title: How to draw on PreviewView?
body: <p>I have a PreviewView instance on which i want to draw a rect based on object identifies using Firebase and Image Analyser use case.</p>
  <p>However, unlike in Text/ SurfaceView PreviewView doesn't let any Canvas to be drawn on top of it.</p>
  <p>What's the alternative?</p>
  <p><strong>Further Edits:</strong></p>
  <p>Tried the below earlier:</p>
  <pre><code>Canvas objectFrameCanvas = new Canvas();
  Paint pen = new Paint();
  pen.setColor(Color.RED);
  pen.setStrokeWidth(8F);
  pen.setStyle(Paint.Style.STROKE);
  
  objectFrameCanvas.drawRect(100,150,200, 250, pen);
  
  TextureView textureView = new TextureView(this);
  textureView.draw(objectFrameCanvas);
  
  mPreviewView.addView(textureView);
  </code></pre>
  <p>Create a child forviewgroup : textureView.
  Make new canvas objectFrameCanvas, draw rectangle on it, then draw canvas on textureView. Then add this to view group (PreviewView)</p>
  <p>Still doesnt give me the requisite result it should.</p>
  <p>By the way am using this inside my ImageAnanysis usecase</p>
  <pre><code>imageAnalysis.setAnalyzer(executor, new ImageAnalysis.Analyzer() {....}
  </code></pre>