Android 实现带字母索引的侧边栏功能

/** * 作者：叶应是叶 * 时间：2017/8/20 11:38 * 描述： */public class LetterIndexView extends View { public interface OnTouchingLetterChangedListener {  void onHit(String letter);  void onCancel(); } private OnTouchingLetterChangedListener touchingLetterChangedListener; private Paint paint; private boolean hit; private final String[] letters = {"↑", "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", "#"}; private final int DEFAULT_WIDTH; public LetterIndexView(Context context) {  this(context, null); } public LetterIndexView(Context context, @Nullable AttributeSet attrs) {  this(context, attrs, 0); } public LetterIndexView(Context context, @Nullable AttributeSet attrs, int defStyleAttr) {  super(context, attrs, defStyleAttr);  paint = new Paint();  paint.setAntiAlias(true);  paint.setTextAlign(Paint.Align.CENTER);  paint.setColor(Color.parseColor("#565656"));  DEFAULT_WIDTH = dpToPx(context, 24); } @Override protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {  setMeasuredDimension(getWidthSize(widthMeasureSpec), getDefaultSize(getSuggestedMinimumHeight(), heightMeasureSpec)); } private int getWidthSize(int widthMeasureSpec) {  int widthMode = MeasureSpec.getMode(widthMeasureSpec);  int widthSize = MeasureSpec.getSize(widthMeasureSpec);  switch (widthMode) {   case MeasureSpec.AT_MOST: {    if (widthSize >= DEFAULT_WIDTH) {     return DEFAULT_WIDTH;    } else {     return widthSize;    }   }   case MeasureSpec.EXACTLY: {    return widthSize;   }   case MeasureSpec.UNSPECIFIED:   default:    return DEFAULT_WIDTH;  } } @Override public boolean dispatchTouchEvent(MotionEvent event) {  switch (event.getAction()) {   case MotionEvent.ACTION_DOWN:    hit = true;    onHit(event.getY());    break;   case MotionEvent.ACTION_MOVE:    onHit(event.getY());    break;   case MotionEvent.ACTION_UP:   case MotionEvent.ACTION_CANCEL:    hit = false;    if (touchingLetterChangedListener != null) {     touchingLetterChangedListener.onCancel();    }    break;  }  invalidate();  return true; } @Override protected void onDraw(Canvas canvas) {  if (hit) {   //字母索引条背景色   canvas.drawColor(Color.parseColor("#bababa"));  }  float letterHeight = ((float) getHeight()) / letters.length;  float width = getWidth();  float textSize = letterHeight * 5 / 7;  paint.setTextSize(textSize);  for (int i = 0; i < letters.length; i++) {   canvas.drawText(letters[i], width / 2, letterHeight * i + textSize, paint);  } } private void onHit(float offset) {  if (hit && touchingLetterChangedListener != null) {   int index = (int) (offset / getHeight() * letters.length);   index = Math.max(index, 0);   index = Math.min(index, letters.length - 1);   touchingLetterChangedListener.onHit(letters[index]);  } } public void setOnTouchingLetterChangedListener(OnTouchingLetterChangedListener onTouchingLetterChangedListener) {  this.touchingLetterChangedListener = onTouchingLetterChangedListener; } private int dpToPx(Context context, float dpValue) {  float scale = context.getResources().getDisplayMetrics().density;  return (int) (dpValue * scale + 0.5f); }}

/** * 作者：叶应是叶 * 时间：2017/8/20 11:39 * 描述： */public class IndexControl { private final ListView listView; private final TextView tv_hint; private final Map<String, Integer> letterMap; public IndexControl(ListView contactsListView, LetterIndexView letterIndexView,      TextView tv_hint, Map<String, Integer> letterMap) {  this.listView = contactsListView;  this.tv_hint = tv_hint;  this.letterMap = letterMap;  letterIndexView.setOnTouchingLetterChangedListener(new LetterChangedListener()); } private class LetterChangedListener implements LetterIndexView.OnTouchingLetterChangedListener {  @Override  public void onHit(String letter) {   tv_hint.setVisibility(View.VISIBLE);   tv_hint.setText(letter);   int index = -1;   if ("↑".equals(letter)) {    index = 0;   } else if (letterMap.containsKey(letter)) {    index = letterMap.get(letter);   }   if (index < 0) {    return;   }   index += listView.getHeaderViewsCount();   if (index >= 0 && index < listView.getCount()) {    listView.setSelectionFromTop(index, 0);   }  }  @Override  public void onCancel() {   tv_hint.setVisibility(View.INVISIBLE);  } }}