Android -- RecyclerView实现顶部吸附效果

1，先来看一下今天实现的效果：

2,这次的效果是使用ItemDecoration来实践的，来看一看我们的实现吧

　　第一步：首先添加依赖，由于我们这些数据是请求网络的，所以一下我们添加网络框架依赖、RecyclerView、Glide依赖

apply plugin: 'com.android.application'

apply plugin: 'com.neenbedankt.android-apt'

android {

    compileSdkVersion 25

    buildToolsVersion "25.0.2"

    defaultConfig {

        applicationId "com.qianmo.stickyitemdecoration"

        minSdkVersion 15

        targetSdkVersion 25

        versionCode 1

        versionName "1.0"

        testInstrumentationRunner "android.support.test.runner.AndroidJUnitRunner"

    }

    buildTypes {

        release {

            minifyEnabled false

            proguardFiles getDefaultProguardFile('proguard-android.txt'), 'proguard-rules.pro'

        }

    }

}

dependencies {

    compile fileTree(dir: 'libs', include: ['*.jar'])

    androidTestCompile('com.android.support.test.espresso:espresso-core:2.2.2', {

        exclude group: 'com.android.support', module: 'support-annotations'

    })

    compile 'com.android.support:appcompat-v7:25.1.1'

    //添加reccycleview

    compile 'com.android.support:recyclerview-v7:25.1.1'

    //添加glide，需要依赖V4包

    compile 'com.github.bumptech.glide:glide:3.7.0'

    compile 'com.android.support:support-v4:25.1.1'

    //添加水波纹效果

    compile 'com.balysv:material-ripple:1.0.2'

    //添加butter注解

    compile 'com.jakewharton:butterknife:8.2.1'

    apt 'com.jakewharton:butterknife-compiler:8.2.1'

    //添加网络框架

    compile 'io.reactivex:rxjava:1.1.0'

    compile 'io.reactivex:rxandroid:1.1.0'

    compile 'com.squareup.retrofit2:retrofit:2.0.0-beta4'

    compile 'com.squareup.retrofit2:converter-gson:2.0.0-beta4'

    compile 'com.squareup.retrofit2:adapter-rxjava:2.0.0-beta4'

    compile 'com.google.code.gson:gson:2.6.2'

    testCompile 'junit:junit:4.12'

}

　　第二步：主界面的xml文件就只是一个简单的RecyclerView控件，首先来实例化我们的RecyclerView

recyclerView = (RecyclerView) findViewById(R.id.recyclerView);

　　第三步：获取网络请求数据，首先我们要创建MovieServiceApi接口，并使用GET请求访问目标接口

　　请求地址

http://api.meituan.com/mmdb/movie/v2/list/rt/order/coming.json?ci=1&limit=12&token=&__vhost=api.maoyan.com&utm_campaign=AmovieBmovieCD-1&movieBundleVersion=6801&utm_source=xiaomi&utm_medium=android&utm_term=6.8.0&utm_content=868030022327462&net=255&dModel=MI%205&uuid=0894DE03C76F6045D55977B6D4E32B7F3C6AAB02F9CEA042987B380EC5687C43&lat=40.100673&lng=116.378619&__skck=6a375bce8c66a0dc293860dfa83833ef&__skts=1463704714271&__skua=7e01cf8dd30a179800a7a93979b430b2&__skno=1a0b4a9b-44ec-42fc-b110-ead68bcc2824&__skcy=sXcDKbGi20CGXQPPZvhCU3%2FkzdE%3D

　　MovieServiceApi.java

package com.qianmo.stickyitemdecoration.api;

import com.qianmo.stickyitemdecoration.base.BaseResponse;

import com.qianmo.stickyitemdecoration.bean.MovieBean;

import retrofit2.http.GET;

import rx.Observable;

/**

 * Created by wangjitao on 2017/3/3 0003.

