ItemsControl基于内容的不同模板
本文关键字：于内容 ItemsControl | 更新日期: 2023-09-27 18:29:11
请确定以下不起作用的原因，我正在尝试实现一个聊天消息窗口，在该窗口中，每条消息都将根据MessageDirection呈现不同的风格。为此，我使用了一个绑定到Messages属性的ItemsControl
在ChatWindow类中，我有以下
public static readonly DependencyProperty MessagesProperty = DependencyProperty.Register(
"Messages",
typeof(ObservableCollection<Message>),
typeof(ChatWindow),
new PropertyMetadata(null));
public ObservableCollection<Message> Messages
{
get
{
return (ObservableCollection<Message>)this.GetValue(MessagesProperty);
}
set
{
this.SetValue(MessagesProperty, value);
}
}
我在ResourceDictionary 中定义了以下内容
<ScrollViewer x:Name="srcMessages" Margin="0,0,0,0" VerticalScrollBarVisibility="Visible">
<StackPanel>
<ItemsControl ItemsSource="{Binding Path=Messages, RelativeSource={RelativeSource AncestorType={x:Type chat:ChatWindow}}}" x:Name="Messages">
<ItemsControl.ItemTemplate>
<DataTemplate>
<chat:MessageContentPresenter Content="{Binding}">
<chat:MessageContentPresenter.InboundTemplate>
<DataTemplate>
<Grid>
<Grid.RowDefinitions>
<RowDefinition Height="Auto" />
<RowDefinition Height="Auto" />
</Grid.RowDefinitions>
<Grid Grid.Row="0">
<Grid.ColumnDefinitions>
<ColumnDefinition Width="94" />
<ColumnDefinition Width="Auto" />
<ColumnDefinition Width="*" />
</Grid.ColumnDefinitions>
<StackPanel Grid.Column="1" Orientation="Horizontal">
<TextBlock Text="Username One" FontSize="10" Foreground="#adadad"></TextBlock>
<TextBlock Text=" - " FontSize="10" Foreground="#adadad"></TextBlock>
<TextBlock Text="11:45 AM" FontSize="10" Foreground="#adadad"></TextBlock>
</StackPanel>
</Grid>
<Grid Grid.Row="1">
<Grid.ColumnDefinitions>
<ColumnDefinition Width="18" />
<ColumnDefinition Width="65" />
<ColumnDefinition Width="5" />
<ColumnDefinition Width="6" />
<ColumnDefinition Width="230" />
<ColumnDefinition Width="*" />
</Grid.ColumnDefinitions>
<Image Grid.Column="1" Height="60" Width="60" Source="pack://siteoforigin:,,,/Resources/noavatar.png" StretchDirection="Both" Stretch="Fill">
<Image.Clip>
<EllipseGeometry Center="30,30" RadiusX="30" RadiusY="30" />
</Image.Clip>
</Image>
<Polygon Grid.Column="3" Points="0,0 -4,3 0,6 0,0" StrokeThickness="2" HorizontalAlignment="Right" VerticalAlignment="Center" Fill="#d8d7dc" Stroke="#d8d7dc"></Polygon>
<Border Grid.Column="4" BorderBrush="#d8d7dc" BorderThickness="1" Background="#d8d7dc" Padding="5">
<TextBlock TextWrapping="Wrap" Text="This is a message in a chat window..." VerticalAlignment="Top" FontSize="12" Foreground="#000000"></TextBlock>
</Border>
</Grid>
</Grid>
</DataTemplate>
</chat:MessageContentPresenter.InboundTemplate>
<chat:MessageContentPresenter.OutboundTemplate>
<DataTemplate>
<Grid>
<Grid.RowDefinitions>
<RowDefinition Height="Auto" />
<RowDefinition Height="Auto" />
</Grid.RowDefinitions>
<Grid Grid.Row="0">
<Grid.ColumnDefinitions>
<ColumnDefinition Width="*" />
<ColumnDefinition Width="Auto" />
<ColumnDefinition Width="94" />
</Grid.ColumnDefinitions>
<StackPanel Grid.Column="1" HorizontalAlignment="Right" Orientation="Horizontal">
<TextBlock Text="Username One" FontSize="10" Foreground="#adadad"></TextBlock>
