Future用来异步操作。
1.延时发送Future.then()
Future.delayed(new Duration(seconds: 1),(){
return "hello world";
}).then((value) => print(value));
2.异常捕获Future.catchError
Future.delayed(new Duration(seconds: 1),(){
// return "hello world";
throw AssertionError("error");
}).then((value) => print(value))
.catchError((e)=>print(e));
捕获异常的另一种表现方式
Future.delayed(new Duration(seconds: 1),(){
// return "hello world";
throw AssertionError("error");
}).then((value) => print(value),onError: (e){print(e);});
3.Future.whenComplete异步操作执行完毕执行的操作，比如在这里处理弹窗。
Future.delayed(new Duration(seconds: 1),(){
// return "hello world";
throw AssertionError("error");
}).then((value) => print(value))
.catchError((e)=>print(e)).whenComplete(() => print("弹个弹窗"));
4.Future.wait用来等待多个异步任务，执行完毕之后，比如多个网络请求，再执行then中的代码。
Future.wait([Future.delayed(new Duration(seconds: 2),(){return "hello";}),
Future.delayed(new Duration(seconds: 3),(){return "world";})])
.then((value) => print(value));
async/wait;
使用async来表示异步调用函数是异步的，
wait必须写在async的包含体中
task() async {
try{
String id = await login("alice","******");
String userInfo = await getUserInfo(id);
await saveUserInfo(userInfo);
//执行接下来的操作
} catch(e){
//错误处理
print(e);
}
}
Stream也可以用来接收异步信息，一般用来网络下载和文件读取。
Stream.fromFutures([Future.delayed(new Duration(seconds: 1),(){return "hello1";}),
Future.delayed(new Duration(seconds: 2),(){throw AssertionError("Error");}),
Future.delayed(new Duration(seconds: 3),(){return "hello3";})])
.listen((event) {print(event);},onError: (e){print(e);},onDone: (){
print("弹出提示");
