详解android使用ItemDecoration 悬浮导航栏效果

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

/**   * 联网请求所需的url   */   public String url="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";//联网获取数据     getDataFromNet();/**    * 使用okhttpUtils进行联网请求数据    */   private void getDataFromNet() {     OkHttpUtils.         get()         .url(url)         .build()         .execute(new StringCallback() {           @Override           public void onError(okhttp3.Call call, Exception e, int id) {             Log.e("TAG", "联网失败" + e.getMessage());           }           @Override           public void onResponse(String response, int id) {             Log.e("TAG", "联网成功==" + response);             //联网成功后使用fastjson解析             processData(response);           }         });   }/**    * 使用fastjson进行解析    *    * @param json    */   private void processData(String json) {     //这里使用GsonFormat生成对应的bean类     JSONObject jsonObject = parseObject(json);     String data = jsonObject.getString("data");     JSONObject dataObj = JSON.parseObject(data);     String coming = dataObj.getString("coming");     List<WaitMVBean.DataBean.ComingBean> comingslist = parseArray(coming, WaitMVBean.DataBean.ComingBean.class);     //测试是否解析数据成功 //    String strTest = comingslist.get(0).getCat(); //    Log.e("TAG", strTest + "222");      //解析数据成功,设置适配器-->     }   }

//解析数据成功,设置适配器       MyRecyclerAdapter adapter = new MyRecyclerAdapter( mContext,comingslist);       recyclerView.setAdapter(adapter);

public class MyRecyclerAdapter extends RecyclerView.Adapter {   private final List<WaitMVBean.DataBean.ComingBean> comingslist;   private final Context mContext;   private final LayoutInflater mLayoutInflater;   public MyRecyclerAdapter(Context mContext, List<WaitMVBean.DataBean.ComingBean> comingslist) {     this.mContext = mContext;     this.comingslist = comingslist;     mLayoutInflater = LayoutInflater.from(mContext);   }   @Override   public RecyclerView.ViewHolder onCreateViewHolder(ViewGroup parent, int viewType) {     return new MyViewHolder(mLayoutInflater.inflate(R.layout.date_item, null));   }   @Override   public void onBindViewHolder(RecyclerView.ViewHolder holder, int position) {     MyViewHolder myholder = (MyViewHolder) holder;     myholder.setData(position);   }   @Override   public int getItemCount() {     return comingslist.size();   }   class MyViewHolder extends RecyclerView.ViewHolder {     private TextView mv_name;     private TextView mv_dec;     private TextView mv_date;     private ImageView imageView;     public MyViewHolder(View itemView) {       super(itemView);       mv_name = (TextView) itemView.findViewById(R.id.mv_name);       mv_dec = (TextView) itemView.findViewById(R.id.mv_dec);       mv_date = (TextView) itemView.findViewById(R.id.mv_date);       imageView = (ImageView) itemView.findViewById(R.id.image);     }     public void setData(int position) {       WaitMVBean.DataBean.ComingBean coming = comingslist.get(position);       String name = coming.getNm();       mv_name.setText(name);       String date = coming.getShowInfo();       mv_date.setText(date);       String dec = coming.getScm();       mv_dec.setText(dec);       //注：当你发下图片无法打开是，做个字符串替换即可       String imagUrl = coming.getImg();       String newImagUrl = imagUrl.replaceAll("w.h", "50.80");       //使用Glide加载图片       Glide.with(mContext)           .load(newImagUrl)           .into(imageView);     }   } }

