一，介绍SectionIndexer

package android.widget;/*** 接口可以被adapter实现，使AbsListView的sections之间可以快速滑动* 一个secton是一群列表，有很多相似点，例如他们可能以相同的字母开头，或者是来自同一个歌手的歌曲* ExpandableListAdapters认为groups和sections是同一个缩放组，应该返回一个合适的位置* 可以看一下AbsListView中setFastScrollEnabled(boolean)方法*/
public interface SectionIndexer {//返回一个代表sections列表的非空的数组对象//当滑动的时候，这个list view可以调用toString()来显示预览文本。//例如，一个adapter可以返回代表字母表中字母的字符串数组，或者返回section titles的对象数组Object[] getSections();//提供section索引，通过section数组对象，返回adapter中section开始的位置int getPositionForSection(int sectionIndex);//提供adapter中的位置，在section数组对象中返回相应的section索引//如果postion位置在索引开始位置之前，则返回0int getSectionForPosition(int position);
}

这么一说仿佛有点抽象，给个图就知道了：

getSectionForPosition() 通过该项的位置，获得所在分类组的索引号

getPositionForSection() 根据分类列的索引号获得该序列的首个位置

二，具体实现

2.1 定义侧面字母栏

public class SideBar extends AppCompatTextView {private String[] letters = new String[]{"A", "B", "C", "D", "E", "F", "G", "H", "I","J", "K", "L", "M", "N", "O", "P", "Q", "R", "S", "T", "U", "V","W", "X", "Y", "Z", "#"};/*** 三种不同的画笔*/private Paint textPaint;private Paint bigTextPaint;private Paint scaleTextPaint;private Canvas canvas;private int itemH;private int w;private int h;/*** 普通情况下字体大小*/float singleTextH;/*** 缩放离原始的宽度*/private float scaleWidth;/*** 滑动的Y*/private float eventY = 0;/*** 缩放的倍数*/private int scaleSize = 1;/*** 缩放个数item，即开口大小*/private int scaleItemCount = 6;private ISideBarSelectCallBack callBack;/*** 回调接口*/public interface ISideBarSelectCallBack {void onSelectStr(int index, String selectStr);}public SideBar(Context context) {super(context);}public SideBar(Context context, @Nullable AttributeSet attrs) {super(context, attrs);}public SideBar(Context context, @Nullable AttributeSet attrs, int defStyleAttr) {super(context, attrs, defStyleAttr);init(attrs);}/*** 初始化函数** @param attrs attr*/private void init(AttributeSet attrs) {if (attrs != null) {TypedArray ta = getContext().obtainStyledAttributes(attrs, R.styleable.SideBar);scaleSize = ta.getInteger(R.styleable.SideBar_scaleSize, 1);scaleItemCount = ta.getInteger(R.styleable.SideBar_scaleItemCount, 6);scaleWidth = ta.getDimensionPixelSize(R.styleable.SideBar_scaleWidth, dp(100));ta.recycle();}textPaint = new Paint(Paint.ANTI_ALIAS_FLAG);textPaint.setColor(getCurrentTextColor());textPaint.setTextSize(getTextSize());textPaint.setTextAlign(Paint.Align.CENTER);bigTextPaint = new Paint(Paint.ANTI_ALIAS_FLAG);bigTextPaint.setColor(getCurrentTextColor());bigTextPaint.setTextSize(getTextSize() * (scaleSize + 3));bigTextPaint.setTextAlign(Paint.Align.CENTER);scaleTextPaint = new Paint(Paint.ANTI_ALIAS_FLAG);scaleTextPaint.setColor(getCurrentTextColor());scaleTextPaint.setTextSize(getTextSize() * (scaleSize + 1));scaleTextPaint.setTextAlign(Paint.Align.CENTER);}public void setDataResource(String[] data) {letters = data;invalidate();}public void setOnStrSelectCallBack(ISideBarSelectCallBack callBack) {this.callBack = callBack;}/*** 设置字体缩放比例*/public void setScaleSize(int scale) {scaleSize = scale;invalidate();}/*** 设置缩放字体的个数，即开口大小*/public void setScaleItemCount(int scaleItemCount) {this.scaleItemCount = scaleItemCount;invalidate();}private int dp(int px) {final float scale = getContext().getResources().getDisplayMetrics().density;return (int) (px * scale + 0.5f);}@Overridepublic boolean onTouchEvent(MotionEvent event) {switch (event.getAction()) {case MotionEvent.ACTION_DOWN:case MotionEvent.ACTION_MOVE:if (event.getX() > (w - getPaddingRight() - singleTextH - 10)) {eventY = event.getY();invalidate();return true;}else {eventY = 0;invalidate();break;}case MotionEvent.ACTION_CANCEL:eventY = 0;invalidate();return true;case MotionEvent.ACTION_UP:if (event.getX() > (w - getPaddingRight() - singleTextH - 10)) {eventY = 0;invalidate();return true;}elsebreak;}return super.onTouchEvent(event);}@Overrideprotected void onDraw(Canvas canvas) {this.canvas = canvas;DrawView(eventY);}private void DrawView(float y) {int currentSelectIndex = -1;if (y != 0) {for (int i = 0; i < letters.length; i++) {float currentItemY = itemH * i;float nextItemY = itemH * (i + 1);if (y >= currentItemY && y < nextItemY) {currentSelectIndex = i;if (callBack != null) {callBack.onSelectStr(currentSelectIndex, letters[i]);}//画大的字母Paint.FontMetrics fontMetrics = bigTextPaint.getFontMetrics();float bigTextSize = fontMetrics.descent - fontMetrics.ascent;canvas.drawText(letters[i], w - getPaddingRight() - scaleWidth - bigTextSize, singleTextH + itemH * i, bigTextPaint);}}}drawLetters(y, currentSelectIndex);}private void drawLetters(float y, int index) {w = getMeasuredWidth();h = getMeasuredHeight();itemH = h / letters.length;Paint.FontMetrics fontMetrics = textPaint.getFontMetrics();singleTextH = fontMetrics.descent - fontMetrics.ascent;for (int i = 0; i < letters.length; i++) {canvas.drawText(letters[i], w - getPaddingRight(), singleTextH + itemH * i, textPaint);}}
}

