I have several RestKit gets that all use the same format:
[[RKClient sharedClient] get:endString queryParameters:params delegate:self];
I have a masterMethod that essentially refreshes all my user's restful data that looks like this
-(void)masterMethod
{
[self get1];
[self get2];
[self get3];
[self get4];
[self get5];
}
Where all the gets are in the same format as the one above. All of this code is in a class that includes the delegate method:
- (void)request:(RKRequest*)request didLoadResponse:(RKResponse*)response
However, I think something is going wrong when I try to call all give gets in the same method. It's as though the delegate didLoadResponse & didRecieveResponse methods are overlapping or getting release or something. Is there a way to make a master queue to handle this huge call? Or is something else going wrong.
I'm getting a BAD_ACCESS error somewhere in the masterMethod call.
Thanks, any help greatly appreciated.
What are you getting? If you're pulling down objects you should us the isKindOfClass method to distinguish the objects in objectLoader:didLoadObjects and set appropriately.
- (void)objectLoader:(RKObjectLoader*)objectLoader didLoadObjects:(NSArray*)objects {
if ([[objects objectAtIndex:0] isKindOfClass:[Apple class]]) {
Apple *apple = [objects objectAtIndex:0];
}
else if ([[objects objectAtIndex:0] isKindOfClass:[Banana class]]) {
Banana *banana = [objects objectAtIndex:0];
}
}
If you're pulling data from the request response, look into setting userdata on the request object, then checking the userdata in request:didLoadResponse. For more information see RestKit: distinguish multiple requests in didLoadResponse:.
Related
I am converting my application from Syncronous to Asyncronous HTTP requests and have ran into a problem that looks like it will require quite a big reworking of how the application handles its data. Let me try to explain
Previously it was like this:
-Class1, Class2 and Class3 were all subclasses of UIViewController
-Helper class
-Content display class
They do broadly different things but the common trait is their interaction with the helper class. They gather details of a request in a number of different ways from a user and then eventually send a request to the helper class.
When it was done syncronously the helper class would return the data. Each class would then interpret the data (XML files) and pass them on to the Content display class via a segue
So something broadly like this:
Class1:
//Get user input
SomeData *data = [helperclass makerequest];
id vcData = [data process];
[self performSegueWithIdentifier:#"segueIdentifier"];
---
- (void)prepareForSegue:(UIStoryboardSegue *)segue
{
DestinationViewController *destination = (DestinationViewController *)segue.destinationViewController;
destination.data = vcData;
}
Content display class:
- (void)viewDidLoad
{
[super viewDidLoad];
[self.data presentdata];
}
Now it looks like this
I dealt with this problem by first making it work with Class1 with a view to deploying the fix to class2 and class3. So class1 and helper now interact like this
Class1:
//Get user input
SomeData *data = [helperclass makerequestWithSender:self];
id vcData = [data process];
[self performSegueWithIdentifier:#"segueIdentifier"];
---
- (void)prepareForSegue:(UIStoryboardSegue *)segue
{
DestinationViewController *destination = (DestinationViewController *)segue.destinationViewController;
destination.data = vcData;
}
Now the biggest problem I am facing is how to get the data from helperclass back to Class1. I managed to get it to work by doing
(void)makeRequestWithSender:(Class1*)sender
{
[NSURLConnection sendAsynchronousRequest:...
{
[sender sendData:data];
}
}
However, when I have came to roll this out to the other 2 GUI classed which will compose the request I am having difficulty with. My first thought was to set sender:(id) but that fails at the line [sender sendData:data] telling me that id does not have an method sendData: or similar.
Hopefully I wasn't too vague here and you guys can help. If required I will be able to post code snippets but for now can anyone help with a better suggestion about how to structure the code for this request?
You basically want to use the 'observer pattern' or a (maybe) slightly changed setup, so you can use delegation.
Observer pattern
You gain the mechanic via the NSNotificationCenter and NSNotifications. Your 3 different UIViewController subclasses each subscribe to a specific NSNotification and you notify them via posting a notification via the NSNotificationCenter.
