I have a class, that gets some data using NSURLConnection. It's method getData creates a request to a server and when some data recieved, method connection:didRecieveData: updates some properties.
- (void)getData
{
NSMutableURLRequest *request = [NSMutableURLRequest requestWithURL:dataURL];
NSURLConnection *connectionWithRequest = [NSURLConnection connectionWithRequest:request delegate:self];
}
- (void)connection:(NSURLConnection *)connection didReceiveData:(NSData *)data
{
// Processing data
dataProperty = processedData;
}
The problem is, when I create an instance of this class and call method getData, I can't immediately get object's properties, because data is not received yet. I've read Apple reference about delegates and protocols, but I don't understand how to implement delegate method for this class, that would work like connection:didRecieveData: for NSURLConnection.
Can you explain me how to do this? I would be very glad, if you just post a link to an example. Thank you.
I don't understand how to implement delegate method for this class, that would work like connection:didRecieveData: for NSURLConnection.
The same way NSURLConnection does:
Give this object a property named delegate.
Set that property to another object.
In connectionDidReceiveData:, send a message to the delegate.
In the delegate, implement the method that the other object will be calling.
NSMutableURLRequest *request = [NSMutableURLRequest requestWithURL:[NSURL URLWithString:#"YOUR API URL"]];
NSString *email = #"username#gmail.com";
NSString *password = #"123456";
NSString *deviceToken = #"simulator";
NSString *deviceType = #"1";
NSString *post = [NSString stringWithFormat:#"email=%#&password=%#&deviceToken=%#&deviceType=%#",email,password,deviceToken,deviceType];
NSData *requestBodyData = [post dataUsingEncoding:NSUTF8StringEncoding];
request.HTTPMethod = #"POST";
request.HTTPBody = requestBodyData;
[NSURLConnection sendAsynchronousRequest:request queue:[NSOperationQueue mainQueue]
completionHandler:^(NSURLResponse response, NSData responseData, NSError *error)
{
NSLog(#"%#",responseData);
NSDictionary *dic = [NSJSONSerialization JSONObjectWithData:responseData options:NSJSONReadingMutableContainers error:nil];
NSLog(#"%#",dic[#"data"]);
}];
Related
I am trying to use the code below to 'trigger' the web address. The web server doesn't return any data. But the NSURLConnection is being established.
NSString *serverAddressTest = #"http://domain.com";
NSString *fullWebAddress = [NSString stringWithFormat:#"%#?CustomerName=%#&ContactNo=%#&Products=%#",serverAddressTest,customer,contactnumber,allProductsInString];
NSURL *url = [NSURL URLWithString:fullWebAddress];
NSURLRequest *theRequest=[NSURLRequest requestWithURL:url];
NSURLConnection *theConnection=[[NSURLConnection alloc] initWithRequest:theRequest delegate:self];
if (theConnection) {
NSMutableData *webData = [NSMutableData data];
NSLog(#"%#",webData);
}
else {
NSMutableData *webData = [NSMutableData data];
NSLog(#"%#",webData);
}
When you write:
NSURLConnection *theConnection=[[NSURLConnection alloc] initWithRequest:theRequest
delegate:self];
you are starting an asynchronous url connection.
Then immediately after that you are testing whether the connection was successful or not and creating an instance of NSMutableData with local scope. Your NSURLConnectionDelegate methods (which you haven't posted) will not have access to this locally-scoped NSMutableData variable.
Have you indeed implemented the methods of the NSURLConnectionDelegate protocol?
Try to send synchronous request to localise the problem:
NSError *error;
NSData *returnData = [NSURLConnection sendSynchronousRequest: theRequest
returningResponse: nil
error: &error];
NSLog(#"error = %#, \ndata = %#", error, returnData);
You also need to also implement the delegate Protocols. ( As NSBum says)
Using Apples example
shown here is the data is returned when the parts are put together.:
NSURLRequest *theRequest=[NSURLRequest requestWithURL:[NSURL URLWithString:#"http://www.apple.com/"]
cachePolicy:NSURLRequestUseProtocolCachePolicy
timeoutInterval:60.0];
// Create the NSMutableData to hold the received data.
// receivedData is an instance variable declared elsewhere.
receivedData = [NSMutableData dataWithCapacity: 0];
// create the connection with the request
// and start loading the data
NSURLConnection *theConnection=[[NSURLConnection alloc] initWithRequest:theRequest delegate:self];
if (!theConnection) {
// Release the receivedData object.
receivedData = nil;
NSLog(#"FAIL " );
// Inform the user that the connection failed.
}
}
- (void)connection:(NSURLConnection *)connection didReceiveResponse:(NSURLResponse *)response
{
NSLog(#" response %#", response);
// This method is called when the server has determined that it
// has enough information to create the NSURLResponse object.
