I have a simple code using stream builder but I keep getting missing return. And I have two return in my code as follow:

               Expanded(
                  flex: 1,
                  child: Column(
                    children: [
                      const Text('Temperature:'),
                      StreamBuilder<List<int>>(
                          stream: stream,
                          builder: (BuildContext context,
                              AsyncSnapshot<List<int>> snapshot) {
                            if (snapshot.hasError) {
                              return Text('Error: ${snapshot.error}');
                            } else if (snapshot.connectionState ==
                                ConnectionState.active) {
                              // geting data from bluetooth
                              temperature = _dataParser(snapshot.data);
                              if (temperature != "nan") {
                                return Text(temperature);
                              }
                            }
                          }),
                    ],
                  ),
                ),

CodePudding user response：

You're getting error because you have no "default return". You have return for two cases:

1. snapshot.hasError
2. snapshot.connectionState == ConnectionState.active

But if both conditions are false - your code will return null.

Adjust your code like this:

Expanded(
  flex: 1,
  child: Column(
    children: [
      const Text('Temperature:'),
      StreamBuilder<List<int>>(
          stream: stream,
          builder: (BuildContext context,
              AsyncSnapshot<List<int>> snapshot) {                           
                if (snapshot.connectionState == ConnectionState.waiting) {
                    return CircularProgressIndicator();
                } else if (snapshot.connectionState == ConnectionState.active || snapshot.connectionState == ConnectionState.done) {
                    if (snapshot.hasError) {
                        return const Text('Error');
                    }
                    if (snapshot.hasData) {
                        temperature = _dataParser(snapshot.data);
                        if (temperature == "nan") {
                            return Text("Wrong temperature");
                        } 
                        return Text(temperature);
                    } else {
                        return const Text('Empty data');
                    }
                } else {
                    return Text('State: ${snapshot.connectionState}');
                }
        }),
        ],
    ),
),

It's just sample code, you can adjust it in way that best fits your needs