The following code is an example of how you can approach the problem in your viewcontroller subclasses:
- (void)viewWillAppear:(BOOL)animated {
[super viewWillAppear:animated];
// subscribe to a specific notification
[[NSNotificationCenter defaultCenter] addObserver:self selector:#selector(doSomethingWithTheData:) name:#"MyDataChangedNotification" object:nil];
}
- (void)viewWillDisappear:(BOOL)animated {
[super viewWillDisappear:animated];
// do not forget to unsubscribe the observer, or you may experience crashes towards a deallocated observer
[[NSNotificationCenter defaultCenter] removeObserver:self];
}
...
- (void)doSomethingWithTheData:(NSNotification *)notification {
// you grab your data our of the notifications userinfo
MyDataObject *myChangedData = [[notification userInfo] objectForKey:#"myChangedDataKey"];
...
}
In your helper class, after the data changed you have to inform the observers, e.g.
-(void)myDataDidChangeHere {
MyDataObject *myChangedData = ...;
// you can add you data to the notification (to later access it in your viewcontrollers)
[[NSNotificationCenter defaultCenter] postNotificationName:#"MyDataChangedNotification" object:nil userInfo:#{#"myChangedDataKey" : myChangedData}];
}
via #protocol
Presuming all your UIViewController subclasses reside in a parent viewcontroller, you can implement a protocol in your helper class and make the parent viewcontroller the delegate. Then the parent viewcontroller may inform the child uiviewcontrollers via passing a message.
Your helper class declaration could look like this (presuming ARC):
#protocol HelperDelegate;
#interface Helper : NSObject
#property (nonatomic, weak) id<HelperDelegate> delegate;
...
#end
#protocol HelperDelegate <NSObject>
-(void)helper:(Helper *)helper dataDidChange:(MyDataObject*)data;
#end
In the helper implementation you would inform the delegate via:
...
if ([self.delegate respondsToSelector:#selector(helper:dataDidChange:)]) {
[self.delegate helper:self dataDidChange:myChangedDataObject];
}
...
Your parent viewcontroller would need to be the delegate of the helper class and implement its protocol; a rough sketch, in the declaration
#interface ParentViewController : UIViewController <HelperDelegate>
and for the implementation in short version
// you alloc init your helper and assign the delegate to self, also of course implement the delegate method
-(void)helper:(Helper *)helper dataDidChange:(MyDataObject*)data {
[self.myCustomChildViewController doSomethingWithTheNewData:data];
}
Besides..
You might ask yourself which method to prefer. Both are viable, the main difference is that via the observer pattern you get more objects to be informed 'at once', whereas a protocol can only have one delegate and that one has to forward the message if needed. There are a lot of discussions around about pros and cons. I'd suggest you read up on them once you made up your mind (sorry ain't got enough reputation to post more than two links, so please search on stackoverflow). If something is unclear, please ask.
Some reasonable ideas here. To elaborate/add my opinion:
First, which object ought to tell the downloader (HelperClass) to begin downloading? My practice is to do this in the view controller that will present the data. So I generally start network requests after a segue (like in viewWillAppear: of the presented vc), not before.
Next, when one class needs to execute code provided for another, I first think about if it makes sense to do it using a block. Very often (not always) blocks make more sense and provide more readable code than, say, delegate, notification, KVO, etc. I think NSURLConnection completion, for example, is better suited to blocks than delegate. (and Apple kind of agrees, having introduced + (void)sendAsynchronousRequest:(NSURLRequest *)request queue:(NSOperationQueue *)queue completionHandler:(void (^)(NSURLResponse*, NSData*, NSError*))handler).
So my pattern for your app would be this:
// Class1.m
// when user has completed providing input
...
// don't do any request yet. just start a segue
[self performSegueWithIdentifier:#"ToContentDisplayClass" sender:self];
...
