WPF ListView中的转换器，使用缓存的值作为参数

Question

I have an application that manages documents of different type. In a document manager I diaplay the documents in a ListView. I have created some converter to diaplay special aspacts of a document without messing with the document class itself. One column in the list view shall display an icon that represent the document type and a document number. The columns shall look like

 <icon> D 1 <icon> D 11 ... 

The document number shall be padded left to fit the biggest number.

Currently I have a converter which creates the desired term

public object Convert(object value, Type targetType, object parameter, System.Globalization.CultureInfo culture)
D{
    System.Windows.Controls.ListView view = (System.Windows.Controls.ListView)parameter;
    int count = (view.Items.Count.ToString().Count());
    string id = "D" + value.ToString().PadLeft(count);
    return id;
}

The converter is used in a CellTemplate where the converter parameter is listview itself

<TextBlock Text="{Binding Number, Converter={StaticResource docIDConverter}, ConverterParameter={x:Reference Documents}}" />

I know the amount of documents in a project and can provide it as propperty of my window class

    /// <summary>
    /// The amount of documents contained in a project
    /// </summary>
    int documentCount = 0;
    public int DocumentCount {
        get { 
            if(this.documentCount == 0)
                documentCount = Project.Documents.Count;
            return documentCount;
        }
    }

This works but I consider this as bad style and it may be slow on big lists.

How can I use the propperty DocumentCount as parameter to the converter. Or How can I use the propperty DocumentCount as binding in a multi value converter Thanks Clemens Hoffmann

Answer 1

ConverterParameters are not dependency properties. Thus, you can't bind to them. But you can use multi-binding to get the same effect:

<Style TargetType="FrameworkElement">
    <Setter Property="Text">
        <Setter.Value>
            <MultiBinding Converter="{StaticResource docIDConverter}">
                <Binding Path="DocumentCount" RelativeSource="RelativeSource={RelativeSource FindAncestor, AncestorType={x:Type UserControl}}"/>
            </MultiBinding>
        </Setter.Value>
    </Setter>
</Style>

The multi-value converter now gets an array of source values as input:

public class AccessLevelToVisibilityConverter : IMultiValueConverter {
    public object Convert(
            object[] values, Type targetType, object parameter, CultureInfo culture)
       {
            int count = values.All(v => (v is int);
            string id = "D" + values.All(v => (v is TypeYouAreExpectingHere).ToString().PadLeft(count);
            return id;
        }

        public object[] ConvertBack(
            object value, Type[] targetTypes, object parameter, CultureInfo culture)
        {
            throw new NotSupportedException();
        }
    }