I was sending 10 requests of url (in a for in loop) to web service
and expected to get 10 JSON format data as return separately
here's my code:
NSArray *reqArray = [10 requests of url inside];
NSMutableArray * saveArray = [prepare to store 10 JSON data in here];
NSInteger counter = [reqArray count];
for (NSURLRequest *request in reqArray) {
[NSURLConnection sendAsynchronousRequest:request
queue:[NSOperationQueue mainQueue]
completionHandler:^(NSURLResponse *response, NSData *data, NSError *error) {
NSDictionary *result1 = [NSJSONSerialization JSONObjectWithData:data options:NSJSONReadingMutableContainers error:nil];
NSDictionary *result2 = [result1 objectForKey:#"keyForValueIWant"];
[saveArray addObject:result2];
counter -- ;
if (counter == 0) {
NSLog(#"all done");
}
}];
}
the completionHandler never gets executed and I always get nothing in return.
is there anything I misunderstand bout the NSURLConnetion or I did it wrong?
any advice would be appreciated!
EDIT
I found code gets executed after all the other code in viewDidLoad (where I put it) are done
even I tried to wrap it in dispatch_async(dispatch_get_main_queue(), ^{},
what could make it work immediately whenever I call it? sendSynchronous request?
I guess that you are starting those connections off the main loop, try with:
NSArray *reqArray = [10 requests of url inside];
NSMutableArray * saveArray = [prepare to store 10 JSON data in here];
NSInteger counter = [reqArray count];
for (NSURLRequest *request in reqArray) {
dispatch_async(dispatch_get_main_queue(), ^{
[NSURLConnection sendAsynchronousRequest:request
queue:[NSOperationQueue mainQueue]
completionHandler:^(NSURLResponse *response, NSData *data, NSError *error) {
NSDictionary *result1 = [NSJSONSerialization JSONObjectWithData:data options:NSJSONReadingMutableContainers error:nil];
NSDictionary *result2 = [result1 objectForKey:#"keyForValueIWant"];
[saveArray addObject:result2];
counter -- ;
if (counter == 0) {
NSLog(#"all done");
}
}];
});
}
Because NSURLConnection needs a runloop to execute, if the runloop ends, the connections ends.
Related
I have an iOS app with a function which is in charge of making an asynchronous network request. The request itself works just fine, but the problem I am having is with the function return statement which is causing errors.
Here is my function:
-(NSArray *)get_data:(NSString *)size {
// Set up the data request.
NSURL *url = [NSURL URLWithString:[NSString stringWithFormat:#"http://mywebsite.com/info.json"]];
NSURLRequest *url_request = [NSURLRequest requestWithURL:url];
NSOperationQueue *queue = [[NSOperationQueue alloc] init];
// Begin the asynchronous data loading.
[NSURLConnection sendAsynchronousRequest:url_request queue:queue completionHandler:^(NSURLResponse *response, NSData *data, NSError *error) {
if (error == nil) {
// Convert the response JSON data to a dictionary object.
NSError *my_error = nil;
NSDictionary *feed = [NSJSONSerialization JSONObjectWithData:data options:NSJSONReadingMutableLeaves error:&my_error];
if (feed != nil) {
// Store the returned data in the data array.
NSArray *topping_data;
for (int loop = 0; loop < [[feed objectForKey:#"toppings_data"] count]; loop++) {
NSString *size_name = [NSString stringWithFormat:#"%#", [[[feed objectForKey:#"toppings_data"] objectAtIndex:loop] valueForKey:#"Size"]];
if ([size_name isEqualToString:size]) {
topping_data = [[feed objectForKey:#"toppings_data"] objectAtIndex:loop];
}
}
return topping_data;
}
else {
return #[#"no data"];
}
}
else {
return #[#"no data"];
}
}];
}
I am getting the following error message on the line of code [NSURLConnection sendAsync....:
Incompatible block pointer types sending 'NSArray *(^)(NSURLResponse
*__strong, NSData *__strong, NSError *__strong)' to parameter of type 'void (^ _Nonnull)(NSURLResponse * _Nullable __strong, NSData *
_Nullable __strong, NSError * _Nullable __strong)'
What am I doing wrong here?
