Xamarin Forms - async Task “Signature (return type

Question

when I update Xamarin forms to 3.2.0 or higher, I am getting the following error:

Error       Position 68:29. Signature (return type) of EventHandler
"TimeToSport.Views.ItemsPage.OnCanvasViewPaintSurfaceAsync" doesn't match
the event type  TimeToSport 
E:\Xamarin Projects\TimeToSport_master\TimeToSport\TimeToSport\Views\Main\ItemsPage.xaml    68  

The error is coming from this code (xaml):

<skia:SKCanvasView x:Name="canvas" 
 PaintSurface="OnCanvasViewPaintSurfaceAsync" 
 Grid.Row="2" 
/>

In the CS file:

SKCanvas canvas = surface.Canvas;

When I was working with Xamarin forms version 3.1.0, I didn't get this error and everything worked. However, I have to update Xamarin forms for some new features I need to use.

How can I fix this error?

EDIT:

OnCanvasViewPaintSurfaceAsync:

    async Task OnCanvasViewPaintSurfaceAsync(object sender, SKPaintSurfaceEventArgs args1)

    {
        args = args1;
        await drawGaugeAsync();

    }

public async Task drawGaugeAsync()
    {
        // Radial Gauge Constants
        int uPadding = 130;
        int side = 370;
        int radialGaugeWidth = 20;

        // Line TextSize inside Radial Gauge
        int lineSize1 = 220;
        int lineSize2 = 70;
        int lineSize3 = 80;

        // Line Y Coordinate inside Radial Gauge
        int lineHeight1 = 175;
        int lineHeight2 = 275;
        int lineHeight3 = 350;

        // Start & End Angle for Radial Gauge
        //float startAngle = (360/24)*23+90;
        float sweepAngle = 360;

        try
        {

            // Getting Canvas Info 
            SKImageInfo info = args.Info;
            SKSurface surface = args.Surface;
            SKCanvas canvas = surface.Canvas;
            progressUtils.setDevice(info.Height, info.Width);
            canvas.Clear();


            //canvas.DrawColor(SKColor.Parse("#2196F3")); //Background upper
            // Getting Device Specific Screen Values
            // -------------------------------------------------

            // Top Padding for Radial Gauge
            float upperPadding = progressUtils.getFactoredHeight(uPadding);

            /* Coordinate Plotting for Radial Gauge
            *
            *    (X1,Y1) ------------
            *           |   (XC,YC)  |
            *           |      .     |
            *         Y |            |
            *           |            |
            *            ------------ (X2,Y2))
            *                  X
            *   
            *To fit a perfect Circle inside --> X==Y
            *       i.e It should be a Square
            */

            // Xc & Yc are center of the Circle
            int Xc = info.Width / 2;
            float Yc = progressUtils.getFactoredHeight(side);
            float Yc2 = progressUtils.getFactoredHeight(445);

            // X1 Y1 are lefttop cordiates of rectange
            int X1 = (int)(Xc - Yc);
            int Y1 = (int)(Yc - Yc + upperPadding + 9); //+55

            int X12 = (int)(Xc - Yc2);
            int Y12 = (int)(Yc2 - Yc2 + upperPadding - 22.5);

            // X2 Y2 are rightbottom cordiates of rectange
            int X2 = (int)(Xc + Yc);
            int Y2 = (int)(Yc + Yc + upperPadding + 9); //+55

            int X22 = (int)(Xc + Yc2);
            int Y22 = (int)(Yc2 + Yc2 + upperPadding - 22.5);



            //  Empty Gauge Styling // basis
            SKPaint paint1 = new SKPaint
            {
                Style = SKPaintStyle.Stroke,
                IsAntialias = true,
                Color = Color.FromHex("#f7f7f7").ToSKColor(),                   // Colour of Radial Gauge
                StrokeWidth = progressUtils.getFactoredWidth(radialGaugeWidth - 10), // Width of Radial Gauge
                StrokeCap = SKStrokeCap.Butt                                 // Round Corners for Radial Gauge
            };

            // Filled Gauge Styling // slaap
            SKPaint paint2 = new SKPaint
            {
                Style = SKPaintStyle.Stroke,
                IsAntialias = true,
                Color = Color.FromHex("#183f7c").ToSKColor(),                   // Overlay Colour of Radial Gauge
                StrokeWidth = progressUtils.getFactoredWidth(radialGaugeWidth + 10), // Overlay Width of Radial Gauge
                StrokeCap = SKStrokeCap.Butt                                 // Round Corners for Radial Gauge
            };