自定义view，主要作用就是，显示侧面的字母栏，后期点击或者滑动时，能显示出点击的大字母。

2.2 xml布局

联系人界面的xml布局：

<RelativeLayoutxmlns:android="http://schemas.android.com/apk/res/android"xmlns:tools="http://schemas.android.com/tools"android:layout_width="match_parent"android:layout_height="match_parent"tools:context=".fragment.ChatFragment"><androidx.recyclerview.widget.RecyclerViewandroid:id="@+id/recyclercontactlistId"android:layout_width="match_parent"android:layout_height="match_parent"/><com.Jason.materialdesign.widget.SideBarandroid:id="@+id/sidebar"android:layout_width="match_parent"android:layout_height="match_parent"android:layout_alignParentRight="true"android:background="@android:color/transparent"android:paddingRight="10dp"android:textSize="15sp" />
</RelativeLayout>

2.3 实现 adapter 主要是实现SectionIndexer接口

这个adapter主要是联系人的item布局，这个相对来说能理解，都直接原生库原生接口，应该能明白。主要是就是实现sectionIndexer接口，这儿稍微注意点。

public class ContactsAdapter extends RecyclerView.Adapter<ContactsAdapter.ContactsListHolder> implements SectionIndexer {/*** 联系人分区*/private SparseIntArray mPositionOfSection;/*** 联系人分区*/private SparseIntArray mSectionOfPosition;// 联系人列表private List<ContactData> mContactDataList;public ContactsAdapter(List<ContactData> contactDatas) {this.mContactDataList = contactDatas;}@NonNull@Overridepublic ContactsListHolder onCreateViewHolder(@NonNull ViewGroup parent, int viewType) {View view = LayoutInflater.from(parent.getContext()).inflate(R.layout.recycler_list_item_contact, parent,false);ContactsListHolder holder = new ContactsListHolder(view);return holder;}@Overridepublic void onBindViewHolder(@NonNull ContactsListHolder holder, int position) {ContactData contactData = mContactDataList.get(position);if (contactData != null){holder.avaterView.setImageResource(R.mipmap.default_avatar);holder.nameTxt.setText(contactData.getUserName());}}@Overridepublic int getItemCount() {return mContactDataList.size();}/***SectionIndexer分区方法*/@Overridepublic Object[] getSections() {mPositionOfSection = new SparseIntArray();mSectionOfPosition = new SparseIntArray();// 传入的联系人数量int count = mContactDataList.size();// list后期转换为arrayList<String> list = new ArrayList<>();list.add("");mPositionOfSection.put(0, 0);mSectionOfPosition.put(0, 0);// 开始分区for (int i = 1; i < count; i++){String letter = mContactDataList.get(i).getFirstLetter();int section = list.size() - 1;if (list.get(section) != null && !list.get(section).equals(letter)){list.add(letter);section++;mPositionOfSection.put(section, i);}mSectionOfPosition.put(i, section);}return list.toArray(new String[list.size()]);}/***SectionIndexer分区方法*/@Overridepublic int getPositionForSection(int sectionIndex) {return mPositionOfSection.get(sectionIndex);}/***SectionIndexer分区方法*/@Overridepublic int getSectionForPosition(int position) {return mSectionOfPosition.get(position);}/*** 普通联系人holder*/class ContactsListHolder extends RecyclerView.ViewHolder {ImageView avaterView;TextView nameTxt;public ContactsListHolder(View  view) {super(view);avaterView = (ImageView)view.findViewById(R.id.avatar);nameTxt = (TextView)view.findViewById(R.id.name);}}
}

