详解android使用ItemDecoration 悬浮导航栏效果

开始逐渐领略到ItemDecoration的美~

今天让我 使用 ItemDecoration 来完成 可推动的悬浮导航栏的效果，最终实现的效果如下图：

具体实现步骤如下：

根据我前面的文章所讲的RecyclerView的基本使用，我们先来完成基本的recyclerView：

第一步：布局里写一个RecyclerView

第二步：实例化

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

第三步：获取所需的数据 (这里我们来个真实点的情景，去联网请求数据)

 
  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();
 
  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); 
          } 
        }); 
  }
 
  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--> 
    } 
  }

第四步：解析数据成功后，创建并设置适配器,并传递相关数据

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

适配器：

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); 
    } 
  } 
}

item的布局：

<?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="神奇動物在哪裏" 
      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="神奇動物城，法師顯超能" 
      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>

第五步：一定不能忘！！！

recycleView不仅要设置适配器还要设置布局管理者,否则图片不显示

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

此时RecyclerView简单的完成效果如下：

下面开始做 可推动的 悬浮导航栏：

第一步：首先我们来写一个类，它起标记的作用，来放每一个item的对应的悬浮栏的字符串

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

第二步：自定义一个SectionDecoration 类 继承 RecyclerView的ItemDecoration

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); 
    } 
  } 
   
  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); 
  } 
}

第三步：在向list集合中先把每一个item的 起“标记”作用的字符串都加进去

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); 
    } 
  }

第四步：在setAdapter() 前，为RecyclerView添加ItemDecoration:

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 ""; 
        } 
      }));

这样就完成了~

再看一眼最终效果感受一下：

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