 * E-Mail：543441727@qq.com

 * 电影网API

 */

public interface MovieApiService {

    @GET("v2/list/rt/order/coming.json?ci=1&limit=12&token=&__vhost=api.maoyan.com&utm_campaign=AmovieBmovieCD-1&movieBundleVersion=6801&utm_source=xiaomi&utm_medium=android&utm_term=6.8.0&utm_content=868030022327462&net=255&dModel=MI%205&uuid=0894DE03C76F6045D55977B6D4E32B7F3C6AAB02F9CEA042987B380EC5687C43&lat=40.100673&lng=116.378619&__skck=6a375bce8c66a0dc293860dfa83833ef&__skts=1463704714271&__skua=7e01cf8dd30a179800a7a93979b430b2&__skno=1a0b4a9b-44ec-42fc-b110-ead68bcc2824&__skcy=sXcDKbGi20CGXQPPZvhCU3%2FkzdE%3D")

    Observable<BaseResponse<MovieBean>> getMovieDatas();

}

　　创建数据接口响应的Bean

　　BaseResponse.java

package com.qianmo.stickyitemdecoration.base;

/**

 * Created by wangjitao on 2017/3/3 0003.

 * E-Mail：543441727@qq.com

 * 数据返回体的基本接收类,由于本次接口没有code和message

 */

public class BaseResponse<T> {

    //    private int code;

//    private String message;

    private T data;

//    public String getMessage() {

//        return message;

//    }

//

//    public void setMessage(String message) {

//        this.message = message;

//    }

//

//    public int getCode() {

//        return code;

//    }

//

//    public void setCode(int code) {

//        this.code = code;

//    }

    public T getData() {

        return data;

    }

    public void setData(T data) {

        this.data = data;

    }

}

　　MovieBean.java

package com.qianmo.stickyitemdecoration.bean;

import java.util.List;

/**

 * Created by wangjitao on 2017/3/3 0003.

 * E-Mail：543441727@qq.com

 * 用于数据接收实体类

 */

public class MovieBean {

    private List<ComingBean> coming ;

    public List<ComingBean> getComing() {

        return coming;

    }

    public void setComing(List<ComingBean> coming) {

        this.coming = coming;

    }

}

　　ComingBean.java

package com.qianmo.stickyitemdecoration.bean;

import java.util.List;

/**

 * Created by Administrator on 2017/3/3 0003.

 * E-Mail：543441727@qq.com

 */

public class ComingBean {

    /**

     * boxInfo : 喵，即将上映

     * cat : 动作,科幻

     * civilPubSt : 0

     * comingTitle : 3月10日 周五

     * desc : 主演:亚伦·保尔,肖恩·宾,琳娜·海蒂

     * dir : 野末武志

     * dur : 116

     * effectShowNum : 0

     * fra : 日本

     * frt : 2016-08-19

     * globalReleased : false

     * headLineShow : false

     * headLinesVO : []

     * id : 346383

     * img : http://p0.meituan.net/w.h/movie/5be09f397d474988afaf930ac5346243715496.png

     * late : false

     * localPubSt : 0

     * mk : 0

     * nm : 最终幻想15：王者之剑

     * pn : 98

     * preShow : false

     * proScore : 0

     * proScoreNum : 0

     * pubDate : 1489075200000

     * pubDesc : 2017-03-10大陆上映

     * pubShowNum : 0

     * recentShowDate : 0

     * recentShowNum : 0

     * rt : 2017-03-10

     * sc : 0

     * scm : 法力渐微弱，勇士卫祖国

     * showCinemaNum : 0

     * showInfo : 2017-03-10 下周五上映

     * showNum : 0

     * showst : 4

     * snum : 903

     * star : 亚伦·保尔,肖恩·宾,琳娜·海蒂

     * ver : 2D

     * videoId : 83711

     * videoName : 魔法机械版预告片

     * videourl : http://maoyan.meituan.net/movie/videos/854x480df7f69dd367b4dd5829c98d1a5a07dfa.mp4

