I am using Restkit in my iOS app to make a GET call to my server. I am able to get the call to work just fine, except that it is supposed to be asynchronous and it is blocking my main thread. I am basically using their exact sample to make the request from their github page which is as follows:
NSURLRequest *request = [NSURLRequest requestWithURL:[NSURL URLWithString:#"http://mywebapi.com/Article"]];
RKObjectRequestOperation *operation = [[RKObjectRequestOperation alloc] initWithRequest:request responseDescriptors:#[responseDescriptor]];
[operation setCompletionBlockWithSuccess:^(RKObjectRequestOperation *operation, RKMappingResult *result) {
Article *article = [result firstObject];
NSLog(#"Mapped the article: %#", article);
} failure:^(RKObjectRequestOperation *operation, NSError *error) {
NSLog(#"Failed with error: %#", [error localizedDescription]);
}];
[operation start];
This blocks all main thread executions (such as my transitions) until the success block is called. Wrapping this call inside of a dispatch_queue does resolve the issue, but it is my understanding that this method is supposed to be asynchronous on its own.
Am I missing some configuration on the RKObjectRequestOperation, or is there a different method I should be calling for an async call?
I found the answer to this question here:
RestKit Makes UI Unresponsive
Basically, you do need to add it to an NSOperationQueue, otherwise it will run the call on the main thread.
Related
So I am trying to access a json file online and I can get the contents of the JSON file when I run the completion block using AFHTTPRequestOperation method. But when I try to NSLog outside the completion block, it becomes null. I was wondering why this is happening and how I would go about fixing this. Below is the code I have so far:
AFHTTPRequestOperation *operation = [[AFHTTPRequestOperation alloc] initWithRequest:request];
[operation setCredential:credentials];
[operation setResponseSerializer:[AFJSONResponseSerializer alloc]];
[operation setCompletionBlockWithSuccess:^(AFHTTPRequestOperation *operation, id responseObject) {
NSLog(#"Success %#", responseObject);
jsonOutputData = [NSMutableArray arrayWithObject:responseObject];
self.newsFeedArray = [NSMutableArray arrayWithArray:[jsonOutputData copy]];
}failure:^(AFHTTPRequestOperation *operation, NSError *error){
NSLog(#"Failure: %#", error);
}];
[manager.operationQueue addOperation:operation];
NSLog(#"%#", self.newsFeedArray);
The NSLog with Success shows the JSON but the NSLog with the self.newsFeedArray shows (null). I am just wondering why this is happening. If you need more clarification, let me know. Any help would be appreciated!
Thanks!
The success and failure blocks get called asynchronously. So self.newsFeedArray simply has not been set yet at the time of the last NSLog call, because the operation has not completed.
You could wait for the operation to complete (e.g., [operation waitUntilFinished]) but you almost certainly don't want to do this, especially on the main thread. Rather have the completion blocks trigger the desired behaviour.
I've got subclass of AFHTTPClient
The main idea is that i call all API through my singleton of AFHTTPClient subclass, and all requests goes through 1 points for error handling and HUD displaying.
This is entry point for every API calls:
-(void) makeRequestWithPath:(NSString*) path andParams:(NSDictionary*) params
success:(void (^)( id JSON, AFHTTPRequestOperation *operation)) success
failure:(void (^)( NSError *error)) failure
And i've got many methods for API calls something like that:
-(void) getListMainTreeWithSuccess:(void (^)( id JSON, AFHTTPRequestOperation *operation)) success
failure:(void (^)( NSError *error)) failure
{
[self makeRequestWithPath:#"objects/selectlist" andParams:nil success:^(id JSON, AFHTTPRequestOperation *operation) {
success(JSON,operation);
} failure:^(NSError *error) {
failure(error);
}];
}
This works just fine for my needs. But i faced problem that i need to make serial request in loop through my AFHTTPClient subclass and make some action when all of them are finished , I found method
-(void)enqueueBatchOfHTTPRequestOperationsWithRequests:(NSArray *)urlRequests
progressBlock:(void (^)(NSUInteger numberOfFinishedOperations, NSUInteger totalNumberOfOperations))progressBlock
completionBlock:(void (^)(NSArray *operations))completionBlock
which should solve my issue, but the problem is that i call all methods through AFHTTPClient and it's methods getPath: and postPath: and previous way forces me to rewrite everything and makes my subclass completely useless, because I need to add there NSArray of AFHTTPRequestoperation, which is not possible to construct or extract from my subclass and my methods. Previously i tried to use __block 's to synchronise requests with semaphore and something else but i failed to get what i need, please help me!
