TextWatch 接口方法如下：
方法执行顺序：beforeTextChanged() --> onTextChanged() --> afterTextChanged()
new TextWatcher() {
/**
* This method is called to notify you that,
* within s, the count characters beginning at
* start are about to be replaced by
* new text with length after.
* It is an error to attempt to make changes to s from this callback
*
* 在原来字符串 s 中，从 start 位置开始
* 正打算用 after 长度新字符串 替换 count 长度字符串
* @param s
* @param start
* @param count
* @param after
*/
@Override
public void beforeTextChanged(CharSequence s, int start, int count, int after) {
}
/**
* This method is called to notify you that,
* within s, the count characters beginning at start
* have just replaced old text that had length before.
* It is an error to attempt to make changes to s from this callback.
*
* 在改变后的字符串 s 中，从 start 位置开始
* 将 before 位的字符串 替换成为 count 位的字符串
*
* @param s 改变前的字符串
* @param start 开始发生替换初始index
* @param before 被替换掉字符串的大小
* @param count 替换字符串的大小
*/
@Override
public void onTextChanged(CharSequence s, int start, int before, int count) {
}
/**
* 改变完后 对结果进一步的修改 注意不要发生迭代死循环
*/
@Override
public void afterTextChanged(Editable s) {
}
也可以通过打印日志的方式进行验证。
通过对count、after、before等进行判定实现字符串自动补充，自动删除多个等操作，增强交互。