<?xml version="1.0" encoding="utf-8"?> <LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"   android:layout_width="wrap_content"   android:layout_height="wrap_content"   android:background="#ffffff"   android:gravity="center_vertical"   android:orientation="horizontal">   <ImageView     android:id="@+id/image"     android:layout_width="70dp"     android:layout_height="110dp"     android:layout_marginBottom="5dp"     android:layout_marginLeft="10dp"     android:layout_marginRight="8dp"     android:layout_marginTop="5dp" />   <LinearLayout     android:layout_width="0dp"     android:layout_height="wrap_content"     android:layout_marginLeft="6dp"     android:layout_weight="1"     android:orientation="vertical">     <TextView       android:id="@+id/mv_name"       android:layout_width="wrap_content"       android:layout_height="wrap_content"       android:text="神奇物在哪"       android:textColor="#000000"       android:textSize="15sp" />     <LinearLayout       android:layout_width="wrap_content"       android:layout_height="wrap_content"       android:orientation="horizontal">       <TextView         android:layout_width="wrap_content"         android:layout_height="wrap_content"         android:text="观众"         android:textColor="#55000000"         android:textSize="14sp" />       <TextView         android:id="@+id/tv_people"         android:layout_width="wrap_content"         android:layout_height="wrap_content"         android:text="9.0 "         android:textColor="#FFCE42"         android:textSize="18sp" />       <TextView         android:layout_width="wrap_content"         android:layout_height="wrap_content"         android:text=" | 专业"         android:textColor="#55000000"         android:textSize="14sp" />       <TextView         android:id="@+id/tv_professional"         android:layout_width="wrap_content"         android:layout_height="wrap_content"         android:text="6.7"         android:textColor="#FFCE42"         android:textSize="18sp" />     </LinearLayout>     <TextView       android:id="@+id/mv_dec"       android:layout_width="wrap_content"       android:layout_height="wrap_content"       android:layout_marginTop="8dp"       android:text="神奇物城，法超能"       android:textColor="#99000000"       android:textSize="11sp" />     <TextView       android:id="@+id/mv_date"       android:layout_width="wrap_content"       android:layout_height="wrap_content"       android:layout_marginTop="10dp"       android:text="今天165家影院放映2088场"       android:textColor="#99000000"       android:textSize="11sp" />   </LinearLayout> </LinearLayout>

GridLayoutManager manager = new GridLayoutManager(this, 1);       recyclerView.setLayoutManager(manager);

public class NameBean {   String name;   public String getName() {     return name;   }   public void setName(String name) {     this.name = name;   } }

