Make canvas draw
<p>In my app i have 2 classes, the main and a class that draws an arc like this</p>

<pre><code>public class MyView extends View {

//public static Bitmap arc;
public static Bitmap arc = Bitmap.createBitmap(480, 480, Bitmap.Config.ARGB_8888);
public static Context context;



 // CONSTRUCTOR
    public MyView(Context context) {
        super(context);
        setFocusable(true);

    }
    public MyView(Context context, AttributeSet attrs) {

        super( context, attrs );
        }

        public MyView(Context context, AttributeSet attrs, int defStyle) {

        super( context, attrs, defStyle );
        }


    @Override
    protected void onDraw(Canvas canvas) {

      //  canvas.drawColor(Color.CYAN);

        Paint p = new Paint();
        // smooths
        p.setAntiAlias(true);
        p.setColor(Color.RED);
        p.setStyle(Paint.Style.FILL); 
        p.setStrokeWidth(5);
        canvas.setBitmap(arc);
        // opacity
      //  p.setAlpha(0x80); 


        final RectF oval = new RectF();
        p.setStyle(Paint.Style.FILL);
        /*
         * drawArc(RectF oval, float startAngle, float sweepAngle, boolean useCenter, Paint paint)
         *
         * oval - The bounds of oval used to define the shape and size of the arc
         * startAngle - Starting angle (in degrees) where the arc begins
         * sweepAngle - Sweep angle (in degrees) measured clockwise
         * useCenter - If true, include the center of the oval in the arc, and close it if it is being stroked. This will draw a wedge
         * paint - The paint used to draw the arc
         */


        oval.set(0, 0, 480, 480);
        canvas.drawArc(oval, 90, 90, true, p);


    }


}
</code></pre>

<p>The arc is drawing correctly, now in my main activity i want to change the drawable of an imageview with the generated bitmap, and i use this method to do it</p>

<pre><code>void changeBitmap () 
{

    ImageView central = (ImageView) findViewById(R.id.imageView1);
    central.setImageBitmap(MyView.arc);

}
</code></pre>

<p>But i get blank bitmap because my canvas didn't start drawing, how can i start my MyView activity to draw the canvas?
Also how can i make it redraw when a value has changed?</p>
