Question

I have the following class:

public class MainActivity extends Activity {
/** Called when the activity is first created. */

String value = "0";

@Override
public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    getWindow().setFlags(WindowManager.LayoutParams.FLAG_FULLSCREEN,
            WindowManager.LayoutParams.FLAG_FULLSCREEN);

        setContentView(new GaugeAnimation(this));

       }

     }

My GuageAnimation class is as follows:

public class GaugeAnimation extends View{

private Path p;
private Paint cPaint = new Paint();
private int width = 200;
private int angleStart = 135;
private int sweep = 90;
private int value=0;

Bitmap bottom = BitmapFactory.decodeResource(getResources(), R.drawable.dashboard_rpm_bottom);
Bitmap top= BitmapFactory.decodeResource(getResources(), R.drawable.dashboard_rpm_active);

public GaugeAnimation(Context context){
    super (context);

        //Arc Equations & etc.... 

}

@Override
public void onDraw(Canvas c){


    Paint paint = new Paint();
    paint.setFilterBitmap(false);
    paint.setColor(Color.BLUE);
    c.translate(55,320);       

    //Draw bottom image on canvas

  c.save();

    p.addArc(new RectF(0,0,width,width), angleStart, sweep);
    p.lineTo(width/2, width/2);


    c.clipPath(p);

    //draw Image on top

    c.restore();

   invalidate()

}


 }

so basically this crops a circular image one piece at a time based on arc equations. I want to show an animation like the circle’s pieces all being filled in (so showing each clipped path which demonstrates a circle being built). So i was thinking of doing a for loop like:

 for (int i=0; i<100; i++) {
   sweep=i;
   p.addArc(new RectF(0,0,width,width), angleStart, sweep);
    p.lineTo(width/2, width/2);

    c.clipPath(p);
        invalidate();
 }

but this doesn’t work it just draws the end result when i=100, anyone have an idea as to how i can do this?

Answer 1

Currently your loop is performed on the main thread and keeps it busy, so it will not actually update the UI until you finish.

You should do the loop in a background thread (using Timer or AsyncTask) and perform the paint on main thread. Note that without a short sleep, it will probably would look like an animation too much, it will be pretty fast.