顶部标题栏随滑动时的渐变隐藏和渐变显示

各位早上好,话不多说,先上效果图:

注意顶部:首页TextView的变化(显示和隐藏)!

首先分析下:UI状态,其是由RecyclerView添加头部组成+RecyclerView
头部添加和RecyclerView分别引用如下:具体的分装数据的过程这里就不在说明,下篇博客会更加深入的写关于RecyclerView总添加多种不同type类型

compile 'com.bartoszlipinski.recyclerviewheader:library:1.2.1'
compile 'com.android.support:recyclerview-v7:25.3.1'

第一步:生成布局视图

<FrameLayout xmlns:android="http://schemas.android.com/apk/res/android"
             xmlns:tools="http://schemas.android.com/tools"
             android:background="#f2f2f2"
             android:layout_width="match_parent"
             android:layout_height="match_parent">
    <android.support.v7.widget.RecyclerView
        android:id="@+id/recycler"
        android:layout_width="match_parent"
        android:layout_height="match_parent"/>
    <TextView
        android:background="#ffffff"
        android:paddingTop="5dp"
        android:paddingBottom="5dp"
        android:gravity="center_horizontal"
        tools:visibility="visible"
        android:textColor="#000000"
        android:textSize="20sp"
        android:id="@+id/home_text"
        android:visibility="invisible"
        android:text="首页"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"/>
</FrameLayout>

第二步:直接上其他主要的代码,其注释很详细,不多说

public class MainActivity extends AppCompatActivity {

    private TextView mTextView;
    private int mTextViewHeight;
    private RecyclerView mRecyclerView;
    private RecyclerViewHeader mRecyclerViewHeader;
    //头部图片(轮播图的高度)
    private int mRecyclerHeaderBannerHeight;
    //头部的高度
    private int mRecyclerHeaderHeight;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        mTextView = (TextView) findViewById(R.id.home_text);
        //recyclerView填充数据(忽略不计)
        initData();
        mRecyclerView = (RecyclerView) findViewById(R.id.recycler);
        mRecyclerView.setLayoutManager(new LinearLayoutManager(this));
        mRecyclerView.setAdapter(mAdapter);
        //获取到文本的高度
        mTextViewHeight = mTextView.getHeight();

        //轮播图片的高度--和xml图片的高度是一样的
        mRecyclerHeaderBannerHeight = (int) getResources().getDimension(R.dimen.home_page_banner_height);
        //RecyclerView每个Item之间的距离,和Adapter中设置的距离一样
        final int recyclerItemHeight = (int) getResources().getDimension(R.dimen.home_page_list_item_margin_top);

        //添加头部视图,其布局文件就忽略
        mRecyclerViewHeader = RecyclerViewHeader.fromXml(this, R.layout.list_item_prime_product_header);

        //设置其滑动事件
        mRecyclerView.addOnScrollListener(new RecyclerView.OnScrollListener() {
            @Override
            public void onScrolled(RecyclerView recyclerView, int dx, int dy) {
                //设置其透明度
                float alpha = 0;
                int scollYHeight = getScollYHeight(true, mRecyclerHeaderHeight);
                //起始截止变化高度,如可以变化高度为mRecyclerHeaderHeight
                int baseHeight = mRecyclerHeaderBannerHeight - recyclerItemHeight - mTextViewHeight;
                if(scollYHeight >= baseHeight) {
                    //完全不透明
                    alpha = 1;
                }else {
                //产生渐变效果
                    alpha = scollYHeight / (baseHeight*1.0f);
                }
                mTextView.setAlpha(alpha);
                super.onScrolled(recyclerView, dx, dy);
            }
        });
        //将头部视图添加到RecyclerView中
        mRecyclerViewHeader.attachTo(mRecyclerView);
        //第一次进来其状态显示
        mRecyclerViewHeader.post(new Runnable() {
            @Override
            public void run() {
                mRecyclerHeaderHeight =  mRecyclerViewHeader.getHeight();
                mTextViewHeight = mTextView.getHeight();
                mTextView.setVisibility(View.VISIBLE);
                mTextView.setAlpha(0);
            }
        });
    }

第三步:获取其滑动的距离

/**
     * 计算RecyclerView滑动的距离
     * @param hasHead 是否有头部
     * @param headerHeight RecyclerView的头部高度
     * @return 滑动的距离
     */
    private int getScollYHeight(boolean hasHead, int headerHeight) {
        LinearLayoutManager layoutManager = (LinearLayoutManager) mRecyclerView.getLayoutManager();
        //获取到第一个可见的position,其添加的头部不算其position当中
        int position = layoutManager.findFirstVisibleItemPosition();
        //通过position获取其管理器中的视图
        View firstVisiableChildView = layoutManager.findViewByPosition(position);
        //获取自身的高度
        int itemHeight = firstVisiableChildView.getHeight();
        //有头部
        if(hasHead) {
            return headerHeight + itemHeight*position - firstVisiableChildView.getTop();
        }else {
            return itemHeight*position - firstVisiableChildView.getTop();
        }
    }

以上:就可以实现其效果!