All I am trying to avoid, is the function returning BEFORE the asynchronous request has completed. Otherwise the function will not return any data, which is not what I want.
Thanks for your time, Dan.
best way to return data in async block is make a block callback as argument of function and callback return value here:
- (void)get_data:(NSString *)size completionHandler:(void (^)(NSArray *array))completionHandler {
// ...
[NSURLConnection sendAsynchronousRequest:url_request queue:queue completionHandler:^(NSURLResponse *response, NSData *data, NSError *error) {
// ...
completionHandler(array);
// ...
}];
}
use :
[self get_data:someString completionHandler:^(NSArray *array) {
// process array here
}];
The block returns nothing:
void ^(NSURLResponse *, NSData *, NSError *)
So you cannot return things:
return #[#"no data"];
The code that calls the block is not interested in what it returns; if you want to store state then add an instance variable or call a method.
Change
[NSURLConnection sendAsynchronousRequest:url_request queue:queue completionHandler:^(NSURLResponse *response, NSData *data, NSError *error)
to
[NSURLConnection sendAsynchronousRequest:url_request queue:queue completionHandler:^(NSURLResponse *_Nullable response, NSData *_Nullable data, NSError *_Nullable error)
I'm new to Objective-C, just wondering how to use NSArray object outside from JSON.
For example:
NSURL *url = [NSURL URLWithString:#"http://acumen-locdef.elasticbeanstalk.com/service/countries"];
NSURLRequest *request = [NSURLRequest requestWithURL:url];
NSMutableArray *myFinalListArray = [[NSMutableArray alloc] init];
[NSURLConnection sendAsynchronousRequest:request
queue:[NSOperationQueue mainQueue]
completionHandler:^(NSURLResponse *response,
NSData *data, NSError *connectionError)
{
if (data.length > 0 && connectionError == nil)
{
NSMutableArray *greeting = [NSJSONSerialization JSONObjectWithData:data
options:0
error:NULL];
for (NSDictionary *countryList in greeting) {
[myFinalListArray addObject:countryList[#"name"]];
}
}
NSLog(#"%#",myFinalListArray); //(This one showing all results..)
}];
NSLog(#"%#",myFinalListArray); //(This one giving empty result)
I have defined myFinalListArray and added objects in for loop.
If you use NSLog inside the loop or outside the loop it will show you results. But if I use this after }]; (after the code is ending.),
it's giving me empty array.
If you are accessing myFinalListArray in tableview then you can reload tableview inside the block after fetching data.
Or if you are accessing this array in some other task then you have to make notification call (have to add observer) and then post notification that will call some other method and access your array there and do your further stuff.
The block of code associated with sendAsynchronousRequest isn't executed until the network fetch has completed; this takes some time. While the network fetch is happening your code continues to execute, starting with the line immediately after sendAsynchronousRequest which is NSLog(#"%#",myFinalListArray); - but because the network operation hasn't completed you get an empty array.
In the block you need to include the code that you need to process the array, update your user interface or whatever (If you update UI make sure you dispatch the operation on the main thread)
This will work. You can try with this.
- (void)viewDidLoad {
[super viewDidLoad];
NSMutableArray *myFinalListArray = [[NSMutableArray alloc] init];
//Pass here the reference the a array. It will return you the array of you county when downloaded complete.
