Angular JS 中未调用 Promise 回调 [英] Promise callback not called in Angular JS

问题描述

如果我从 doStuff 调用 connect，我会收到消息 套接字已连接"，但是 回调 没有被调用.我在这里缺少什么?

If I call connect from doStuff, I get the message that "the socket is connected", but the callback is not called. What am I missing here?

 $scope.connect = function() {
    var defer = $q.defer();
    ws = new WebSocket("ws://server.com:port");
    ws.onopen = function(){  
        console.log("Socket connected");
        defer.resolve("socket connected");
    };
    return defer.promise;
}

$scope.doStuff = function() {
    $scope.connect().then(function(data) {
        console.log("And we're off!", data);
    });
}

推荐答案

在 AngularJS 中，promise 结果在 $digest 循环内异步传播.因此，您使用 then() 注册的回调函数只会在进入 $digest 循环时被调用.

In AngularJS promise results are propagated asynchronously, inside a $digest cycle. So, your callback function registered with then() will only be called upon entering a $digest cycle.

因此，当您的套接字连接时，我们处于摘要循环中.then() 创建了一个新的 promise，但是 then() 的结果直到下一个摘要循环才会传播，这个循环永远不会出现(因为没有 $timeout 或 $http 或 DOM 事件来触发).正如@Ajay 刚刚发布的那样，如果您添加 $scope.$apply()，它将导致一个摘要循环，您将看到结果.

So, when your socket connects, we are in a digest cycle. then() creates a new promise, but the results of that then() will not be propagated until the next digest cycle, which never comes (because there is no $timeout, or $http, or DOM event to trigger one). As @Ajay just posted, if you add $scope.$apply(), it will cause a digest cycle and you'll see the results.

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