ListView的head消失页面导航栏的渐变出现和隐藏

1.Fragment页面xml布局：

<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"
 xmlns:ptr="http://schemas.android.com/apk/res-auto"
 tools:context=".fragment.home.HomeStoreFragment"
 >
    <com.handmark.pulltorefresh.library.PullToRefreshListView
 android:id="@+id/lv_home_store_list"
 android:layout_width="match_parent"
 android:layout_height="match_parent"
 ptr:ptrDrawable="@drawable/default_ptr_flip"
 ptr:ptrAnimationStyle="flip"
 />
    
    <LinearLayout
 android:id="@+id/ll_top_search"
 android:layout_width="match_parent"
 android:layout_height="60dp"
 android:background="@color/zuti"
 android:visibility="invisible"
 >
        <LinearLayout
 android:layout_width="match_parent"
 android:layout_height="match_parent"
 android:layout_marginLeft="15dp"
 android:layout_marginRight="15dp"
 android:layout_marginTop="8dp"
 android:layout_marginBottom="8dp"
 android:background="@drawable/shape_edit_cornor"
 android:gravity="center"
 >
            <ImageView
 android:id="@+id/iv_search_icon"
 android:layout_width="30dp"
 android:layout_height="30dp"
 android:src="@drawable/icon_navbar_search"
 android:layout_marginRight="5dp"
 />
            <EditText
 android:id="@+id/et_store_search"
 android:layout_width="wrap_content"
 android:layout_height="wrap_content"
 android:hint="输入商家或商品名"
 android:textColorHint="@color/shenhui"
 android:background="@null"
 />
        LinearLayout>
    LinearLayout>
RelativeLayout>

2.主要代码：

private boolean isFlingScroll;
private View headView;
private PullToRefreshListView lvHomeStore;

initView(){
    lvHomeStore = (PullToRefreshListView) view.findViewById(R.id.lv_home_store_list);
    lvHomeStore.setMode(PullToRefreshBase.Mode.BOTH);
    ListView listView = lvHomeStore.getRefreshableView();
    headView = initHeadView();
    AbsListView.LayoutParams layoutParams = new AbsListView.LayoutParams(AbsListView.LayoutParams.MATCH_PARENT, AbsListView.LayoutParams.WRAP_CONTENT);//这句要加上去
    headView.setLayoutParams(layoutParams);
    listView.addHeaderView(headView);
    lvHomeStore.setAdapter(adapter);
    lvHomeStore.setOnScrollListener(this);
}

@Override
    public void onScrollStateChanged(AbsListView view, int scrollState) {
        if (scrollState == SCROLL_STATE_FLING) {//手指离开手机界面，Listview还在滑动
            isFlingScroll = true;
        } else if (scrollState == SCROLL_STATE_TOUCH_SCROLL) {//手指在界面上滚动的情况
            isFlingScroll = false;
        }
    }

    @Override
    public void onScroll(AbsListView view, int firstVisibleItem, int visibleItemCount, int totalItemCount) {
        showSearchBarShow();
    }

    private void showSearchBarShow() {
        int headBottomToParentTop = headView.getHeight() + headView.getTop();
        Log.d("homeStore", "headView.getHeight(): " + headView.getHeight());
        Log.d("homeStore", "headView.getTop(): " + headView.getTop());
        Log.d("homeStore", "headBottomToParentTop: " + headBottomToParentTop);
        if (!isFlingScroll) {//手指在界面滑动的情况
            int height = layoutSearch.getHeight();
            Log.d("homeStore", "height: " + height);
            if (headBottomToParentTop > height) {
                layoutSearch.setVisibility(View.INVISIBLE);
            } else if (headBottomToParentTop <= height) {//缓慢滑动，这部分代码工作正常，快速滑动，里面的数据就跟不上节奏了。
                float alpha = (height - headBottomToParentTop) * 1f / height;
                Log.d("homeStore", "alpha: " + alpha);
                layoutSearch.setAlpha(alpha);
                layoutSearch.setVisibility(View.VISIBLE);
            }
            if (!headView.isShown()){//解决快速滑动，上部分代码不能正常工作的问题。
                layoutSearch.setAlpha(1);
                layoutSearch.setVisibility(View.VISIBLE);
            }
        } else {//手指离开，listview还在滑动，一般情况是列表快速滑动，这种情况直接设置导航栏的可见性
            if (!headView.isShown()) {
                if (!layoutSearch.isShown()){
                    layoutSearch.setVisibility(View.VISIBLE);
                    layoutSearch.setAlpha(1);
                }
            } else {
                if (layoutSearch.isShown()){
                    layoutSearch.setVisibility(View.INVISIBLE);
                }
            }
        }
    }