[self getURLResponse:&myFinalListArray];
NSLog(#"countryArray:%#",myFinalListArray);
}
-(void)getURLResponse:(NSMutableArray**)countryArray{
NSURL *url = [NSURL URLWithString:#"http://acumen-locdef.elasticbeanstalk.com/service/countries"];
NSURLRequest *request = [NSURLRequest requestWithURL:url];
NSMutableArray *myFinalListArray = [[NSMutableArray alloc] init];
NSURLResponse *response;
NSError *error = nil;
NSData *data = [NSURLConnection sendSynchronousRequest:
request returningResponse:&response error:&error];
NSMutableArray *greeting = [NSJSONSerialization JSONObjectWithData:data options:0 error:nil];
for (NSDictionary *countryList in greeting) {
[myFinalListArray addObject:countryList[#"name"]];
}
*countryArray = [[NSMutableArray alloc]initWithArray:myFinalListArray copyItems:YES];
}
-(void)sendRequest
{
NSURL *url = [NSURL URLWithString:#"http://acumen-locdef.elasticbeanstalk.com/service/countries"];
NSURLRequest *request = [NSURLRequest requestWithURL:url];
NSMutableArray *myFinalListArray = [[NSMutableArray alloc] init];
[NSURLConnection sendAsynchronousRequest:request
queue:[NSOperationQueue mainQueue]
completionHandler:^(NSURLResponse *response,
NSData *data, NSError *connectionError) {
if (data.length > 0 && connectionError == nil)
{
NSMutableArray *greeting = [NSJSONSerialization JSONObjectWithData:data
options:0
error:NULL];
if( !myFinalListArray )
{
myFinalListArray=[[NSMutableArray alloc]init];
}
for (NSDictionary *countryList in greeting) {
[myFinalListArray addObject:countryList[#"name"]];
}
}
[self printArray];
}];
}
//create method that will execute after response
-(void) printArray
{
NSLog(#"%#",myFinalListArray); //(This one showing all results..)
}
Use
__block NSMutableArray *myFinalListArray = [[NSMutableArray alloc] init];
This should work.
Happy Coding.
sendAsynchronousRequest runs asynchronously, meaning that the code below is already performed while the request is still running, so the NSLog is logging the empty array.
Only when the request finishes, the array is filled up but your outer NSLog was already performed.
Basically I want a way to issue a NSURLRequest multiple times in a loop until a certain condition has been met. I am using a rest api but the rest api only allows up to a maximum of 1,000 results at a time. So if i have, lets say 1,500 total, i want to make a request to get the first 1,000 then i need to get the rest with another almost exact request , except the startAt: parameter is different(so i could go from 1001 - 1500. I want to set this up in a while loop(while i am done loading all the data) and am just reading about semaphores but its not working out like I expected it to. I don't know how many results I have until i make the first request. It could be 50, 1000, or 10,000.
here is the code:
while(!finishedLoadingAllData){
dispatch_semaphore_t semaphore = dispatch_semaphore_create(0);
NSURLRequest *myRequest = [self loadData: startAt:startAt maxResults:maxResults];
[NSURLConnection sendAsynchronousRequest:myRequest
queue:[NSOperationQueue mainQueue]
completionHandler:^(NSURLResponse *response, NSData *data, NSError *error) {
if(error){
completionHandler(issuesWithProjectData, error);
}
else{
NSDictionary *issuesDictionary = [[NSDictionary alloc] initWithDictionary:[NSJSONSerialization JSONObjectWithData:data options:NSJSONReadingMutableContainers error:&error]];
[issuesWithProjectData addObjectsFromArray:issuesDictionary[#"issues"]];
if(issuesWithProjectData.count == [issuesDictionary[#"total"] integerValue]){
completionHandler([issuesWithProjectData copy], error);
finishedLoadingAllData = YES;
}
else{
startAt = maxResults + 1;
maxResults = maxResults + 1000;
}
}
dispatch_semaphore_signal(semaphore);
}];
dispatch_semaphore_wait(semaphore, DISPATCH_TIME_FOREVER);
}
Basically I want to keep the while loop waiting until the completion block finished. Then and only then do i want the while loop to check if we have all of the data or not(and if not, make another request with the updated startAt value/maxResults value.
Right now it just hangs on dispatch_semaphore_wait(semaphore, DISPATCH_TIME_FOREVER);
What am i doing wrong or what do i need to do? Maybe semaphores are the wrong solution. thanks.
Ok. The more I look, the more I don't think its a bad idea to have semaphores to solve this problem, since the other way would be to have a serial queue, etc. and this solution isn't all that more complicated.