// It can be called multiple times, for example in the case of a
// redirect, so each time we reset the data.
// receivedData is an instance variable declared elsewhere.
[receivedData setLength:0];
}
- (void)connection:(NSURLConnection *)connection didReceiveData:(NSData *)data
{
// Append the new data to receivedData.
// receivedData is an instance variable declared elsewhere.
[receivedData appendData:data];
NSLog(#" receivedData %#", receivedData);
}
receivedData is not local but declared elsewhere. (NSMutableData* receivedData;)
I do not use this much so cannot expand further without reading the docs fully myself; which is what you need to do. :-)
I am trying to call a class method that takes a string and posts it to a site to receive a JSON response(among some other variables I have stored in the DataClass). I am stuck trying to return the data in the form of a response and can not at this point even NSLog the returned data. The question is, now that I have called my class method, how can the class method wait to return a response from an HTTP POST to return data? Once I return my JSON, I can expand it to a dictionary and process from there. Help is appreciated :)
Class Method:
//
// APISample.m
//
// Created by Sam on 1/6/13.
// Copyright (c) 2013 Sam. All rights reserved.
//
#import "APISample.h"
#import "DataClass.h"
#implementation APISample
#synthesize first_name = _first_name;
#synthesize last_name = _last_name;
#synthesize profile_pic_url = _profile_pic_url;
#synthesize responseData;
-(id)init
{
self = [super init];
return self;
NSLog(#"Loaded APISample and fetching");
}
+(id)getDataAboutUser:(NSString *)user_request_id;
{
DataClass *userdata=[DataClass getInstance];
NSLog(#"Loaded APISample and fetching %#", user_request_id);
NSMutableURLRequest *user_fetch_details = [[NSMutableURLRequest alloc] initWithURL:[NSURL URLWithString:#"http://10.0.23.161/users/user_fetch_details.php"]];
[user_fetch_details setHTTPMethod:#"POST"];
NSMutableString *postString = [NSMutableString stringWithString:#"id=123"];
[postString appendString:#"&userrequest_id="];
[postString appendString:[userdata.str_userid copy]];
[postString appendString:#"&user_id="];
[postString appendString:[userdata.str_userid copy]];
[postString appendString:#"&identifier="];
[postString appendString:[userdata.str_identifier copy]];
[user_fetch_details setValue:[NSString stringWithFormat:#"%d", [postString length]] forHTTPHeaderField:#"Content-length"];
[user_fetch_details setHTTPBody:[postString dataUsingEncoding:NSUTF8StringEncoding]];
NSURLConnection *connection=[[NSURLConnection alloc] initWithRequest:user_fetch_details delegate:self];
NSMutableData *responseData=[NSMutableData data];
[responseData appendData:[NSURLConnection connection:didReceiveData];
if (connection) {
// Create the NSMutableData that will hold
// the received data
// receivedData is declared as a method instance elsewhere
NSMutableData *responseData=[NSMutableData data];
} else {
// inform the user that the download could not be made
}
NSLog(#"Received Data %#", [[NSString alloc] initWithData:responseData encoding:NSASCIIStringEncoding]);
return [[NSString alloc] initWithData:responseData encoding:NSASCIIStringEncoding];
}
- (void)connection:(NSURLConnection *)connection didReceiveData:(NSData *)data {
[responseData appendData:data];
NSString *receivedDataString = [[NSString alloc] initWithData:responseData encoding:NSUTF8StringEncoding];
if ([receivedDataString isEqualToString: #"error"]) {
UIAlertView *errorAlert = [[UIAlertView alloc] initWithTitle:#"Error"
message:#"An error has occured. The application will now exit. Unexpected Response!"
delegate:nil
cancelButtonTitle:#"Close"
otherButtonTitles:nil];
[errorAlert show];
exit(0);
}else{
NSError* error;
NSDictionary* json = [NSJSONSerialization
JSONObjectWithData:responseData
options:kNilOptions
error:&error];
NSString *firstnameResponse = [json objectForKey:#"first_name"];
NSString *lastnameResponse = [json objectForKey:#"last_name"];
NSString *profile_pic_urlResponse = [json objectForKey:#"profile_pic_url"];
NSLog(#"didReceiveData %# analysed " , firstnameResponse);
}
}
- (void)connectionDidFinishLoading:(NSURLConnection *)connection {
NSLog(#"connectionDidFinishLoading");
NSLog(#"Succeeded! Received %d bytes of data",[self.responseData length]);
}
#end
I receive no data in the log after "Received Data" and do not see my error messages. Thanks you
The design pattern you are describing is called a CallBack. You need to be notified of an event occurring at some point in the future. In objective-c there are 4 main forms of callbacks.
