flutter - How to check length of value in onchange method in flutter

Question

Check value of Textfield in onChange method is empty or not if user remove all values from Textfield show in TextView "0".

Mean I want real time change and show change in TextView.

examples:

when user add value its work fine

when user remove all values here is

TextFormField(
                          keyboardType: TextInputType.number,
                          textInputAction: TextInputAction.done,
                          maxLines: 1,
                          controller: _paidController,

                      onChanged: (text) {
                        int newValue = int.parse(text);
                        setState(() {
                          if (text.trim().isEmpty) {
                            _paidController.text = "0";

                            print("set 0");

                            unpaid = 0;
                            paid = 0;

                          } else {
                            paid = newValue;
                            unpaid = grandTotal.toInt() - paid;
                          }
                        });
                      },

                      onFieldSubmitted: (value) {
                        int newValue = int.parse(value);
                        setState(() {
                          if (value.isEmpty) {
                            paid = 0;
                            unpaid = grandTotal.toInt();
                          }
                          paid = newValue;
                          unpaid = grandTotal.toInt() - paid;
                        });
                      },
                      cursorColor: Theme.of(context).primaryColor,
                      style: TextStyle(
                        fontFamily: "Light",
                        color: Theme.of(context).primaryColor,
                      ),
                      decoration: InputDecoration(
                        filled: true,
                        fillColor: Colors.white,
                        labelStyle: TextStyle(
                          color: Color(0XFF17145A),
                          fontFamily: "Light",
                        ),
                        labelText: 'Paid Amount',
                      ),
                    ),

标签： flutterdart

Answer 1

Use text.trim().isEmpty to check whether there has value on textField.

  onChanged: (text) {
      if (text.trim().isEmpty){
        _paidController.text = "0";  // set to zero if no value
        unpaid = grandTotal.toInt();
      }else{
        unpaid = grandTotal.toInt() - paid;
      }
   }