Android--快速定位索引

先看张效果图

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列表是用RecyclerView，demo中RecyclerView都是封装好的，小编是直接拿过来用的，至于怎么封装RecyclerView，绘制RecyclerView的分割线等等，有个半年经验左右应该是会封装的，至于不会，那就研究下我的代码是怎么封装的。哈哈！

具体思路：

1、对汉字进行A_Z排序
2、绘制字母A-Z索引LetterSideBarView  
3、触摸响应手指的touch事件，需要考虑View的事件分发   
4、绘制RecyclerView的分割线  

LetterSideBarView

public class LetterSideBarView extends View {

private Context mContext;
//画笔
private Paint mPaint;
private String[] mLetters = {"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"};
//手指当前触摸的字母
private String mTouchLetter;
//手指是否触摸
private boolean mCurrentIsTouch;
// 设置触摸监听
private SideBarTouchListener mTouchListener;

public LetterSideBarView(Context context) {
    this(context, null);
}


public LetterSideBarView(Context context, @Nullable AttributeSet attrs) {
    this(context, attrs, 0);
}

public LetterSideBarView(Context context, @Nullable AttributeSet attrs, int defStyleAttr) {
    super(context, attrs, defStyleAttr);
    this.mContext = context;
    mPaint = new Paint();
    mPaint.setAntiAlias(true);
    mPaint.setTextSize(DensityUtil.sp2px(this.getContext(), 14));
    mPaint.setColor(Color.BLACK);
}

@Override
protected void onDraw(Canvas canvas) {
    super.onDraw(canvas);
    //每一个字母的高度
    float singleHeight = ( float ) getHeight() / mLetters.length;
    //不断循环把绘制字母
    for (int i = 0; i < mLetters.length; i++) {
        String letter = mLetters[i];
        //获取字体的宽度
        Rect rect = new Rect();
        mPaint.getTextBounds(letter, 0, letter.length(), rect);
        float measureTextWidth = rect.width();
        //获取内容的宽度
        int contentWidth = getWidth() - getPaddingLeft() - getPaddingRight();
        float x = getPaddingLeft() + (contentWidth - measureTextWidth) / 2;
        //计算基线位置
        Paint.FontMetrics fontMetrics = mPaint.getFontMetrics();
        float baseLine = singleHeight / 2 + (singleHeight * i) +
                (fontMetrics.bottom - fontMetrics.top) / 2 - fontMetrics.bottom;
        //画字母，后面onTouch的时候需要处理高亮
        if (mLetters[i].equals(mTouchLetter) && mCurrentIsTouch) {
            mPaint.setTextSize(DensityUtil.sp2px(mContext, 18));
            mPaint.setColor(Color.RED);
            canvas.drawText(letter, x, baseLine, mPaint);
        } else {
            mPaint.setTextSize(DensityUtil.sp2px(mContext, 14));
            mPaint.setColor(Color.BLACK);
            canvas.drawText(letter, x, baseLine, mPaint);
        }
    }
}

@Override
public boolean onTouchEvent(MotionEvent event) {
    switch (event.getAction()) {
        case MotionEvent.ACTION_DOWN:
        case MotionEvent.ACTION_MOVE:
            //计算出当前触摸的字母，获取当前的位置
            float currentMoveY = ( int ) event.getY();
            int itemHeight = (getHeight() - getPaddingTop() - getPaddingBottom()) / mLetters.length;
            //当前的位置=currentMoveY/字母的高度
            int currentPosition = ( int ) currentMoveY / itemHeight;
            if (currentPosition < 0) {
                currentPosition = 0;
            }
            if (currentPosition > mLetters.length - 1) {
                currentPosition = mLetters.length - 1;
            }
            mTouchLetter = mLetters[currentPosition];
            mCurrentIsTouch = true;
            if (mTouchListener != null) {
                mTouchListener.onTouch(mTouchLetter, true);
            }
            break;
        case MotionEvent.ACTION_UP:
            mCurrentIsTouch = false;
            if (mTouchListener != null) {
                mTouchListener.onTouch(mTouchLetter, false);
            }
            break;
    }
    invalidate();

    return true;
}


public void setOnSideBarTouchListener(SideBarTouchListener touchListener) {
    this.mTouchListener = touchListener;
}