Target Action Pairing (this is what is used with buttons, and things of the like. "When this button is pressed notify my target, and tell them to execute this action")
Delegation (you are using a form of delegation in the code above with NSURLConnection. When you see the word 'delegate' i want you to think 'helper object'. You are saying, "hey NSURLConnection, when important events happen, i would like you to tell this delegate (helper object) about these events)
Notifications (these are used a lot when dealing with model objects changing)
and finally... the one i would recommend for your purposes...
Blocks.
A block is a very cool variable. Most variables hold data. A block is a variable which holds code to be executed at some point in the future. So in your situation you could pass a completion block along with your method getDataAboutUser:(NSString *)user_request_id. So it would look like this.
getDataAboutUser:(NSString*)string withCompletion:(void(^)(NSData *finishedData))cBlock
Store that cBlock as an instanceVar. Then when your NSURLConnection finishes downloading all its data, you will execute the cBlock, passing in the finished data as an argument.
Blocks are a fairly complicated things if you have not used them before, so i would reccomend taking 20 minutes and reading this.
Since you need your method to wait for a response before returning, you can use NSURLConnection's convenience class method sendSynchronousRequest to carry out a synchronous request instead of creating and managing an NSURLConnection instance asynchronously.
So instead of your [[NSURLConnection alloc] init...] line you can do this:
NSURLResponse *response = nil;
NSError *error = nil;
NSData *responseData = [NSURLConnection sendSynchronousRequest:user_fetch_details returningResponse:&response error:&error];
Following which you can immediately parse the JSON from responseData instead of doing that in the connection:didReceiveData delegate.
Edit: Just saw user698846's suggestion to modify your method signature to take a completion block. That's also a good and possibly cleaner way to approach your problem if you are at liberty to change your method signature (i.e. nobody is requiring your function to return synchronously). Either way, sendSynchronousRequest is possibly the easiest way out and there's no shame in it especially if there's nothing your app nor your user can do while waiting for the request to complete.
This is some code:
NSURLResponse *response = nil;
NSError *error = nil;
NSData *responseData = [NSURLConnection sendSynchronousRequest:user_fetch_details returningResponse:&response error:&error];
How does one use NSURLConnection delegate callbacks when using the
+ (void)sendAsynchronousRequest:(NSURLRequest *)request
queue:(NSOperationQueue*) queue
completionHandler:(void (^)(NSURLResponse*, NSData*, NSError*))
method?
I would like to be able to access the caching delegate callback on the queue handling the completion block.
You don't. You need to use the NSURLConnection method, initWithRequest:delegate:, instead of sendAsynchronousRequest, to use the delegate call back methods.
Just use it like this
NSURL *url = [NSURL URLWithString:kURL];
NSMutableURLRequest *request = [NSMutableURLRequest requestWithURL : url
cachePolicy : NSURLRequestReloadIgnoringCacheData
timeoutInterval : 30];
NSString *params = [NSString stringWithFormat:#"param=%d",digits];
[request setHTTPMethod:#"POST"];
[request setHTTPBody:[params dataUsingEncoding:NSUTF8StringEncoding]];
[NSURLConnection sendAsynchronousRequest:request
queue:[NSOperationQueue mainQueue]
completionHandler:^(NSURLResponse *response, NSData *taxiData, NSError *error) {
//Snippet - Do sth. (block)
}
Hope this help.
EDIT: Sorry, I didn't read your question clearly. +sendAsynchronousRequest did not require delegates method.
EDIT2: or, maybe, this will help you
In order to use delegate methods with NSURLConnection you need to instantiate a NSURLConnection variable. Since
+ (void)sendAsynchronousRequest:(NSURLRequest *)request
queue:(NSOperationQueue*) queue
completionHandler:(void (^)(NSURLResponse*, NSData*, NSError*))
is a superclass method you can't use it.
It looks like I didn't get the concept of blocks completely yet...
In my code I have to get out the JSON data from the asychronous block to be returned to from the 'outer' method. I googled and found that if defining a variable with __block, the v̶i̶s̶i̶b̶i̶l̶i̶t̶y̶ _mutability_ of that variable is extended to the block.
But for some reason returned json object is nil.I wonder why?
- (NSMutableDictionary *)executeRequestUrlString:(NSString *)urlString
{
__block NSMutableDictionary *json = nil;
NSURL *url = [NSURL URLWithString:urlString];
NSMutableURLRequest *request = [NSMutableURLRequest requestWithURL:url];
[request setHTTPShouldHandleCookies:YES];
[request setHTTPMethod:#"GET"];
[request setValue:#"application/x-www-form-urlencoded" forHTTPHeaderField:#"Content-type"];
NSString *cookieString = [self.userDefaults objectForKey:SAVED_COOKIE];
[request addValue:cookieString forHTTPHeaderField:#"Cookie"];
[NSURLConnection sendAsynchronousRequest:request
queue:[NSOperationQueue currentQueue]
completionHandler:^(NSURLResponse *response, NSData *data, NSError *error)
{
NSLog(#"dataAsString %#", [NSString stringWithUTF8String:[data bytes]]);
NSError *error1;
NSMutableDictionary * innerJson = [NSJSONSerialization
JSONObjectWithData:data
options:kNilOptions
error:&error1];
json = innerJson;
}];
return json;
}
First, to answer your question:
But for some reason returned json object is nil. I wonder why?