The problem is, you are requesting the completion handler to be run on the main thread
[NSURLConnection sendAsynchronousRequest:myRequest
queue:[NSOperationQueue mainQueue]
completionHandler:^(NSURLResponse *response, NSData *data, NSError *error)
and you are probably creating the NSURL request in the main thread. Hence while it waits for the semaphore to be released on the mainthread, the NSURL completion handler is waiting for the mainthread to be free of its current run loop. So create a new operation queue.
would it not be easier to do something like this instead:
dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{ //run on a background thread
while(!finishedLoadingAllData){
NSURLRequest *myRequest = [self loadData: startAt:startAt maxResults:maxResults];
NSHTTPURLResponse *response = nil;
NSError *error = nil;
NSData *responseData = [NSURLConnection sendSynchronousRequest:myRequest returningResponse:&response error:&error]; //blocks until completed
if(response.statusCode == 200 && responseData != nil){ //handle response and set finishedLoadingAllData when you want
//do stuff with response
dispatch_sync(dispatch_get_main_queue(), ^{
//do stuff on the main thread that needs to be done
}
}
});
Please dont do that.. NSURLConnection sendAsynchronousRequest will be loading itself in loop for you, if your data is in chunk.. try this instead..
__block NSMutableData *fragmentData = [NSMutableData data];
[[NSOperationQueue mainQueue] cancelAllOperations];
[NSURLConnection sendAsynchronousRequest:request queue:[NSOperationQueue mainQueue] completionHandler:^(NSURLResponse *response, NSData *data, NSError *error)
{
[fragmentData appendData:data];
if ([data length] == 0 && error == nil)
{
NSLog(#"No response from server");
}
else if (error != nil && error.code == NSURLErrorTimedOut)
{
NSLog(#"Request time out");
}
else if (error != nil)
{
NSLog(#"Unexpected error occur: %#", error.localizedDescription);
}
else if ([data length] > 0 && error == nil)
{
if ([fragmentData length] == [response expectedContentLength])
{
// finished loading all your data
}
}
}];
I've created two chunky json response from server handling method.. And one of them is this, so hope this will be useful to you as well.. Cheers!! ;)
I have a NSURLConnection (two of them), and they're running in the wrong order.
Here's my method:
- (void)loginToMistarWithPin:(NSString *)pin password:(NSString *)password {
NSURL *url = [NSURL URLWithString:#"https://mistar.oakland.k12.mi.us/novi/StudentPortal/Home/Login"];
//Create and send request
NSMutableURLRequest *request = [[NSMutableURLRequest alloc] initWithURL:url];
[request setHTTPMethod:#"POST"];
NSString *postString = [NSString stringWithFormat:#"Pin=%#&Password=%#",
[self percentEscapeString:pin],
[self percentEscapeString:password]];
NSData * postBody = [postString dataUsingEncoding:NSUTF8StringEncoding];
[request setHTTPBody:postBody];
[NSURLConnection sendAsynchronousRequest:request queue:[NSOperationQueue mainQueue] completionHandler:^(NSURLResponse *response, NSData *data, NSError *error)
{
// do whatever with the data...and errors
if ([data length] > 0 && error == nil) {
NSError *parseError;
NSDictionary *responseJSON = [NSJSONSerialization JSONObjectWithData:data options:0 error:&parseError];
if (responseJSON) {
// the response was JSON and we successfully decoded it
NSLog(#"Response was = %#", responseJSON);
} else {
// the response was not JSON, so let's see what it was so we can diagnose the issue
NSString *loggedInPage = [[NSString alloc] initWithData:data encoding:NSUTF8StringEncoding];
NSLog(#"Response was not JSON (from login), it was = %#", loggedInPage);
}
}
else {
NSLog(#"error: %#", error);
}
}];
//Now redirect to assignments page
NSURL *homeURL = [NSURL URLWithString:#"https://mistar.oakland.k12.mi.us/novi/StudentPortal/Home/PortalMainPage"];
NSMutableURLRequest *requestHome = [[NSMutableURLRequest alloc] initWithURL:homeURL];
[request setHTTPMethod:#"POST"];
[NSURLConnection sendAsynchronousRequest:requestHome queue:[NSOperationQueue mainQueue] completionHandler:^(NSURLResponse *homeResponse, NSData *homeData, NSError *homeError)
{
// do whatever with the data...and errors
if ([homeData length] > 0 && homeError == nil) {
NSError *parseError;
NSDictionary *responseJSON = [NSJSONSerialization JSONObjectWithData:homeData options:0 error:&parseError];
if (responseJSON) {
// the response was JSON and we successfully decoded it
NSLog(#"Response was = %#", responseJSON);
} else {
// the response was not JSON, so let's see what it was so we can diagnose the issue
NSString *homePage = [[NSString alloc] initWithData:homeData encoding:NSUTF8StringEncoding];
NSLog(#"Response was not JSON (from home), it was = %#", homePage);
}
}
else {
NSLog(#"error: %#", homeError);
}
}];
}
- (NSString *)percentEscapeString:(NSString *)string
{
NSString *result = CFBridgingRelease(CFURLCreateStringByAddingPercentEscapes(kCFAllocatorDefault,
(CFStringRef)string,
(CFStringRef)#" ",
(CFStringRef)#":/?#!$&'()*+,;=",
kCFStringEncodingUTF8));
return [result stringByReplacingOccurrencesOfString:#" " withString:#"+"];
}
So, it's two NSURLConnection's that are added to the [NSOperationQueue mainQueue]. What my output is showing me is that the second NSURLConnection is running before the first one. So it tries to go to the page where I download data before I'm logged in, so it (obviously) returns a "You're not logged in" error.