- (void)prepareForSegue:(UIStoryboardSegue *)segue sender:(id)sender {
// don't do a request yet, just marshall the data needed for the request
// and send it to the vc who actually cares about the request/result
if ([segue.identifier isEqualToString:#"ToContentDisplayClass"]) {
NSArray *userInput = // collect user input in a collection or custom object
ContentDisplayClass *vc = segue.destinationViewController;
vc.dataNeededForRequest = userInput;
}
...
Then in ContentDisplayClass.m
// this is the class that will present the result, let it make the request
- (void)viewWillAppear:(BOOL)animated {
[super viewWillAppear:animated];
HelperClass *helper = [[HelperClass alloc]
initWithDataNeededForRequest:self.dataNeededForRequest];
// helper class forms a request using the data provided from the original vc,
// then...
[helper sendRequestWithCompletion:^(NSURLResponse *response, NSData *data, NSError *error) {
if (!error) {
// interpret data, update view
self.label.text = // string we pulled out of data
} else {
// present an AlertView? dismiss this vc?
}
}];
This depends on HelperClass implementing the block form of NSURLConnection
// HelperClass.m
- (id)initWithDataNeededForRequest:(id)dataNeededForRequest {
// standard init pattern, set properties from the param
}
- (void)sendRequestWithCompletion:(void (^)(NSURLResponse *, NSData *, NSError *))completion {
NSURLRequest *request = ...
// the stuff we need to formulate the request has been setup in init
// use NSURLConnection block method
[NSURLConnection sendAsynchronousRequest:request
queue:[NSOperationQueue mainQueue]
completionHandler:completion];
}
Edit - there are several rationale's for making the VC transition before starting the network request:
1) Build the standard behavior around the success case: unless the app is about testing network connections, the success case is that the request works.
2) The cardinal principal for an app is to be responsive, to do something sensible immediately upon user actions. So when the user does something to initiate the request, an immediate vc transition is good. (what instead? a spinner?). The newly presented UI might even reduce the perceived latency of the request by giving user something new to look at while it runs.
3) What should an app do when a request fails? If the app doesn't really need the request to be useful, then doing nothing is a good option, so you'd want to be on the new vc. More typically, the request is necessary to proceed. The UI should be "responsive" to request failure, too. Typical behavior is to present an alert that offers some form of "retry" or "cancel". For either choice, the place the UI wants to be is on the new vc. Retry is more obvious, because that's where it always is when it tries to fetch the data. For cancel, the way to be "responsive" to cancel is to go back to the old vc, a vc transition back isn't ugly, it's what the user just asked for.
I'm not 100% clear on how you're handling the data now, but to change your data to asynchronous calls, I would use blocks. For instance your current synchronous code like this:
//Get user input
data = [helperclass makerequest]
sendData = [data process]
would turn into something like this:
//Get user input
data = [helperclass makerequestWithSuccess:^{
sendData = [data process]
}];
Using a success block will allow you to wait to process the data until the makerequest was finished.
Your new makerequest function would now look like this:
-(void)makerequestWithSuccess:(void (^)(void))success{
// Put your makerequest code here
// After your makerequest is completed successfully, call:
success();
}
Hope this helps!
I'm not sure that I understood your problem correctly, but if it's sort of:
Start task A asynchronously.
When task A finished successfully, get its result and start task B whose input is result A.
When task B finished successfully, get its result and start task C whose input is result B.
...
When finished successfully, be happy, otherwise print error.
