UWP Xaml，在运行时更改ContentControl的DataTemplate，具体取决于其DataContext的属性值

Question

Please I have a ContentControl , which displays the details of a items clicked on a ListView , the Item clicked is set at runtime as the Content control's DataContext , and I am willing to know how to change this ContentControl 's DataTemplate every time the Datacontext is updated, depending on a value of the DataContext a DataTemplateSelector but, the template is set only once and when the DataContext changes, this initial template doesn't update if it is suposed to. So, I decided to proceed by using VisualTriggers , but this seems not to work either, since the DataTemplate does not even show when I use this approach. This is my code when I used DataTriggers:

<ContentControl x:Name="baseTemplate" DataContext="{Binding Selected}">
                <VisualStateManager.VisualStateGroups>
                    <VisualStateGroup>
                        <VisualState x:Name="Uno">
                            <VisualState.StateTriggers>
                                <dataTriggers:FocusDataTrigger
                                dataTriggers:FocusDataTrigger.TriggerValue="Uno"
                                dataTriggers:FocusDataTrigger.DataValue="{Binding DataContext.Type}"/>
                            </VisualState.StateTriggers>
                            <VisualState.Setters>
                                <Setter Target="baseTemplate.Template" Value="{StaticResource UnoTemplate}"/>
                            </VisualState.Setters>
                        </VisualState>
                        <VisualState x:Name="Duo">
                            <VisualState.StateTriggers>
                                <dataTriggers:FocusDataTrigger
                                dataTriggers:FocusDataTrigger.TriggerValue="Duo"
                                dataTriggers:FocusDataTrigger.DataValue="{Binding  DataContext.Type}"/>
                            </VisualState.StateTriggers>
                            <VisualState.Setters>
                                <Setter Target="baseTemplate.Template" Value="{StaticResource detailTemplateSelector}"/>
                            </VisualState.Setters>
                        </VisualState>
                    </VisualStateGroup>
                </VisualStateManager.VisualStateGroups>
            </ContentControl>

I wish to make the DataTemplate change everytime the value set to the DataContext has a property Type of value "Uno" or "Duo" Please help!, I have tried as much as I could, but I can't find a solution for this.

I use a custom DataTrigger

public class FocusDataTrigger : StateTriggerBase
{
    #region DataValue
    public static readonly DependencyProperty DataValueProperty =
        DependencyProperty.RegisterAttached("DataValue", typeof(object),
            typeof(FocusDataTrigger), new PropertyMetadata(null, DataValueChanged));

    public static object GetDataValue(DependencyObject obj)
    {
        return obj.GetValue(DataValueProperty);
    }
    public static void SetDataValue(DependencyObject obj, object value)
    {
        obj.SetValue(DataValueProperty, value);
    }
    #endregion

    #region TriggerValue

    public static readonly DependencyProperty TriggerValueProperty =
        DependencyProperty.RegisterAttached("TriggerValue", typeof(object),
            typeof(FocusDataTrigger), new PropertyMetadata(false, TriggerValueChanged));


    public static object GetTriggerValue(DependencyObject obj)
    {
        return obj.GetValue(TriggerValueProperty);
    }
    public static void SetTriggerValue(DependencyObject obj, object value)
    {
        obj.SetValue(TriggerValueProperty, value);
    }

    #endregion

    private static void TriggerStateCheck(DependencyObject target, object datavalue, object triggerValue)
    {
        FocusDataTrigger trigger = target as FocusDataTrigger;
        if (trigger == null) return;
        trigger.SetActive(triggerValue == datavalue);
    }
    private static void TriggerValueChanged(DependencyObject target, DependencyPropertyChangedEventArgs e)
    {
        object datavalue = target.GetValue(FocusDataTrigger.DataValueProperty);
        TriggerStateCheck(target, datavalue, e.NewValue);
    }
    private static void DataValueChanged(DependencyObject target,
        DependencyPropertyChangedEventArgs e)
    {
        object triggerValue = target.GetValue(FocusDataTrigger.TriggerValueProperty);
        TriggerStateCheck(target, e.NewValue, triggerValue);
    }
}

Answer 1

It seems you are going to a wrong direction.

Your template will change based on a property changed.

I'm not so sure what you mean here. DataContextChanged means you are switching your datacontext. But it seems here you just want to change things based on a property value, am I right on this?

Try do something with the following steps:

1. Create a DataTemplateSelector:

    public class CCDataTemplateSelector: DataTemplateSelector { public DataTemplate FirstTemplate { get; set; } public DataTemplate SecondTemplate { get; set; } protected override DataTemplate SelectTemplateCore(object item, DependencyObject container) { var model = item as DemoModel; if (model == null) return null; if (model.ID >= 2) return FirstTemplate; else return SecondTemplate; } } 

2. Then in your XAML you can write something like this:

     <StackPanel.Resources> <DataTemplate x:Key="FirstTemplate"> xxxxx </DataTemplate> <DataTemplate x:Key="SecondTemplate"> xxxxx </DataTemplate> <local:CCDataTemplateSelector FirstTemplate="{StaticResource FirstTemplate}" SecondTemplate="{StaticResource SecondTemplate}" x:Key="DataTemplateSelector" /> <Style TargetType="ContentControl"> <Setter Property="ContentTemplateSelector" Value="{StaticResource DataTemplateSelector}" /> </Style> </StackPanel.Resources> 

In this way the template will different based on the value you set in your model.