flutter升级后WhitelistingTextInputF

将WhitelistingTextInputFormatter(RegExp("[0-9]"))升级FilteringTextInputFormatter.allow(RegExp("[0-9]")),
一下为新方法

1.只允许输入数

TextField(
      inputFormatters: [
       FilteringTextInputFormatter.allow(RegExp("[0-9.]")),
      ],
   ),

2.only allow a to Z

TextField(
   FilteringTextInputFormatter.allow(RegExp('[a-zA-Z]')
   ),

3.禁止abF!.

inputFormatters: [
      FilteringTextInputFormatter.deny(RegExp('[abF!.]')
              ),
            ],

4.允许输入大小写字母，但是禁止abF!.

inputFormatters: [     
                 FilteringTextInputFormatter.allow(RegExp('[a-zA-Z]')),
                 FilteringTextInputFormatter.deny(RegExp('[abFeG]')),
             
            ],