            //  Empty Gauge Styling // voeding
            SKPaint paint3 = new SKPaint
            {
                Style = SKPaintStyle.Stroke,
                IsAntialias = true,
                Color = Color.FromHex("#c45256").ToSKColor(),                   // Colour of Radial Gauge
                StrokeWidth = progressUtils.getFactoredWidth(radialGaugeWidth + 10), // Width of Radial Gauge
                StrokeCap = SKStrokeCap.Butt                                 // Round Corners for Radial Gauge
            };

            // Filled Gauge Styling // sport
            SKPaint paint4 = new SKPaint
            {
                Style = SKPaintStyle.Stroke,
                IsAntialias = true,
                Color = Color.FromHex("#5bd363").ToSKColor(),                   // Overlay Colour of Radial Gauge
                StrokeWidth = progressUtils.getFactoredWidth(radialGaugeWidth + 15), // Overlay Width of Radial Gauge
                StrokeCap = SKStrokeCap.Butt                                  // Round Corners for Radial Gauge
            };

            SKPaint paint5 = new SKPaint // voeding na sport
            {
                Style = SKPaintStyle.Stroke,
                IsAntialias = true,
                Color = Color.FromHex("#c45256").ToSKColor(),                   // Overlay Colour of Radial Gauge
                StrokeWidth = progressUtils.getFactoredWidth(radialGaugeWidth + 10), // Overlay Width of Radial Gauge
                StrokeCap = SKStrokeCap.Butt                              // Round Corners for Radial Gauge
            };

            SKPaint paint6 = new SKPaint // lokale tijd
            {
                Style = SKPaintStyle.Stroke,
                IsAntialias = true,
                Color = Color.FromHex("#ffb342").ToSKColor(),                   // Overlay Colour of Radial Gauge
                StrokeWidth = progressUtils.getFactoredWidth(radialGaugeWidth + 25), // Overlay Width of Radial Gauge
                StrokeCap = SKStrokeCap.Butt                              // Round Corners for Radial Gauge
            };

            SKPaint paint7 = new SKPaint // vierkant 1 
            {
                Style = SKPaintStyle.StrokeAndFill,
                IsAntialias = true,
                Color = Color.FromHex("#ffffff").ToSKColor(),                   // Overlay Colour of Radial Gauge
                StrokeWidth = progressUtils.getFactoredWidth(radialGaugeWidth + 60), // Overlay Width of Radial Gauge
                StrokeCap = SKStrokeCap.Round                              // Round Corners for Radial Gauge
            };


            // Defining boundaries for Gauge
            SKRect rect = new SKRect(X1, Y1, X2, Y2);
            SKRect rectBackground1 = new SKRect(X1 - 75, Y1 - 75, X2 + 75, Y2 + 75);
            SKRect rect2 = new SKRect(X12, Y12, X22, Y22);

            //canvas.DrawRect(rect, paint1);
            //canvas.DrawOval(rect, paint1);

            // Rendering Empty Gauge
            SKPath path7 = new SKPath();
            //path7.AddRoundedRect(rectBackground1, 5, 5, SKPathDirection.Clockwise);
            //canvas.DrawPath(path7, paint7);

            SKPath path1 = new SKPath();
            path1.AddArc(rect, -90, sweepAngle);
            canvas.DrawPath(path1, paint1);

            // Rendering Filled Gauge
            SKPath path2 = new SKPath();
            path2.AddArc(rect, (360 / 24) * 23 - 90, (float)sweepAngleSlider.Value);
            canvas.DrawPath(path2, paint2);

            SKPath path3 = new SKPath();
            path3.AddArc(rect, (360 / 24) * 8.50f - 90, (float)sweepAngleSlider2.Value);
            canvas.DrawPath(path3, paint3);

            SKPath path4 = new SKPath();
            path4.AddArc(rect, (360 / 24) * 9.25f - 90, (float)sweepAngleSlider3.Value);
            canvas.DrawPath(path4, paint4);

            SKPath path5 = new SKPath();
            path5.AddArc(rect, (360 / 24) * 12f - 90, (float)sweepAngleSlider4.Value);
            canvas.DrawPath(path5, paint5);

            //lokale tijd onderaan


            /*// Rendering Empty Gauge
            SKPath path3 = new SKPath();
            path3.AddArc(rect2, startAngle, sweepAngle);
            canvas.DrawPath(path3, paint3);

            // Rendering Filled Gauge
            SKPath path4 = new SKPath();
            path4.AddArc(rect2, startAngle, (float)sweepAngleSlider2.Value);
            canvas.DrawPath(path4, paint4);*/


