Android 实现当下最流行的吸顶效果

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)

/**
 * 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--> 

 }
 }

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);
 }
 }
 /**
 * 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);
 }
}

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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