angular $q，如何在for循环中和之后链接多个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，每次迭代都调用异步函数.

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，但不是在 for 循环中先前的所有调用都得到解决之前.

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.

我目前的问题是，要么在所有异步调用完成之前执行 for 循环之后的代码块，要么根本不执行.

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(完整代码请参见 fiddle):

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/.

目前看起来执行顺序没问题(见控制台输出).

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立即返回而没有做任何实际工作.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 fiddle 的 outcommented 块中看到它.

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.

当我使用真正的写入文件和读取文件的函数时，最后一个代码块在最后一个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，错误可能出在这些读/写函数之一中，但我想验证我在这里发布的代码没有任何问题.

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

你需要使用的是 $q.all 将多个 promise 组合成一个，只有在所有 promise 都解决后才会解决.

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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