2.4 ContactFragment的代码，包括一些初始化，比较排序等

public class ContactFragment extends Fragment {private ContactsAdapter mContactsAdapter;private RecyclerView mRecyclerView;private SideBar mSideBar;@Overridepublic void onCreate(Bundle savedInstanceState) {super.onCreate(savedInstanceState);}@Overridepublic View onCreateView(LayoutInflater inflater, ViewGroup container,Bundle savedInstanceState) {// Inflate the layout for this fragmentView view = inflater.inflate(R.layout.fragment_contact, container, false);initContacts(view);return view;}/*** 装载数据* @param view 根view*/private void initContacts(View view){mRecyclerView = view.findViewById(R.id.recyclercontactlistId);mSideBar = view.findViewById(R.id.sidebar);mContactsAdapter = new ContactsAdapter(initTestData());LinearLayoutManager verticalLayoutManager = new LinearLayoutManager(this.getContext());mRecyclerView.setLayoutManager(verticalLayoutManager);mRecyclerView.setAdapter(mContactsAdapter);}/*** 初始化测试数据* @return*/private List<ContactData> initTestData(){List<ContactData> contactData = new ArrayList<>();contactData.add(new ContactData("alibaba", "123456", 1));contactData.add(new ContactData("tencent", "654321", 2));contactData.add(new ContactData("spaceon", "999999", 3));contactData.add(new ContactData("666", "0000", 4));contactData.add(new ContactData("老黄", "18381680077", 0));contactData.add(new ContactData("ligj", "1550805", 9));return contactData;}
}

初始化数据这里，还需要对首字母进行排序：

  /*** 联系人数据排序** @return*/private List<ContactData> getOrderContacts(List<ContactData> contactDataList) {List<ContactData> contactOrderList = new ArrayList<>(contactDataList.size());// 排序for (ContactData contactData : contactDataList) {String name = contactData.getUserName();String head = PinyinUtils.getPinyin(name.trim());//英文字符串时不能正确返回拼音首字母head = head.length() > 1 ? head.substring(0, 1) : head;head = (head.compareToIgnoreCase("A") < 0 || head.compareToIgnoreCase("Z") > 0) ? "#" : head;contactData.setFirstLetter(head);//根据head值进行排序从A-Zif (head.equals("#")) {contactOrderList.add(contactOrderList.size(), contactData);}else {int i;for (i = 0; i < contactOrderList.size(); i++) {String head1 = contactOrderList.get(i).getFirstLetter();if (head.compareToIgnoreCase(head1) <= 0 || head1.compareTo("#") == 0) {break;}}contactOrderList.add(i, contactData);}}//把首字母相同的归为一组（清空首字母）String lastHead = "";for (ContactData d : contactOrderList) {if (!lastHead.equals("")) {if (lastHead.equals(d.getFirstLetter())) {d.setFirstLetter("");}else {lastHead = d.getFirstLetter();}}else {lastHead = d.getFirstLetter();}}return contactOrderList;}

另外，sideBar的点击事件还要传进去。adpter的刷新等也要设置。具体见完整代码。

三，结果图

此专栏上一篇文章：BottomNavigationView+ViewPager+Fragment仿微信底部导航栏

github代码：我的github

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