How to add items to Dictionary - xaml

Question

I'm trying to create a TemplateSelector which recognizes if an implements an interface and applies a DataTemplate for it.
I'd like to use this selector in following way:
<ListView Grid.Column="0"
ItemsSource="{Binding Media}"
SelectionMode="None">
<ListView.ItemTemplateSelector>
<selectors:InterfaceAwareTemplateSelector>
<DataTemplate x:Key="IMedia">
<Image Source="{Binding PreviewImage}" />
</DataTemplate>
<DataTemplate x:Key="IDocument">
<TextBlock Text="test" />
</DataTemplate>
</selectors:InterfaceAwareTemplateSelector>
</ListView.ItemTemplateSelector>
</ListView>
I end up with following implementation:
[ContentProperty(Name = "Items")]
public class InterfaceAwareTemplateSelector: DataTemplateSelector {
public DataTemplate DefaultTemplate { get; set; }
public Dictionary<Type, DataTemplate> Items { get; set; }
public InterfaceAwareTemplateSelector() {
Items = new Dictionary<Type, DataTemplate>();
}
protected override DataTemplate SelectTemplateCore(object item, DependencyObject container)
{
var result = (
from t in Items
where t.Key.GetTypeInfo().IsAssignableFrom(item.GetType().GetTypeInfo())
select t.Value).FirstOrDefault();
return result ?? DefaultTemplate;
}
}
It of course doesn't work, otherwise I wouldn't write this question :) Application crushes with a message a xaml cannot be parsed:
A first chance exception of type 'Windows.UI.Xaml.Markup.XamlParseException' occurred in Hicron.ProductCatalog.MainUI.exe
WinRT information: E_UNKNOWN_ERROR [Line: 47 Position: 39]
An exception of type 'Windows.UI.Xaml.Markup.XamlParseException' occurred in Hicron.ProductCatalog.MainUI.exe but was not handled in user code
WinRT information: E_UNKNOWN_ERROR [Line: 47 Position: 39]
Additional information: Unspecified error
What's wrong with that dictionary? Normally I'd use CompositeCollection and merge multiple sources but this class is missing in WinRT :(
EDIT
In terms of fixing dictionary problem I've changed dictionary to list of custom types. Still can't create a custom type with Type set from XAML. I could use a string but than I can't manage it in code unless I specify fully qualified type name.
[ContentProperty(Name = "Items")]
public class InterfaceAwareTemplateSelector: DataTemplateSelector {
public DataTemplate DefaultTemplate { get; set; }
public List<InterfaceAwareTemplateSelectorItem> Items { get; set; }
public InterfaceAwareTemplateSelector() {
Items = new List<InterfaceAwareTemplateSelectorItem>();
}
protected override DataTemplate SelectTemplateCore(object item, DependencyObject container) {
if (item == null) {
return DefaultTemplate;
}
var result = (
from t in Items
where t.Type.GetTypeInfo().IsAssignableFrom(item.GetType().GetTypeInfo())
select t.Template).FirstOrDefault();
return result ?? DefaultTemplate;
}
}
public class InterfaceAwareTemplateSelectorItem
{
public Type Type { get; set; }
public DataTemplate Template { get; set; }
}
Corresponding XAML:
// somewhere in page tag
xmlns:bo="using:/*long long namespace*/.BusinessObjects"
// somewhere in XAML file
<ListView Grid.Column="0"
ItemsSource="{Binding Media}"
SelectionMode="None">
<ListView.ItemTemplateSelector>
<selectors:InterfaceAwareTemplateSelector>
<selectors:InterfaceAwareTemplateSelectorItem Type="bo:IMedia">
<selectors:InterfaceAwareTemplateSelectorItem.Template>
<DataTemplate>
<Image Source="{Binding PreviewImage}"
Tapped="ImageTapped" />
</DataTemplate>
</selectors:InterfaceAwareTemplateSelectorItem.Template>
</selectors:InterfaceAwareTemplateSelectorItem>
<selectors:InterfaceAwareTemplateSelectorItem Type="bo:IDocument">
<selectors:InterfaceAwareTemplateSelectorItem.Template>
<DataTemplate>
<TextBlock Text="pa8u4mrapwu" />
</DataTemplate>
</selectors:InterfaceAwareTemplateSelectorItem.Template>
</selectors:InterfaceAwareTemplateSelectorItem>
</selectors:InterfaceAwareTemplateSelector>
</ListView.ItemTemplateSelector>
</ListView>

Answer 1

Okay, so using this:
public interface IFake1 { }
public interface IFake2 { }
public class TemplateItem
{
public DataTemplate Template { get; set; }
public string Interface { get; set; }
}
public class MySelector : DataTemplateSelector
{
public List<TemplateItem> Templates { get; set; }
}
I could do this:
<GridView>
<GridView.ItemTemplateSelector>
<local:MySelector>
<local:MySelector.Templates>
<local:TemplateItem Interface="IFake1">
<local:TemplateItem.Template>
<DataTemplate>
<!-- TODO -->
</DataTemplate>
</local:TemplateItem.Template>
</local:TemplateItem>
<local:TemplateItem Interface="IFake2">
<local:TemplateItem.Template>
<DataTemplate>
<!-- TODO -->
</DataTemplate>
</local:TemplateItem.Template>
</local:TemplateItem>
</local:MySelector.Templates>
</local:MySelector>
</GridView.ItemTemplateSelector>
</GridView>
The error appears in the Type you are using. I could not get that to work. Had to use String. Should be simple to parse form there.
Best of luck!

