Android 背景图片的缩放实现

Android 背景图片的缩放

 ONE Goal ,ONE Passion !

我们看到一些效果,控件中的背景图片会慢慢变大,但是控件不会随着图片的放大而变大.效果如下:

分析:

想让图片变大,而且控件本身大小不能改变,那么就要改变图片自身大小,而不能改变控件大小.

实现原理:

1,首先拿到我们要放大的图片bitmap.

2,使用Bitmap.createBitmap().创建一个bitmap的副本.

3,使用matrix去改变图片副本本身大小

4,使用ValueAnimator去根据变化率将副本绘制出来.

自定义View

 public class ScaleImage extends View {
  
  private Drawable background;
  
  private Bitmap bitmapCopy;
  
  float scal = 1f;
  
  private float orgFrac = 1.3f;
  
  private int widthSize;
  
  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);
      
      matrix.setScale(orgFrac + scal, 1, bitmapCopy.getWidth() / 2, bitmapCopy.getHeight() / 2);
      canvas.drawBitmap(bitmapCopy, matrix, null);
    }
  }
  
  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;
  
  public void addBackgroundCilckListener(OnBackgroundCilckListener listener) {
    this.listener = listener;
  }
  public interface OnBackgroundCilckListener {
    void backgroundClick();
  }
  }

跑起来

 image = (ScaleImage) findViewById(R.id.image);
    image.startScale(R.drawable.parallax_img);
    image.addBackgroundCilckListener(new ScaleImage.OnBackgroundCilckListener() {
      @Override
      public void backgroundClick() {
      }
    });

小提琴家

matrix使用待续

好了.直接使用控件,我们将资源文件中的Drawable传入就可以了.

感谢阅读，希望能帮助到大家，谢谢大家对本站的支持！

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