UPDATE:
It seems that it is not possible to even use enqueueBatchOfHTTPRequestOperations method (even with rewriting all my code) because this method needs array of http request operations, but it's not possible to construct POST request with them.
I solved this with an increment/decrement pending download system and tied the HUD to that.
[networkStatus beginNetworkActivity];
[client someRESTActionWithCompletion:^(id object, NSError *error) {
[networkStatus endNetworkActivity];
if (error) {
// Handle the error ...
}
if (![networkStatus hasNetworkActivity]) {
// All downloads have finished
}
}];
I keep the network status object separate which from the AFHTTPClient subclass, but it can be built into the client if that's what you want.
Network status keeps an internal counter. -beginNetworkActivity increments the counter, if the counter was 0, then it displays a HUD. -endNetworkActivity decrements the counter, if the counter becomes 0, then it dismisses the HUD. -hasNetworkActivity returns YES if the counter greater than 0.
Other Notes: I combine the success and failed callbacks into a single completion callback. I keep the network status logic separate from the client because sometime I'll use a singleton network status object, sometimes I'll use a created instance, sometimes I won't use one at all. It all depends on the needs to the higher level logic.
Again, as #MikePollard said, create AFHTTPRequestOperation using
[AFHHTPClient HTTPRequestOperationWithRequest:success:failure:]
For this method create NSURLRequest using (or use another one, pick which one is suitable for you). Here you can also specify, which method to use POST, GET or any other.
[AFHTTPClient requestWithMethod:
path:
parameters:]
After that save all operation to an NSArray, and schedule them using:
[AFHTTPClient enqueueBatchOfHTTPRequestOperationsWithRequests:
progressBlock:
completionBlock:]
Code example:
NSMutableArray *ops = [NSMutableArray new];
NSMutableURLRequest *request1 = [[AFHTTPClient sharedClient] requestWithMethod:#"GET"
path:#"MyEndpoint"
parameters:#{#"key1": #"value"}];
AFHTTPRequestOperation *op1 = [[AFHTTPClient sharedClient] HTTPRequestOperationWithRequest:request1
success:^(AFHTTPRequestOperation *operation, id responseObject) {
NSLog(#"Success!");
}
failure:^(AFHTTPRequestOperation *operation, NSError *error) {
NSLog(#"Failure!");
}];
[ops addObject:op1];
NSMutableURLRequest *request2 = [[AFHTTPClient sharedClient] requestWithMethod:#"POST"
path:#"MyAnotherEndpoint"
parameters:#{#"key2": #(104)}];
AFHTTPRequestOperation *op2 = [[AFHTTPClient sharedClient] HTTPRequestOperationWithRequest:request2
success:^(AFHTTPRequestOperation *operation, id responseObject) {
NSLog(#"Success!");
}
failure:^(AFHTTPRequestOperation *operation, NSError *error) {
NSLog(#"Failure!");
}];
[ops addObject:op2];
[[AFHTTPClient sharedClient] enqueueBatchOfHTTPRequestOperationsWithRequests:ops
progressBlock:^(NSUInteger numberOfFinishedOperations, NSUInteger totalNumberOfOperations) {
NSLog(#"numberOfFinishedOperations: %d totalNumberOfOperations %d",
numberOfFinishedOperations,
totalNumberOfOperations);
}
completionBlock:^(NSArray *operations) {
NSLog(#"All operation compelted!");
}];
- (BOOL)do_a_Restkit_request_and_return_a_boolean
{
[manager postObject:nil path:#"/mypath" parameters:#{#"password":password} success:^(RKObjectRequestOperation *operation, RKMappingResult *mappingResult) {
myResult = [mappingResult firstObject] == 5;
} failure:^(RKObjectRequestOperation *operation, NSError *error) {
}];
return myResult;
}
Hello I would like to make a RestKit call like the above Synchronous so as to return myResult after the call of the Success block.
You can use an approach like this:
NSMutableURLRequest *request = // create a request…
RKObjectRequestOperation *operation = [manager objectRequestOperationWithRequest:request success:nil failure:nil];
[operation start];
[operation waitUntilFinished];
BOOL myResult = NO;
if (!operation.error) {
myResult = [operation.mappingResult firstObject] == 5;
}
return myResult;
Notes:
The completion blocks are called after the operation is finished, so if you provide success/failure blocks, they won't be called until after the method returns
(This is why I suggest you pass nil into the completion blocks.)
waitUntilFinished will block whatever thread you're on, so make sure it's not the main thread.
If you need help creating request, see Creating Request Objects in the RKObjectManager Class Reference.
Again, if you can rewrite your code to work asynchronously, that will probably be better than this solution.
