Xamarin Forms android button custom renderer

Here it is. A ripple-enabled button with CornerRadius and Padding.

You'll have to add the usings, the namespace and the ExportRenderer attribute.

MainActivity.Activity is a property of type Context that I set when the app initializes. Just add this line: Activity = this; in the OnCreate method, before Forms.Init.

public class ButtonRenderer : Xamarin.Forms.Platform.Android.ButtonRenderer
{
    // Your Button class
    Button button;

    float radius = 0;
    //--------------------------------------------------------------------------------//
    public ButtonRenderer() : base(MainActivity.Activity) { }

    protected override void OnElementChanged(ElementChangedEventArgs<Xamarin.Forms.Button> e)
    {
        base.OnElementChanged(e);

        button = Element as Button;

        if (e.OldElement == null)
        {
            if (IsPostLollipopAndroid) Control.Elevation = 2;

            radius = (float)button.CornerRadius;

            if (button.Padding != null)
            {
                Control.SetPadding(ToPx((int)button.Padding.Left), ToPx((int)button.Padding.Top), ToPx((int)button.Padding.Right), ToPx((int)button.Padding.Bottom));
            }

            SetColors();

            Control.SetMinHeight(0);
            Control.SetMinimumHeight(0);
            Control.SetMinWidth(0);
            Control.SetMinimumWidth(0);
        }
    }
    protected override void OnElementPropertyChanged(object sender, PropertyChangedEventArgs e)
    {
        base.OnElementPropertyChanged(sender, e);

        switch (e.PropertyName)
        {
            case nameof(VisualElement.BackgroundColor):
            case nameof(Button.PressedColor):
                {
                    SetColors();

                    break;
                }
            case nameof(Button.Padding):
                {
                    if (button.Padding != null)
                    {
                        Control.SetPadding((int)button.Padding.Left, (int)button.Padding.Top, (int)button.Padding.Right, (int)button.Padding.Bottom);
                    }

                    break;
                }
        }
    }

    public override bool DispatchTouchEvent(MotionEvent e)
    {
        if (!Element.InputTransparent) return base.DispatchTouchEvent(e);
        else return true;
    }

    void SetColors()
    {
        radius = (float)button.CornerRadius;

        StateListDrawable list = new StateListDrawable();

        if (IsPreLollipopAndroid)
        {
            GradientDrawable pressedDrawable;

            if (Element.BackgroundColor != Color.Transparent)
            {
                Android.Graphics.Color pressedColor = ChangeColorBrightness(Element.BackgroundColor, (button.PressedColor == ButtonPressedColor.Dark) ? 1f - (float).15 : 1f + (float).15).ToAndroid();
                pressedDrawable = new GradientDrawable(GradientDrawable.Orientation.LeftRight, new int[] { pressedColor, pressedColor });

                pressedDrawable.SetCornerRadius(ToPxFloat(radius));
            }
            else
            {
                Android.Graphics.Color pressedColor = (button.PressedColor == ButtonPressedColor.Dark) ? Color.Black.MultiplyAlpha(.15).ToAndroid() : Color.White.MultiplyAlpha(.15).ToAndroid();
                pressedDrawable = new GradientDrawable(GradientDrawable.Orientation.LeftRight, new int[] { pressedColor, pressedColor });

                pressedDrawable.SetCornerRadius(ToPxFloat(radius));
            }

            list.AddState(new int[] { Android.Resource.Attribute.StatePressed }, pressedDrawable);

            //--------------------------------------------------------------------------------//

            Android.Graphics.Color color = Element.BackgroundColor.ToAndroid();
            var normalDrawable = new GradientDrawable(GradientDrawable.Orientation.LeftRight, new int[] { color, color });

            normalDrawable.SetCornerRadius(ToPxFloat(radius));

            list.AddState(new int[] { -Android.Resource.Attribute.StatePressed }, normalDrawable);

            Control.Background = list;
        }
        else
        {
            GradientDrawable normalDrawable = new GradientDrawable();
            normalDrawable.SetCornerRadius(ToPxFloat(radius));
            normalDrawable.SetColor(Element.BackgroundColor.ToAndroid());

            float[] outerRadii = Enumerable.Repeat(ToPxFloat(radius), 8).ToArray();

            RoundRectShape r = new RoundRectShape(outerRadii, null, null);

            ShapeDrawable shapeDrawable = new ShapeDrawable(r);
            shapeDrawable.Paint.Color = Color.White.ToAndroid();

            var pressedColor = (button.PressedColor == ButtonPressedColor.Dark) ? Color.Black.MultiplyAlpha(.15).ToAndroid() : Color.White.MultiplyAlpha(.15).ToAndroid();
            var ripple = new RippleDrawable(ColorStateList.ValueOf(pressedColor), normalDrawable, shapeDrawable);

            Control.Background = ripple;
        }
    }

    public static int ToPx(double dp)
    {
        return (int)Android.Util.TypedValue.ApplyDimension(Android.Util.ComplexUnitType.Dip, (float)dp, Droid.MainActivity.Activity.Resources.DisplayMetrics);
    }

    public static float ToPxFloat(double dp)
    {
        return Android.Util.TypedValue.ApplyDimension(Android.Util.ComplexUnitType.Dip, (float)dp, Droid.MainActivity.Activity.Resources.DisplayMetrics);
    }

    public static bool IsPreLollipopAndroid => Android.OS.Build.VERSION.SdkInt < Android.OS.BuildVersionCodes.Lollipop;
    public static bool IsPostLollipopAndroid => Android.OS.Build.VERSION.SdkInt >= Android.OS.BuildVersionCodes.Lollipop;

    public static Color ChangeColorBrightness(Color color, float factor)
    {
        return Color.FromRgba(color.R * factor, color.G * factor, color.B * factor, color.A);
    }
}

The Button class has Padding, CornerRadius and PressedColor (an enum with Dark and Light fields).

Hope it helps!