How to make Alert Dialog working in flutter - flutter

Question

I am using below code to register the user, there is an option to upload image , if it is null the user won't be registered, that is working accurately, only thing I am facing is that if the image is null it should the alert dialog to the user , but the alert dialog is not working at all.
How should I implement the alert dialog?
if (avatarImageFile != null ) {
FirebaseAuth.instance
.createUserWithEmailAndPassword(
email: emailInputController.text,
password: pwdInputController.text)
.then((currentUser) =>
Firestore.instance
.collection("users")
.document(currentUser.user.uid)
.setData({
"username": userNameInputController.text,
"email": emailInputController.text,
})
.then((result) =>
{
uploadFile(currentUser.user.uid),
print(currentUser.user.getIdToken()),
currentUser.user.sendEmailVerification(),
Navigator.pushAndRemoveUntil(
context,
MaterialPageRoute(
builder: (context) =>
MainScreen(
)),
(_) => false),
})
.catchError((err) => print(err)))
.catchError((err) => print(err));
}
else {
print("Please Upload the Image");
AlertDialog(
title: Text("Image Required"),
content: Text("Please upload the image"),
actions: <Widget>[
FlatButton(
child: Text("Close"),
onPressed: () {
Navigator.of(context).pop();
},
)
],
);
}

Answer 1

You need to use the function showDialog so the dialog appears:
else {
print("Please Upload the Image");
showDialog(
context: context,
builder: (BuildContext context) {
return AlertDialog(
title: Text("Image Required"),
content: Text("Please upload the image"),
actions: <Widget>[
FlatButton(
child: Text("Close"),
onPressed: () {
Navigator.of(context).pop();
},
)
],
);
};
);
}

Answer 2

Peter Haddad's answer solves the problem but I would suggest placing the AlertDialog in a widget so that it would be easy to reuse the AlertDialog again. Here is how I did it for my project:
Dialogs.dart:
import 'package:flutter/material.dart';
enum alertDialogAction { cancel, save }
class Dialogs {
static Future<alertDialogAction> alertDialog(
BuildContext context,
String title,
String body,
String cancel,
String save,
) {
Future<alertDialogAction> action = showDialog(
context: context,
barrierDismissible: true,
builder: (BuildContext context) {
return AlertDialog(
shape: RoundedRectangleBorder(
borderRadius: BorderRadius.circular(10),
),
title: Text(title),
content: Text(body),
actions: <Widget>[
FlatButton(
onPressed: () =>
Navigator.pop(context, alertDialogAction.cancel),
child: Text(cancel)),
RaisedButton(
color: Colors.orange,
onPressed: () =>
Navigator.of(context).pop(alertDialogAction.save),
child: Text(
save,
style: TextStyle(color: Colors.white),
)),
],
);
});
return (action != null) ? action : alertDialogAction.cancel;
}
Here is how you can call it:
onPressed:() async {
final action= await Dialogs.alertDialog(context,"Title","Body","Cancel","Save");
//cancel and save are the button text for cancel and save operation
if(action==alertDialogAction.save){
//do something
Navigator.pop(context);
}
}

Answer 3

You can also show a dialog box using scaffold, for example,
Scaffold.of(context).showSnackBar(SnackBar(content: AlertDialog(content: Text('Alert!!!'))));
But you have to keep in mind that context should be of the current scaffold.
So you might want to wrap the body property (in Scaffold) in a Builder Widget and then when you use context inside that builder widget, that context will be of current scaffold.

Answer 4

showDialog(
context: context,
builder: (BuildContext context) {
return AlertDialog(
title: Text("Your Title!!!"),
content: Text("Your Content!!!"),
actions: <Widget>[
FlatButton(
child: Text("Close"),
onPressed: () {
Navigator.of(context).pop();
},
)
],
);
};
);