     * vnum : 9

     * weight : 1

     * wish : 22799

     * wishst : 0

     */

    private String boxInfo;

    private String cat;

    private int civilPubSt;

    private String comingTitle;

    private String desc;

    private String dir;

    private int dur;

    private int effectShowNum;

    private String fra;

    private String frt;

    private boolean globalReleased;

    private boolean headLineShow;

    private int id;

    private String img;

    private boolean late;

    private int localPubSt;

    private int mk;

    private String nm;

    private int pn;

    private boolean preShow;

    private int proScore;

    private int proScoreNum;

    private long pubDate;

    private String pubDesc;

    private int pubShowNum;

    private int recentShowDate;

    private int recentShowNum;

    private String rt;

    private int sc;

    private String scm;

    private int showCinemaNum;

    private String showInfo;

    private int showNum;

    private int showst;

    private int snum;

    private String star;

    private String ver;

    private int videoId;

    private String videoName;

    private String videourl;

    private int vnum;

    private int weight;

    private int wish;

    private int wishst;

    private List<?> headLinesVO;

    public String getBoxInfo() {

        return boxInfo;

    }

    public void setBoxInfo(String boxInfo) {

        this.boxInfo = boxInfo;

    }

    public String getCat() {

        return cat;

    }

    public void setCat(String cat) {

        this.cat = cat;

    }

    public int getCivilPubSt() {

        return civilPubSt;

    }

    public void setCivilPubSt(int civilPubSt) {

        this.civilPubSt = civilPubSt;

    }

    public String getComingTitle() {

        return comingTitle;

    }

    public void setComingTitle(String comingTitle) {

        this.comingTitle = comingTitle;

    }

    public String getDesc() {

        return desc;

    }

    public void setDesc(String desc) {

        this.desc = desc;

    }

    public String getDir() {

        return dir;

    }

    public void setDir(String dir) {

        this.dir = dir;

    }

    public int getDur() {

        return dur;

    }

    public void setDur(int dur) {

        this.dur = dur;

    }

    public int getEffectShowNum() {

        return effectShowNum;

    }

    public void setEffectShowNum(int effectShowNum) {

        this.effectShowNum = effectShowNum;

    }

    public String getFra() {

        return fra;

    }

    public void setFra(String fra) {

        this.fra = fra;

    }

    public String getFrt() {

        return frt;

    }

    public void setFrt(String frt) {

        this.frt = frt;

    }

    public boolean isGlobalReleased() {

        return globalReleased;

    }

    public void setGlobalReleased(boolean globalReleased) {

        this.globalReleased = globalReleased;

    }

    public boolean isHeadLineShow() {

        return headLineShow;

    }

    public void setHeadLineShow(boolean headLineShow) {

        this.headLineShow = headLineShow;

    }

    public int getId() {

        return id;

    }

    public void setId(int id) {

        this.id = id;

    }

    public String getImg() {

        return img;

    }

    public void setImg(String img) {

        this.img = img;

    }

    public boolean isLate() {

        return late;

    }

    public void setLate(boolean late) {

        this.late = late;

    }

    public int getLocalPubSt() {

        return localPubSt;

    }

    public void setLocalPubSt(int localPubSt) {

        this.localPubSt = localPubSt;

    }

    public int getMk() {

        return mk;

    }

    public void setMk(int mk) {

        this.mk = mk;

    }

    public String getNm() {

        return nm;

    }

    public void setNm(String nm) {

        this.nm = nm;

    }

    public int getPn() {

        return pn;

    }

    public void setPn(int pn) {

        this.pn = pn;

    }

    public boolean isPreShow() {

        return preShow;

    }

    public void setPreShow(boolean preShow) {

        this.preShow = preShow;

    }

    public int getProScore() {

        return proScore;

    }

    public void setProScore(int proScore) {

        this.proScore = proScore;

    }

    public int getProScoreNum() {

        return proScoreNum;

