Flutter/Dart - PageViewBuilder 提供的数据的空检查错误

Question

我在 PageViewBuilder;

提供的数据上收到以下空检查错误

The following _CastError was thrown building:
Null check operator used on a null value

When the exception was thrown, this was the stack: 
#0      _StageBuilderState.createViewItem (package:speakoholic/screens/mainStage.dart:488:161)
#1      _StageBuilderState.build.<anonymous closure> (package:speakoholic/screens/mainStage.dart:138:18)

488行是speakcraft.tagname!调用这个函数时；

child: editIcon(
       context: context, 
       userid:speakcraft.userid!, 
       audioid:speakcraft.audioid!, 
       title: speakcraft.title!, 
       tagname:speakcraft.tagname!),

而第 138 行是 createViewItem

   PageView.builder(
    itemCount: widget.speakcrafts.length,        
    itemBuilder: (context, int currentIndex) {
      return createViewItem(widget.speakcrafts[currentIndex], context, currentIndex, widget.speakcrafts.length );
    },       
  );

这是函数；

Widget editIcon({
  required BuildContext? context, 
  required int? userid, 
  required int? audioid, 
  required String? title, 
  required String? tagname}) {
  return
    FutureBuilder<int?>(                       
        ///some stuff
    );
}

如何解决这些 nullcheck 错误？

Answer 1

问题是您试图通过 Bang ! 运算符（也称为 null 断言运算符）来使用不可为 null 的值来消除可空性：tagname:speakcraft.tagname!.

另一方面，您的属性可以为空，因为 String? tagname 意味着 tagname 可以是 null。

因此，为了避免这种情况，您可以更改 editIcon 方法：

editIcon(
   ...
   tagname:speakcraft?.tagname ?? 'some default value'),

Flutter/Dart - PageViewBuilder 提供的数据的空检查错误

Flutter/Dart - Null Check Error with data provided by PageViewBuilder

null-check

dart

flutter

flutter-pageview