形如：183 2185 9453

类源码：

 public static int mobileChanged(CharSequence s, int start, int before, int count, EditText editText,int changdu) {
        StringBuilder sb = new StringBuilder();
        int index=s.length();
        if(changdu<s.length()){
            //如果是输入字符
            switch (s.length()){
                case 4:
                    //1832
                    Log.i("9私聊","4");
                    sb.append(s.charAt(0));
                    sb.append(s.charAt(1));
                    sb.append(s.charAt(2));
                    sb.append(" ");
                    sb.append(s.charAt(3));

                    index++;
                    editText.setText(sb.toString());
                    editText.setSelection(index);
                    break;
                case 9:
                    //183 21859
                    Log.i("9私聊","9");
                    sb.append(s.charAt(0));
                    sb.append(s.charAt(1));
                    sb.append(s.charAt(2));
                    sb.append(s.charAt(3));
                    sb.append(s.charAt(4));
                    sb.append(s.charAt(5));
                    sb.append(s.charAt(6));
                    sb.append(s.charAt(7));
                    sb.append(" ");
                    sb.append(s.charAt(8));
                    index++;
                    editText.setText(sb.toString());
                    editText.setSelection(index);
                    break;
            }
        }else{
            //删除字符

            //如果是输入字符
            switch (s.length()){
                case 4:
                    //183 2
                    Log.i("9私聊","5");
                    sb.append(s.charAt(0));
                    sb.append(s.charAt(1));
                    sb.append(s.charAt(2));
                    index--;
                    editText.setText(sb.toString());
                    editText.setSelection(index);
                    break;
                case 9:
                    //183 2185 9
                    Log.i("9私聊","10");
                    sb.append(s.charAt(0));
                    sb.append(s.charAt(1));
                    sb.append(s.charAt(2));
                    sb.append(s.charAt(3));
                    sb.append(s.charAt(4));
                    sb.append(s.charAt(5));
                    sb.append(s.charAt(6));
                    sb.append(s.charAt(7));
                    index--;
                    editText.setText(sb.toString());
                    editText.setSelection(index);
                    break;
            }
        }


        return index;
    }

activity里面调用：

private TextWatcher numberWatcher =new TextWatcher() {
        private int changchu;
        @Override
        public void beforeTextChanged(CharSequence s, int start, int count, int after) {
        }
        @Override
        public void onTextChanged(CharSequence s, int start, int before, int count) {
           changchu= ForNumber.mobileChanged(s,start,before,count,et_number,changchu);
            
        }
        @Override
        public void afterTextChanged(Editable s) {

        }
    };

onTextChanged参数解释及实现EditText字数监听