DisMissState.build.<anonymous closure>.<anonymous closure>-CodePudding

I have a problem when I try to delete the item and it doesn't accept to delete the item. I am using ConfirmDismiss.

Error:

Unhandled Exception: type 'Null' is not a subtype of type 'bool' _DisMissState.build.. (package:advanced_part_2/dismissible.dart:84:30)

_DismissibleState._handleDismissStatusChanged (package:flutter/src/widgets/dismissible.dart:498:11)

Code:

 confirmDismiss: (DismissDirection dir) async {
                if (dir == DismissDirection.startToEnd) {
              //    AlertDialog ad =
                  final bool res = await showDialog(
                    context: context,
                    builder: (BuildContext context) {
                      return AlertDialog(
                        content: Text('Are You Sure you want to delete'),
                        actions:<Widget> [
                          ElevatedButton(
                              onPressed: () {
                                Navigator.of(context).pop();
                              },
                              child: Text(
                                'cancel',

                              )),
                          ElevatedButton(
                              onPressed: () {
                                setState(() {
                                  genList.removeAt(index);
                                });
                                Navigator.of(context).pop();
                              },
                              child: Text(
                                'Delete',
                                style: TextStyle(color: Colors.red),
                              ))
                        ],
                      );
                    },
                  );
                  return res;
                } else {
                  return true;
                }
              },

CodePudding user response：

It is because when your calling the following code:

final bool res = await showDialog(...);

it will return a null value, see https://api.flutter.dev/flutter/material/showDialog.html

And, you also not giving any return value when clicking the button:

ElevatedButton(
     onPressed: () {
        Navigator.of(context).pop();
      },
      child: Text(
        'cancel',

      )),

You can't use Navigator.of(context).pop();. Instead, you need to use either:

Navigator.pop(context, false);

Navigator.pop(context, true);

Then, after that, you need to handle the nullable returned value from show dialog by giving a default value when null. Something like this:

bool res = await showDialog(...);
if(res == null) res = false;

CodePudding user response：

showDialog can return null when the dialog is dismissed (e.g. user clicks outside the dialog) so you've to account for that by changing the type to:

final bool? res = await showDialog(/* your code */);

then in your logic below, you have to check for null:

if(res == null) {
 // handle dismiss
} else if (res == false) {
 // handle cancel
} else {
 // handle confirm/true
}

As @Er1 mentioned in the comment, you'll also need to pass true or false when popping the dialog:

Navigator.of(context).pop(true);
// or
Navigator.of(context).pop(false);

The above still applies since barrierDismissible is true by default.

CodePudding user response：

final bool res = await showDialog(
                    context: context,
                    barrierDismissible: false,
                    builder: (BuildContext context) {
                      return AlertDialog(
                        content: Text('Are You Sure you want to delete'),
                        actions:<Widget> [
                          ElevatedButton(
                              onPressed: () {
                                Navigator.of(context).pop(false);
                              },
                              child: Text(
                                'cancel',

                              )),
                          ElevatedButton(
                              onPressed: () {
                                setState(() {
                                  genList.removeAt(index);
                                });
                                Navigator.of(context).pop(true);
                              },
                              child: Text(
                                'Delete',
                                style: TextStyle(color: Colors.red),
                              ))
                        ],
                      );
                    },
                  );

Add false and true to the pop() to make the showDialog return a boolean.

But keep in mind if you don't set barrierDismissible in showDialog to false you can get null returned if you tap outside of the dialog.