You need to either embrace the asynchronous nature of network communication and background processing of the response, or use a different API / technology specifically for making synchronous requests. RestKit and AFNetworking are based more around the former.
Embracing asynchronous is the best option...
That said, you could use RestKit to create the NSURLRequest, then use NSURLConnection to synchronously download the response, then use RKMapperOperation to perform the mapping (and wait for completion with addOperations:waitUntilFinished:).
Say I have this method that given a URL returns a UIImage:
- (void)getUIImageFromURL:(NSURL *)URL {
NSURLRequest *request = [NSURLRequest requestWithURL:URL];
AFHTTPRequestOperation *imageOperation = [[AFHTTPRequestOperation alloc] initWithRequest:request];
imageOperation.responseSerializer = [AFImageResponseSerializer serializer];
[imageOperation setCompletionBlockWithSuccess:^(AFHTTPRequestOperation *operation, id responseObject) {
return (UIImage *)responseObject;
} failure:^(AFHTTPRequestOperation *operation, NSError *error) {
}];
[imageOperation start];
}
But it keeps giving me this error:
Incompatible block pointer types sending 'UIImage *(^)(AFHTTPRequestOperation *__strong, _strong id)' to parameter of type 'void (^)(AFHTTPRequestOperation *_strong, __strong id)'
I'm somewhat new to blocks, so perhaps I'm approaching this completely backwards. How best would I implement a method like this?
You cannot return an image from inside a block. This is an asynchronous API and cannot be used in the manner you are attempting to. Either use a blocking API, where the method is blocking until the image is downloaded (a bad solution), or implement support for the asynchronous API. For instance, pass a completion block to your getImage method and call it with in the completion block of the download operation. In this block, do what you need with the image.
The callback block in setCompletionBlockWithSuccess: is a void block, you can't change it's return type.
In your case, you would probably set the image inside of your block, instead of returning an image.
[imageOperation setCompletionBlockWithSuccess:^(AFHTTPRequestOperation *operation, id responseObject) {
self.myImage.image = [UIImage imageWithData:responseObject];
} failure:^(AFHTTPRequestOperation *operation, NSError *error) {
}];
However, if you are dealing with AFNetworking and images, there are category methods that should greatly simplify retrieval and cacheing.
[self.myImage setImagewithURL:URL];
You are calling an asynchronous method with two blocks for handling success and failure. By the time one of these handlers is called, your calling method is long gone. It doesn't make any sense to think you could return data to it, because it is gone.
In the success block and failure block, you give instructions what to do when the operation has succeeded or failed. There is nobody there to return anything to. What you do is add code in the block to process and store the result of success in the right place, or to handle errors in the correct way.
I download asynchronously some object, I store it in array. Next for each object I download some coordinates with geocoding (it is also asynchronously), and update my database for each object with new parameters which is coordinate. My method looks like this:
- (void)downloadObjectsWithTitle:(NSString *)title andHandler:(void(^)(NSMutableDictionary *result))handler {
AFHTTPClient *httpClient = [[AFHTTPClient alloc] initWithBaseURL:url];
NSMutableURLRequest *request = [httpClient requestWithMethod:#"GET"
path:nil
parameters:nil];
AFHTTPRequestOperation *operation = [[AFHTTPRequestOperation alloc] initWithRequest:request];
[httpClient registerHTTPOperationClass:[AFHTTPRequestOperation class]];
[operation setCompletionBlockWithSuccess:^(AFHTTPRequestOperation *operation, id responseObject) {
//I get here array of objects
//now for each object I want to download geocoding localization so i called another asynchronyous method getLocationWithTitle:andHandler;
for(int i = 0; i < resutArray.count; i++) {
[self downloadLocationWithString:[dictionary objectForKey:#"string"] andHandler:^(NSMutableDictionary *result) {
//update database;
}];
}
handler(dictionary);
} failure:^(AFHTTPRequestOperation *operation, NSError *error) {
NSLog(#"Error: %#", error);
}];
[operation start];
}
My question is how to downalod coordinates for each object and that fire:
handler(dictionary);
so wait for each coordinates download (for each object) before quit method (fire handler).
Thnaks for all sugestions.
Maintain a count of all the tasks. When it's zero you're done.
Assuming you're using dispatch_async in downloadLocationWithString: on a concurrent queue:
dispatch_barrier_async(queue, ^{
// will only be called after all the blocks submitted to queue have finished.
}];
(If you're using serial queue, simply call handler at the last line of the last block)
Try a global flag. set NO first. In download block, after download complete set flag to yes. You can check that flag.