Xamarin Forms iOS renderer Dimensions - xamarin.forms

Question

I’m trying to create a “generic” renderer for iOS and I have trouble figuring out the dimensions of the renderer.
The class of the renderer in the PCL is very simple and the only “peculiar” is that inherits from a View since I want to have it as a generic renderer
public class ExampleView : View { }
In the XAML, it is also very typical
<renderers:ExampleView />
The definition of the renderer in the iOS project is the following
public class ExampleRenderer : ViewRenderer<ExampleView, UIView>
{
protected override void OnElementChanged(ElementChangedEventArgs<ExampleView> e)
{
base.OnElementChanged(e);
if (Control == null)
{
SetNativeControl(new UIView(new CGRect(0, 0, 0, 300)));
}
}
}
The interesting part here is that the class inherits from ViewRenderer<ExampleView, UIView>
It seems that although I specify that the width of the render to be 0, the actual renderer takes the entire width of the page.
In fact whatever value I put as width, will be disregarded, and the renderer will occupy the entire page.
This is not bad, it is unintentional and this is what bother me. (or Am I doing something wrong?)
So the question here is how can find in my custom render, the width that occupies?

Answer 1

It is not the renderer, but the native control that is taking up the space. The renderer is doing it's job i.e. keep the native control in sync with forms control - which includes layout parse requests.
To control the size constraints I would recommend using the properties WidthRequest or HeightRequest on forms Element to do that. It will automatically trickle down to the native Control.Frame through the renderer.
EDIT-1
If you want to update your native controls (or subviews) based on current bounds you can use OnElementPropertyChanged to track the changes. There can many reasons that can cause a size-update - like device-orientation change, parent layout, first layout pass etc.
public class ExampleRenderer : ViewRenderer<ExampleView, UIView>
{
protected override void OnElementPropertyChanged(object sender, System.ComponentModel.PropertyChangedEventArgs e)
{
base.OnElementPropertyChanged(sender, e);
if (e.PropertyName == VisualElement.WidthProperty.PropertyName ||
e.PropertyName == VisualElement.HeightProperty.PropertyName)
{
if(Element != null && Element.Bounds.Height > 0 && Element.Bounds.Width > 0)
{
//update size on native control's subviews
// or use SetNeedsDisplay() to re-draw
//Note: force update to Control's size is not recommended (as it is recommended it be same as forms element)
//Instead add a subview that you can update for size here
}
}
}