ScrollView的滑动渐变效果

原理：主要是在ScrollView滑动的时候，计算Y轴偏移量的值y，然后float alpha = (float) y / height(图片或视频的高度值);
mTitle.setAlpha(alpha);

1，自定义可滑动的ObservableScrollView

public class ObservableScrollView extends ScrollView {

    private ScrollViewListener scrollViewListener = null;

    public ObservableScrollView(Context context) {
        super(context);
    }
    public ObservableScrollView(Context context, AttributeSet attrs,
                                int defStyle) {
        super(context, attrs, defStyle);
    }
    public ObservableScrollView(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);
        }
    }
    public interface ScrollViewListener {
        void onScrollChanged(ScrollView scrollView, int x, int y, int oldx, int oldy);
    }
}

2,计算偏移量实现效果

mScrollView.setScrollViewListener(new ObservableScrollView.ScrollViewListener() {
            @Override
            public void onScrollChanged(ScrollView scrollView, int x, int y, int oldx, int oldy) {
                Log.e("===z","偏移量 = " + y);
                //计算偏移量
                int height = mImageView.getHeight();
                if (y <= height) {
                    float alpha = (float) y / height;
                    mTitle.setAlpha(alpha);
                } else {
                    //将标题栏的颜色设置为完全不透明状态
                    mTitle.setAlpha(1.0f);
                }
            }
        });

代码