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Created attachment 18343 [details]
We experienced a strange relationship between Grid properties IsVisible, Children, RowDefinitions, and ColumnDefinitions. When manipulating all these properties, in some cases children do not become visible as expected.
The scenario is:
* Clear current Children and Row-/ColumnDefinitions. They must not be empty.
* Set IsVisible=false.
* Add new instances to children and Row-/ColumnDefinitions.
* Set IsVisible=true.
* Children are not visible as expected.
Changing the view hierarchy somewhere else fixes the problem. I assume that this forces a re-layout. Also, any other order of doing this seems to work ok.
We could observe the behavior with:
* Xamarin.Forms 126.96.36.199 amd Xamarin.Forms 188.8.131.52
* iOS 9.3.1 and iOS 10.0.2
Attached is an example app:
* Use the upper button to toggle the grid children. Notice that the first show works, the second show does not work.
* Use the lower button to trigger a view hierarchy change, after which the children are visible.
* Look at the ToggleGrid() method to observe or manipulate the call order of property changes.
* Observe the console log to notice that the children X, Y, Width and Height are not updated when the problem occurs.
Created attachment 18402 [details]
Complete test app
I'm attaching the complete example, it should be able to demonstrate the unrelated problem mentioned here: http://stackoverflow.com/questions/40512273/xamarin-xbuild-warning-when-building-shproj-files.
Thanks for the reproduction which does show the behavior, and for good measure I've checked it against the latest prerelease and nightly builds as well. It does look to occur on Android, too, so this will require further investigation.