    }

    public void setProScoreNum(int proScoreNum) {

        this.proScoreNum = proScoreNum;

    }

    public long getPubDate() {

        return pubDate;

    }

    public void setPubDate(long pubDate) {

        this.pubDate = pubDate;

    }

    public String getPubDesc() {

        return pubDesc;

    }

    public void setPubDesc(String pubDesc) {

        this.pubDesc = pubDesc;

    }

    public int getPubShowNum() {

        return pubShowNum;

    }

    public void setPubShowNum(int pubShowNum) {

        this.pubShowNum = pubShowNum;

    }

    public int getRecentShowDate() {

        return recentShowDate;

    }

    public void setRecentShowDate(int recentShowDate) {

        this.recentShowDate = recentShowDate;

    }

    public int getRecentShowNum() {

        return recentShowNum;

    }

    public void setRecentShowNum(int recentShowNum) {

        this.recentShowNum = recentShowNum;

    }

    public String getRt() {

        return rt;

    }

    public void setRt(String rt) {

        this.rt = rt;

    }

    public int getSc() {

        return sc;

    }

    public void setSc(int sc) {

        this.sc = sc;

    }

    public String getScm() {

        return scm;

    }

    public void setScm(String scm) {

        this.scm = scm;

    }

    public int getShowCinemaNum() {

        return showCinemaNum;

    }

    public void setShowCinemaNum(int showCinemaNum) {

        this.showCinemaNum = showCinemaNum;

    }

    public String getShowInfo() {

        return showInfo;

    }

    public void setShowInfo(String showInfo) {

        this.showInfo = showInfo;

    }

    public int getShowNum() {

        return showNum;

    }

    public void setShowNum(int showNum) {

        this.showNum = showNum;

    }

    public int getShowst() {

        return showst;

    }

    public void setShowst(int showst) {

        this.showst = showst;

    }

    public int getSnum() {

        return snum;

    }

    public void setSnum(int snum) {

        this.snum = snum;

    }

    public String getStar() {

        return star;

    }

    public void setStar(String star) {

        this.star = star;

    }

    public String getVer() {

        return ver;

    }

    public void setVer(String ver) {

        this.ver = ver;

    }

    public int getVideoId() {

        return videoId;

    }

    public void setVideoId(int videoId) {

        this.videoId = videoId;

    }

    public String getVideoName() {

        return videoName;

    }

    public void setVideoName(String videoName) {

        this.videoName = videoName;

    }

    public String getVideourl() {

        return videourl;

    }

    public void setVideourl(String videourl) {

        this.videourl = videourl;

    }

    public int getVnum() {

        return vnum;

    }

    public void setVnum(int vnum) {

        this.vnum = vnum;

    }

    public int getWeight() {

        return weight;

    }

    public void setWeight(int weight) {

        this.weight = weight;

    }

    public int getWish() {

        return wish;

    }

    public void setWish(int wish) {

        this.wish = wish;

    }

    public int getWishst() {

        return wishst;

    }

    public void setWishst(int wishst) {

        this.wishst = wishst;

    }

    public List<?> getHeadLinesVO() {

        return headLinesVO;

    }

    public void setHeadLinesVO(List<?> headLinesVO) {

        this.headLinesVO = headLinesVO;

    }

}

　　第四部：创建适配器

　　MyAdapter.java

package com.qianmo.stickyitemdecoration.adapter;

import android.content.Context;

import android.support.v7.widget.RecyclerView;

import android.view.LayoutInflater;

import android.view.View;

import android.view.ViewGroup;

import android.widget.ImageView;

import android.widget.TextView;

import com.bumptech.glide.Glide;

import com.qianmo.stickyitemdecoration.R;

import com.qianmo.stickyitemdecoration.bean.ComingBean;

import java.util.List;

import static java.lang.System.load;

/**

 * Created by Administrator on 2017/3/3 0003.

