async 和 await

• Future 链式调用 更清晰
• 异步操作依赖关系比较复杂 可使用async await
• async await 调用逻辑更清晰
• async await 异常处理 try{}catch(){} 即可
• async 修饰的方法 总是返回Future对象 不会阻塞主线程
• await 关键字只有在async修饰的方法内才有效
• 都是把事件交给 EventLoop

登录流程Future写法

void main() {Future.value(["username","password"]).then((value){login(value[0],value[1]);print("${DateTime.now().millisecondsSinceEpoch} >> 登录中...");sleep(Duration(seconds: 5));return '{"id": 10001,"name": "John","classGrade": "三年二班","birthday": "2005-12-12 12:12:12", "age": 30}';}).then((value){return value;}).then((value){print("${DateTime.now().millisecondsSinceEpoch} >> "+value);  //jsonvar json = jsonDecode(value);int id = json['id'];getUserInfo(id);print("${DateTime.now().millisecondsSinceEpoch} >> 获取用户信息...");sleep(Duration(seconds: 5));return "成功,缓存数据，跳转首页";}).catchError((value){}).whenComplete((){print("登录流程结束!");});
}login(String username,String password){print("${DateTime.now().millisecondsSinceEpoch} >> ${username}请求登录!");
}
getUserInfo(int id){print("${DateTime.now().millisecondsSinceEpoch} >> ${id}获取用户信息!");
}

运行结果

1703727827384 >> username请求登录!
1703727827384 >> 登录中...
1703727832400 >> {"id": 10001,"name": "John","classGrade": "三年二班","birthday": "2005-12-12 12:12:12", "age": 30}
1703727832418 >> 10001获取用户信息!
1703727832418 >> 获取用户信息...
登录流程结束!

async/await 写法

import 'dart:convert';
import 'dart:io';void main() async{var loginResult = await login("aaa", "123");var userInfo = await getUserInfo(loginResult);print(userInfo);
}Future<String> login(String username,String password){print("${DateTime.now().millisecondsSinceEpoch} >> ${username}请求登录!");return  Future.value([username,password]).then((value){print("${DateTime.now().millisecondsSinceEpoch} >> 登录中...");sleep(Duration(seconds: 5));return '{"id": 10001,"name": "John","classGrade": "三年二班","birthday": "2005-12-12 12:12:12", "age": 30}';}).then((value){return value;});
}
Future<String> getUserInfo(String value){return Future((){print("${DateTime.now().millisecondsSinceEpoch} >> "+value);  //jsonvar json = jsonDecode(value);print("${DateTime.now().millisecondsSinceEpoch} >> 获取用户信息...");sleep(Duration(seconds: 5));return "成功,缓存数据，跳转首页";});
}

请求结果

1703727905612 >> aaa请求登录!
1703727905617 >> 登录中...   //5s等待返回结果
1703727910642 >> {"id": 10001,"name": "John","classGrade": "三年二班","birthday": "2005-12-12 12:12:12", "age": 30}
1703727910660 >> 获取用户信息...    //5s等待
1703727915670 >> 成功,缓存数据，跳转首页   

async 修饰的方法 总是返回Future对象 不会阻塞主线程

import 'dart:convert';
import 'dart:io';void main(){var login = startLogin();print("login.runtimeType>>${login.runtimeType}");
}startLogin() async{var loginResult = await login("aaa", "123");var userInfo = await getUserInfo(loginResult);print("${DateTime.now().millisecondsSinceEpoch} >> "+userInfo);
}Future<String> login(String username,String password){return  Future.value([username,password]).then((value){print("${DateTime.now().millisecondsSinceEpoch} >> 登录中...");sleep(Duration(seconds: 5));return '{"id": 10001,"name": "John","classGrade": "三年二班","birthday": "2005-12-12 12:12:12", "age": 30}';}).then((value){return value;});
}
Future<String> getUserInfo(String value){return Future((){print("${DateTime.now().millisecondsSinceEpoch} >> "+value);  //jsonvar json = jsonDecode(value);print("${DateTime.now().millisecondsSinceEpoch} >> 获取用户信息...");sleep(Duration(seconds: 5));return "成功,缓存数据，跳转首页";});
}

结果：

login.runtimeType>>Future<dynamic>  //类型是Future

await 关键字只有在async修饰的方法内才有效