Flutter Prevent FutureBuilder from running twice-CodePudding

I am using FutureBuilder in flutter to fill up a drop down menu DropdownButtonFormField, i have the method

                            onChanged: (String? newValue) {
                              setState(() {
                                dropdownBrokers = newValue!;
                              });
                            },

Which allows the widget to rebuild and then assign the new value selected from the dropdown list. However, i am now experiencing a problem from my research stating that whenever the setState() is called, the future builder runs again, which makes my dropdown menu populate again. This is the full code snippet

     FutureBuilder <List<Broker>>(
      future: brokerData,
      builder: (context, snapshot){
        if(snapshot.hasData){
          //do what needs to be done here
          List<Broker>? data = snapshot.data;
          for(var i = 0; i< data!.length; i  ){
            _brokers.add(data[i].firmName);
            print(data[i].firmName);
          }

             return Container(
                      padding: EdgeInsets.all(10),
                      child: InputDecorator(
                        decoration: InputDecoration(
                            labelStyle: TextStyle(
                                color: Colors.grey
                            ),
                            isDense: true,
                            contentPadding: EdgeInsets.all(7.0),
                            errorStyle: TextStyle(color: Colors.redAccent, fontSize: 16.0),
                            hintText: 'Select Broker',
                            border: OutlineInputBorder(borderRadius: BorderRadius.circular(5.0))),
                        child: DropdownButtonHideUnderline(
                          child: DropdownButtonFormField<String>(
                            alignment: Alignment.center,
                            value: dropdownBrokers,
                            icon: const Icon(Icons.arrow_downward),
                            iconSize: 24,
                            elevation: 16,
                            style: const TextStyle(color: Colors.indigo),

                            
                            onChanged: (String? newValue) {
                              setState(() {
                                dropdownBrokers = newValue!;
                              });
                            },

                            items: _brokers.map<DropdownMenuItem<String>>((String value) {
                              return DropdownMenuItem<String>(
                                value: value,
                                child: Text(value),
                              );
                            }).toList(),
                          ),
                        ),
                      ),
                    ),
  );

Also i get an error when i reselect an item. How do i prevent the FutureBuilder from running twice

CodePudding user response：

FutureBuilder will always be rendered once unless recreated in the build method. So the solution to this can be done in two ways: 1: Only calling brokerData in the FutureBuilder method or 2: Only calling ```brokerData`` in the initState override. You can not do both.

And I assume the data to be populated in the dropdown comes from the future builder. Then use snapshot.data of the future instead of an already created value in this case:

items: _brokers.map<DropdownMenuItem<String>>((String value) {
                             return DropdownMenuItem<String>(
                               value: value,
                               child: Text(value),
                             );

Change to:

items: snapshot.data.map<DropdownMenuItem<String>>((String value) {
                              return DropdownMenuItem<String>(
                                value: value,
                                child: Text(value),
                              );