flutter - 如何修复错误 "This function has a return type of Column, but doesn' t 以返回语句结尾”

Question

正在开发一个演示聊天应用程序，尝试从 firestore 返回数据。并收到错误。

child: Column(
      mainAxisAlignment: MainAxisAlignment.spaceBetween,
      crossAxisAlignment: CrossAxisAlignment.stretch,
      children: <Widget>[
        StreamBuilder<QuerySnapshot>(
          stream: _firestore.collection('messagees').snapshots(),
          builder: (context, snapshot) {
            if (snapshot.hasData) {
              final messages = snapshot.data.documents;
              List<Text> messageWidgets = [];
              for (var message in messages) {
                final messageText = message.data['text'];
                final messageSender = message.data['sender'];
                final messageWidget =
                    Text('$messageText from $messageSender');
                messageWidgets.add(messageWidget);
              }

              return Column(
                children: messageWidget,
              );
            }
          },
        ),

我确实有一个返回语句，所以不应该出现这个错误

Answer 1

如果快照没有数据你还没有写返回类型widget

child: Column(
  mainAxisAlignment: MainAxisAlignment.spaceBetween,
  crossAxisAlignment: CrossAxisAlignment.stretch,
  children: <Widget>[
    StreamBuilder<QuerySnapshot>(
      stream: _firestore.collection('messagees').snapshots(),
      builder: (context, snapshot) {
        if (snapshot.hasData) {
          final messages = snapshot.data.documents;
          List<Text> messageWidgets = [];
          for (var message in messages) {
            final messageText = message.data['text'];
            final messageSender = message.data['sender'];
            final messageWidget =
                Text('$messageText from $messageSender');
            messageWidgets.add(messageWidget);
          }

          return Column(
            children: messageWidget,
          );
        }else{ // put this else block
          return Container(
             child: Text('No Data Found'),
          ),
         }
      },
    ),