Dart 正则表达式错误尝试调用使用？

Question

我有

Error: Method 'group' cannot be called on 'RegExpMatch?' because it is potentially null.

 - 'RegExpMatch' is from 'dart:core'.

Try calling using ?. instead.

                final everything = match.group(0);

我的源代码在下面，只是一个简单的正则表达式。

我应该在哪里解决这个问题？？

RegExp regExp = new RegExp(r'[0-9][0-9]');

RegExpMatch match = regExp.firstMatch(results.text);
         
final everything = match.group(0);

---

我是这样改源码的

  RegExp regExp = new RegExp(r'C(S|N)-[0-9][0-9][0-9]-[0-9][0-9][0-9]');

  if (regExp.hasMatch(results.text)){
     
        RegExpMatch match = regExp.firstMatch(results.text);
         
        final everything = match!.group(0);
        _showMyDialog(everything);
          
  }

仍然发生错误。

lib/camera_preview_scanner.dart:77:44: Error: A value of type 'RegExpMatch?' can't be assigned to a variable of type 'RegExpMatch' because 'RegExpMatch?' is nullable and 'RegExpMatch' isn't.

 - 'RegExpMatch' is from 'dart:core'.

                RegExpMatch match = regExp.firstMatch(results.text);

                                           ^

lib/camera_preview_scanner.dart:79:36: Warning: Operand of null-aware operation '!' has type 'RegExpMatch' which excludes null.

 - 'RegExpMatch' is from 'dart:core'.

                final everything = match!.group(0);

---

解决方案

使用RegExp! 代替RegExp

  RegExp! regExp = new RegExp(r'C(S|N)-[0-9][0-9][0-9]-[0-9][0-9][0-9]');

  if (regExp.hasMatch(results.text)){
     
        RegExpMatch match = regExp.firstMatch(results.text);
         
        final everything = match!.group(0);
        _showMyDialog(everything);
          
  }

Answer 1

做

final everything = match!.group(0);

或更好

if(match != null){ 
   final everything = match!.group(0);
}