 * E-Mail：543441727@qq.com

 */

public class MyAdapter extends RecyclerView.Adapter<MyAdapter.ViewHolder> {

    private Context context;

    private List<ComingBean> datas;

    public MyAdapter(Context context, List<ComingBean> datas) {

        this.context = context;

        this.datas = datas;

    }

    @Override

    public ViewHolder onCreateViewHolder(ViewGroup parent, int viewType) {

        View view = LayoutInflater.from(context).inflate(R.layout.item_recyclerview, parent, false);

        return new ViewHolder(view);

    }

    @Override

    public void onBindViewHolder(final ViewHolder holder, int position) {

        String imagUrl = datas.get(position).getImg();

        String newImagUrl = imagUrl.replaceAll("w.h", "50.80");

        Glide

                .with(context)

                .load(newImagUrl)

                .error(R.mipmap.ic_launcher)

                .into(holder.img);

        holder.tv_time.setText(datas.get(position).getPubDesc());

        holder.tv_title.setText(datas.get(position).getNm());

        holder.tv_introduce.setText(datas.get(position).getDesc());

        holder.tv_score_major_real.setText(datas.get(position).getDur()+"");

        holder.tv_score_people_real.setText(datas.get(position).getPn()+"");

    }

    @Override

    public int getItemCount() {

        return datas == null ? 0 : datas.size();

    }

    class ViewHolder extends RecyclerView.ViewHolder {

        ImageView img;

        TextView tv_title;

        TextView tv_introduce;

        TextView tv_score_major_real;

        TextView tv_score_people_real;

        TextView tv_time;

        public ViewHolder(View view) {

            super(view);

            img = (ImageView) view.findViewById(R.id.img);

            tv_title = (TextView) view.findViewById(R.id.tv_title);

            tv_introduce = (TextView) view.findViewById(R.id.tv_introduce);

            tv_score_major_real = (TextView) view.findViewById(R.id.tv_score_major_real);

            tv_score_people_real = (TextView) view.findViewById(R.id.tv_score_people_real);

            tv_time = (TextView) view.findViewById(R.id.tv_time);

        }

    }

}

　　第五步：自定义ItemDecoration，使头部悬浮，具体思路代码中有了，就不在分析了

　　FloatingItemDecoration.java

package com.qianmo.stickyitemdecoration.view;

import android.content.Context;

import android.content.res.TypedArray;

import android.graphics.Canvas;

import android.graphics.Color;

import android.graphics.Paint;

import android.graphics.Rect;

import android.graphics.drawable.ColorDrawable;

import android.graphics.drawable.Drawable;

import android.support.annotation.ColorInt;

import android.support.annotation.Dimension;

import android.support.annotation.DrawableRes;

import android.support.v4.content.ContextCompat;

import android.support.v7.widget.LinearLayoutManager;

import android.support.v7.widget.RecyclerView;

import android.text.TextUtils;

import android.util.TypedValue;

import android.view.View;

import java.util.HashMap;

import java.util.Map;

/**

 * Created by Administrator on 2017/3/3 0003.

 * E-Mail：543441727@qq.com

 */

public class FloatingItemDecoration extends RecyclerView.ItemDecoration {

    private static final String TAG = "FloatingItemDecoration";

    private static final int[] ATTRS = new int[]{android.R.attr.listDivider};

    private Drawable mDivider;

    private int dividerHeight;

    private int dividerWidth;

    private Map<Integer, String> keys = new HashMap<>();

    private int mTitleHeight;

    private Paint mTextPaint;

    private Paint mBackgroundPaint;

    private float mTextHeight;

    private float mTextBaselineOffset;

    private Context mContext;

    /**

     * 滚动列表的时候是否一直显示悬浮头部

     */

    private boolean showFloatingHeaderOnScrolling = true;

    public FloatingItemDecoration(Context context) {

        final TypedArray a = context.obtainStyledAttributes(ATTRS);

        mDivider = a.getDrawable(0);

        a.recycle();

        this.dividerHeight = mDivider.getIntrinsicHeight();

        this.dividerWidth = mDivider.getIntrinsicWidth();

        init(context);

