給大家分享一個很實用的城市選擇列表，城市列表估計大家都很熟悉，在此記錄一下

效果圖

效果圖.gif

城市數據在assets下的China_cities.db文件

一、控件的測量

public class SideLetterBar extends View {
    private static final String[] b = {"定位", "熱門", "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 int choose = -1;
    private Paint paint = new Paint();
    private boolean showBg = false;
    private OnLetterChangedListener onLetterChangedListener;
    private TextView overlay;

    public SideLetterBar(Context context, AttributeSet attrs, int defStyle) {
        super(context, attrs, defStyle);
    }

    public SideLetterBar(Context context, AttributeSet attrs) {
        super(context, attrs);
    }

    public SideLetterBar(Context context) {
        super(context);
    }

    /**
     * 設置懸浮的textview
     * @param overlay
     */
    public void setOverlay(TextView overlay){
        this.overlay = overlay;
    }

    @SuppressWarnings("deprecation")
    @Override
    protected void onDraw(Canvas canvas) {
        super.onDraw(canvas);
        if (showBg) {
            canvas.drawColor(Color.TRANSPARENT);
        }

        int height = getHeight();
        int width = getWidth();
        int singleHeight = height / b.length;
        for (int i = 0; i < b.length; i++) {
            paint.setTextSize(getResources().getDimension(R.dimen.side_letter_bar_letter_size));
            paint.setColor(getResources().getColor(R.color.cp_gray));
            paint.setAntiAlias(true);
            if (i == choose) {
                paint.setColor(getResources().getColor(R.color.cp_gray_deep));
//                paint.setFakeBoldText(true);  //加粗
            }
            float xPos = width / 2 - paint.measureText(b[i]) / 2;
            float yPos = singleHeight * i + singleHeight;
            canvas.drawText(b[i], xPos, yPos, paint);
            paint.reset();
        }

    }

    @Override
    public boolean dispatchTouchEvent(MotionEvent event) {
        final int action = event.getAction();
        final float y = event.getY();
        final int oldChoose = choose;
        final OnLetterChangedListener listener = onLetterChangedListener;
        final int c = (int) (y / getHeight() * b.length);

        switch (action) {
            case MotionEvent.ACTION_DOWN:
                showBg = true;
                if (oldChoose != c && listener != null) {
                    if (c >= 0 && c < b.length) {
                        listener.onLetterChanged(b[c]);
                        choose = c;
                        invalidate();
                        if (overlay != null){
                            overlay.setVisibility(VISIBLE);
                            overlay.setText(b[c]);
                        }
                    }
                }

                break;
            case MotionEvent.ACTION_MOVE:
                if (oldChoose != c && listener != null) {
                    if (c >= 0 && c < b.length) {
                        listener.onLetterChanged(b[c]);
                        choose = c;
                        invalidate();
                        if (overlay != null){
                            overlay.setVisibility(VISIBLE);
                            overlay.setText(b[c]);
                        }
                    }
                }
                break;
            case MotionEvent.ACTION_UP:
                showBg = false;
                choose = -1;
                invalidate();
                if (overlay != null){
                    overlay.setVisibility(GONE);
                }
                break;
        }
        return true;
    }

    @Override
    public boolean onTouchEvent(MotionEvent event) {
        return super.onTouchEvent(event);
    }

    public void setOnLetterChangedListener(OnLetterChangedListener onLetterChangedListener) {
        this.onLetterChangedListener = onLetterChangedListener;
    }

    public interface OnLetterChangedListener {
        void onLetterChanged(String letter);
    }

}

二、實現類的關鍵部分

    public CityListAdapter(Context mContext, List<City> mCities) {
        this.mContext = mContext;
        this.mCities = mCities;
        this.inflater = LayoutInflater.from(mContext);
        if (mCities == null){
            mCities = new ArrayList<>();
        }
        mCities.add(0, new City("定位", "0"));
        mCities.add(1, new City("熱門", "1"));
        int size = mCities.size();
        letterIndexes = new HashMap<>();
        sections = new String[size];
        for (int index = 0; index < size; index++){
            //當前城市拼音首字母
            String currentLetter = PinyinUtils.getFirstLetter(mCities.get(index).getPinyin());
            //上個首字母，如果不存在設為""
            String previousLetter = index >= 1 ? PinyinUtils.getFirstLetter(mCities.get(index - 1).getPinyin()) : "";
            if (!TextUtils.equals(currentLetter, previousLetter)){
                letterIndexes.put(currentLetter, index);
                sections[index] = currentLetter;
            }
        }
    }

最后給出demo的地址，歡迎大家訪問和使用。
https://gitee.com/oubajunping/chengshixuanzeliebiao