<TextBlock Text=" - " FontSize="10" Foreground="#adadad"></TextBlock>
<TextBlock Text="11:45 AM" FontSize="10" Foreground="#adadad"></TextBlock>
</StackPanel>
</Grid>
<Grid Grid.Row="1">
<Grid.ColumnDefinitions>
<ColumnDefinition Width="*" />
<ColumnDefinition Width="230" />
<ColumnDefinition Width="6" />
<ColumnDefinition Width="5" />
<ColumnDefinition Width="65" />
<ColumnDefinition Width="18" />
</Grid.ColumnDefinitions>
<Image Grid.Column="4" Height="60" Width="60" Source="pack://siteoforigin:,,,/Resources/noavatar.png" StretchDirection="Both" Stretch="Fill">
<Image.Clip>
<EllipseGeometry Center="30,30" RadiusX="30" RadiusY="30" />
</Image.Clip>
</Image>
<Polygon Grid.Column="2" Points="0,0 4,3 0,6 0,0" StrokeThickness="2" HorizontalAlignment="Right" VerticalAlignment="Center" Fill="#4fcd00" Stroke="#4fcd00"></Polygon>
<Border Grid.Column="1" BorderBrush="#4fcd00" BorderThickness="1" Background="#4fcd00" Padding="5">
<TextBlock TextWrapping="Wrap" Text="This is a message in a chat window..." VerticalAlignment="Top" FontSize="12" Foreground="#000000"></TextBlock>
</Border>
</Grid>
</Grid>
</DataTemplate>
</chat:MessageContentPresenter.OutboundTemplate>
</chat:MessageContentPresenter>
</DataTemplate>
</ItemsControl.ItemTemplate>
</ItemsControl>
</StackPanel>
</ScrollViewer>
MessageContentPresenter如下
public class MessageContentPresenter : ContentControl
{
#region Public Properties
public DataTemplate InboundTemplate { get; set; }
public DataTemplate OutboundTemplate { get; set; }
#endregion
#region Methods
protected override void OnContentChanged(object oldContent, object newContent)
{
base.OnContentChanged(oldContent, newContent);
var message = newContent as Message;
if (message.Direction == MessageDirection.Inbound)
{
this.ContentTemplate = this.InboundTemplate;
}
else
{
this.ContentTemplate = this.OutboundTemplate;
}
}
#endregion
}
当我运行这段代码时，一切都很好，OnContentChanged方法对Messages集合中的每个项执行一次。问题是InboundTemplate和OutboundTemplate都是null。
我真的不明白问题出在哪里，也不明白为什么这两个模板都是null，非常感谢您的帮助。
实际上，您可以使用DataTemplateSelector。
但另一种选择是使用DataTemplate+ContentControl和Style:
首先，由于我们不需要MessageContentPresenter类，请删除它。因此，您需要从XAML中删除ItemsControl.ItemTemplate。
其次，将DataTemplate+ContentControl和Style添加到Window.Resources.
试试这个给你一些线索：
<DataTemplate DataType="{x:Type local:Message}">
<ContentControl Content="{Binding Direction}">
<ContentControl.Style>
<Style TargetType="{x:Type ContentControl}">
<Style.Triggers>
<DataTrigger Binding="{Binding Direction}" Value="{x:Static local:MessageDirection.Inbound}">
<Setter Property="ContentTemplate">
<Setter.Value>
<DataTemplate>
<Button Background="Green">Inbound</Button>
</DataTemplate>
</Setter.Value>
</Setter>
</DataTrigger>
<DataTrigger Binding="{Binding Direction}" Value="{x:Static local:MessageDirection.Outbound}">
<Setter Property="ContentTemplate">
<Setter.Value>
<DataTemplate>
<Button Background="Red">Outbound</Button>
</DataTemplate>
</Setter.Value>
</Setter>
</DataTrigger>
</Style.Triggers>
</Style>
</ContentControl.Style>
</ContentControl>
</DataTemplate>