DataTemplate未在数据透视Windows Phone 8.1中加载

Question

I'm trying to display different layouts in pivot items in a wp8.1 app (UNIAPP ). Ideally I would like to load different pages but since I could figure this out, I thought I'd try with the basics first as I'd use this before but for some reason I can't get this to work.

My pivot items are loaded dynamically based on the provided ViewModel

 <Pivot.ItemTemplate>
   <DataTemplate>
     <controls:DataTemplateSelector Content="{Binding}"
      HorizontalContentAlignment="Stretch"
      VerticalContentAlignment="Stretch">
    </controls:DataTemplateSelector>
   /DataTemplate>
 </Pivot.ItemTemplate>

My resources are defined as follows within the same xaml page

<Page.Resources>
    <DataTemplate x:Key="MyApp.ViewModel.PIDetailsVM">
        <Button Content="test" Foreground="White"></Button>
    </DataTemplate>
    <DataTemplate x:Key="MyApp.ViewModel.PIListVM">
        <Button Content="test" Foreground="White"></Button>
    </DataTemplate>
</Page.Resources>

My DataTemplateSelector is defined as follows:

public class DataTemplateSelector : ContentControl
{
  protected override void OnContentChanged(object oldContent, 
  object newContent)
  {
    ContentTemplate = this.FindResource<DataTemplate>(newContent.GetType
    ().FullName);
  }
}

It is being triggered whenever I go to a new pivot item, but the ContentTemplate is always null.

The newContent.GetType().FullName returns the relevant viewmodel name which I can see being displayed in the relevant pivot.

One thing I noticed is that the DataTemplateSelector class (this) has no resources when I check it via this.Resources.count(), so it's obviously not finding them but how do I fix this?

UPDATE:

My DataTemplates are not getting loaded in my Pivot Items. There is obviously a problem with the .NET IDE as whenever I add or remove a from Content="{Binding}" it displays the button within the pivot item but that's within the IDE. Unfortunately, at run-time, it just displays the name of my viewmodel.

Thought the behaviour is erratic in the IDE, the fact that the button from my DataTemplate is displaying when messing around with the Content="{Binding<space>" would make you think that the code and xaml are correct but it's definitely not working at run-time.

Any idea what's wrong why my DataTemplates are not displaying in pivot item?

Thanks.

Answer 1

This is a partial answer. By this I mean that I did find a work-around to my problem but I did not resolve the issue itself.

My DataTemplateSelector which gets triggered whenever the pivot changes call a extension function called FindResource:

public static class ControlExtensions
{
    public static T FindResource<T>(this DependencyObject initial, 
    string key) where T : DependencyObject
    {
        DependencyObject current = initial;

        while (current != null)
        {
            if (current is FrameworkElement)
            {
                if ((current as FrameworkElement).Resources.
                     ContainsKey(key))
                {
                    return (T)(current as FrameworkElement).Resources[key];
                }
            }
            current = VisualTreeHelper.GetParent(current);
        }

        if (Application.Current.Resources.ContainsKey(key))
        {
            return (T)Application.Current.Resources[key];
        }

        return default(T);
    }
}

For some strange reason, Windows Phone 8.1 (WinRT) does not like having the data templates in while it is not a problem in WP8/WP8.1 Silverlight.

As mentioned, this is unstable in the IDE where it sometimes displays the DataTemplate, and sometimes it doesn't depending on whether or not I add a space after the Binding keyword to the Content="{Binding}" . One thing for sure is that it never works at run-time, well not at least not with the above code.

VisualTreeHelper.GetParent(current) always returns null no matter what. I've checked at debug time if I somehow could access the resources, but to no avail.

How did I fix it? Well, I moved my data templates to a resource dictionary

<DataTemplate x:Key="MyApp.ViewModel.PIDetailsVM">
    <Button Content="test" Foreground="White"></Button>
</DataTemplate>

<DataTemplate x:Key="MyApp.ViewModel.PIListVM">
    <Button Content="test" Foreground="White"></Button>
</DataTemplate>

The second I did this, the second part of my FindResources kicks in since the Current object is always null, no matter what

if (Application.Current.Resources.ContainsKey(key))
  {
    return (T)Application.Current.Resources[key];
  }

and it finds the relevant DataTemplate and displays it accordingly in my pivot control based on the relevant PivotItem ViewModel.

Now, I'm not out of the woods yet as I have no idea if binding to the relevant viewmodel will work but that's a whole other story!

If anyone knows why DataTemplate cannot be found when defined in Pages.Resources or Grid.Resources, please update the post as I'd love to know why.

Thanks.