A code example would look like this:
typedef (void)(^completion_block_t)(id result);
-(void) asyncTaskA:(completion_block_t)completionHandler;
-(void) asyncTaskBWithInput:(id)input completion:(completion_block_t)completionHandler;
-(void) asyncTaskCWithInput:(id)input completion:(completion_block_t)completionHandler;
-(void) asyncSomethingWithCompletion:(completion_block_t)completionHandler;
-(void) asyncSomethingWithCompletion:(completion_block_t)completionHandler
{
[self asyncTaskA:^(id resultA){
if (![resultA isKindOfClass:[NSError class]]) {
[self asyncTaskBWithInput:resultA completion:^(id resultB){
if (![resultB isKindOfClass:[NSError class]]) {
[self asyncTaskCWithInput:resultB completion:^(id resultC) {
completionHandler(resultC);
}];
}
else {
completionHandler(resultB); // error;
}
}];
}
else {
completionHandler(resultA); // error
}
}];
}
And you use it like:
[self asyncSomethingWithCompletion:^(id result){
if ([result isKindOfClass:[NSError class]]) {
NSLog(#"ERROR: %#", error);
}
else {
// success!
self.myData = result;
}
}];
The "continuation" and error handling makes this a bit confusing (and Objective-C syntax doesn't really add for more readability).
Another example with a third party library support:
The same logic can be written as this:
-(Promise*) asyncTaskA;
-(Promise*) asyncTaskBWithInput;
-(Promise*) asyncTaskCWithInput;
-(Promise*) asyncSomething;
- (Promise*) asyncSomething
{
return [self asyncTaskA]
.then(id^(id result) {
return [self asyncTaskBWithInput:result];
}, nil)
.then(id^(id result) {
return [self asyncTaskCWithInput:result];
}, nil);
}
And it is used as follows:
[self asyncSomething]
.then(^(id result) {
self.myData = result;
return nil;
},
^id(NSError* error) {
NSLog(#"ERROR: %#", error);
return nil;
});
If you like the latter more, the "Promise" framework is available on GitHub: RXPromise - I'm the author ;)
I'm not sure if what I've done in the past is relevant to your problem, but what I've done is create a download class that has a delegate protocol with a single method: -(void)downloadFinished:(id) data.
Any class that needs to get asynchronous data, creates an instance of this download class, and sets itself as the delegate. I call downloadFinished: from both connection:didFailWithError: and connectionDidFinishLoading:. Then, in the implementation of that method in the delegate, I check whether the data's class is NSData or NSError, and evaluate that data however is appropriate for that class.
I'm new to the concept of delegates and selectors when used with notifications. So my first question is,
1) Let's say you have a button that has a delegate that implements some doWork method. If you want the same functionality that's in the method, is it 'ok' to just call that method? I didn't know if that was considered good coding practices and/or if you should do that, or do something different in getting that type of functionality. Like if that is ok architecture?
2) Similarly, with NSNotificationCenter, I see some code that posts a notification. Then there's a HandleSegmentedControl:(NSNotification *)notification method. If I want to manually have that functionality, but without pressing the segment control, is it 'ok' to just take that functionality out of that method and put it in a new method so it would look like this:
Original:
- (void)HandleSegmentedControl:(NSNotification *)notification {
NSDictionary *dict = [userInfo notification];
// do stuff with the dictionary
}
New:
- (void)HandleSegmentedControl:(NSNotification *)notification {
NSDictionary *dict = [userInfo notification];
[self newMethod:dict];
}
- (void)newMethod:(NSDictionary *)dict {
// do stuff with the dictionary
}
- (void)myOtherMethodThatNeedsTheSameFunctionality {
NSDictionary *dict = // create some dictionary
[self newMethod:dict];
}
Sorry if these are basic questions. I'm not sure what the best practices are for things like this and wanted to start the right way. Thanks.
If the delegate protocol implements the doWork method as a required method, then yes. However, if it is an optional method, or if you want to be extra safe, you should use
if ([delegate respondsToSelector:#selector(doWork)]) {
[delegate doWork];
}
Sure, that seems like a reasonable thing to do. It is a common way to make your code more robust. The notification's userInfo is there so you can send data as you like. However, I think in your code you meant [notification userInfo] not [userInfo notification].
long time listener, first time caller.
