Objective-C：来自jquery回调的json响应

Question

I'm building and iOS application and trying to get the json data from a url similar to:

example.com/ajax/u.php?callback=jQuery84054761566_1389381628746

Is anyone familiar with these types of callbacks?

Typical HTTP requests in obj-c return 200 status and a null response object with this url.

Answer 1

That's a JSONP callback used for...well, JSONP. JSONP is used on webpages to avoid the 'same origin' restriction. That is, a webpage loaded from a certain domain (say abc.com) cannot call/access resources on a separate domain (say xyz.com).

The way they (web front-end developers) get around this is by using the <script> tag which is exempt from this restriction. However the return of a <script> tag would just be parsed - to cause it to execute something, you tell it a function name that exists in your JavaScript code, in this case, jQuery84054761566_1389381628746.

So instead of returning a regular JavaScript object, say

{key : 'value'}

the server then returns a function invocation

jQuery84054761566_1389381628746({key : 'value'}) 

and you have, in your webpage JavaScript, the function definition for jQuery84054761566_1389381628746 that does something:

jQuery84054761566_1389381628746 = function(data){
  alert(data.key);
};

iOS does not have this same-origin/cross-site restriction so you don't need JSONP - you can call whatever server you want.