Looking up a deactivated widget's ancestor is unsafe

I am new in Flutter and I am trying receive data with a Dialog. When a click in textField the error of image2 appear...

show(BuildContext context){

    var dialog = Dialog(
      child: Container(
        margin: EdgeInsets.all(8.0),
        child: Form(
          child: Column(
            mainAxisSize: MainAxisSize.min,
            children: <Widget>[
              TextFormField(
                decoration: InputDecoration(
                    labelText: "Insira o número de telefone",
                    border: OutlineInputBorder(
                        borderRadius: BorderRadius.all(Radius.circular(2.0)))),
              ),
              Row(
                mainAxisAlignment: MainAxisAlignment.end,
                children: <Widget>[
                  FlatButton(
                      onPressed: () {
                        Navigator.of(context).pop();
                      },
                      child: Text("Cancelar")),
                  FlatButton(
                      onPressed: () {
                        Navigator.of(context).pop();
                      },
                      child: Text("Aceitar"))
                ],
              )
            ],
          ),
        ),
      ),
    );

    showDialog(context: context,builder: (context){
      return dialog;
    });
  }

This is my code.

I/flutter (31032): Looking up a deactivated widget's ancestor is unsafe.
I/flutter (31032): At this point the state of the widget's element tree is no longer stable. To safely refer to a
I/flutter (31032): widget's ancestor in its dispose() method, save a reference to the ancestor by calling
I/flutter (31032): inheritFromWidgetOfExactType() in the widget's didChangeDependencies() method.
I/flutter (31032): 

Solution 1:

Declare a global variable

    final GlobalKey<ScaffoldState> _scaffoldKey = GlobalKey<ScaffoldState>();

then register the key on your widget build's scaffold eg

    @override
    Widget build(BuildContext context) {
     return Scaffold(
       key: _scaffoldKey,
       ...

then on the dialog

show(BuildContext context){

var dialog = Dialog(
  child: Container(
    margin: EdgeInsets.all(8.0),
    child: Form(
      child: Column(
        mainAxisSize: MainAxisSize.min,
        children: <Widget>[
          TextFormField(
            decoration: InputDecoration(
                labelText: "Insira o número de telefone",
                border: OutlineInputBorder(
                    borderRadius: BorderRadius.all(Radius.circular(2.0)))),
          ),
          Row(
            mainAxisAlignment: MainAxisAlignment.end,
            children: <Widget>[
              FlatButton(
                  onPressed: () {
                    Navigator.of(context).pop();
                  },
                  child: Text("Cancelar")),
              FlatButton(
                  onPressed: () {
                    Navigator.of(context).pop();
                  },
                  child: Text("Aceitar"))
            ],
          )
        ],
      ),
    ),
  ),
);

Pass that scaffold context to the showDialog method

showDialog(context: _scaffoldKey.currentContext ,builder: (context){
  return dialog;
 });
}

Solution 2:

Try This

Give different context name for dialog

 showDialog(context: context,builder: (dialogContex){
              return Dialog(
                child: Container(
                  margin: EdgeInsets.all(8.0),
                  child: Form(
                    child: Column(
                      mainAxisSize: MainAxisSize.min,
                      children: <Widget>[
                        TextFormField(
                          decoration: InputDecoration(
                              labelText: "Insira o número de telefone",
                              border: OutlineInputBorder(
                                  borderRadius: BorderRadius.all(Radius.circular(2.0)))),
                        ),
                        Row(
                          mainAxisAlignment: MainAxisAlignment.end,
                          children: <Widget>[
                            FlatButton(
                                onPressed: () {
                                  Navigator.of(dialogContex).pop();
                                },
                                child: Text("Cancelar")),
                            FlatButton(
                                onPressed: () {
                                  Navigator.of(context).pop();
                                },
                                child: Text("Aceitar"))
                          ],
                        )
                      ],
                    ),
                  ),
                ),
              );
            });

Solution 3:

I got the same error when attempting to open a dialog and I found a solution here: github flutter issues. Specifically, I followed the poster's recommendation, which was to create a GlobalKey and associate it with the Scaffold widget, and use the context from that key when creating the dialog. In my case, I have a globally accessible object which holds the GlobalKey:

MyGlobals myGlobals = MyGlobals();
class MyGlobals {
  GlobalKey _scaffoldKey;
  MyGlobals() {
    _scaffoldKey = GlobalKey();
  }
  GlobalKey get scaffoldKey => _scaffoldKey;
}

In the Scaffold widget constructor call:

Scaffold(
  appBar: ...,
  body: ...,
  drawer: ...,
  key: myGlobals.scaffoldKey,
)

And in the showDialog call:

showDialog<String>(
  barrierDismissible: ...,
  builder: ...,
  context: myGlobals.scaffoldKey.currentContext,
);