Xamarin Forms - UWP custom renderer: how to add a child to a stacklayout

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Xamarin Forms - UWP custom renderer: how to add a child to a stacklayout



I'm trying to insert a UWP specific child in the custom renderer of a StackLayout.
However, in the sample code below, Control is always null whereas my StackLayout has Children. Maybe StackPanel is not what StackLayout is rendered into in UWP.


StackLayout


Control


null


StackLayout


StackPanel


StackLayout


public class MyRenderer : ViewRenderer<StackLayout, StackPanel>

private bool _childAdded;

protected override void OnElementPropertyChanged(object sender, System.ComponentModel.PropertyChangedEventArgs e)

if (!_childAdded && Control?.Children != null)

_childAdded = true;
Control.Children.Insert(0, new Windows.UI.Xaml.Shapes.Rectangle());

base.OnElementPropertyChanged(sender, e);





2 Answers
2



Some modification in you are cade because you are calling base.OnElementPropertyChanged(sender,e) after code implementation. Just try to use below code.


public class MyRenderer : ViewRenderer<StackLayout, StackPanel>

private bool _childAdded;

protected override void OnElementPropertyChanged(object sender, System.ComponentModel.PropertyChangedEventArgs e)

base.OnElementPropertyChanged(sender, e);
if(Control==null)
return;
if (!_childAdded && Control.Children != null)

_childAdded = true;
Control.Children.Insert(0, new Windows.UI.Xaml.Shapes.Rectangle());








Tks, but I don't see how starting with the base implementation would change anything. However, you made me realise that this is not Children which is null but Control. Hence the issue is surely that the StackLayout implementation in UWP may not be StackPanel.
– François
9 hours ago


Children


null


Control


StackLayout


StackPanel



The StackLayout (Layout) renderer is ViewRenderer and implemented on UWP by FrameworkElement; Renderer Base Classes and Native Controls.


StackLayout


Layout


ViewRenderer


FrameworkElement



Theoretical renderer:


public class MyRenderer : ViewRenderer<StackLayout, FrameworkElement>
...






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