无法在 flutter 中实现 DropdownButton

Question

I am trying to implement a simple DropdownButton with which the user can select a currency.

 Container(
        height: 150.0,
        alignment: Alignment.center,
        padding: EdgeInsets.only(bottom: 30.0),
        color: Colors.lightBlue,
        child: DropdownButton<String>(
          items: [
            DropdownMenuItem(child: Text('USD')),
            DropdownMenuItem(child: Text('EUR')),
            DropdownMenuItem(child: Text('GBP')),
          ],
          value: 'USD',
          onChanged: (value) {
            print(value);
          },
        ),
      ),

But i am getting below error

Failed assertion: line 620 pos 15: 'items == null || items.isEmpty || value == null || items.where((DropdownMenuItem<T> item) => item.value == value).length == 1': is not true.

How to overcome this error? Thanks in advance

Answer 1

As per the Documentation here

Your DropdownButton items expects a DropdownMenuItem with both child and value

So Use DropdownMenuItem as

items: [
            DropdownMenuItem(child: Text('USD'), value: 'USD'),
            DropdownMenuItem(child: Text('EUR'), value: 'EUR'),
            DropdownMenuItem(child: Text('GBP'), value: 'GBP'),
          ],

For dynamic dropdown use it as.

  var dropdownvalue = 'USD';

 items: <String>['USD', 'EUR', 'GPB']
              .map<DropdownMenuItem<String>>((String value) {
            return DropdownMenuItem<String>(
              value: value,
              child: Text(value),
            );
          }).toList(),
          value: dropdownvalue,
          onChanged: (value) {
            setState(() {
              dropdownvalue = value;
            });
          },

Hope it solves!