[forms-devel] Fwd: Fixing SetNativeControl logic when replacing native controls

Toni Petrina tonipetrina at hotmail.com
Sat Jul 9 16:13:12 UTC 2016

Hi everyone,


In the middle of writing the proposal and testing out the code that will fix the issue below I stumbled upon the following code in Xamarin.Forms.Platform.Android.AppCompat namespace:


    public abstract class ViewRenderer<TView, TControl> : Android.ViewRenderer<TView, TControl> where TView : View where TControl : global::Android.Views.View
        protected abstract TControl CreateNativeControl();


This is exactly what I am proposing, but pulled up to the Android.ViewRenderer class.

Should I continue writing my proposal and can I send pull request into the evolution repository or do we have to discuss it here first?



Toni Petrina

Begin forwarded message:


From: Toni Petrina <tonipetrina at hotmail.com>

Subject: [forms-devel] Fixing SetNativeControl logic when replacing native controls

Date: 2 July 2016 at 18:22:42 GMT+2

To: <forms-devel at lists.xamarin.com>




It is hard to replace a native control inside a renderer with your own. You cannot even replace ListView in Android because there are nasty NullRefs happening if you do so! Consider the following code:


var ctx = Context;
nativeListView = new AListView(ctx);
_refresh = new SwipeRefreshLayout(ctx);
_refresh.AddView(nativeListView, LayoutParams.MatchParent);
SetNativeControl(nativeListView, _refresh);



If I want to use my subclass instead of Android.Widget.ListView, I have to reimplement entire ListViewRenderer which is impossible due to all internal classes. It would be much better if there is a method called GetNativeControll so that the above code looks more like:


protected override AListView GetNativeControl() => new AListView(Context);


var ctx = Context;
nativeListView = GetNativeControl();

This way I can override the default control to be used with my own subclass.



Toni Petrina


P.S. Not having markdown in email is frustrating!

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