How to customize a Button to have a gradient color background?

Question

There already is a solution on how to create a layout with a gradient color background, but when I'm trying to implement it, it tells me that the Android renderer is obsolete and that I should use the one from Xamarin.Forms.Platform.Android.FastRenderers

If I change the code to

public class GradientStackLayout : StackLayout 
{
    // ...
}

instead of

public class GradientStackLayout : VisualElementRenderer<StackLayout>
{
    // ...
}

the compiler would complain that there are no DispatchDraw and OnElementChanged methods.

Should I use the obsolete renderer? Is there any new method to implement custom renderers?

Jessie Zhang -MSFT · Accepted Answer · 2019-11-15 06:43:36Z

1

You just add a construct function in class GradientColorStackRenderer in Xamarin android.

public GradientColorStackRenderer(Context context):base(context)
    {
    }

So the whole code is as follows:

[assembly: ExportRenderer(typeof(GradientColorStack), typeof(GradientColorStackRenderer))]
namespace GradientBackgroundApp.Droid
{
 public class GradientColorStackRenderer: VisualElementRenderer<StackLayout>
{

    private Color StartColor { get; set; }
    private Color EndColor { get; set; }

    // add the construct here
    public GradientColorStackRenderer(Context context):base(context)
    {
    }

    protected override void DispatchDraw(global::Android.Graphics.Canvas canvas)
    {
        #region for Vertical Gradient
        //var gradient = new Android.Graphics.LinearGradient(0, 0, 0, Height,
        #endregion

        #region for Horizontal Gradient
        var gradient = new Android.Graphics.LinearGradient(0, 0, Width, 0,
        #endregion

               this.StartColor.ToAndroid(),
               this.EndColor.ToAndroid(),
               Android.Graphics.Shader.TileMode.Mirror);

        var paint = new Android.Graphics.Paint()
        {
            Dither = true,
        };
        paint.SetShader(gradient);
        canvas.DrawPaint(paint);
        base.DispatchDraw(canvas);
    }

    protected override void OnElementChanged(ElementChangedEventArgs<StackLayout> e)
    {
        base.OnElementChanged(e);

        if (e.OldElement != null || Element == null)
        {
            return;
        }
        try
        {
            var stack = e.NewElement as GradientColorStack;
            this.StartColor = stack.StartColor;
            this.EndColor = stack.EndColor;
        }
        catch (Exception ex)
        {
            System.Diagnostics.Debug.WriteLine(@"ERROR:", ex.Message);
        }
    }
  }
 }

answered Nov 15, 2019 at 6:43

Jessie Zhang -MSFT

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4 Comments

user666 Over a year ago

yes it worked .how do you find it? If I have questions again how should I do?

Jessie Zhang -MSFT Over a year ago

When we encounter a problem, we usually analyze the Log first and if we can't find the reason,we can try to search the Log on Google. For general problem, there will be some solutions. :)

user666 Over a year ago

ok.thankyou .by the way .where to see the code of the element in xamarin such as Label,Image. I can not see it in the github.

Jessie Zhang -MSFT Over a year ago

Are you talking about this link? github.com/xamarin/Xamarin.Forms

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