    }

    /**

     * 自定义分割线

     *

     * @param context

     * @param drawableId 分割线图片

     */

    public FloatingItemDecoration(Context context, @DrawableRes int drawableId) {

        mDivider = ContextCompat.getDrawable(context, drawableId);

        this.dividerHeight = mDivider.getIntrinsicHeight();

        this.dividerWidth = mDivider.getIntrinsicWidth();

        init(context);

    }

    /**

     * 自定义分割线

     * 也可以使用{@link Canvas#drawRect(float, float, float, float, Paint)}或者{@link Canvas#drawText(String, float, float, Paint)}等等

     * 结合{@link Paint}去绘制各式各样的分割线

     *

     * @param context

     * @param color         整型颜色值，非资源id

     * @param dividerWidth  单位为dp

     * @param dividerHeight 单位为dp

     */

    public FloatingItemDecoration(Context context, @ColorInt int color, @Dimension float dividerWidth, @Dimension float dividerHeight) {

        mDivider = new ColorDrawable(color);

        this.dividerWidth = (int) TypedValue.applyDimension(TypedValue.COMPLEX_UNIT_DIP, dividerWidth, context.getResources().getDisplayMetrics());

        this.dividerHeight = (int) TypedValue.applyDimension(TypedValue.COMPLEX_UNIT_DIP, dividerHeight, context.getResources().getDisplayMetrics());

        init(context);

    }

    private void init(Context mContext) {

        this.mContext = mContext;

        mTextPaint = new Paint();

        mTextPaint.setAntiAlias(true);

        mTextPaint.setTextSize(TypedValue.applyDimension(TypedValue.COMPLEX_UNIT_SP, 16, mContext.getResources().getDisplayMetrics()));

        mTextPaint.setColor(Color.WHITE);

        Paint.FontMetrics fm = mTextPaint.getFontMetrics();

        mTextHeight = fm.bottom - fm.top;//计算文字高度

        mTextBaselineOffset = fm.bottom;

        mBackgroundPaint = new Paint();

        mBackgroundPaint.setAntiAlias(true);

        mBackgroundPaint.setColor(Color.MAGENTA);

    }

    @Override

    public void onDraw(Canvas c, RecyclerView parent, RecyclerView.State state) {

        super.onDraw(c, parent, state);

        drawVertical(c, parent);

    }

    @Override

    public void onDrawOver(Canvas c, RecyclerView parent, RecyclerView.State state) {

        super.onDrawOver(c, parent, state);

        if (!showFloatingHeaderOnScrolling) {

            return;

        }

        int firstVisiblePos = ((LinearLayoutManager) parent.getLayoutManager()).findFirstVisibleItemPosition();

        if (firstVisiblePos == RecyclerView.NO_POSITION) {

            return;

        }

        String title = getTitle(firstVisiblePos);

        if (TextUtils.isEmpty(title)) {

            return;

        }

        boolean flag = false;

        if (getTitle(firstVisiblePos + 1) != null && !title.equals(getTitle(firstVisiblePos + 1))) {

            //说明是当前组最后一个元素，但不一定碰撞了

//            Log.e(TAG, "onDrawOver: "+"==============" +firstVisiblePos);

            View child = parent.findViewHolderForAdapterPosition(firstVisiblePos).itemView;

            if (child.getTop() + child.getMeasuredHeight() < mTitleHeight) {

                //进一步检测碰撞

//                Log.e(TAG, "onDrawOver: "+child.getTop()+"$"+firstVisiblePos );

                c.save();//保存画布当前的状态

                flag = true;

                c.translate(0, child.getTop() + child.getMeasuredHeight() - mTitleHeight);//负的代表向上

