Question

I want to make an app which shows cardio graph in real time. That means i want to measure heart bit and want to show the bit rate in graph in my application. But i wondering to draw the cardio graph. I have gone through many sample graph codes but dint get any clue to draw cardio graph. Is there any clue from any body?

Answer 1

For this specific application, you may want to draw the graph “by hand” using Path and a SurfaceView.

Get a Paint instance ready during initialization:

Paint paint = new Paint(Paint.ANTI_ALIAS_FLAG);
paint.setStyle(Paint.Style.STROKE);
paint.setStrokeWidth(3);
paint.setColor(Color.GREEN);  //Change to what you want

When you need to update the graphic, clear the scene and build the line path (adapt this to your needs) :

canvas.drawColor(Color.WHITE);

Path path = new Path();
path.moveTo(0, yourValueAt(0));
for(int sec = 1; sec < 30; sec++)
    path.lineTo(sec, yourValueAt(sec));

canvas.drawPath(path, paint);

You may also use quadTo or cubicTo instead of lineTo.

If you want your graph to have a realtime animation effect (i.e. sliding to the left while data is coming on the right), you may draw on a SurfaceView in a similar way to the famous LunarLander example (following code is a simplified version):

class DrawingThread extends Thread {
    @Override
    public void run() {
        while (running) {
            Canvas c = null;
            try {
                c = mSurfaceHolder.lockCanvas(null);
                synchronized (mSurfaceHolder) {
                    doDraw(c);
                }
            } finally {
                if (c != null) mSurfaceHolder.unlockCanvasAndPost(c);
            }
            synchronized (this) {
                //Optional but saves battery life.
                //You may compute the value to match a given max framerate..
                this.wait(SOME_DELAY_IN_MS); 
            }
        }
    }
}

Where mSurfaceHolder is obtained by calling yourSurfaceView.getHolder() and doDraw is where
you call canvas.drawPath() and all your drawing code.