Bug 60349 - Specifying DataType on DataTemplate where the Poco has a generic property fails to compile
Summary: Specifying DataType on DataTemplate where the Poco has a generic property fai...
Alias: None
Product: Forms
Classification: Xamarin
Component: Forms ()
Version: 2.4.0
Hardware: PC Windows
: Normal major
Target Milestone: ---
Assignee: Bugzilla
Depends on:
Reported: 2017-10-24 15:05 UTC by Paul Kiar
Modified: 2017-11-14 00:06 UTC (History)
4 users (show)

Tags: datatemplate, datatype, generic, ac
Is this bug a regression?: ---
Last known good build:

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Description Paul Kiar 2017-10-24 15:05:00 UTC
To Reproduce:
Create a xamarin forms project as defined in this forum post:


edit the Deal model object and add a property:

public bool? Test {get;set;}

Try to compile and you get this error:

Xamarin.Forms.\build\portable-win+net45+wp80+win81+wpa81\Xamarin.Forms.targets(73,3): error : Member 'System.Nullable`1' is declared in another module and needs to be imported

Also fails if it has a property on the poco of Tuple<bool,bool> which leads me to believe it's a problem with generics.
Comment 1 Paul Kiar 2017-10-24 15:09:39 UTC
You may have to add a binding to this property to the DealControl

<Label Text="{Binding Test}" />
Comment 2 David Britch 2017-11-13 12:41:13 UTC
I've created a sample that uses nullables, generics, and compiled bindings and eventually had no problems getting it working. The key was when specifying the x:DataType attribute.

If I used the blog post syntax (x:DataType="models:Deal"), some features worked, some didn't. For example:

    <StackLayout x:DataType="local:CompiledBindingsViewModel">

The above let me use compiled bindings for displaying view model properties. But a two-way binding had no luck (but no crash), and I was able to produce a crash when binding to a nullable. However, when I changed to the following syntax, all problems vanished (two-way bindings sprang into life, crashes no longer happened):

    <StackLayout x:DataType="{x:Type local:CompiledBindingsViewModel}">

Similarly, I had an identical issue when using compiled bindings on a DataTemplate. The following code caused a crash (the model uses nullables and generics):

                <DataTemplate x:DataType="local:Person">

But changing to the following made it work:

                <DataTemplate x:DataType="{x:Type local:Person}">

Note: I'm using Forms
Comment 3 Paul Kiar 2017-11-13 15:05:00 UTC
Fantastic, what's the resolution going forward?
1.  Should the x:Type part be always added?
2.  is there going to be a issue to fix the other syntax?
3.  perhaps error on the other syntax with a suggestion to use this syntax?
4.  Documentation change?

For now can I use the x:Type part of the syntax?  Will it be deprecated when fixed?