The variable that you are returning has not been set at the time when you return it. You cannot harvest the results immediately after the sendAsynchronousRequest:queue:completionHandler: method has returned: the call has to finish the roundtrip before calling back your block and setting json variable.
Now a quick note on what to do about it: your method is attempting to convert an asynchronous call into a synchronous one. Try to keep it asynchronous if you can. Rather than expecting a method that returns a NSMutableDictionary*, make a method that takes a block of its own, and pass the dictionary to that block when the sendAsynchronousRequest: method completes:
- (void)executeRequestUrlString:(NSString *)urlString withBlock:(void (^)(NSDictionary *jsonData))block {
// Prepare for the call
...
// Make the call
[NSURLConnection sendAsynchronousRequest:request
queue:[NSOperationQueue currentQueue]
completionHandler:^(NSURLResponse *response, NSData *data, NSError *error) {
NSLog(#"dataAsString %#", [NSString stringWithUTF8String:[data bytes]]);
NSError *error1;
NSMutableDictionary * innerJson = [NSJSONSerialization
JSONObjectWithData:data options:kNilOptions error:&error1
];
block(innerJson); // Call back the block passed into your method
}];
}
When you call sendAsynchronousRequest:queue:completionHandler:, you've requested an asynchronous request. So it queues the request and the block and returns immediately. At some point in the future the request is made, and some point after that the completion block is run. But by that time, return json has long since run.
If you want to be able to return the data synchronously, then you must make a synchronous request. That will hang this thread until it completes, so it must not be the main thread.
Check the string when converting data coming from server using below code:
NSLog(#"dataAsString %#", [NSString stringWithUTF8String:[data bytes]]);
if the string is in a proper JSON format, ONLY then your JSON object will be correct.
Hope this hepls!!
In my application I want to use the NSURLConnection class. So please tell me how to use this one? This contain the lot of delegate methods, please tell me how to use them?
Initiate the connection using
self.responseData = [NSMutableData data];
NSURL *url = [NSURL URLWithString:#"http://sampleurl/"];
NSMutableURLRequest *request = [NSMutableURLRequest requestWithURL:url];
connection = [[NSURLConnection alloc] initWithRequest:request delegate:self];
[connection autorelease];
and you can catch the response in the connectionDidFinishLoading delegate method
#pragma mark - NSURLConnection Delegate Methods
- (void)connection:(NSURLConnection *)connection didReceiveResponse:(NSURLResponse *)response {
[self.responseData setLength:0];
}
- (void)connection:(NSURLConnection *)connection didReceiveData:(NSData *)data {
[self.responseData appendData:data];
}
- (void)connection:(NSURLConnection *)connection didFailWithError:(NSError *)error {
NSLog(#"Connection failed: %#", [error description]);
}
- (void)connectionDidFinishLoading:(NSURLConnection *)connection {
//Getting your response string
NSString *responseString = [[NSString alloc] initWithData:self.responseData encoding:NSUTF8StringEncoding];
self.responseData = nil;
}
For your memory leak problem
Declare the response data in interface file
NSMutableData *_responseData;
with property as below
#property (nonatomic, retain) NSMutableData *responseData;
and synthesize it
#synthesize responseData = _responseData;
Dont release it anywhere (We have used convenient constructors for allocation). We have already set it to nil in connectionDidFinishLoading method.
In iOS 5 and OS X 10.7 or later you can load data asynchronously using the following:
NSURL *url = [NSURL URLWithString:#"http://sampleurl/"];
NSMutableURLRequest *request = [NSMutableURLRequest requestWithURL:url];
[NSURLConnection sendAsynchronousRequest:request queue:[NSOperationQueue currentQueue]
completionHandler: ^(NSURLResponse * response, NSData * data, NSError * error) {
NSHTTPURLResponse * httpResponse = (NSHTTPURLResponse*)response;
if(httpResponse.statusCode == 200) {
//your code to handle the data
}
}
];
Or if you want to do it synchronously (not recommended if you are loading large data as it will hang the application) (available in OS X 10.2+ and iOS 2.0+)
NSURL *url = [NSURL URLWithString:#"http://sampleurl/"];
NSMutableURLRequest *request = [NSMutableURLRequest requestWithURL:url];
NSURLResponse * response;
NSError * error;
NSData * data = [NSURLConnection sendSynchronousRequest:request returningResponse:&response error:&error];