            }

        }

        int left = parent.getPaddingLeft();

        int right = parent.getWidth() - parent.getPaddingRight();

        int top = parent.getPaddingTop();

        int bottom = top + mTitleHeight;

        c.drawRect(left, top, right, bottom, mBackgroundPaint);

        float x = TypedValue.applyDimension(TypedValue.COMPLEX_UNIT_DIP, 10, mContext.getResources().getDisplayMetrics());

        float y = bottom - (mTitleHeight - mTextHeight) / 2 - mTextBaselineOffset;//计算文字baseLine

        c.drawText(title, x, y, mTextPaint);

        if (flag) {

            //还原画布为初始状态

            c.restore();

        }

    }

    @Override

    public void getItemOffsets(Rect outRect, View view, RecyclerView parent, RecyclerView.State state) {

        super.getItemOffsets(outRect, view, parent, state);

        int pos = parent.getChildViewHolder(view).getAdapterPosition();

        if (keys.containsKey(pos)) {//留出头部偏移

            outRect.set(0, mTitleHeight, 0, 0);

        } else {

            outRect.set(0, dividerHeight, 0, 0);

        }

    }

    /**

     * *如果该位置没有，则往前循环去查找标题，找到说明该位置属于该分组

     *

     * @param position

     * @return

     */

    private String getTitle(int position) {

        while (position >= 0) {

            if (keys.containsKey(position)) {

                return keys.get(position);

            }

            position--;

        }

        return null;

    }

    private void drawVertical(Canvas c, RecyclerView parent) {

        int left = parent.getPaddingLeft();

        int right = parent.getWidth() - parent.getPaddingRight();

        int top = 0;

        int bottom = 0;

        for (int i = 0; i < parent.getChildCount(); i++) {

            View child = parent.getChildAt(i);

            final RecyclerView.LayoutParams params = (RecyclerView.LayoutParams) child.getLayoutParams();

            if (!keys.containsKey(params.getViewLayoutPosition())) {

                //画普通分割线

                top = child.getTop() - params.topMargin - dividerHeight;

                bottom = top + dividerHeight;

                mDivider.setBounds(left, top, right, bottom);

                mDivider.draw(c);

            } else {

                //画头部

                top = child.getTop() - params.topMargin - mTitleHeight;

                bottom = top + mTitleHeight;

                c.drawRect(left, top, right, bottom, mBackgroundPaint);

//                float x=child.getPaddingLeft()+params.leftMargin;

                float x = TypedValue.applyDimension(TypedValue.COMPLEX_UNIT_DIP, 10, mContext.getResources().getDisplayMetrics());

                float y = bottom - (mTitleHeight - mTextHeight) / 2 - mTextBaselineOffset;//计算文字baseLine

//                Log.e(TAG, "drawVertical: "+bottom );

                c.drawText(keys.get(params.getViewLayoutPosition()), x, y, mTextPaint);

            }

        }

    }

    public void setShowFloatingHeaderOnScrolling(boolean showFloatingHeaderOnScrolling) {

        this.showFloatingHeaderOnScrolling = showFloatingHeaderOnScrolling;

    }

    public void setKeys(Map<Integer, String> keys) {

        this.keys.clear();

        this.keys.putAll(keys);

    }

    public void setmTitleHeight(int titleHeight) {

        this.mTitleHeight = titleHeight;

    }

}

　　第六步：设置ItemDecoration，设置适配器

 final FloatingItemDecoration floatingItemDecoration=new FloatingItemDecoration(this, Color.GRAY,1,1);

        floatingItemDecoration.setKeys(keys);

        floatingItemDecoration.setmTitleHeight((int) TypedValue.applyDimension(TypedValue.COMPLEX_UNIT_DIP,50,getResources().getDisplayMetrics()));

        recycleview.addItemDecoration(floatingItemDecoration);

        adapter = new MyAdapter(mContext, datas);

        recycleview.setHasFixedSize(true);

        recycleview.setAdapter(adapter);

