Bug 20592 - GetHeightForRow not called when using TableView.Scrolled event
Summary: GetHeightForRow not called when using TableView.Scrolled event
Alias: None
Product: iOS
Classification: Xamarin
Component: Xamarin.iOS.dll ()
Version: master
Hardware: Macintosh Mac OS
: --- normal
Target Milestone: Untriaged
Assignee: Bugzilla
Depends on:
Reported: 2014-06-14 12:42 UTC by Christian Rishøj
Modified: 2014-06-16 05:24 UTC (History)
4 users (show)

Is this bug a regression?: ---
Last known good build:

Minimal reproduction of the problem (10.97 KB, application/zip)
2014-06-14 12:42 UTC, Christian Rishøj

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Description Christian Rishøj 2014-06-14 12:42:33 UTC
Created attachment 7073 [details]
Minimal reproduction of the problem

Description of Problem:

In a UITableViewController subclass, I normally use GetHeightForRow to implement dynamically sized cells. This works fine, until I register an event listener using TableView.Scrolled += (...). As soon as I do this, GetHeightForRow is no longer called.

Steps to reproduce the problem:
1. Run the attached minimal project
2. Observe that the rows are sized dynamically
3. Uncomment the event listener in the controller's ViewDidLoad method and run again
4. Observe that the rows now have fixed height

Comment 1 Rolf Bjarne Kvinge [MSFT] 2014-06-16 05:24:06 UTC
This is a variation of the Xamarin.iOS limitation where you can't use the Objective-C delegate logic and C# events at the same time [1]

What happens is managed events (TableView.Scrolled) uses the [Weak]Delegate property under the hood, but in this case Objective-C has set the WeakDelegate to the TestTableViewController instance (which is what's driving the GetHeightForRow overload to actually work). So when you attach to the Scrolled event, you end up setting WeakDelegate to something else, thus breaking GetHeightForRow.

Here's a potential solution: http://stackoverflow.com/a/17474025/183422

[1] http://spouliot.wordpress.com/2012/03/26/events-vs-objective-c-delegates/