Selected items not displayed the DropdownButton in Flutter-CodePudding

i am a beginner of flutter.iam creating a DropdownButton to list the items.item was loading well on DropdownButton .but loading item selected not displayed at the DropdownButton i don't know. what i tried so far i attached below. what is the wrong here onChanged: (value) => setState(() => this.valueschoose = value,

DropdownButton<String>(
                    items: <String>['A', 'B', 'C', 'D'].map((String value) {
                      return DropdownMenuItem<String>(
                        value: value,
                        child: Text(value),
                      );
                    }).toList(),
                    onChanged: (value) => setState(() => this.valueschoose = value,
    
                  )),

CodePudding user response：

you forget to use value in the dropdown widget

 String? dropdownvalue;
  Widget build(BuildContext context) {
    return DropdownButton<String>(
        value: dropdownvalue, // here need to add value of dropdown
        items: <String>['A', 'B', 'C', 'D'].map((String value) {
          return DropdownMenuItem<String>(
            value: value,
            child: Text(value),
          );
        }).toList(),
        onChanged: (value) => setState(
              () => dropdownvalue = value,
            ));
  }

Visit for the completed code

CodePudding user response：

you are missing this value of dropdown button

DropdownButton<String>(
                    value: this.valueschoose,
                    items: <String>['A', 'B', 'C', 'D'].map((String value) {
                      return DropdownMenuItem<String>(
                        value: value,
                        child: Text(value),
                      );
                    }).toList(),
                    onChanged: (value) => setState(() => this.valueschoose = value,
    
                  )),