How can i call the Future<string> rest api in flutter?

Question

How can I call the Future API? This is my API code

class ApiClient{

  Future<String> getPasswordToken(String username, String password) async {
    var response =
        await http.post(Uri.parse(this.apiBaseUrl + "/auth/token"), headers: {
      "Accept": "application/json"
    }, body: {
      "username": username,
      "password": password
    });

    if (response.statusCode == 200) {
      var token = OAuthToken.fromJson(json.jsonDecode(response.body));
      return token.accessToken;
    } else {
      throw Exception('Failed to fetch access token');
    }
  }
}

And am using the below container to call the API. Based on the API response need to navigate another screen I have struck the calling API in onPressed

var apiClient = new ApiClient();
Container(
      margin: const EdgeInsets.only(top: 20.0),
      padding: const EdgeInsets.only(left: 20.0, right: 20.0),
      child: new Row(
        children: <Widget>[
          new Expanded(
            child: FlatButton(
              shape: new RoundedRectangleBorder(
                  borderRadius: new BorderRadius.circular(28.0)),
              splashColor: this.primaryColor,
              color: this.primaryColor,
              child: new Row(
                children: <Widget>[
                  new Padding(
                    padding: const EdgeInsets.only(left: 20.0),
                    child: Text(
                      "LOGIN",
                      style: TextStyle(color: Colors.white),
                    ),

                  ),

                 new Expanded(
                    child: Container(),
                  ),
                  new Transform.translate(
                    offset: Offset(15.0, 0.0),
                    child: new Container(
                      padding: const EdgeInsets.all(5.0),
                      child: FlatButton(
                        shape: new RoundedRectangleBorder(
                            borderRadius: new BorderRadius.circular(28.0)),
                        splashColor: Colors.white,
                        color: Colors.white,
                        child: Icon(
                          Icons.arrow_forward,
                          color: this.primaryColor,
                        ),
                      onPressed: apiClient.getPasswordToken("",""),

                  /*        child:new FutureBuilder(future: apiClient.getClientToken(),
                            builder: (BuildContext context, AsyncSnapshot response) {
                              response.hasData==false? new SignIn(): new Scaffold(
                                appBar: new AppBar(title: new Text("Future Builder"),),
                                body: new Center(
                                  child: new Text("Build your widgets"),
                                ),
                              );
                            }
                        );*/
                      ),
                    ),
                  )
                ],
              ),
              onPressed: () => {},
              //onPressed: apiClient.getPasswordToken(emailInputField.key,emailInputField.key),
            ),
          ),
        ],
      ),
    );

I tried the above code. it showing The argument type 'Future' can't be assigned to the parameter type '() → void

Solution

This should do what you want:

onPressed: () => apiClient.getPasswordToken("",""),

or

onPressed: () async {
  var result = await apiClient.getPasswordToken("","");
  print(result);
  setState(() => this.foo = result); // you can omit `this.` it's just for demonstration purposes that this line would modify the widgets state
}

Comments

[sekhar]

Thank u. How can navigate to next page after getting the response code 200?

[Günter Zöchbauer]

Your getPasswordToken throws an exception when the result is not 200, you you can just wrap the code in the onPressed: () async { try { await getPasswordToken(); Navigator.of(context)....} on Exception catch(e) { ...} with one of the methods that has replace or push and remove in them docs.flutter.io/flutter/widgets/Navigator-class.html to get the login page from the history stack and replace it by a different one.