AngularJS Promise重试 [英] AngularJS Promise retries

问题描述

我在使重试功能正常工作时遇到了一些麻烦，并希望获得一些帮助.我有一个要调用的$ resource，直到出现成功情况或超过最大重试次数为止.

I am having some trouble getting a retry function to work and was hoping for some assistance. I have a $resource that I want to have called until a success condition occurs or the maximum retries has been exceeded.

我似乎遇到的问题是，在我的重试功能中，我正在调用另一个promise，而这就是检查条件的地方.通过几次重试后，删除添加的promise并创建默认的成功条件，我可以使代码正常运行，但是我无法弄清楚如何正确地将新的promise调用添加到函数中.

The issue I seem to be running into is that within my retry function I am calling another promise and that is where the condition would be checked. I could get the code to function as intended by removing the added promise and creating a default success condition after a few retries but I cannot figure out how to correctly add the new promise call into the function.

resource是Angular $ resource的替代品，它返回$ promise

resource is a stand-in for an Angular $resource which returns a $promise

我的代码如下:

resource.$promise.then(function (response) {
  return keepTrying(state, 5);
 }).then(function (response) {

 }).catch(function (err) {
   console.log(err);
 });

以及keepTrying函数:

And the keepTrying function:

function keepTrying(state, maxRetries, deferred) {
  deferred = deferred || $q.defer();
  resource.$promise.then(function (response) {
    success = response;
  });
  if (success) {
    return deferred.resolve(success);
  } else if (maxRetries > 0) {
    setTimeout(function () {
      keepTrying(state, maxRetries - 1, deferred);
     }, 1000);
   } else if (maxRetries === 0) {
     deferred.reject('Maximum retries exceeded');
   }
   return deferred.promise;
 }

推荐答案

尝试的问题在于，您不是在重新查询资源，而是一遍又一遍地使用对已查询资源的承诺.

The problem with your attempt is that you are not re-querying the resource, but using the promise for an already-queried resource over and over.

您需要做的是使用一个函数，该函数将(a)启动查询，并(b)返回该启动查询的promise.像这样:

What you need to do is use a function that will (a) initiate the query, and (b) return the promise for that initiated query. Something like this:

function () { return $resource.get().$promise; }

然后，您可以将其传递给类似的内容，然后进行重试.

Then you can pass it into something like this, that will do the retries.

function retryAction(action, numTries) {
    return $q.when()
        .then(action)
        .catch(function (error) {
            if (numTries <= 0) {
                throw error;
            }
            return retryAction(action, numTries - 1);
        });
}

这是您要如何开始的方法:

Here's how you would start this off:

retryAction(function () { return $resource.get().$promise; }, 5)
.then(function (result) {
    // do something with result 
});

关于此方法的一件好事是，即使传递给它的函数在调用它时抛出错误，或者根本不返回promise，重试功能和通过已解决的promise返回结果仍然可以工作.

One nice thing about this approach is that even if the function that you pass to it throws an error upon invoking it, or doesn't return a promise at all, the retry functionality and the returning of the result via a resolved promise will still work.

示例

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