wpf ContentControl.ContentTemplateSelector 动态选择模板

ContentControl.ContentTemplateSelector dynamically select template

提问by SubmarineX

I set a ContentControl in the right of Window, and set Content binding Items (it's type is ObservableCollection). Now I want to achieve it: if there are no item, ContentControl select first DataTemplate, and add a item into items, ContentControl will select second DataTemplate to display some info.

我在Window的右侧设置了一个ContentControl，并设置了Content binding Items（它的类型是ObservableCollection）。现在我想实现它：如果没有项目，ContentControl选择第一个DataTemplate，并在项目中添加一个项目，ContentControl将选择第二个DataTemplate显示一些信息。

Like this:

像这样：

The problem is when I add one item into items, ContentControl didnot update and change DataTemplate, I have a try to set mode, UpdateSourceTrigger, etc., but failed. In ViewModel, after delete a item, I use this statements, it will work well <1>:

问题是当我将一个项目添加到项目中时，ContentControl没有更新和更改DataTemplate，我尝试设置模式，UpdateSourceTrigger等，但失败了。在 ViewModel 中，删除项目后，我使用此语句，它会运行良好<1>：

private void ExecuteDeleteClientCommand()
{
    ...
    if (DeleteClient(item))
    {
        ObservableCollection<MyViewModel> tmp = TabItems;
        TabItems = null;
        TabItems = tmp;
    }
}

.

.

<ContentControl 
    ContentTemplateSelector="{StaticResource MyDataTemplateSelector}" 
    Content="{Binding Items}"/>

.

.

public class SingleClientDataTemplateSelector : DataTemplateSelector
{
    public override DataTemplate SelectTemplate(object item, 
        DependencyObject container)
    {
        ObservableCollection<MyViewModel> obj = 
            item as ObservableCollection<MyViewModel>;
        if (null == obj || 0 == obj.Count)
        {
            return App.Current.FindResource("NullItemDataTemplate") as DataTemplate;
        }
        return App.Current.FindResource("DefaultDataTemplate") as DataTemplate;
    }
}

Edited:use this way is also failed after delete one item:

编辑：删除一项后使用这种方式也失败：

RaisePropertyChanging(ItemsPropertyName);
RaisePropertyChanged(ItemsPropertyName);

but I wonder why it work well with <1>.

但我想知道为什么它与<1>一起工作得很好。

Edited2It's the delcaration:

Edited2这是声明：

public const string ItemsPropertyName = "Items";
private ObservableCollection<MyViewModel> items = new ObservableCollection<MyViewModel>();
public ObservableCollection<SingleClientDetailViewModel> TabItems
{
    get { return items; }
    set 
    { 
        if (items == value) { return;}
        RaisePropertyChanging(ItemsPropertyName);
    items = value;
    RaisePropertyChanged(ItemsPropertyName);
    }
}

回答by Mat J

ContentControlwill listen only for PropertyChangedevents and not for CollectionChangedevent. You'll need to use either an ItemsControlor any of its other versions like ListViewfor this behavior.

ContentControl将只监听PropertyChanged事件而不是CollectionChanged事件。对于这种行为，您需要使用 anItemsControl或其任何其他版本ListView。

As a workaround, you can create a Stylefor the ContentControland instead of TemplateSelector, define a DataTriggeron Items.Countand set the ContentTemplateaccordingly. Something like,

作为一种解决方法，您可以Style为ContentControl和而不是TemplateSelector定义一个DataTriggeronItems.Count并相应地设置ContentTemplate。就像是，

        <ContentControl Content="{Binding Items}">
        <ContentControl.Style>
            <Style TargetType="ContentControl">
                <Setter Property="ContentTemplate" Value="{StaticResource DefaultDataTemplate}" />
                <Style.Triggers>
                    <DataTrigger Binding="{Binding Path=Items}" Value="{x:Null}">
                        <Setter Property="ContentTemplate" Value="{StaticResource NullItemDataTemplate}" />
                    </DataTrigger>
                    <DataTrigger Binding="{Binding Path=Items.Count}" Value="0">
                        <Setter Property="ContentTemplate" Value="{StaticResource NullItemDataTemplate}" />
                    </DataTrigger>
                </Style.Triggers>
            </Style>
        </ContentControl.Style>
    </ContentControl>