title: Use of canvas.DrawBitmap() in android plot
body: <p>I am totally new in android and
  I am plotting graph on Custom View. But it is clearing previous  random plot automatically.
  Is Drawbitmap()  required . Will Drawbitmap() prevent it from clearing  the canvas randomly.?</p>
  
  <pre><code> @Override
  public void onDraw(Canvas canvas) 
  {
  
  
    drawStuff(canvas);
  }
  
   public void drawStuff(Canvas canvas) 
  {
  
    PlotRealTimeGraph(canvas);
   }  
  </code></pre>
  
  <p>Here this is my timer   where I am invalidating this canvas to redraw  </p>
  
  <pre><code> Timer t = new Timer();
      t.schedule(new TimerTask() {
         @Override
          public void run() 
          {
  
           postInvalidate(chanX_count1, 0, chanX_count1+7, graphheight);
          }
  
   },1000,40);    
  </code></pre>
  
  <p>1.Here I want to ask , Shall I use drawbitmap() If yes !  then how please  suggest?<br>
  2. What if I will use this timer on Activity and Invalidate  this from there. Any help?</p>