好久不寫安卓相關的文章了，最近專案需要就做了一個recylerview和頂部導航欄聯動，並且導航欄要有摺疊效果，樓層效果，大體效果如下（手機錄屏，解析度不是很高）

下面來講解具體實現

一，先看佈局檔案

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout
    xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
 

    android:orientation="vertical">


    <android.support.v7.widget.RecyclerView
        android:id="@+id/rv_list"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:layout_marginTop="50dp"/>
    <com.example.qcl.demo.floorview.FloorView
 
        android:id="@+id/widget_show_all_tabs"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:background="@color/colorWhite"
        android:visibility="visible"/>
</RelativeLayout>

佈局檔案裡用到了FloorView這個自定義控制元件。

二，來看自定義控制元件FloorView

package com.example.qcl.demo.floorview;

import android.content.Context;
import android.support.annotation.Nullable;
import android.support.v7.widget.LinearSmoothScroller;
import android.support.v7.widget.RecyclerView;
import android.util.AttributeSet;
import android.util.DisplayMetrics;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.ImageView;
import android.widget.LinearLayout;
import android.widget.TextView;

import com.alibaba.android.vlayout.VirtualLayoutManager;
import com.example.qcl.demo.R;
import com.google.android.flexbox.FlexboxLayoutManager;

import java.util.ArrayList;
import java.util.List;

public
 
 class FloorView extends LinearLayout {
    private Context context;
    private View widgetView;
    private RecyclerView recyclerView;
    MyAdapter myAdapter;

    private boolean isArrowDown;
    private ImageView ivArrow;

    VirtualLayoutManager vLayoutManager;

    private int selectNum = 0;
    private List<String> listAll;
    private List<String> listFirstLine;

    public FloorView(Context context) {
        this(context, null);
    }

    public FloorView(Context context, @Nullable AttributeSet attrs) {
        this(context, attrs, -1);
    }

    public FloorView(Context context, @Nullable AttributeSet attrs, int defStyleAttr) {
        super(context, attrs, defStyleAttr);
        this.context = context;
        widgetView = inflate(context, R.layout.widget_indicator_floor_view, this);
        initRecylerView();
        initArrow();
    }

    private void initArrow() {
        ivArrow = widgetView.findViewById(R.id.iv_arrow);
        ivArrow.setOnClickListener(new OnClickListener() {
            @Override
            public void onClick(View v) {
                if (isArrowDown) {

                } else {

                }
                isArrowDown = !isArrowDown;
                setArrow(isArrowDown);
            }
        });
    }

    private void initRecylerView() {
        recyclerView = widgetView.findViewById(R.id.rv_list);
        //設定flexbox
        FlexboxLayoutManager layoutManager = new FlexboxLayoutManager(context);
        //        layoutManager.setFlexDirection(FlexDirection.ROW);
        //        layoutManager.setJustifyContent(JustifyContent.FLEX_END);
        recyclerView.setLayoutManager(layoutManager);
        myAdapter = new MyAdapter();
        recyclerView.setAdapter(myAdapter);
    }

    public void addDisplayItem(ArrayList<String> lists, int num) {
        if (lists == null) {
            return;
        }
        listAll = lists;
        myAdapter.setSelectPosition(num);

        if (lists.size() > 4) {
            listFirstLine = lists.subList(0, 4);
            ivArrow.setVisibility(View.VISIBLE);
            setArrow(true);
            myAdapter.setListData(listFirstLine);
            myAdapter.notifyDataSetChanged();
        } else {
            ivArrow.setVisibility(View.GONE);
            myAdapter.setListData(listAll);
            myAdapter.notifyDataSetChanged();
        }
    }

    //展開或者摺疊的箭頭
    public void setArrow(boolean isDown) {
        if (isDown) {
            ivArrow.setImageResource(R.drawable.arrow_down);
            myAdapter.setListData(listAll);
            myAdapter.notifyDataSetChanged();
        } else {
            ivArrow.setImageResource(R.drawable.arrow_up);
            myAdapter.setListData(listFirstLine);
            myAdapter.notifyDataSetChanged();
        }
    }

    public void setRecyclerView(RecyclerView outRecyclerView, VirtualLayoutManager
            vLayoutManager2) {
        this.vLayoutManager = vLayoutManager2;
        outRecyclerView.addOnScrollListener(new RecyclerView.OnScrollListener() {
            @Override
            public void onScrollStateChanged(RecyclerView recyclerView, int newState) {
                super.onScrollStateChanged(recyclerView, newState);
                int firstVisibleItemPosition = vLayoutManager.findFirstVisibleItemPosition();
                myAdapter.setSelectPosition((firstVisibleItemPosition / 5) % 8);
            }

            @Override
            public void onScrolled(RecyclerView recyclerView, int dx, int dy) {
                super.onScrolled(recyclerView, dx, dy);
            }
        });
    }

    public void selectPosition(int position) {
        if (vLayoutManager == null) {
            return;
        }
        LinearSmoothScroller smoothScroller = new LinearSmoothScroller
                (context) {
            @Override
            protected int getVerticalSnapPreference() {
                return LinearSmoothScroller.SNAP_TO_START;
            }