　　完整的MainActivity代码如下：

package com.qianmo.stickyitemdecoration;

import android.content.Context;

import android.graphics.Color;

import android.os.Bundle;

import android.support.v7.app.AppCompatActivity;

import android.support.v7.widget.GridLayoutManager;

import android.support.v7.widget.RecyclerView;

import android.util.TypedValue;

import com.qianmo.stickyitemdecoration.adapter.MyAdapter;

import com.qianmo.stickyitemdecoration.api.MovieApiService;

import com.qianmo.stickyitemdecoration.base.BaseResponse;

import com.qianmo.stickyitemdecoration.bean.ComingBean;

import com.qianmo.stickyitemdecoration.bean.MovieBean;

import com.qianmo.stickyitemdecoration.bean.NameBean;

import com.qianmo.stickyitemdecoration.utils.Constant;

import com.qianmo.stickyitemdecoration.view.FloatingItemDecoration;

import java.util.ArrayList;

import java.util.HashMap;

import java.util.List;

import java.util.Map;

import butterknife.BindView;

import butterknife.ButterKnife;

import retrofit2.Retrofit;

import retrofit2.adapter.rxjava.RxJavaCallAdapterFactory;

import retrofit2.converter.gson.GsonConverterFactory;

import rx.Subscriber;

import rx.android.schedulers.AndroidSchedulers;

import rx.schedulers.Schedulers;

public class MainActivity extends AppCompatActivity {

    @BindView(R.id.recycleview)

    RecyclerView recycleview;

    private List<ComingBean> datas;

    private Map<Integer,String> keys=new HashMap<>();//存放所有key的位置和内容

    private MyAdapter adapter;

    private Context mContext = MainActivity.this;

    @Override

    protected void onCreate(Bundle savedInstanceState) {

        super.onCreate(savedInstanceState);

        setContentView(R.layout.activity_main);

        ButterKnife.bind(this);

        initData();

    }

    /**

     * 请求数据

     */

    private void initData() {

        datas = new ArrayList<>();

        requestNetwork();

    }

    /**

     * 初始化UI

     */

    private void initView() {

        GridLayoutManager manager = new GridLayoutManager(this, 1);

        recycleview.setLayoutManager(manager);

        keys.put(0,"欧美大片");

        keys.put(2,"国产剧透");

        keys.put(4,"印度神剧");

        final FloatingItemDecoration floatingItemDecoration=new FloatingItemDecoration(this, Color.GRAY,1,1);

        floatingItemDecoration.setKeys(keys);

        floatingItemDecoration.setmTitleHeight((int) TypedValue.applyDimension(TypedValue.COMPLEX_UNIT_DIP,50,getResources().getDisplayMetrics()));

        recycleview.addItemDecoration(floatingItemDecoration);

        adapter = new MyAdapter(mContext, datas);

        recycleview.setHasFixedSize(true);

        recycleview.setAdapter(adapter);

    }

    /**

     * 请求网络

     */

    private void requestNetwork() {

        Retrofit retrofit = new Retrofit.Builder()

                .baseUrl(Constant.BASE_URL)

                .addConverterFactory(GsonConverterFactory.create())

                .addCallAdapterFactory(RxJavaCallAdapterFactory.create())

                .build();

        MovieApiService movieApiService = retrofit.create(MovieApiService.class);

        movieApiService.getMovieDatas()

                .subscribeOn(Schedulers.io())

                .observeOn(AndroidSchedulers.mainThread())

                .subscribe(new Subscriber<BaseResponse<MovieBean>>() {

                    @Override

                    public void onCompleted() {

                    }

                    @Override

                    public void onError(Throwable e) {

                    }

                    @Override

                    public void onNext(BaseResponse<MovieBean> movieBeanBaseResponse) {

                        datas.addAll(movieBeanBaseResponse.getData().getComing());

                        initView();

//                        adapter.notifyDataSetChanged();

                    }

                });

    }

}

　　再上一些github下载地址：https://github.com/543441727/StickyItemDecoration.git

巴特西

Android -- RecyclerView实现顶部吸附效果

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