User1004 postedBehaviors and Triggers are meant to be shared (often through Styles), so you can't rely on BindingContext being unique. For the same fashion, it's not right to keep a reference to _stackLayout as it would cause issue at reuse time.
So, basically, when you use a Trigger or a Behavior, don't handle that as if it was a BindableObject and you'll be fine.
Here's my quick fix to your Behavior (doesn't support changing the ItemTemplate or ItemSource):
```
public class ItemsSourceBehavior : Behavior
{
public BindingBase ItemsSource { get; set; }
public BindingBase ItemTemplate { get; set; }
static readonly BindableProperty ItemsSourceProperty =
BindableProperty.CreateAttached ("ItemsSource", typeof(IEnumerable), typeof(ItemsSourceBehavior), default(IEnumerable),
propertyChanged: ItemsSourceChanged);
static readonly BindableProperty ItemsTemplateProperty =
BindableProperty.CreateAttached ("ItemsSource", typeof(DataTemplate), typeof(ItemsSourceBehavior), default(DataTemplate));
static void ItemsSourceChanged(BindableObject bindable, object oldValue, object newValue)
{
ItemsSourceChanged ((StackLayout)bindable, (IEnumerable)oldValue, (IEnumerable)newValue);
}
static void ItemsSourceChanged(StackLayout layout, IEnumerable oldValue, IEnumerable newValue)
{
layout.Children.Clear ();
var template = layout.GetValue (ItemsTemplateProperty) as DataTemplate;
if (template == null)
return;
foreach (var item in newValue) {
var content = (View)template.CreateContent ();
content.BindingContext = item;
layout.Children.Add (content);
}
}
protected override void OnAttachedTo(StackLayout bindable)
{
base.OnAttachedTo(bindable);
bindable.SetBinding (ItemsTemplateProperty, ItemTemplate);
bindable.SetBinding (ItemsSourceProperty, ItemsSource);
}
}
```
and I use it this way:
<StackLayout Orientation="Horizontal">
<StackLayout.Behaviors>
<local:ItemsSourceBehavior
ItemsSource="{Binding WeatherPeriods}"
ItemTemplate="{Binding itemTemplate}" />
</StackLayout.Behaviors>
</StackLayout>
with this BindingContext:
BindingContext = new {
WeatherPeriods = new [] { "Foo", "Bar", "Baz", "Qux" },
itemTemplate = new DataTemplate (typeof(Label)) {Bindings = {
{ Label.TextProperty, new Binding (".") }
}
} };
but wait, there's a better way to handle this, more in a coming post