public class SectionDecoration extends RecyclerView.ItemDecoration {   private static final String TAG = "SectionDecoration";   private List<NameBean> dataList;   private DecorationCallback callback;   private TextPaint textPaint;   private Paint paint;   private int topGap;   private int alignBottom;   private Paint.FontMetrics fontMetrics;   public SectionDecoration(List<NameBean> dataList, Context context, DecorationCallback decorationCallback) {     Resources res = context.getResources();     this.dataList = dataList;     this.callback = decorationCallback;     //设置悬浮栏的画笔---paint     paint = new Paint();     paint.setColor(res.getColor(R.color.colorGray));     //设置悬浮栏中文本的画笔     textPaint = new TextPaint();     textPaint.setAntiAlias(true);     textPaint.setTextSize(DensityUtil.dip2px(context, 14));     textPaint.setColor(Color.DKGRAY);     textPaint.setTextAlign(Paint.Align.LEFT);     fontMetrics = new Paint.FontMetrics();     //决定悬浮栏的高度等     topGap = res.getDimensionPixelSize(R.dimen.sectioned_top);     //决定文本的显示位置等     alignBottom = res.getDimensionPixelSize(R.dimen.sectioned_alignBottom);   }   @Override   public void getItemOffsets(Rect outRect, View view, RecyclerView parent, RecyclerView.State state) {     super.getItemOffsets(outRect, view, parent, state);     int pos = parent.getChildAdapterPosition(view);     Log.i(TAG, "getItemOffsets：" + pos);     String groupId = callback.getGroupId(pos);     if (groupId.equals("-1")) return;     //只有是同一组的第一个才显示悬浮栏     if (pos == 0 || isFirstInGroup(pos)) {       outRect.top = topGap;       if (dataList.get(pos).getName() == "") {         outRect.top = 0;       }     } else {       outRect.top = 0;     }   }   @Override   public void onDraw(Canvas c, RecyclerView parent, RecyclerView.State state) {     super.onDraw(c, parent, state);     int left = parent.getPaddingLeft();     int right = parent.getWidth() - parent.getPaddingRight();     int childCount = parent.getChildCount();     for (int i = 0; i < childCount; i++) {       View view = parent.getChildAt(i);       int position = parent.getChildAdapterPosition(view);       String groupId = callback.getGroupId(position);       if (groupId.equals("-1")) return;       String textLine = callback.getGroupFirstLine(position).toUpperCase();       if (textLine == "") {         float top = view.getTop();         float bottom = view.getTop();         c.drawRect(left, top, right, bottom, paint);         return;       } else {         if (position == 0 || isFirstInGroup(position)) {           float top = view.getTop() - topGap;           float bottom = view.getTop();           //绘制悬浮栏           c.drawRect(left, top - topGap, right, bottom, paint);           //绘制文本           c.drawText(textLine, left, bottom, textPaint);         }       }     }   }   @Override   public void onDrawOver(Canvas c, RecyclerView parent, RecyclerView.State state) {     super.onDrawOver(c, parent, state);     int itemCount = state.getItemCount();     int childCount = parent.getChildCount();     int left = parent.getPaddingLeft();     int right = parent.getWidth() - parent.getPaddingRight();     float lineHeight = textPaint.getTextSize() + fontMetrics.descent;     String preGroupId = "";     String groupId = "-1";     for (int i = 0; i < childCount; i++) {       View view = parent.getChildAt(i);       int position = parent.getChildAdapterPosition(view);       preGroupId = groupId;       groupId = callback.getGroupId(position);       if (groupId.equals("-1") || groupId.equals(preGroupId)) continue;       String textLine = callback.getGroupFirstLine(position).toUpperCase();       if (TextUtils.isEmpty(textLine)) continue;       int viewBottom = view.getBottom();       float textY = Math.max(topGap, view.getTop());       //下一个和当前不一样移动当前       if (position + 1 < itemCount) {         String nextGroupId = callback.getGroupId(position + 1);         //组内最后一个view进入了header         if (nextGroupId != groupId && viewBottom < textY) {           textY = viewBottom;         }       }       //textY - topGap决定了悬浮栏绘制的高度和位置       c.drawRect(left, textY - topGap, right, textY, paint);       //left+2*alignBottom 决定了文本往左偏移的多少（加-->向左移）       //textY-alignBottom 决定了文本往右偏移的多少 (减-->向上移)       c.drawText(textLine, left + 2 * alignBottom, textY - alignBottom, textPaint);     }   }   /**    * 判断是不是组中的第一个位置    *    * @param pos    * @return    */   private boolean isFirstInGroup(int pos) {     if (pos == 0) {       return true;     } else {       // 因为是根据 字符串内容的相同与否 来判断是不是同意组的，所以此处的标记id 要是String类型       // 如果你只是做联系人列表，悬浮框里显示的只是一个字母，则标记id直接用 int 类型就行了       String prevGroupId = callback.getGroupId(pos - 1);       String groupId = callback.getGroupId(pos);       //判断前一个字符串 与 当前字符串 是否相同       if (prevGroupId.equals(groupId)) {         return false;       } else {         return true;       }     }   }   //定义一个借口方便外界的调用   interface DecorationCallback {     String getGroupId(int position);     String getGroupFirstLine(int position);   } }

setPullAction(comingslist);private void setPullAction(List<WaitMVBean.DataBean.ComingBean> comingslist) {     dataList = new ArrayList<>();     for (int i = 0; i < comingslist.size(); i++) {       NameBean nameBean = new NameBean();       String name0 = comingslist.get(i).getComingTitle();       nameBean.setName(name0);       dataList.add(nameBean);     }   }

recyclerView.addItemDecoration(new SectionDecoration(dataList,mContext, new SectionDecoration.DecorationCallback() {         //返回标记id (即每一项对应的标志性的字符串)         @Override         public String getGroupId(int position) {           if(dataList.get(position).getName()!=null) {             return dataList.get(position).getName();           }           return "-1";         }         //获取同组中的第一个内容         @Override         public String getGroupFirstLine(int position) {           if(dataList.get(position).getName()!=null) {             return dataList.get(position).getName();           }           return "";         }       }));