            //---------------- Drawing Text Over Gauge ---------------------------

            // frequentie dagen
            using (SKPaint skPaint = new SKPaint())
            {
                skPaint.Style = SKPaintStyle.Fill;
                skPaint.IsAntialias = true;
                skPaint.Color = SKColor.Parse("#2b2b2b");
                skPaint.TextAlign = SKTextAlign.Center;
                skPaint.TextSize = progressUtils.getFactoredHeight(lineSize1);
                skPaint.Typeface = SKTypeface.FromFamilyName(
                                    "Arial",
                                    SKFontStyleWeight.Bold,
                                    SKFontStyleWidth.Normal,
                                    SKFontStyleSlant.Upright);



                // Drawing Achieved Minutes Over Radial Gauge
                if (sw_listToggle.IsToggled)
                    canvas.DrawText(/*monthlyWorkout +*/ "3", Xc, Yc + progressUtils.getFactoredHeight(lineHeight1), skPaint);
                else
                    canvas.DrawText(/*dailyWorkout + */ "3-4", Xc, Yc + progressUtils.getFactoredHeight(lineHeight1), skPaint);
            }

            // "per week"
            using (SKPaint skPaint = new SKPaint())
            {
                skPaint.Style = SKPaintStyle.Fill;
                skPaint.IsAntialias = true;
                skPaint.Color = SKColor.Parse("#424242");
                skPaint.TextAlign = SKTextAlign.Center;
                skPaint.TextSize = progressUtils.getFactoredHeight(55);


                //ff een testje
                canvas.DrawText(Application.Current.Properties["geslacht"].ToString(), Xc, Yc + progressUtils.getFactoredHeight(lineHeight2), skPaint);
                canvas.DrawText("06", X2 + 80, (Y1 + Y2) / 2 + 22, skPaint);
                canvas.DrawText("12", Xc, Y2 + 115, skPaint);
                canvas.DrawText("18", X1 - 100, (Y1 + Y2) / 2 + 22, skPaint);
                canvas.DrawText("00", Xc, Y1 - 60, skPaint);
            }

            // Goal Minutes Text Styling
            using (SKPaint skPaint = new SKPaint())
            {
                skPaint.Style = SKPaintStyle.Fill;
                skPaint.IsAntialias = true;
                skPaint.Color = SKColor.Parse("#e2797a");
                skPaint.TextAlign = SKTextAlign.Center;
                skPaint.TextSize = progressUtils.getFactoredHeight(lineSize3);

                // Drawing Text Over Radial Gauge
                // if (sw_listToggle.IsToggled)
                //canvas.DrawText("Goal " + goal + " Min", Xc, Yc + progressUtils.getFactoredHeight(lineHeight3), skPaint);
                //else
                //{
                //canvas.DrawText("Goal " + goal / 30 + " Min", Xc, Yc + progressUtils.getFactoredHeight(lineHeight3), skPaint);
                //}


            }

            sportenTijdText1 = "09:15";
            etenVoorTijdText1 = "08:30";
            etenNaTijdText1 = "09:00";
            slapenTijdText1 = "23:00";
            sportenTijdText2 = "10:45";
            etenVoorTijdText2 = "12:00";
            etenNaTijdText2 = "12:30";
            slapenTijdText2 = "08:00";

            SportKnop.Text = sportenTijdText1 + " - Sporten - " + sportenTijdText2;
            VoedingVoorKnop.Text = etenVoorTijdText1 + " - Eten - " + etenNaTijdText1;
            VoedingNaKnop.Text = etenVoorTijdText1 + " - Eten - " + etenNaTijdText2;
            SlaapKnop.Text = slapenTijdText1 + " - Slapen - " + slapenTijdText2;

            Device.StartTimer(TimeSpan.FromSeconds(1), () =>
            {
                Device.BeginInvokeOnMainThread(() => tijd.Text = DateTime.Now.ToString("HH.mm"));
                Device.BeginInvokeOnMainThread(() => TijdKnop.Text = "Huidige tijd - " + DateTime.Now.ToString("HH:mm"));
                return true;
            });
            SKPath path6 = new SKPath();
            path6.AddArc(rect, (360 / 24) * float.Parse(tijd.Text, CultureInfo.InvariantCulture.NumberFormat) + -91.5f, (float)sweepAngleSlider5.Value);
            canvas.DrawPath(path6, paint6);

        }
        catch (Exception e)
        {
            Debug.WriteLine(e.StackTrace);
        }
    }

Answer 1

From recent Xamarin forms update code behind dont support Task return type as signatures for event handlers.

Remove Task and replace it with void

async void OnCanvasViewPaintSurfaceAsync(object sender, SKPaintSurfaceEventArgs args1)
{
        args = args1;
        await drawGaugeAsync();

}

public async Task drawGaugeAsync(){

}

Update : public async Task drawGaugeAsync() can return Task