你能在返回之前解决一个 angularjs 承诺吗?

问题描述

我正在尝试编写一个返回承诺的函数.但有时请求的信息可以立即获得.我想把它包装在一个承诺中，这样消费者就不需要做出决定.

I am trying to write a function that returns a promise. But there are times when the information requested is available immediately. I want to wrap it in a promise so that the consumer doesn't need to make a decision.

function getSomething(id) {
    if (Cache[id]) {
        var deferred = $q.defer();
        deferred.resolve(Cache[id]); // <-- Can I do this?
        return deferred.promise;
    } else {
        return $http.get('/someUrl', {id:id});
    }
}

像这样使用它:

somethingService.getSomething(5).then(function(thing) {
    alert(thing);
});

问题是回调不会为预先解析的承诺执行.这是合法的事情吗?有没有更好的方法来处理这种情况?

The problem is that the callback does not execute for the pre-resolved promise. Is this a legitimate thing to do? Is there a better way to handle this situation?

推荐答案

简短回答:是的，您可以在返回之前解析 AngularJS 承诺，它会按照您的预期运行.

Short answer: Yes, you can resolve an AngularJS promise before you return it, and it will behave as you'd expect.

来自 JB Nizet 的 Plunkr 但重构为在最初要求的上下文中工作(即函数调用服务)并实际在现场.

From JB Nizet's Plunkr but refactored to work within the context of what was originally asked (i.e. a function call to service) and actually on site.

服务内部...

function getSomething(id) {
    // There will always be a promise so always declare it.
    var deferred = $q.defer();
    if (Cache[id]) {
        // Resolve the deferred $q object before returning the promise
        deferred.resolve(Cache[id]);
        return deferred.promise;
    }
    // else- not in cache
    $http.get('/someUrl', {id:id}).success(function(data){
        // Store your data or what ever....
        // Then resolve
        deferred.resolve(data);
    }).error(function(data, status, headers, config) {
        deferred.reject("Error: request returned status " + status);
    });
    return deferred.promise;

}

控制器内部....

somethingService.getSomething(5).then(
    function(thing) {     // On success
        alert(thing);
    },
    function(message) {   // On failure
        alert(message);
    }
);

希望对大家有所帮助.我没有发现其他答案很清楚.

I hope it helps someone. I didn't find the other answers very clear.

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