嘗試爲對象集合綁定創建IsFirstItem和IsLastItem IValueConverter

最終目標是能夠在列表框中的第一個和最後一個元素上設置特定的ItemContainerStyle;嘗試爲對象集合綁定創建IsFirstItem和IsLastItem IValueConverter

該轉換器迄今有：

public class IsFirstItemConverter : IValueConverter 
{ 
    public object Convert(object value, Type targetType, object parameter, CultureInfo culture) 
    { 
     bool result = false; 
     result = ((IList<object>)parameter).First() == value; 

     return result; 
    } 

    public object ConvertBack(object value, Type targetType, object parameter, System.Globalization.CultureInfo culture) 
    { 
     throw new NotImplementedException(); 
    } 
} 
public class IsLastItemConverter : IValueConverter 
{ 
    public object Convert(object value, Type targetType, object parameter, CultureInfo culture) 
    { 
     bool result = false; 
     result = ((IList<object>)parameter).Last() == value; 

     return result; 
    } 

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

而實現：

<DataTrigger Value="True" Binding="{Binding Converter={StaticResource IsFirstItemConverter},ConverterParameter=Items, ElementName=SubItems}"> 
    <Setter Property="Template"> 
     <Setter.Value> 
      <ControlTemplate TargetType="{x:Type ListBoxItem}"> 
       <StackPanel Orientation="Horizontal"> 
        <TextBlock Text="First"/> 
        <ContentPresenter/> 
       </StackPanel> 
      </ControlTemplate> 
     </Setter.Value> 
    </Setter> 
</DataTrigger>

和錯誤是：

InvalidCastException的：無法轉換類型的對象「System.String '到類型'System.Collections.Generic.IList`1 [System.Object]'。

我確定我搞砸了多個地方，只是沒有足夠的經驗與XAML和綁定縮小在哪裏。

來源

2016-03-04 Wobbles

[Click]（http://stackoverflow.com/a/12131197/1997232）。 – Sinatr

看看[this]（http://stackoverflow.com/questions/13613053/how-can-i-know-if-a-listboxitem-is-the-last-item-inside-a-wpfs-listbox ） –

@Sinatr哦，我的工作比我試圖做的更乾淨，請張貼答案（儘管它只是其他地方的參考），所以我可以接受它。這絕對會被添加到我的常用轉換器庫中。 – Wobbles

以下改編自問題的意見很好地工作：

public class IsLastItemConverter : IValueConverter 
{ 
    public object Convert(object value, Type targetType, object parameter, CultureInfo culture) 
    { 
     DependencyObject item = (DependencyObject)value; 
     ItemsControl ic = ItemsControl.ItemsControlFromItemContainer(item); 

     return ic.ItemContainerGenerator.IndexFromContainer(item) == ic.Items.Count - 1; 
    } 

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

public class IsFirstItemConverter : IValueConverter 
{ 
    public object Convert(object value, Type targetType, object parameter, CultureInfo culture) 
    { 
     DependencyObject item = (DependencyObject)value; 
     ItemsControl ic = ItemsControl.ItemsControlFromItemContainer(item); 

     return ic.ItemContainerGenerator.IndexFromContainer(item) == 0; 
    } 

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

public class IsOnlyItemConverter : IValueConverter 
{ 
    public object Convert(object value, Type targetType, object parameter, CultureInfo culture) 
    { 
     DependencyObject item = (DependencyObject)value; 
     ItemsControl ic = ItemsControl.ItemsControlFromItemContainer(item); 

     return (ic.ItemContainerGenerator.IndexFromContainer(item) == 0 && ic.ItemContainerGenerator.Items.Count == 1); 
    } 

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

實現：

<DataTrigger Binding="{Binding RelativeSource={RelativeSource Self}, Converter={StaticResource IsLastItemConverter}}" Value="True"> 
    <Setter Property="Template"> 
     <Setter.Value> 
      <ControlTemplate TargetType="{x:Type ListBoxItem}"> 
       <StackPanel Orientation="Horizontal"> 
        <TextBlock Text="└"/> 
        <ContentPresenter/> 
       </StackPanel> 
      </ControlTemplate> 
     </Setter.Value> 
    </Setter> 
</DataTrigger>

魔術似乎是ItemsControlFromItemContainer使得它，所以我不必同時通過該項目，它的收集實例到轉換器，但只是項目和轉換器可以推斷父集合。

來源

2016-03-04 15:51:44 Wobbles

嘗試爲對象集合綁定創建IsFirstItem和IsLastItem IValueConverter

回答

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