Capture Xamarin Forms Page as bitmap without attaching to a parent

Issue

Is there a way to create a Xamarin Forms Page or other view structure and capture it's layout to a bitmap without giving it a parent and displaying it first?

I am able to capture an already rendered page like this in Android:

...

       var parent = v as Xamarin.Forms.View;
        
        
        var rend = Platform.GetRenderer((Xamarin.Forms.VisualElement)parent);
        rend.Tracker.UpdateLayout();

        var view = rend.View;


        if (view == null)
            throw new NullReferenceException("Unable to find the main window.");

        var bitmap = Bitmap.CreateBitmap(view.Width, view.Height, Bitmap.Config.Argb8888);

        using (var canvas = new Canvas(bitmap))
        {
            var drawable = view.Background;
            if (drawable != null)
                drawable.Draw(canvas);
            else
                canvas.DrawColor(Color.White);

            view.Draw(canvas);
        }

        var result = new CaptureResult(bitmap) as ICaptureResult;

...

But this does not work if the page has not already been displayed.

I could even work with an "off-screen" solution or a "hidden window" that could host and render the view without the UI being disturbed. I have done this type of operation in WPF, but I can't seem to find a suitable method in Xamarin. Ultimately I would like to create a multi-platform way to do this (Android, iOS) and other platforms when MAUI arrives.

I have also tried adding the following code to create the renderer to force the creation of the Page:

...

        if (rend == null)
            rend = Platform.CreateRendererWithContext((Xamarin.Forms.VisualElement)parent, Android.App.Application.Context);

...

This results in a valid renderer being created, but the resulting bitmap is empty

Solution

After a lot of experimentation, adding these calls prior to capturing the view seem to force the view to render:

...

view.Measure(desiredWidth, desiredHeight);
view.Layout(new Xamarin.Forms.Rectangle(0, 0, desiredWidth, desiredHeight));

...

Answered By - Randall B