public class SideBar extends View {

/** 字母更新的监听器 */

private OnLetterUpdateListener onLetterUpdateListener;

/** 当前的字母指示的位置 */

private int currentIndex = -100;

/** 是否松手 */

private boolean isUp = true;

/** 字母测量的尺寸 */

private float measureText;

/** 数字模拟器 */

private Scroller scroller;

/** 触摸临界值 */

private float touchSlop;

/** 起始位置 */

private int startX = 100;

/** 变化比率 */

private float mX = 100;

//up事件的接口

public interface OnUpListener {

void up();

}

private OnUpListener onUpListener;

public interface OnLetterUpdateListener {

void onLetterUpdate(String letter);

}

public OnUpListener getOnUpListener() {

return onUpListener;

}

public void setOnUpListener(OnUpListener onUpListener) {

this.onUpListener = onUpListener;

}

public void setOnLetterUpdateListener(OnLetterUpdateListener onLetterUpdateListener) {

this.onLetterUpdateListener = onLetterUpdateListener;

}

private static final 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"};

private Paint paint;

// 单元格宽度

private int cellWidth;

// 单元格高度

private float cellHeight;

public SideBar(Context context) {

this(context, null);

}

public SideBar(Context context, AttributeSet attrs) {

this(context, attrs, 0);

}

public SideBar(Context context, AttributeSet attrs, int defStyle) {

super(context, attrs, defStyle);

init();

}

/**

* 初始化数字模拟器

*/

private void init() {

scroller = new Scroller(getContext());

touchSlop = ViewConfiguration.get(getContext()).getTouchSlop();

// 创建一个抗锯齿的画笔

paint = new Paint(Paint.ANTI_ALIAS_FLAG);

// 画笔文本加粗

paint.setTypeface(Typeface.DEFAULT_BOLD);

// 颜色

paint.setColor(getResources().getColor(R.color.text_blue_search));

setTextSize(26);

measureText = paint.measureText("M");

}

@Override

protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {

super.onMeasure(widthMeasureSpec, heightMeasureSpec);

int mHeight = getMeasuredHeight();

cellWidth = getMeasuredWidth();

cellHeight = mHeight * 1.0f / LETTERS.length;

if (!isUp) {

setMeasuredDimension(widthMeasureSpec * 3, heightMeasureSpec);

} else {

setMeasuredDimension(widthMeasureSpec, heightMeasureSpec);

}

}

@Override

protected void onDraw(Canvas canvas) {

// 遍历26个英文字母, 计算坐标, 进行绘制

for (int i = 0; i < LETTERS.length; i++) {

String letter = LETTERS[i];

// 计算x坐标

float dx = 0;

//float x = cellWidth * 0.5f - paint.measureText(letter) * 0.5f + 80;

// float x = cellWidth - paint.measureText(letter);

float x = cellWidth - measureText * 1.5f;

if (!isUp) {

mX = 1.0f;

}

switch (currentIndex - i) {

case -4:

dx = measureText * 1.5f * mX;

paint.setColor(getResources().getColor(R.color.text_blue_search_4));

setTextSize(27);

break;

case -3:

dx = measureText * 2.5f * mX;

paint.setColor(getResources().getColor(R.color.text_blue_search_3));

setTextSize(33);

break;

case -2:

dx = measureText * 4.0f * mX;

paint.setColor(getResources().getColor(R.color.text_blue_search_2));

setTextSize(38);

break;

case -1:

dx = measureText * 5.0f * mX;

paint.setColor(getResources().getColor(R.color.text_blue_search_1));

setTextSize(42);

break;

case 0:

paint.setColor(getResources().getColor(R.color.text_blue_search));

dx = measureText * 6.0f * mX;

setTextSize(50);

break;

case 1:

dx = measureText * 5.0f * mX;

paint.setColor(getResources().getColor(R.color.text_blue_search_1));

setTextSize(42);

break;

case 2:

dx = measureText * 4.0f * mX;

paint.setColor(getResources().getColor(R.color.text_blue_search_2));

setTextSize(38);

break;

case 3:

dx = measureText * 2.5f * mX;

paint.setColor(getResources().getColor(R.color.text_blue_search_2));

setTextSize(33);

break;

case 4:

dx = measureText * 1.5f * mX;

paint.setColor(getResources().getColor(R.color.text_blue_search_3));

setTextSize(28);

break;

default:

dx = 0;

paint.setColor(getResources().getColor(R.color.text_blue_search_4));

setTextSize(26);

break;

}

if (!isUp) { //触摸状态

x -= dx;

} else { //松手状态

x -= dx;

paint.setColor(getResources().getColor(R.color.text_blue_search));

setTextSize(26);

}

// 计算y坐标

Rect bounds = new Rect();

// 获取文本的矩形区域

paint.getTextBounds(letter, 0, letter.length(), bounds);

float y = cellHeight * 0.5f + bounds.height() * 0.5f + i * cellHeight;

// 绘制文本

if (letter.equals("I")) {

x += measureText * 0.2f;

}

canvas.drawText(letter, x, y, paint);

}

}

private int lastIndex = -1;

@Override

public boolean onTouchEvent(MotionEvent event) {

float y;

switch (event.getAction()) {

case MotionEvent.ACTION_DOWN:

scroller.forceFinished(true);

isUp = false;

setPadding(500, 0, 0, 0);

// 获取被点击到的字母索引

y = event.getY();

// 根据y值, 计算当前按下的字母位置

currentIndex = (int) (y / cellHeight);

if (currentIndex != lastIndex) {

if (currentIndex >= 0 && currentIndex < LETTERS.length) {

String letter = LETTERS[currentIndex];

if (onLetterUpdateListener != null) {

onLetterUpdateListener.onLetterUpdate(letter);

}

// 记录上一次触摸的字母

lastIndex = currentIndex;

}

}

break;

case MotionEvent.ACTION_MOVE:

// 获取被点击到的字母索引

y = event.getY();

// 根据y值, 计算当前按下的字母位置

currentIndex = (int) (y / cellHeight);

if (currentIndex != lastIndex) {

if (currentIndex >= 0 && currentIndex < LETTERS.length) {

String letter = LETTERS[currentIndex];

if (onLetterUpdateListener != null) {

onLetterUpdateListener.onLetterUpdate(letter);

}

// 记录上一次触摸的字母

lastIndex = currentIndex;

}

}

break;

case MotionEvent.ACTION_UP:

isUp = true;

lastIndex = -1;

//调用回调里面的方法

if (null != onUpListener) {

onUpListener.up();

}

smaooth();

break;

default:

break;

}

invalidate();

return true;

}

/**

* 开启数字模拟器

*/

private void smaooth() {

scroller.startScroll(startX, 0,

-99, 0, 550);

}

@Override

public void computeScroll() {

// 当scroller数据模拟完毕时, 不应该继续进行递归

// 反之, 如果正在模拟数据才进行递归的操作

if (scroller.computeScrollOffset()) {// 当前还是正在模拟数据中

// 把当前scroller正在模拟的数据取出来, 使用scrollTo方法切换屏幕

mX = ((float) scroller.getCurrX()) / 100f;

// scrollTo(currX, 0);

if (mX == 0.01f) {

setPadding(0, 0, 0, 0);

}

invalidate(); // 在触发当前方法, 相当于递归.

}

}

private void setTextSize(int size) {

paint.setTextSize(size+10);

}

}