I have a basic memory issue I don't understand, that I'm sure just about any one of you will see in a second. I'm playing around, trying to learn various ways of using UIWebViews, getting strings from URLs, and so on. Specifically, I'm trying to obtain one URL from another. In other words, I have uploaded an html page to the web, containing a URL. The address for that page is coded into the app, giving me a "hook" into the app - I can change the contents of that page and send the app a new URL any time I want. Make sense?
So...retrieving the URL? No problem. Passing it into a string for later use - no problem. But when I set up a tap gesture recognizer, which should take that string, convert it back to an NSURL, and open it in Safari, I get a runtime crash. An NSLog call tells me that the string in question keeps being assigned to all sorts of random things.
The relevant bits of my code follow. I'm sure some of you will tell me there are much better ways to do what I want - and that's certainly welcome. But I'd also really love to know what I'm doing wrong for this particular implementation, as I'm sure it's a basic misunderstanding that I'd like to correct.
Thanks in advance. (And sorry about the formatting of the code block - haven't quite got the hang of posting on here!)
#import "Messing_With_Web_ViewsViewController.h"
#implementation Messing_With_Web_ViewsViewController
#synthesize tapView;
NSString *finalURL;
- (void)viewDidLoad {
[super viewDidLoad];
NSString *firstString = #"http://www.my_web_address.html";
//Of course, I have the correct address here.
NSURL *firstUrl = [NSURL URLWithString:firstString];
NSError * error;
finalURL = [NSString stringWithContentsOfURL:firstUrl
encoding:NSASCIIStringEncoding error:&error];
if ( finalURL )
{
NSLog(#"Text=%#", finalURL);
//everything fine up to here; console prints the correct
contents of "my web address"
}
else
{
NSLog(#"Error = %#", error);
}
//Taps
UITapGestureRecognizer *tapRecognizer;
tapRecognizer=[[UITapGestureRecognizer alloc]
initWithTarget:self
action:#selector(foundTap:)];
tapRecognizer.numberOfTapsRequired=1;
tapRecognizer.numberOfTouchesRequired=1;
[tapView addGestureRecognizer:tapRecognizer];
[tapRecognizer release];
}
- (void)foundTap:(UITapGestureRecognizer *)recognizer {
NSLog(#"Trying to load %#", finalURL);
//at this point the app either crashes, or the console shows a random memory object
[[UIApplication sharedApplication] openURL:[NSURL URLWithString: finalURL]];
}
- (void)didReceiveMemoryWarning {
[super didReceiveMemoryWarning];
}
- (void)viewDidUnload {
}
- (void)dealloc {
[finalURL release];
[super dealloc];
}
#end
finalURL = [NSString stringWithContentsOfURL:firstUrl
encoding:NSASCIIStringEncoding error:&error];
The line above creates an instance of NSString which you do not own (because you did not call a method whose name includes 'new', 'alloc' 'retain', or 'copy' on it). That finalURL with therefore eventually be destroyed when it is no longer needed. By the time your -foundTap: method runs finalURL has been deallocated and you are just referencing the memory location where it used to be and which now may contain some other object or random data.
Read the memory management guidelines again and also learn to run the static analyzer which should point out mistakes like this.
I'm fairly new to Objective-C, and it would be really helpful if someone could help me with the following task:
I have a class TheController that has a method DoTask. The goal of DoTask is to reach out to a MasterUtility (also a custom made class) and get Data, and then send it back when it is done (it uses a thread). Specifically, I want it to send it to dataReceiver in ReportsViewController. I think I need to use #selector or something like that. Here is some code:
#implementation ReportsViewController
-(void)doTask {
MasterUtilities *mu = [[MasterUtilities alloc] init];
[mu getDataAndSendTo:[WHAT GOES HERE]]
}
-(void)dataReceiver:(NSArray *)data {
NSLog(#"data: %#",data);
}
#end
Here is MasterUtilities
#implementation MasterUtilities
- (void)getDataAndSendTo:[WHAT GOES HERE] {
NSArray *data = [[NSArray init] alloc];
....getting data here....
[WHAT GOES HERE? HOW DO I CALL THE METHOD (dataReceiver) IN ReportsViewController?]
