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() {      }    });