为什么Facebook在扑朔迷离地登录数据后，futureBuilder回调不调用? [英] why futureBuilder callback is not calling after facebook logged in data in flutter?
问题描述
我是新手，所以如果我错了，请告诉我.在我的应用程序中，我必须使用Facebook登录，所以我在使用的以下代码中使用了RawMaterialButton和onPressed函数
I am newbie in flutter so please let me know if i am wrong.In my application i have to logged in using facebook so i took a RawMaterialButton and in onPressed function in used following code
child: RawMaterialButton(
onPressed: () {
FutureBuilder<String>(
future:
_login(), // function where you call your api
builder: (BuildContext context,
AsyncSnapshot<String> snapshot) {
// AsyncSnapshot<Your object type>
print(snapshot);
if (snapshot.connectionState ==
ConnectionState.done) {
print('${snapshot.data}');
}
if (snapshot.connectionState ==
ConnectionState.waiting) {
return Center(
child: Text('Please wait its loading...'));
} else {
if (snapshot.hasError)
return Center(
child: Text('Error: ${snapshot.error}'));
else
return Center(
child: new Text(
'${snapshot.data}')); // snapshot.data :- get your object which is pass from your downloadData() function
}
},
);
return CircularProgressIndicator();
},
当我按下按钮调用其方法时，我正在获取数据，但是获取这些数据后，将来的构建将不会更新或在Text中显示该数据.这是我的数据提取方法.
when i press the button its calling the method and i am getting data but after getting those data future building is not updating or showing that data in a Text.here is my data fetch method.
Future<String> _login() async {
final result = await FacebookAuth.instance.login();
var tokenString;
switch (result.status) {
case FacebookAuthLoginResponse.ok:
_printCredentials(result);
// get the user data
// final userData = await FacebookAuth.instance.getUserData();
tokenString = result.accessToken.token;
break;
case FacebookAuthLoginResponse.cancelled:
print("login cancelled");
tokenString = "User cancelled";
break;
default:
tokenString = "Login failed";
}
return tokenString;
}
出于调试目的，我也创建了断点，但是它没有直接指向asynchronous snapshot条件状态检查.我无法找到原因.我还检查了以下堆栈问题.
For debug purpose i made break point also but its not directing to the asynchronous snapshot condition state checking.I could not find out the reasons. I also check following stack question also.
为什么FutureBuilder无法在Flutter中获得呼叫? Flutter FutureBuilder未更新
推荐答案
好吧，在onPressed函数中，您正在声明FutureBuilder，这肯定是错误的. FutureBuilder允许您对函数或方法进行异步请求，以使用响应数据来构建窗口小部件或其他组件，具体取决于快照值.当您第一次运行窗口小部件或在StatefulWidget中使用SetState({})时，会发生这种情况.但是，您正在将视图代码与功能代码结合在一起.这是实现FutureBuilder的方法:
Well, in your onPressed function you are declarating a FutureBuilder and it's definitly wrong. FutureBuilder allows you to make an asynchronous request for a function or method to use the response data to build a widget or another depending of the snapshot value. This happens when you run the widget for the first time or use SetState({}) in a StatefulWidget. But you are joining view code with functional code. This is the way to implement a FutureBuilder:
class MyApp extends StatelessWidget {
@override
Widget build(BuildContext context) {
return FutureBuilder(
future: _login(),
builder: (context, snapshot) {
print(snapshot);
if (snapshot.connectionState == ConnectionState.done) {
print('${snapshot.data}');
}
if (snapshot.connectionState == ConnectionState.waiting) {
return Center(child: Text('Please wait its loading...'));
// Or return CircularProgressIndicator();
} else {
if (snapshot.hasError)
return Center(child: Text('Error: ${snapshot.error}'));
else
return Center(
child: new Text(
'${snapshot.data}'));
}
},
);
// if you return something here, it's dead code
}
但是我建议您以这种方式实现FutureBuilder:
But i would suggest you to implement FutureBuilder in this way:
class MyApp extends StatelessWidget {
@override
Widget build(BuildContext context) {
return Container(
alignment: Alignment.center,
child: FutureBuilder(
future: _login(),
builder: (context, snapshot) {
if (snapshot.hasError) // if it has error
return Text('Error: ${snapshot.error}');
if (!snapshot.hasData) {
// if it's loading
return Column(
mainAxisAlignment: MainAxisAlignment.center,
children: [
Text('Please wait its loading...'),
Padding(
padding: EdgeInsets.only(top: 20),
child: Container(
height: 35,
width: 35,
child: CircularProgressIndicator(),
),
),
],
);
} else {
// if everything success
print(snapshot.data);
return Text('${snapshot.data}');
}
},
),
);
}
最后，我想您想要的是使用提供者在登录页面的小部件之间创建通信方式，因为您想通过按一个按钮来更改页面/视图小部件的状态，您可以使用StatefulWidget，但是您可以应该更好地参见本教程. 此处.
Finally, what i think you want is use a Provider to create a comunication way between widgets into your login page because you want to change the State of the page/view widget by pressing a button, u could use a StatefulWidget but u should see this tutorial better. and here is the provider documentation.
Pdst:但是，如果您不想实现提供程序，则可以在按钮中发出_login()请求，例如:
Pdst: But, if u don't want to implement provider you could make the _login() request in the button like:
onPressed: () async {
String response = await _login();
Navigator.push(context, MaterialPageRoute(builder: (context) => ResponseWidget(response)));
}
使用navigator.push()，您可以更改屏幕上的视图/页面/小部件，并显示一个新的小部件，该小部件可能显示一些依赖于响应值的东西.
With navigator.push() you can change the view/page/widget that u have in your screen and show a new widget that could show something deppending the response value.
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