An example showing how to create and use a Drawable that animates.

activity_main.xml

<RelativeLayout 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"
    tools:context=".MainActivity" >

    <ImageView
        android:id="@+id/image"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_centerHorizontal="true"
        android:layout_centerVertical="true" />

</RelativeLayout>

ExpandingCircleAnimationDrawable.java

package com.example.manualanimation;

import android.graphics.Canvas;
import android.graphics.ColorFilter;
import android.graphics.Paint;
import android.graphics.PixelFormat;
import android.graphics.Rect;
import android.graphics.drawable.Animatable;
import android.graphics.drawable.Drawable;
import android.view.animation.AnimationUtils;

public class ExpandingCircleAnimationDrawable extends Drawable implements Animatable, Runnable {

  private Paint mPaint;
	private float mRadius;
	
	private long mStartTicks = 0;
	private boolean mIsRunning = false;
	
	public ExpandingCircleAnimationDrawable(float radius) {
		super();
		
		mRadius = radius;
		
		mPaint = new Paint();
		
		mPaint.setStyle(Paint.Style.STROKE);
		mPaint.setColor(0xfff3f3f3);
		mPaint.setAntiAlias(true);
		mPaint.setStrokeWidth(2);
	}
	
	@Override
	public void draw(Canvas canvas) {
	    float loopPercent = calculateCurrentLoopPercent();

	    float alpha = -(loopPercent * loopPercent) + 1;

	    mPaint.setAlpha((int) (255 * alpha));

	    float radius = loopPercent * mRadius;

	    Rect bounds = getBounds();
	    float x = ((bounds.right - bounds.left) / 2f) + bounds.left;
	    float y = ((bounds.bottom - bounds.top) / 2f) + bounds.top;

	    canvas.drawCircle(x, y, radius, mPaint);
	}
	
	private float calculateCurrentLoopPercent() {
		float loopPercent = 0.5f;
		if (isRunning()) {
			float loopMillis = 5000;
			loopPercent = (AnimationUtils.currentAnimationTimeMillis() - mStartTicks) / loopMillis;
			while (loopPercent > 1) {
				loopPercent -= 1;
				mStartTicks += loopMillis;
			}
		}
		
		return loopPercent;
	}

	@Override
	public void run() {
		invalidateSelf();
		scheduleSelf(this, AnimationUtils.currentAnimationTimeMillis() + (1000/60));
	}

	@Override
	public boolean isRunning() {
		return mIsRunning;
	}

	@Override
	public void start() {
		if (!isRunning()) {
			mIsRunning = true;
			mStartTicks = AnimationUtils.currentAnimationTimeMillis();
			run();
		}
	}

	@Override
	public void stop() {
		if (isRunning()) {
			unscheduleSelf(this);
			mIsRunning = false;
		}
	}

	@Override
	public int getOpacity() {
		return PixelFormat.TRANSLUCENT;
	}

	@Override
	public void setAlpha(int arg0) {
		throw new UnsupportedOperationException();
	}

	@Override
	public void setColorFilter(ColorFilter arg0) {
		throw new UnsupportedOperationException();
	}
	
	@Override
	public int getIntrinsicHeight() {
		return (int) (2 * mRadius);
	}
	
	@Override
	public int getIntrinsicWidth() {
		return (int) (2 * mRadius);
	}
	
	@Override
	public int getMinimumHeight() {
		return (int) (2 * mRadius);
	}
	
	@Override
	public int getMinimumWidth() {
		return (int) (2 * mRadius);
	}
}

MainActivity.java

package com.example.manualanimation;

import android.app.Activity;
import android.os.Bundle;
import android.view.Menu;
import android.widget.ImageView;

public class MainActivity extends Activity {

  ExpandingCircleAnimationDrawable mCircle;
	
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        
        ImageView iv = (ImageView) findViewById(R.id.image);
        
        mCircle = new ExpandingCircleAnimationDrawable(200);
        iv.setImageDrawable(mCircle);
    }

    @Override
    public boolean onCreateOptionsMenu(Menu menu) {
        getMenuInflater().inflate(R.menu.activity_main, menu);
        return true;
    }

    @Override
    protected void onResume() {
    	super.onResume();
    	mCircle.start();
    }
    
    @Override
    protected void onPause() {
    	mCircle.stop();
    	super.onPause();
    }
}