计算出每个字母的基线baseLine，怎么计算呢？

5437668-8051a93a8a68dd67.png

• top line: 文字可绘制区域最顶部的线；
• ascent line: 系统推荐的，文字可绘制区域顶部的线；
• baseline: 文字绘制的基线（在四线格上书写英文字母时的第三条线）；
• descent line: 系统推荐的，文字可绘制区域底部的线；
• bottom line: 文字可绘制区域最底部的线。
  baseline是基线，baseline以上是负值，baseline以下是正值，因此ascent和top都是负值，descent和bottom都是正值。

//计算基线位置
 Paint.FontMetrics fontMetrics = mPaint.getFontMetrics();
 float baseLine = singleHeight / 2 + (singleHeight * i) +(fontMetrics.bottom - fontMetrics.top) / 2 - fontMetrics.bottom;

说下View的事件分发，需要执行ACTION_MOVE事件，ACTION_DOWN事件需要返回true消费这个事件，才能往下执行ACTION_MOVE事件。

MainActivity

public class MainActivity extends AppCompatActivity {
private RecyclerView mRv;
private LetterSideBarView mLetterSideBarView;
private TextView mIndexTv;
private List<Person> mList;
private Handler mHandler = new Handler();
private boolean isScale = false;

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);
    mRv = findViewById(R.id.rv);
    mLetterSideBarView = findViewById(R.id.letterSideBarView);
    mIndexTv = findViewById(R.id.indexTv);
    initRv();
    mLetterSideBarView.setOnSideBarTouchListener(new SideBarTouchListener() {
        @Override
        public void onTouch(String letter, boolean isTouch) {
            for (int i = 0; i < mList.size(); i++) {
                if (letter.equals(mList.get(i).getPinyin().charAt(0) + "")) {
                    mRv.scrollToPosition(i);
                    break;
                }
            }
            showCurrentIndex(letter);
        }
    });
}

private void showCurrentIndex(String letter) {
    mIndexTv.setText(letter);
    if (!isScale) {
        isScale = true;
        ViewCompat.animate(mIndexTv)
                .scaleX(1f)
                .setInterpolator(new OvershootInterpolator())
                .setDuration(380)
                .start();
        ViewCompat.animate(mIndexTv)
                .scaleY(1f)
                .setInterpolator(new OvershootInterpolator())
                .setDuration(380)
                .start();
    }

    mHandler.removeCallbacksAndMessages(null);
    // 延时隐藏
    mHandler.postDelayed(new Runnable() {
        @Override
        public void run() {
            ViewCompat.animate(mIndexTv)
                    .scaleX(0f)
                    .setDuration(380)
                    .start();
            ViewCompat.animate(mIndexTv)
                    .scaleY(0f)
                    .setDuration(380)
                    .start();
            isScale = false;
        }
    }, 380);
}

private void initRv() {
    mList = new ArrayList<>();
    for (int i = 0; i < DataUtil.testData3.length; i++) {
        Person person = new Person(DataUtil.testData3[i]);
        mList.add(person);
    }
    //排序
    Collections.sort(mList);
    PersonAdapter adapter = new PersonAdapter(this, mList, R.layout.person_recycler_item);
    mRv.setAdapter(adapter);
    mRv.setLayoutManager(new LinearLayoutManager(this, LinearLayoutManager.VERTICAL, false)); 
    //添加分割线
    mRv.addItemDecoration(new DefaultItemDecoration(this, R.drawable.default_item));
}

private class PersonAdapter extends CommonRecycleAdapter<Person> {
    public PersonAdapter(Context context, List<Person> mData, int layoutId) {
        super(context, mData, layoutId);
    }

    @Override
    protected void convert(CommonViewHolder holder, Person person, int position) {
        String currentWord = person.getPinyin().charAt(0) + "";
        if (position > 0) {
            String lastWord = mList.get(position - 1).getPinyin().charAt(0) + "";
            //拿当前的首字母和上一个首字母比较,与首字母相同，需要隐藏当前item的索引
            holder.setVisibility(R.id.indexTv, currentWord.equals(lastWord) ? View.GONE : View.VISIBLE);
        } else {
            holder.setVisibility(R.id.indexTv, View.VISIBLE);
        }
        holder.setText(R.id.indexTv, currentWord);
        holder.setText(R.id.userNameTv, person.getName());
    }
}
}

MainActivity大家看代码吧，都是些基础代码。主要是这个：拿当前的首字母和上一个首字母比较,与首字母相同，需要隐藏当前item上面索引。

github地址：https://github.com/StevenYan88/QuickIndex
有不懂的地方可以加小编的微信，小编可以拉你进群讨论！

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