How to add a rectangular overlay in a camera application?

Question

How do I add a rectangular overlay (which should be more like a rectangular frame) in the camera preview? My application consists of a button that opens the camera upon clicking. I need the overlay in that camera preview.

The code for the java file is:

    public class MainActivity extends Activity {
     Button b;
     Intent i;
     Bitmap bmp;
     final static int cameraData = 0;

     @Override
     protected void onCreate(Bundle savedInstanceState) {
         super.onCreate(savedInstanceState);
         setContentView(R.layout.activity_main);
         b = (Button) findViewById(R.id.button);
         InputStream is = getResources().openRawResource(R.drawable.ic_launcher);
         bmp = BitmapFactory.decodeStream(is);
         b.setOnClickListener(new View.OnClickListener() {

            @Override
            public void onClick(View v) {
            // TODO Auto-generated method stub
            i = new Intent(android.provider.MediaStore.ACTION_IMAGE_CAPTURE);
            startActivityForResult(i, cameraData);

        }
    });
 }
}

The Layout file is as follows:

    <LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:orientation="vertical"
tools:context=".MainActivity" >

<TextView
    android:id="@+id/text"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:layout_centerHorizontal="true"
    android:layout_gravity="center"
    android:text="click to take photo" />

<Button
    android:id="@+id/button"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:text="click"
    android:layout_gravity="center" />

</LinearLayout>

Answer 1

First, create a public Class that extends View. Inside its onDraw() method, draw your rectangle. For example:

public class Box extends View {
  private Paint paint = new Paint();
  Box(Context context) {
    super(context);
  }

  @Override
  protected void onDraw(Canvas canvas) { // Override the onDraw() Method
    super.onDraw(canvas);

    paint.setStyle(Paint.Style.STROKE);
    paint.setColor(Color.GREEN);
    paint.setStrokeWidth(10);

    //center
    int x0 = canvas.getWidth()/2;
    int y0 = canvas.getHeight()/2;
    int dx = canvas.getHeight()/3;
    int dy = canvas.getHeight()/3;
    //draw guide box
    canvas.drawRect(x0-dx, y0-dy, x0+dx, y0+dy, paint);
  }
}

Then, in your camera preview Activity, have an instance to your Box class:

Box box = new Box(this);

Finally:

addContentView(box, new LayoutParams(LayoutParams.FILL_PARENT, LayoutParams.FILL_PARENT));

A green rectangle will be drawn onto your camera preview.