iphone RESTful webservices

问题:

Not even sure if the title is correct, however, what I'm trying to do is use the standard NSURLConnection class to handle responses from calling my webservice. I am using the POST method to update a database and the GET method to retrieve rows from the database. The problem I have is that these 2 actions may occur simultaneously so that the methods to handle the request may step on each other. In other words in my "connection didReceiveData" method I have 2 paths through the code depending on whether I'm handling a response from a GET or POST request.

I keep track on which request in being processed by an instance variable called requestType. The problem is that since the requests are being executed simultaneously the instance variable is being changed from GET to POST before the GET completes (or vice-versa). My question is how do I maintain 2 separate requests in this scenario? Do I synchronize the requests? Is there a way for threads to work here? Do I create 2 separate objects for each of the requests and have the logic in "didRecieveData" query for which object is being processed? Any help would be much appreciated!!

回答1:

Dealt with a similar issue in one of our apps. The solution involved creating a class that represents a webservice call, responsible for calling its own url, loading its own data, etc. The call class had a delegate that would handle parsing the responses (in our case, a web service controller). Wound up getting rather complicated, but prevented the issue of NSURLConnections stepping on each other.

回答2:

Seems like you've created a messy problem by having a class that tries to do too many things. I would suggest taking one of the following three approaches:

1) Write two classes, one for updates and one for retrievals. Each class creates it's own private NSURLConnection object and acts as the delegate for the async notifications received from the NSURLConnection. The classes could possible share some utility parsing code or extend a base object that has that parsing code in it. But the key being that the code calling these classes would instantiate one of them, make the call, and then release it. This will keep your code cleaner and will insure that the event notifications don't get intermingled.

2) Create a single class that, depending on initialization, does either a post or a get with it's own private instance of NSURLConnection. When a call needs to be made, instantiate the class, get the results, and then release the class.

3) Write your connection handling classes so they use the synchronous NSURLConnection method and call that call that class in a background thread.

Either way, clean code and clear object orientation will prevent messy scenarios like the one you're describing.

回答3:

Create separate objects that handle the calls. If you want to issue multiple requests at once I would strongly recommend looking at NSOperationQueue, and making these objects subclasses of NSOperation... much nicer way to deal with multiple background requests.

A good example is here:

http://www.cimgf.com/2008/02/16/cocoa-tutorial-nsoperation-and-nsoperationqueue/

The idea there is that you use the non-asyncronous web calls, in operations that are run on separate threads. You can still use asynch calls in NSOperation as well, but doing so is a little trickier and for simple calls you probably do not need to.