A simple example of an Android activity for explaining concepts of property animations

AnimationActivity.java

package com.example.testtest;

import android.app.Activity;
import android.graphics.Canvas;
import android.graphics.Color;
import android.graphics.ColorFilter;
import android.graphics.Paint;
import android.graphics.Rect;
import android.graphics.drawable.Drawable;
import android.os.Bundle;
import android.os.Handler;
import android.os.Message;
import android.os.SystemClock;
import android.view.View;

public class AnimationActivity extends Activity {

  @SuppressWarnings("deprecation")
  @Override
  public void onCreate(final Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    final View view = new View(this);

    final AnimatedCrossDrawable animDrawable = new AnimatedCrossDrawable();
    view.setBackgroundDrawable(animDrawable);

    setContentView(view);

    // Start very simple animation
    // Video: http://www.youtube.com/watch?v=I5C6cNZjIYY
    new LevelAnimator(animDrawable)

    // uncomment the following lines for interpolation example:
    // Video: http://www.youtube.com/watch?v=jBLPEUpdUps

//    {
//
//      private float line(float x1, float y1, float x2, float y2, float x) {
//        return (x - x1) / (x2 - x1) * (y2 - y1) + y1;
//      }
//
//      @Override
//      protected float interpolate(final float fraction) {
//        final float[] x = {0f, 0.2f, 0.4f, 0.6f, 0.8f, 1f};
//        final float[] y = {0f, 0.2f, 0.1f, 0.6f, 0.5f, 1f};
//
//        for (int i = 0; i < x.length; i++) {
//          if (fraction < x[i]) {
//            return line(x[i - 1], y[i - 1], x[i], y[i], fraction);
//          }
//        }
//
//        return fraction;
//      }
//
//    }

    .setDuration(3000)
    .start(0, AnimatedCrossDrawable.MAX_LEVEL);


    // use this code instead to utilize property animations API

//    ObjectAnimator.ofInt(animDrawable, "level", 0, AnimatedCrossDrawable.MAX_LEVEL)
//      .setDuration(3000)
//      .start();

  }


  public static class LevelAnimator extends Handler {

    private static final int MSG_ANIMATE = 1;

    private long startTime, duration;

    private int begin, end;

    private final Drawable drawable;

    public LevelAnimator(final Drawable drawable) {
      this.drawable = drawable;
    }

    @Override
    public void handleMessage(Message msg) {
      switch (msg.what) {
      case MSG_ANIMATE:

        final int curLevel = getLevelValue(interpolate(getFraction(SystemClock.uptimeMillis())));
        drawable.setLevel(curLevel);

        if (SystemClock.uptimeMillis() < startTime + duration) {
          sendEmptyMessage(MSG_ANIMATE);
        }

        break;

      default:
      }
    }

    private float getFraction(final long curTime){
      float passed = curTime - startTime;
      final float fraction = passed /duration;
      return Math.min(fraction, 1.0f);
    }

    protected float interpolate(final float fraction) {
      return fraction;
    }

    private int getLevelValue(final float part) {
      final int interval = end - begin;
      return begin + (int) (part * interval);
    }

    public LevelAnimator setDuration(long duration) {
      this.duration = duration;
      return this;
    }

    public LevelAnimator start(final int begin, final int end){
      startTime = SystemClock.uptimeMillis();

      this.begin = begin;
      this.end = end;

      sendEmptyMessage(MSG_ANIMATE);
      return this;
    }

  }


  public static class AnimatedCrossDrawable extends Drawable {
    private static final int MAX_LEVEL = 100000;

    final Paint paint = new Paint(Paint.ANTI_ALIAS_FLAG);

    {
      paint.setColor(Color.BLUE);
    }

    @Override
    protected boolean onLevelChange(int level) {
      super.onLevelChange(level);
      invalidateSelf();
      return true;
    }

    @Override
    public void draw(final Canvas canvas) {
      Rect bounds = getBounds();
      float part = (float)getLevel() / MAX_LEVEL;
      float x = bounds.left + part * bounds.width();
      float y = bounds.top + part * bounds.height();
      canvas.drawLine(0f, 0f, x, y, paint);
      canvas.drawLine(0f, bounds.bottom, x, bounds.bottom - y, paint);
    }

    @Override
    public void setAlpha(final int alpha) { }

    @Override
    public void setColorFilter(final ColorFilter cf) { }

    @Override
    public int getOpacity() { return 0; }

    @Override
    public int getIntrinsicHeight() { return 0; }
    @Override
    public int getIntrinsicWidth() { return 0; }

  }

}