How to draw a curved line in android?

Question

I am new to Android and I am developing a sample project on drawing lines. I want to draw a curved or elevated line connecting two points (x1,y1 and x2,y2). I tried canvas.drawArc() method, but the RectF values inside the drawArc method is just the x,y center points of circle. It is giving me an arc between my two points. But I want a curved line exactly connecting my two points. Can somebody help me? Thanks in advance.

Answer 1

Declare this method inside onDraw method:

private void drawOvalAndArrow(Canvas canvas){


    Paint circlePaint = new Paint();
    circlePaint.setStyle(Paint.Style.FILL_AND_STROKE);
    circlePaint.setAntiAlias(true);
    circlePaint.setStrokeWidth(2);
    circlePaint.setColor(Color.CYAN);

    float centerWidth = canvas.getWidth()/2; //get center x of display
    float centerHeight = canvas.getHeight()/2; //get center y of display
    float circleRadius = 20; //set radius 
    float circleDistance = 200; //set distance between both circles

    //draw circles
    canvas.drawCircle(centerWidth, centerHeight, circleRadius, circlePaint);
    canvas.drawCircle(centerWidth+circleDistance, centerHeight, circleRadius, circlePaint);


    //to draw an arrow, just lines needed, so style is only STROKE
    circlePaint.setStyle(Paint.Style.STROKE);       
    circlePaint.setColor(Color.RED);

    //create a path to draw on
    Path arrowPath = new Path();

    //create an invisible oval. the oval is for "behind the scenes" ,to set the path´
    //area. Imagine this is an egg behind your circles. the circles are in the middle of this egg
    final RectF arrowOval = new RectF();
    arrowOval.set(centerWidth, 
            centerHeight-80, 
            centerWidth + circleDistance, 
            centerHeight+80);

    //add the oval to path
    arrowPath.addArc(arrowOval,-180,180);

    //draw path on canvas
    canvas.drawPath(arrowPath, circlePaint);


    //draw arrowhead on path start
     arrowPath.moveTo(centerWidth,centerHeight ); //move to the center of first circle
     arrowPath.lineTo(centerWidth-circleRadius, centerHeight-circleRadius);//draw the first arrowhead line to the left
     arrowPath.moveTo(centerWidth,centerHeight );//move back to the center
     arrowPath.lineTo(centerWidth+circleRadius, centerHeight-circleRadius);//draw the next arrowhead line to the right

     //same as above on path end
     arrowPath.moveTo(centerWidth+circleDistance,centerHeight );
     arrowPath.lineTo((centerWidth+circleDistance)-circleRadius, centerHeight-circleRadius);
     arrowPath.moveTo(centerWidth+circleDistance,centerHeight );
     arrowPath.lineTo((centerWidth+circleDistance)+circleRadius, centerHeight-circleRadius);

     //draw the path
     canvas.drawPath(arrowPath,circlePaint);

}

Also this will find the two sides of the screen (Landscape mode) and will draw a perfect curve across the screen

protected void onDraw(Canvas canvas) {
    super.onDraw(canvas);

    PointF mPoint1 = new PointF(w/1.2F, h/1.2F);
    PointF mPoint2 = new PointF(w/24, h/1.2F);
    Path myPath1 = new Path();
    Paint paint  = new Paint();
    paint.setAntiAlias(true);
    paint.setStyle(Style.STROKE);
    paint.setStrokeWidth(2);
    paint.setColor(Color.WHITE);

    myPath1 = drawCurve(canvas, paint, mPoint1, mPoint2);
    canvas.drawPath(myPath1, paint);

}

private Path drawCurve(Canvas canvas, Paint paint, PointF mPointa, PointF mPointb) {

    Path myPath = new Path();
    myPath.moveTo(63*w/64, h/10);
    myPath.quadTo(mPointa.x, mPointa.y, mPointb.x, mPointb.y);
    return myPath;  
}

Useful references on painting in android:

How to draw Arcs in Android using canvas?

Basic Painting with Views