Android 滑动改变头部透明度

ScrollView 自定义滑动监听

public class MyScrollView extends ScrollView {  
  
    private OnScrollistener onScrollistener;  
  
    public OnScrollistener getOnScrollistener() {  
        return onScrollistener;  
    }  
  
    public void setOnScrollistener(OnScrollistener onScrollistener) {  
        this.onScrollistener = onScrollistener;  
    }  
  
    public MyScrollView(Context context, AttributeSet attrs, int defStyle) {  
        super(context, attrs, defStyle);  
    }  
  
    public MyScrollView(Context context, AttributeSet attrs) {  
        super(context, attrs);  
    }  
  
    public MyScrollView(Context context) {  
        super(context);  
    }  
  
    public interface OnScrollistener {  
        void onScroll(int startY, int endY);  
    }  
  
    @Override  
    protected void onScrollChanged(int l, int t, int oldl, int oldt) {  
        onScrollistener.onScroll(oldt, t);  
        super.onScrollChanged(l, t, oldl, oldt);  
    }  
} 

调用

mLevelPrivilege.setOnScrollistener(new MyScrollView.OnScrollistener() {  
     @Override  
     public void onScroll(int startY, int endY) {  
          //根据scrollview滑动更改标题栏透明度  
          dynamicChangeAphla(startY, endY);  
     }  
});  

透明度设置

   /** 
    * 根据内容窗体的移动改变标题栏背景透明度 
    * 
    * @param startY scrollview开始滑动的y坐标（相对值） 
    * @param endY   scrollview结束滑动的y坐标（相对值） 
    */  
   private void dynamicChangeAphla(int startY, int endY) {  
       //获取标题高度  
       int titleHeight = llayoutLevelTitle.getMeasuredHeight();  
       //获取背景高度  
       int backHeight = rlayoutLevelTitle.getMeasuredHeight();  
  
       //获取控件的绝对位置坐标  
       int[] location = new int[2];  
       rlayoutLevelTitle.getLocationInWindow(location);  
       //从屏幕顶部到控件顶部的坐标位置Y  
       int currentY = location[1];  
       //表示回到原位（滑动到顶部）  
       if (currentY >= 0) {  
           llayoutLevelTitle.getBackground().mutate().setAlpha(0);  
       }  
  
     DevUtil.e("zpan","=titleHeight=" + titleHeight + "=backHeight=" + backHeight + "=currentY="+currentY);  
       //颜色透明度改变  
       if (currentY < titleHeight && currentY >= - (backHeight - titleHeight)) {  
           //计算出滚动过程中改变的透明值  
           double y = Math.abs(currentY) * 1.0;  
           double height = (backHeight - titleHeight) * 1.0;  
           int changeValue = (int) (y / height * 255);  
  
           DevUtil.e("zpan", "changeValue=" + changeValue);  
           //判断是向上还是向下  
           if (endY > startY) {//向上;透明度值增加，实际透明度减小  
               llayoutLevelTitle.getBackground().mutate().setAlpha(changeValue);  
           } else if (endY < startY) {//向下；透明度值减小，实际透明度增加  
               llayoutLevelTitle.getBackground().mutate().setAlpha(changeValue);  
           }  
       }  
       //红色背景移除屏幕  
       if (currentY < -(backHeight - titleHeight)) {  
           llayoutLevelTitle.getBackground().mutate().setAlpha(255);  
       }  
   } 

备注：代码比较完整，关键位置都有注释，就不做过多的解释。