所以我一直在尝试使用DART（我的核心语言是C ++和嵌入式C派生）。因此，我的代码可能并不漂亮，因为我更像是一个程序员程序员，但我已经过去并且学习......我一直在围绕等待同步的期货挣扎，基本上，我根本无法让DART等待。以下代码建立与小型嵌入式设备的套接字连接并提取信息。这一切都有效，但注意操作的顺序应该是main（）从控制台获取一些信息，然后应该调用方法cardStatus运行并通过套接字连接从嵌入式设备获取信息。这是等待应该发生的地方。当返回Future时，它应该转到printstuff（）方法。我已经添加了应该按顺序排列的打印语句并阅读：
相反，因为在cardstatus调用上没有发生等待（这非常耗时），我得到：
我已经关注了使用async的另一个主题，并且似乎至少遵循了使用此Other thread的一种可靠方式（我尝试了一个带有类似结果的完成符的.then，所以有一些核心，我觉得我失踪了）..但我已经坚持了一个星期。
下面的代码，以及控制台输出。
import 'dart:io';
import 'dart:async' show Future;
const String STATUS = "#111111;";
String defaultIP = "10.1.14.202";
int defaultConfigPort = 5111;
int defaultControlPort = 6722;
var card = new Map();
getInput(String defaults) {
String takenin = stdin.readLineSync();
if (takenin == '') takenin = defaults;
return takenin;
}
Future main() async {
stdout.write('What is the IP address of the card ($defaultIP): ');
String ipaddress = getInput(defaultIP);
defaultIP = ipaddress;
print ("This should print 1st");
stdout.writeln("Connecting to $defaultIP");
await cardStatus(defaultIP, defaultConfigPort, STATUS, card);
printstuff();
}
printstuff() {
stdout.writeln(card['subnet']);
print ("This should print 3rd");
}
Future cardStatus(String ip, int port, String message, Map card) {
return new Future.delayed(Duration.ZERO, () {
Socket.connect(ip, port).then((socket) {
print('Connected to: '
'${socket.remoteAddress.address}:${socket.remotePort}');
socket.listen((data) {
print(new String.fromCharCodes(data).trim());
List str1 = (new String.fromCharCodes(data).trim().split(','));
print(str1);
print ("This should print 2nd");
//var card = new Map();
card['ip'] = str1[0];
card['subnet'] = str1[1];
card['gateway'] = str1[2];
card['unknown'] = str1[3];
card['persist'] = str1[4] == 'true';
card['build'] = str1[5];
card['serial'] = str1[6].substring(0, 14);
card['cloudpassword'] = str1[6].substring(14, 20);
card['DNS'] = str1[7];
card['cloudhost'] = str1[8];
card['cloudenabled'] = str1[9] == 'true';
print(card['ip']);
},
onDone: () {
print("Done");
socket.destroy();
});
//Send the request
socket.write(message);
});
});
}
这是当前的控制台输出。请注意，如果cardStatus已经完成，则null不应为null，将打印为str1。
What is the IP address of the card (10.1.14.202):
This should print 1st
Connecting to 10.1.14.202
null
This should print 3rd
Connected to: 10.1.14.202:5111
>10.1.14.202,255.255.255.0,10.1.14.1,,0,435,F44900A60040F8000000,192.168.1.1,connect.tutuuu.com,0;
[>10.1.14.202, 255.255.255.0, 10.1.14.1, , 0, 435, F44900A60040F8000000, 192.168.1.1, connect.tutuuu.com, 0;]
This should print 2nd
10.1.14.202
Done
Process finished with exit code 0
感谢您的帮助！
答案 0 :(得分：4)
return之前您遗失了Socket.connect。现在，您的代码刚刚开始连接，但从未等待它。我强烈建议尽可能多地使用新的await / async语法。
以下是一个获取google主页的正在运行的示例：
import 'dart:io';
import 'dart:async' show Future;
Future main() async {
print("This should print 1st");
await cardStatus('www.google.com', 80, 'GET /\nHTTP 1.1\n\n');
printstuff();
}
printstuff() {
print("This should print 3rd");
}
Future cardStatus(String ip, int port, String message) {
return new Future.delayed(Duration.ZERO, () {
return Socket.connect(ip, port).then((socket) {
print('Connected to: '
'${socket.remoteAddress.address}:${socket.remotePort}');
socket.listen((data) {
List str1 = (new String.fromCharCodes(data).trim().split(','));
print(str1.first);
print("This should print 2nd");
}, onDone: () {
print("Done");
socket.destroy();
}, onError: (e) {
print("Error while listening: $e");
});
socket.write(message);
});
});
}
使用等待的稍微编辑的版本，并尝试使用/ catch来处理错误：
import 'dart:io';
import 'dart:async' show Future;
Future main() async {
print("This should print 1st");
await cardStatus('www.google.com', 80, 'GET /\nHTTP 1.1\n\n');
print("This should print 3rd");
}
Future<String> cardStatus(String ip, int port, String message) async {
var socket = await Socket.connect(ip, port);
print('Connected to: '
'${socket.remoteAddress.address}:${socket.remotePort}');
socket.write(message);
print("Sent request");
try {
var response = await socket.fold(
'',
(String acc, List<int> data) =>
acc + new String.fromCharCodes(data).trim());
print("Received response: ${response.substring(0, 10)}");
return response;
} finally {
socket.close();
}
}
答案 1 :(得分：0)
我知道回答了这个问题，但是问题很严重，我对这个概念感到困惑，因此这是另一个让我理解的元素。在dartpad（https://dartpad.dartlang.org/）中尝试此操作（注释在代码中）：
import 'dart:async';
//Just creating a duration to use later
Duration duration = new Duration(milliseconds: 500);
void main() {
//This is what tricked me, printStuff is async so running in parallel processing by default
//There is no need to call the function in a certain way (like a go xxx for a goroutine)
//there is an await in the function so it will wait inside the function only
//i.e. printStuff('a') starts then printStuff('b') starts straight away...already in prallel processing
//Run it and check the output
printStuff('a');
printStuff('b');
//Basically the await is in the function so printStuff is still returning a Future
//i.e. printStuff('a') starts but doesn't wait to complete to start printStuff('b')
}
Future<void> printStuff(String id) async {
for(int i = 0; i <= 5; ++i) {
//this await is waiting for the command to complete to move to the next iteration...
//the i iterations are done one after the other
await new Future.delayed(duration, () {
print(id + i.toString());
});
}
}
然后尝试：
import 'dart:async';
Duration duration = new Duration(milliseconds: 500);
//becuase I use await in main now, I must make it return a future and be async
Future main() async {
//to make it happen one after the other, you need await at a call function level
await printStuff('a');
await printStuff('b');
//Basically this says complete printStuff('a'), then start printStuff('b')...
//and yes technically one doesn't need the second await becuase there is nothing after
}
Future<void> printStuff(String id) async {
for(int i = 0; i <= 5; ++i) {
await new Future.delayed(duration, () {
print(id + i.toString());
});
}
}
所以我个人的误解是异步函数立即被并行调用，而函数中的await则等待真实的但函数本身，而不会影响其他并行处理。