Android 背景图片的缩放实现

 public class ScaleImage extends View {

  /**
   * 设置的背景图片
   */
  private Drawable background;
  /**
   * 画布的背景图片
   */
  private Bitmap bitmapCopy;
  /**
   * 跟随动画实时更新的 放大比例
   */
  float scal = 1f;

  /**
   * 让原图放大 1.3倍,这个值可以随意更改.目的是让原图填充满控件
   */
  private float orgFrac = 1.3f;
  /**
   * 控件宽
   */
  private int widthSize;
  /**
   * 控件高
   */
  private int heightSize;
  private float downY;
  private float downX;


  public ScaleImage(Context context) {
    this(context, null);
  }

  public ScaleImage(Context context, AttributeSet attrs) {
    this(context, attrs, 0);
  }

  public ScaleImage(Context context, AttributeSet attrs, int defStyleAttr) {
    super(context, attrs, defStyleAttr);
  }

  @Override
  protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
    super.onMeasure(widthMeasureSpec, heightMeasureSpec);


    widthSize = MeasureSpec.getSize(widthMeasureSpec);
    heightSize = MeasureSpec.getSize(heightMeasureSpec);


  }

  @Override
  protected void onDraw(final Canvas canvas) {
    super.onDraw(canvas);


    if (background != null) {
      BitmapDrawable bd = (BitmapDrawable) background;
      final Bitmap bitmap = bd.getBitmap();


      final Matrix matrix = new Matrix();

      bitmapCopy = Bitmap.createBitmap(bitmap, 0, 0,
          bitmap.getWidth(), bitmap.getHeight(),
          matrix, true);


      /**
       * float sx, float sy, float px, float py
       *
       * sx,sy x,y方向缩放比例
       * px,py 以px py为轴心进行缩放
       * 放大比例加了默认的orgFrac.是为了在还没有开始缩放时
       * 放图片能够填充控件.如果图片过小的话,可能控件和图片
       * 之间会有边界空白
       *
       * 注意: 这里的px py :matrix作用于哪个对象上,那么px,py就是对象上的坐标点
       * 如 : 这里就是 bitmapCopy 上的px,py坐标点.
       */

      matrix.setScale(orgFrac + scal, 1, bitmapCopy.getWidth() / 2, bitmapCopy.getHeight() / 2);



      canvas.drawBitmap(bitmapCopy, matrix, null);

    }


  }

  /**
   * 开始缩放
   *
   * @param drawableId 需要放大的背景图片
   */
  public void startScale(int drawableId) {


    background = getResources().getDrawable(drawableId);
    if (background == null) {
      throw new RuntimeException("background must not null");
    } else {


      ValueAnimator animator = ValueAnimator.ofFloat(0, 1);
      animator.addUpdateListener(new ValueAnimator.AnimatorUpdateListener() {
        @Override
        public void onAnimationUpdate(ValueAnimator animation) {

          float fraction = (float) animation.getAnimatedValue();

          scal = (float) (0.5 * fraction);
          invalidate();


        }
      });

      animator.setDuration(5000);
      animator.setInterpolator(new BounceInterpolator());

      animator.start();

    }

  }

  @Override
  public boolean onTouchEvent(MotionEvent event) {

    switch (event.getAction()) {
      case MotionEvent.ACTION_DOWN:

        downY = event.getY();
        downX = event.getX();

        break;
      case MotionEvent.ACTION_UP:

        float upY = event.getY();
        float upX = event.getX();


        if (Math.abs(upY - downY) < 5 && Math.abs(upX - downX) < 5) {
          listener.backgroundClick();
        }

        break;
    }


    return true;
  }

  OnBackgroundCilckListener listener;

  /**
   * 点击事件的监听
   *
   * @param listener
   */
  public void addBackgroundCilckListener(OnBackgroundCilckListener listener) {
    this.listener = listener;
  }


  public interface OnBackgroundCilckListener {
    void backgroundClick();
  }


  }

 image = (ScaleImage) findViewById(R.id.image);

    image.startScale(R.drawable.parallax_img);

    image.addBackgroundCilckListener(new ScaleImage.OnBackgroundCilckListener() {
      @Override
      public void backgroundClick() {

      }
    });