android ScrollView 吸顶效果

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout
    xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    tools:context=".MainActivity">
    <com.yechaoa.stickscrollview.MyScrollView
        android:id="@+id/scrollView"
        android:layout_width="match_parent"
        android:layout_height="match_parent">
        <LinearLayout
            android:layout_width="match_parent"
            android:layout_height="match_parent"
            android:orientation="vertical">
            <TextView
                android:id="@+id/tv_top_view"
                android:layout_width="match_parent"
                android:layout_height="200dp"
                android:background="@color/colorPrimary"
                android:gravity="center"
                android:padding="20dp"
                android:text="内容区"
                android:textColor="#fff"
                android:textSize="20sp"/>
            <TextView
                android:layout_width="match_parent"
                android:layout_height="wrap_content"
                android:background="@color/colorAccent"
                android:gravity="center"
                android:padding="20dp"
                android:text="@string/app_name"
                android:textColor="#fff"
                android:textSize="20sp"/>
            <TextView
                android:layout_width="match_parent"
                android:layout_height="800dp"
                android:background="@color/colorPrimary"
                android:gravity="center"
                android:padding="20dp"
                android:text="内容区"
                android:textColor="#fff"
                android:textSize="20sp"/>
        </LinearLayout>
    </com.yechaoa.stickscrollview.MyScrollView>
    <TextView
        android:id="@+id/tv_stick_view"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:background="@color/colorAccent"
        android:gravity="center"
        android:padding="20dp"
        android:text="@string/app_name"
        android:textColor="#fff"
        android:textSize="20sp"
        android:visibility="gone"/>
</RelativeLayout>

        mTopView = findViewById(R.id.tv_top_view);
        mStickView = findViewById(R.id.tv_stick_view);
        MyScrollView mScrollView = findViewById(R.id.scrollView);
        mScrollView.setScrollViewListener(new MyScrollView.ScrollViewListener() {
            @Override
            public void onScrollChanged(MyScrollView scrollView, int x, int y, int oldx, int oldy) {
                if (y > mTopView.getHeight())
                    mStickView.setVisibility(View.VISIBLE);
                else
                    mStickView.setVisibility(View.GONE);
            }
        });

package com.yechaoa.stickscrollview;
import android.content.Context;
import android.util.AttributeSet;
import android.widget.ScrollView;
/**
 * Created by yechao on 2019/1/23.
 * Describe : 带滑动监听的scrollview
 */
public class MyScrollView extends ScrollView {
    public interface ScrollViewListener {
        void onScrollChanged(MyScrollView scrollView, int x, int y, int oldx, int oldy);
    }
    private ScrollViewListener scrollViewListener = null;
    public MyScrollView(Context context) {
        super(context);
    }
    public MyScrollView(Context context, AttributeSet attrs, int defStyle) {
        super(context, attrs, defStyle);
    }
    public MyScrollView(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);
        }
    }
}