            //設定滑動1px所需時間
            @Override
            protected float calculateSpeedPerPixel
            (DisplayMetrics displayMetrics) {
                //縮短每px的滑動時間
                float MILLISECONDS_PER_INCH = getResources().getDisplayMetrics()
                        .density * 0.03f;
                return MILLISECONDS_PER_INCH / displayMetrics.density;
                //返回滑動一個pixel需要多少毫秒
            }
        };
        smoothScroller.setTargetPosition(position * 5);
        vLayoutManager.startSmoothScroll(smoothScroller);
        myAdapter.setSelectPosition(position);
    }


    /**
     * 用內部類來寫adapter
     */
    public class MyAdapter extends RecyclerView.Adapter<MyAdapter.ViewHolder> {
        private List<String> contents;

        public void setListData(List<String> lists) {
            this.contents = lists;
        }

        public void setSelectPosition(int num) {
            selectNum = num;
            notifyDataSetChanged();
        }


        //建立新View，被LayoutManager所呼叫
        @Override
        public ViewHolder onCreateViewHolder(ViewGroup viewGroup, int viewType) {
            View view = LayoutInflater.from(viewGroup.getContext()).inflate(R.layout.item_floor, viewGroup, false);
            ViewHolder vh = new ViewHolder(view);
            return vh;
        }

        //將資料與介面進行繫結的操作
        @Override
        public void onBindViewHolder(ViewHolder viewHolder, final int position) {
            viewHolder.mTextView.setText(contents.get(position));
            if (selectNum == position) {
                viewHolder.mTextView.setBackgroundResource(R.drawable.shape_show_all_indicator_rectangle_active);
                viewHolder.mTextView.setTextColor(0xff12CFC9);
            } else {
                viewHolder.mTextView.setBackgroundResource(R.drawable.shape_show_all_indicator_rectangle);
                viewHolder.mTextView.setTextColor(0xff666666);
            }
            viewHolder.mTextView.setOnClickListener(new View.OnClickListener() {
                @Override
                public void onClick(View v) {
                    setSelectPosition(position);
                    selectPosition(position);
                }
            });
        }

        //獲取資料的數量
        @Override
        public int getItemCount() {
            return contents.size();
        }

        //自定義的ViewHolder，持有每個Item的的所有介面元素
        class ViewHolder extends RecyclerView.ViewHolder {

            TextView mTextView;

            ViewHolder(View view) {
                super(view);
                mTextView = view.findViewById(R.id.tv);
            }
        }


    }

}

是不是感覺程式碼挺多的，其實原理很簡單
- 1，FlexboxLayoutManager+ RecyclerView實現流式佈局
- 2，RecyclerView的MyAdapter來實現摺疊或者展開效果

//展開或者摺疊的箭頭
    public void setArrow(boolean isDown) {
        if (isDown) {
            ivArrow.setImageResource(R.drawable.arrow_down);
            myAdapter.setListData(listAll);
            myAdapter.notifyDataSetChanged();
        } else {
            ivArrow.setImageResource(R.drawable.arrow_up);
            myAdapter.setListData(listFirstLine);
            myAdapter.notifyDataSetChanged();
        }
    }
  ```
通過往myAdapter裡傳入第一行4個數據，或者傳入全部資料來實現摺疊和展開。

####三，列表和導航欄聯動

outRecyclerView.addOnScrollListener(new RecyclerView.OnScrollListener() {
@Override
public void onScrollStateChanged(RecyclerView recyclerView, int newState) {
super.onScrollStateChanged(recyclerView, newState);
int firstVisibleItemPosition = vLayoutManager.findFirstVisibleItemPosition();
myAdapter.setSelectPosition((firstVisibleItemPosition / 5) % 8);
}

        @Override
        public void onScrolled(RecyclerView recyclerView, int dx, int dy) {
            super.onScrolled(recyclerView, dx, dy);
        }
    });

主要通過監聽RecyclerView的第一個可見條目的位置來實現導航欄的跟隨選中

####四，點選導航欄實現列表錨點

LinearSmoothScroller smoothScroller = new LinearSmoothScroller
(context) {
@Override
protected int getVerticalSnapPreference() {
return LinearSmoothScroller.SNAP_TO_START;
}

        //設定滑動1px所需時間
        @Override
        protected float calculateSpeedPerPixel
        (DisplayMetrics displayMetrics) {
            //縮短每px的滑動時間
            float MILLISECONDS_PER_INCH = getResources().getDisplayMetrics()
                    .density * 0.03f;
            return MILLISECONDS_PER_INCH / displayMetrics.density;
            //返回滑動一個pixel需要多少毫秒
        }
    };
    smoothScroller.setTargetPosition(position * 5);

“`