angular $ q，如何在for循环内和执行后链接多个promise [英] angular $q, How to chain multiple promises within and after a for-loop

问题描述

我想要一个for循环，该循环在每次迭代时调用异步函数.

I want to have a for-loop which calls async functions each iteration.

在for循环之后，我想执行另一个代码块，但在解决for循环中的所有先前调用之前，不要执行.

After the for-loop I want to execute another code block, but not before all the previous calls in the for-loop have been resolved.

目前，我的问题是，在for循环之后执行的代码块是否在所有异步调用完成之前执行，或者根本不执行.

My problem at the moment is, that either the code-block after the for-loop is executed before all async calls have finished OR it is not executed at all.

带有FOR循环的代码部分及其后的代码块(有关完整代码，请参见小提琴 ):

The code part with the FOR-loop and the code block after it (for complete code, please see fiddle):

[..]
function outerFunction($q, $scope) {
    var defer = $q.defer();    
    readSome($q,$scope).then(function() {
        var promise = writeSome($q, $scope.testArray[0])
        for (var i=1; i < $scope.testArray.length; i++) {
             promise = promise.then(
                 angular.bind(null, writeSome, $q, $scope.testArray[i])
             );                                  
        } 
        // this must not be called before all calls in for-loop have finished
        promise = promise.then(function() {
            return writeSome($q, "finish").then(function() {
                console.log("resolve");
                // resolving here after everything has been done, yey!
                defer.resolve();
            });   
        });        
    });   

    return defer.promise;
}

我创建了一个jsFiddle，可以在这里找到 http://jsfiddle.net/riemersebastian/B43u6/3/.

I've created a jsFiddle which can be found here http://jsfiddle.net/riemersebastian/B43u6/3/.

目前看来执行顺序很好(请参阅控制台输出).

At the moment it looks like the execution order is fine (see the console output).

我的猜测是，这仅仅是因为每个函数调用都会立即返回而无需进行任何实际工作.我试图用setTimeout延迟defer.resolve，但失败了(即最后一个代码块从未执行过).您可以在小提琴的注释框内看到它.

My guess is, that this is simply because every function call returns immediately without doing any real work. I have tried to delay the defer.resolve with setTimeout but failed (i.e. the last code block was never executed). You can see it in the outcommented block in the fiddle.

当我使用写入文件和从文件读取的真实函数时，最后一个代码块在最后一次写操作完成之前执行，这不是我想要的.

When I use the real functions which write to file and read from file, the last code block is executed before the last write operation finishes, which is not what I want.

当然，该错误可能出在其中的一个读/写函数中，但我想验证一下我在此处发布的代码没有问题.

Of course, the error could be in one of those read/write functions, but I would like to verify that there is nothing wrong with the code I have posted here.

推荐答案

您需要使用的是 $ q.all ，它将多个诺言合并为一个诺言，只有当所有诺言都得到解决时，该诺言才能得到解决.

What you need to use is $q.all which combines a number of promises into one which is only resolved when all the promises are resolved.

在您的情况下，您可以执行以下操作:

In your case you could do something like:

function outerFunction() {

    var defer = $q.defer();
    var promises = [];

    function lastTask(){
        writeSome('finish').then( function(){
            defer.resolve();
        });
    }

    angular.forEach( $scope.testArray, function(value){
        promises.push(writeSome(value));
    });

    $q.all(promises).then(lastTask);

    return defer.promise;
}

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