How to fix "the method 'cancel' called on null" while working with http requests flutter - flutter

Question

I'm trying to athenticate using APIs from a flutter app but i get these errors everytime i click Login Button
final resp = await http.post("http://192.168.73.5/myserv/login.php", body: {
"login": "login",
"apid": "re0b53fd92d4b1593db1880az322d66ea9d4",
"email": _email,
"pass": _password,
});
var __data =json.decode(resp.body);
if (__data.length == 0) {
final snackbar = SnackBar(
content: Text('Server error'),
);
scaffoldKey.currentState.showSnackBar(snackbar);
} else if (__data[0]['resp'] == 'error') {
final snackbar = SnackBar(
content: Text('Password or email is incorrect!'),
);
scaffoldKey.currentState.showSnackBar(snackbar);
} else if (__data[0]['resp'] == 'sucess') {
final snackbar = SnackBar(
content: Text('You are logged in'),
);
scaffoldKey.currentState.showSnackBar(snackbar);
Navigator.of(context)
.pushReplacement(MaterialPageRoute(builder: (context) => HomeApp()));
}
}
══╡ EXCEPTION CAUGHT BY WIDGETS LIBRARY ╞═══════════════════════════════════════════════════════════
I/flutter (29517): The following NoSuchMethodError was thrown while finalizing the widget tree:
I/flutter (29517): The method 'cancel' was called on null.
I/flutter (29517): Receiver: null
I/flutter (29517): Tried calling: cancel()
I/flutter (29517): When the exception was thrown, this was the stack:

Answer 1

My suggestion would be to take a look to your dispose method. There you might notice a statement calling a cancel method on something that was never initiated or used, only declared. In my case I got this error because at the disposed method I was trying to cancel a subscription to a Firebase service that I had not used. I never attached a listener to it, therefore when trying to cancel it, Flutter complained saying "the method cancel was called on null". I deleted the unnecessary line at dispose method and the error resolved. Hope the explanation helps somebody.