How do I schedule them one after another?
The issue, as I suspect you have realized, is that you're doing asynchronous network requests (which is good; you don't want to block the main queue), so there's no assurance of the order they'll finish.
The quickest and easiest answer is to simply put the call to the second request inside the completion block of the first one, not after it. You don't want to be making that second one unless the first one succeeded anyway.
To keep your code from getting unwieldy, separate the login from the request for main page. And you can use the completion block pattern which is common with asynchronous methods. You add a parameter to loginToMistarWithPin that specifies what it should do when the request finishes. You might have one completion block handler for success, and one for failure:
- (void)loginToMistarWithPin:(NSString *)pin password:(NSString *)password success:(void (^)(void))successHandler failure:(void (^)(void))failureHandler {
NSURL *url = [NSURL URLWithString:#"https://mistar.oakland.k12.mi.us/novi/StudentPortal/Home/Login"];
//Create and send request
NSMutableURLRequest *request = [[NSMutableURLRequest alloc] initWithURL:url];
[request setHTTPMethod:#"POST"];
NSString *postString = [NSString stringWithFormat:#"Pin=%#&Password=%#",
[self percentEscapeString:pin],
[self percentEscapeString:password]];
NSData * postBody = [postString dataUsingEncoding:NSUTF8StringEncoding];
[request setHTTPBody:postBody];
[NSURLConnection sendAsynchronousRequest:request queue:[NSOperationQueue mainQueue] completionHandler:^(NSURLResponse *response, NSData *data, NSError *error)
{
// do whatever with the data...and errors
if ([data length] > 0 && error == nil) {
NSError *parseError;
NSDictionary *responseJSON = [NSJSONSerialization JSONObjectWithData:data options:0 error:&parseError];
if (responseJSON) {
// the response was JSON and we successfully decoded it
NSLog(#"Response was = %#", responseJSON);
// assuming you validated that everything was successful, call the success block
if (successHandler)
successHandler();
} else {
// the response was not JSON, so let's see what it was so we can diagnose the issue
NSString *loggedInPage = [[NSString alloc] initWithData:data encoding:NSUTF8StringEncoding];
NSLog(#"Response was not JSON (from login), it was = %#", loggedInPage);
if (failureHandler)
failureHandler();
}
}
else {
NSLog(#"error: %#", error);
if (failureHandler)
failureHandler();
}
}];
}
- (void)requestMainPage {
//Now redirect to assignments page
NSURL *homeURL = [NSURL URLWithString:#"https://mistar.oakland.k12.mi.us/novi/StudentPortal/Home/PortalMainPage"];
NSMutableURLRequest *requestHome = [[NSMutableURLRequest alloc] initWithURL:homeURL];
[requestHome setHTTPMethod:#"GET"]; // this looks like GET request, not POST
[NSURLConnection sendAsynchronousRequest:requestHome queue:[NSOperationQueue mainQueue] completionHandler:^(NSURLResponse *homeResponse, NSData *homeData, NSError *homeError)
{
// do whatever with the data...and errors
if ([homeData length] > 0 && homeError == nil) {
NSError *parseError;
NSDictionary *responseJSON = [NSJSONSerialization JSONObjectWithData:homeData options:0 error:&parseError];
if (responseJSON) {
// the response was JSON and we successfully decoded it
NSLog(#"Response was = %#", responseJSON);
} else {
// the response was not JSON, so let's see what it was so we can diagnose the issue
NSString *homePage = [[NSString alloc] initWithData:homeData encoding:NSUTF8StringEncoding];
NSLog(#"Response was not JSON (from home), it was = %#", homePage);
}
}
else {
NSLog(#"error: %#", homeError);
}
}];
}
Then, when you want to login, you can do something like:
[self loginToMistarWithPin:#"1234" password:#"pass" success:^{
[self requestMainPage];
} failure:^{
NSLog(#"login failed");
}];
Now, change those successHandler and failureHandler block parameters to include whatever data you need to pass back, but hopefully it illustrates the idea. Keep your methods short and tight, and use completion block parameters to specify what an asynchronous method should do when it's done.
