android scrollview 滑动 改变标题栏颜色

/**
* 自定义ScrollView
* Created by Home-Pc on 2017/7/4.
*/
public class CustomScrollView extends ScrollView {
public CustomScrollView(Context context) {
super(context);
}

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

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

/**
* 重写该方法是为了处理进入页面直接显示到页面最底部，
* 重写该方法后，既可以处理完成正常加载进入页面
* @param rect
* @return
*/
@Override
protected int computeScrollDeltaToGetChildRectOnScreen(Rect rect) {
return 0;
}

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

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

private 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);
}
}

}

而其activity 用法

private void initScrollView() {
    ViewTreeObserver vto = titleViewGroup.getViewTreeObserver();
    vto.addOnGlobalLayoutListener(new ViewTreeObserver.OnGlobalLayoutListener() {
        @Override
        public void onGlobalLayout() {
            titleViewGroup.getViewTreeObserver().removeGlobalOnLayoutListener(
                    this);
            titleHeight = titleViewGroup.getHeight();
            WheatHomeScrollView.setScrollViewListener(WheatHomeActivity.this);
        }
    });
}

@Override
public void onScrollChanged(CustomScrollView scrollView, int x, int y, int oldx, int oldy) {
    // Log.i("TAG", "y--->" + y + "    height-->" + height);
    if (y <= 0) {
        titleViewGroup.setBackgroundColor(Color.argb((int) 0, 227, 29, 26));
    } else if (y > 0 && y <= titleHeight) {
        float scale = (float) y / titleHeight;
        float alpha = (255 * scale);
        // 只是layout背景透明(仿知乎滑动效果)
        titleViewGroup.setBackgroundColor(Color.argb((int) alpha, 255, 255, 255));
    } else {
        titleViewGroup.setBackgroundColor(Color.argb((int) 255, 255, 255, 255));
    }
}

该类需要实现ScrollViewListener