Answer 2

See if it works if you replace Dictionary<Type, DataTemplate> with ResourceDictionary. I'm betting at least one of the problems is that the key in x:Key="IMedia" can't be implicitly converted to Type. You could also just try using string as the key type.

Answer 3

I finally managed to fix it. Unfortunately I couldn't get a conversion from string to Type in XAML so I had to stick to strings :/ Not very convenient but at least works. That's what I ended up with:
XAML
<ListView Grid.Column="0"
ItemsSource="{Binding Media}"
SelectionMode="None">
<ListView.ItemTemplateSelector>
<selectors:InterfaceAwareTemplateSelector>
<DataTemplate x:Key="IMedia">
<Image Source="{Binding PreviewImage}" Tapped="ImageTapped"/>
</DataTemplate>
<DataTemplate x:Key="IDocument">
<commonItems:DocumentItemPresenter TappedCommand="{Binding DataContext.OpenDocument, ElementName=PageRoot}"/>
</DataTemplate>
</selectors:InterfaceAwareTemplateSelector>
</ListView.ItemTemplateSelector>
</ListView>
Selector itself:
[ContentProperty(Name = "Items")]
public class InterfaceAwareTemplateSelector: DataTemplateSelector {
public DataTemplate DefaultTemplate { get; set; }
public Dictionary<string, DataTemplate> Items { get; set; }
public InterfaceAwareTemplateSelector() {
Items = new Dictionary<string, DataTemplate>();
}
protected override DataTemplate SelectTemplateCore(object item, DependencyObject container) {
if (item == null) {
return DefaultTemplate;
}
var result = (
from ii in item.GetType().GetTypeInfo().ImplementedInterfaces
from dt in Items
where ii.Name == dt.Key
select dt.Value).FirstOrDefault();
return result ?? DefaultTemplate;
}
}
I upvoted Filip & Jerry because I found your tips helpful. Thank you guys.

Answer 4

If anyone is interested how this problem was solved below is final implementation and a usage example.
Usage:
<GridView ....>
<GridView.ItemTemplateSelector>
<selectors:InterfaceAwareTemplateSelector>
<!-- ReSharper disable once Xaml.RedundantResource -->
<DataTemplate x:Key="INewsContainer" selectors:InterfaceAwareTemplateSelector.Priority="1">
<ctrls:ItemsContainerTile Width="350" Height="350"
ItemTappedCommand="{Binding DataContext.OpenNewsDetails, ElementName=PageRoot}"/>
</DataTemplate>
<!-- ReSharper disable once Xaml.RedundantResource -->
<DataTemplate x:Key="ISimpleMaterial" selectors:InterfaceAwareTemplateSelector.Priority="0">
<ctrls:GenericTile Width="350" Height="350"
TappedCommand="{Binding DataContext.OpenDetails, ElementName=PageRoot}" />
</DataTemplate>
</selectors:InterfaceAwareTemplateSelector>
</GridView.ItemTemplateSelector>
.... the rest of XAML
The priority is to control the order in which datatamples should be checked. This way we can control what happens if multiple keys matches the object being converted.
Implementation:
[ContentProperty(Name = "Items")]
public class InterfaceAwareTemplateSelector: DataTemplateSelector {
public DataTemplate DefaultTemplate { get; set; }
public Dictionary<string, DataTemplate> Items { get; set; }
public InterfaceAwareTemplateSelector() {
Items = new Dictionary<string, DataTemplate>();
}
protected override DataTemplate SelectTemplateCore(object item, DependencyObject container) {
if (item == null) {
return DefaultTemplate;
}
var results = (
from ii in item.GetType().GetTypeInfo().ImplementedInterfaces
from dt in Items
where ii.Name == dt.Key
select dt)
.ToArray();
if (results.Length > 1) {
var orderedResults =
from r in results
where IsPrioritySet(r.Value)
orderby GetPriority(r.Value) descending
select r;
if (orderedResults.Any()) {
return orderedResults.First().Value;
}
throw new AmbigiousResolveTemplateFound(item.GetType(), results.Select(x => x.Key));
}
else if (results.Length == 1) {
return results[0].Value;
}
return DefaultTemplate;
}
#region PriorityProperty
public static readonly DependencyProperty PriorityProperty =
DependencyProperty.RegisterAttached(
"Priority",
typeof(int),
typeof(InterfaceAwareTemplateSelector),
new PropertyMetadata(0));
public static int GetPriority(DependencyObject item) {
if (item == null) { throw new ArgumentNullException("item"); }
return (int)item.GetValue(PriorityProperty);
}
public static void SetPriority(DependencyObject item, int value) {
if (item == null) { throw new ArgumentNullException("item"); }
item.SetValue(PriorityProperty, value);
}
public static bool IsPrioritySet(DependencyObject item) {
if (item == null) { throw new ArgumentNullException("item"); }
var result = item.ReadLocalValue(PriorityProperty);
return result != DependencyProperty.UnsetValue;
}
#endregion
}
Hope someone will find this implementation helpful. Once again, many thanks to Filip and Jerry for your help.