Can you check the below link. It is about forcing one operation to wait for another.
NSOperation - Forcing an operation to wait others dynamically
Hope this helps.
This code loads a table view:
- (void)viewDidLoad
{
[super viewDidLoad];
//test data
NSURL *url =[[NSURL alloc] initWithString:urlString];
// NSLog(#"String to request: %#",url);
[ NSURLConnection
sendAsynchronousRequest:[[NSURLRequest alloc]initWithURL:url]
queue:[[NSOperationQueue alloc]init]
completionHandler:^(NSURLResponse *response, NSData *data, NSError *connectionError) {
if([data length] >0 && connectionError ==nil){
NSArray *arrTitle=[[NSArray alloc]init];
NSString *str=[[NSString alloc] initWithData:data encoding:NSUTF8StringEncoding];
arrTitle= [Helper doSplitChar:[Helper splitChar20] :str];
self.tableView.delegate = self;
self.tableView.dataSource = self;
[self fecthDataToItem:arrTitle];
[self.tableView reloadData];
NSLog(#"Load data success");
}else if (connectionError!=nil){
NSLog(#"Error: %#",connectionError);
}
}];
// arrTitle = [NSArray arrayWithObjects:#"ee",#"bb",#"dd", nil];
}
And it takes 10 - 15s to load. How can I make this faster?
.
Thanks Rob and rmaddy, problem is solve.
As rmaddy points out, you must do UI updates on the main queue. Failure to do so will, amongst other things, account for some of the problems you're experiencing.
The queue parameter of sendAsynchronousRequest indicates the queue upon which you want the completion block to run. So, you can simply specify [NSOperationQueue mainQueue]:
NSURLRequest *request = [NSURLRequest requestWithURL:url];
[NSURLConnection sendAsynchronousRequest:request queue:[NSOperationQueue mainQueue] completionHandler:^(NSURLResponse *response, NSData *data, NSError *connectionError) {
if([data length] > 0 && connectionError == nil) {
NSString *str = [[NSString alloc] initWithData:data encoding:NSUTF8StringEncoding];
NSArray *arrTitle = [Helper doSplitChar:[Helper splitChar20] :str];
self.tableView.delegate = self;
self.tableView.dataSource = self;
[self fecthDataToItem:arrTitle];
[self.tableView reloadData];
} else if (connectionError!=nil) {
NSLog(#"Error: %#",connectionError);
}
}];
Or, if you where doing something slow or computationally expensive/slow within that block, go ahead and use your own background queue, but then dispatch the UI updates back to the main queue, e.g.:
[NSURLConnection sendAsynchronousRequest:request queue:[[NSOperationQueue alloc] init] completionHandler:^(NSURLResponse *response, NSData *data, NSError *connectionError) {
// do something computationally expensive here
// when ready to update the UI, dispatch that back to the main queue
[[NSOperationQueue mainQueue] addOperationWithBlock:^{
// update your UI here
}];
}];
Either way, you should always do UI updates (and probably model updates, too, to keep that synchronized) on the main queue.