Bug 55716 - Bindable properties for reference types re-use default values
Summary: Bindable properties for reference types re-use default values
Alias: None
Product: Forms
Classification: Xamarin
Component: Forms ()
Version: 2.3.4
Hardware: PC Mac OS
: Normal normal
Target Milestone: ---
Assignee: Stephane Delcroix
Depends on:
Reported: 2017-04-28 10:29 UTC by Rhi
Modified: 2017-05-30 09:45 UTC (History)
4 users (show)

Tags: bindableproperty default ac
Is this bug a regression?: ---
Last known good build:

Sample to reproduce the issue (68.56 KB, application/zip)
2017-04-29 05:48 UTC, Rhi

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Description Rhi 2017-04-28 10:29:06 UTC
If a bindable property for a type such as a List<T> is created with a default of new List<T>, it seems to re-use the same container object for different unrelated instances of the BindableObject.
The effect here is that if there are 5 BindableObjects declared in XAML and all of them have 1 bindable property of reference type, they all end up have a bindable property with 5 objects, because they all use the same reference object provided in the default parameter.
Comment 1 Rhi 2017-04-29 05:48:18 UTC
Created attachment 21899 [details]
Sample to reproduce the issue

ExtendedToolbar is a custom control with a bindable property which is an IList of ToolbarItems.
If the property is declared with a default value, it seems to add 6 toolbar items to each container stacklayout,
whereas if the property is declared with a defaultValueCreator func param, things work as expected.

PS : Please do a restore packages since adding packages subfolder from the project takes it over the attachment size limit.
Comment 2 Paul DiPietro [MSFT] 2017-05-08 17:18:25 UTC
Thanks for the reproduction project. I will mark this as confirmed until there's further investigation.
Comment 3 Stephane Delcroix 2017-05-30 09:45:21 UTC
Yes, default values are reused.

If you use reference types, you should use the defaultValueCreator delegate instead, that will create a new default value. This is how we do it for, e.g. Grid.ColumnDfinition