Android仿京东搜索框渐变效果

//自定义ScrollView
public class CustomView extends ScrollView {

 public interface ScrollViewListener {
 void onScrollChanged(CustomView customView, int x, int y, int oldx, int oldy);
 }

 private ScrollViewListener scrollViewListener = null;

 public CustomView(Context context) {
 super(context);
 }

 public CustomView(Context context, AttributeSet attrs,
   int defStyle) {
 super(context, attrs, defStyle);
 }

 public CustomView(Context context, AttributeSet attrs) {
 super(context, attrs);
 }

 public void setScrollViewListener(ScrollViewListener scrollViewListener) {
 this.scrollViewListener = scrollViewListener;
 }

 @Override
 protected void onScrollChanged(int x, int y, int oldx, int oldy) {
 super.onScrollChanged(x, y, oldx, oldy);
 if (scrollViewListener != null) {
  scrollViewListener.onScrollChanged(this, x, y, oldx, oldy);
 }
 }
}

 @Override
 public void onViewCreated(View view, @Nullable Bundle savedInstanceState) {
 super.onViewCreated(view, savedInstanceState);
 //搜索框在布局最上面
 line.bringToFront();
 mScrollview.setScrollViewListener(new CustomView.ScrollViewListener() {
  @Override
  public void onScrollChanged(CustomView customView, int x, int y, int oldx, int oldy) {
  if (y <= 0) {
   line.setBackgroundColor(Color.argb((int) 0, 227, 29, 26));//AGB由相关工具获得，或者美工提供
  } else if (y > 0 && y <= imageHeight) {
   //获取ScrollView向下滑动图片消失的比例
   float scale = (float) y / imageHeight;
   //更加这个比例,让标题颜色由浅入深
   float alpha = (255 * scale);
   // 只是layout背景透明
   line.setBackgroundColor(Color.argb((int) alpha, 255, 255, 255));
  }
  }
 });