TextInput如何限制输入字符为某些字符
======================

TextInput的inputFilter属性可设置正则表达式，用于校验输入字符。校验不通过时，输入无效。参考代码如下：

@Entry
@Component
struct Index {
  controller: TextInputController = new TextInputController();

  build() {
    Column() {
      TextInput({ placeholder: 'Please input a password', text: '123456', controller: this.controller })
        .type(InputType.Password)
        .placeholderColor(Color.Gray)
        .inputFilter('\[0-9\]', (val) => { _//Only allow the input of characters 0-9, other characters are invalid_
          console.error('TextInputExample : ' + val);
      _    // Invalid input return 0_
          return 0;
        })
    }
  }
}