve(this.Name);
if (obj == null)
{
    var strArray = new string[1]{ this.Name };
    obj = xamlNameResolver.GetFixupToken((IEnumerable<string>)strArray, true);
}
return obj;

显然,GetFixUpToken方法抛出异常,但原因是Resolve方法.当通过名称查找ColumnDefinition时,此Resolve方法返回有效对象,但在为RowDefinition执行完全相同的操作时返回NULL.

GetFixUpToken抛出的错误是:"NotImplementedException",这是在查看IXamlNameResolver的源代码时所期望的(在本例中是Type:XamlNameResolverImpl)

查看此XamlNameResolverImpl的源代码时,您可以看到方法"GetFixUpToken"为空并抛出NotImplemented异常(请查看http://dotnetinside.com/en/framework/Microsoft+Expression/Microsoft.Expression.WpfPlatform/WpfMarkupExtensionValueSetter)

public object GetFixupToken(IEnumerable<string> names, bool canAssignDirectly)
{
      throw new NotImplementedException();
}
public object GetFixupToken(IEnumerable<string> names)
{
      throw new NotImplementedException();
}

但问题是,正如我已经说过的那样,是Resolve调用,它对于columndefinition工作正常,但对于rowdefinitions却失败了......:

柱:

行:

此时,我不知道该怎么办......

源代码(示例项目)可从以下网址获得:http://www.frederikprijck.net/stuff/MarkupExtension.rar

Answer 1

这是一个解决方案，虽然与您的实现不同，但可以完成工作。

创建一个 IValueConverter 以与 Binding 一起使用，而不是 MarkupExtension：

public class GridDefinitionConverter : IValueConverter
    {
        public object Convert(object value, Type targetType, object parameter, System.Globalization.CultureInfo culture)
        {
            var definition = value as DefinitionBase;
            int toReturn = 0;
            if (definition != null)
            {
                var grid = (definition as FrameworkContentElement).Parent as Grid;

                if (grid != null && definition is RowDefinition)
                    toReturn = grid.RowDefinitions.IndexOf(definition as RowDefinition);

                if (grid != null && definition is ColumnDefinition)
                    toReturn = grid.ColumnDefinitions.IndexOf(definition as ColumnDefinition);
            }
            return toReturn;
        }

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

然后将其放入您的 XAML 中：

<Grid.Resources>
    <me:GridDefinitionConverter x:Key="gridDefinitionConverter" />
</Grid.Resources>

并像这样实现它：

<Label Grid.Row="{Binding ElementName=TitleRow, Converter={StaticResource gridDefinitionConverter}}" />