}
#end
Can anyone fill in the areas that indicate "WHAT GOES HERE"? Thank you!!
You could use a block:
typedef void (^Callback)(NSArray*);
[somebody doSomethingAndPerform:^(NSArray *data) {
// do whatever you want with the data
}];
- (void) doSomethingAndPerform: (Callback) callback
{
NSArray *data = …;
callback(data);
}
This is very flexible, but maybe too complex. If you want something simpler, you can always just pass the selector and target, just as you thought:
[somebody doSomethingAndCall:#selector(dataReceiver:) on:self];
- (void) doSomethingAndCall: (SEL) selector on: (id) target
{
NSArray *data = …;
[target performSelector:selector withObject:data];
}
Or you can use a protocol:
#protocol DataConsumer
- (void) handleData: (NSArray*) data;
#end
// this class has to implement DataConsumer
[somebody doSomethingAndNotify:self];
- (void) doSomethingAndNotify: (id <DataConsumer>) consumer
{
NSArray *data = …;
[consumer handleData:data];
}
This solution is a bit heawyweight, but the advantage is that the compiler catches some errors for you. There’s also more coupling, but it’s far from being a problem.
You have to use the Target-Action design pattern, which is widely used in Cocoa.
Good luck!
You may wish to reconsider how you approach this problem.
Rather than trying to get your MasterUtilities instance to send the data to your other method, why not have your getData method return the data from the method and then have your ReportsViewController pass the data to dataReciever: ?
Serious Problem here... i'm getting ECX_BAD_ACCESS if i try to NSLog an instance variable of my custom object. Following Function is called in my ViewController, payload holds String Data which is pulled from a url.
- (void) initVcardWithData:(NSString *)payload {
NSLog(#"1. initVcardWithData");
aVCard = [[vcardItem alloc] initWithPayload:payload];
VCardViewController *aVCardViewController = [[VCardViewController alloc] initWithVCard:aVCard];
[self presentModalViewController:aVCardViewController animated:YES];
[aVCard release];
}
So far so good. The initWithWithVCard function is as follows, theVCard and theVCardN are defined in #implementation and also set as a #property (nonatomic, retain) in (.h).:
-(id)initWithVCard:(vcardItem *)aVCard {
if(self = [super init]) {
theVCard = [aVCard retain];
theVCardN = [theVCard.PersonName retain];
}
NSLog(#"---- vCardViewController :: initWithVcard :: FirstName: %#", theVCard.PersonName.FirstName);
return self;
}
If i access the theVCardN object in my ViewController aVCardViewController within ViewDidLoad everything works like a charm. I set some labels with data from that object.
If i then try to access the instance variables from theVCardN within a function which is called from an IBAction which is connected to a button in View, i get an EXC_BAD_ACCESS error at the debugger console. The Function which tries to pull data from the instance variables is as follows:
-(IBAction)addressbookButtonTapped {
NSLog(#"RETAIN COUNT FOR theVCard: %i", [theVCard retainCount]);
NSLog(#"RETAIN COUNT FOR theVCardN: %i", [theVCardN retainCount]);
NSLog(#"Save to Adressbook: %#", theVCardN.FirstName);
//[self dismissModalViewControllerAnimated:YES];
}
The RetainCounter for theVCardN right before calling NSLog outputs "1". The NSLog Line then returns EXC_BAD_ACCESS in Debugger Console.
Any idea ?
Do not call -retainCount. Absolute retain counts are useless.
retainCount returns the absolute retain count of an object. The actual value will be an implementation detail that is very often completely out of your control as the system frameworks may do any number of things internally to cause the retain count to be modified in ways you don't expect.
It is useless for debugging and their are a wealth of tools that are specifically focused on tracking down these kinds of issues.
First, if there is a crash, there is a backtrace. Post it. Probably not that interesting in this case, but, still, always look to the backtrace to at least confirm that it is crashing where/how you think it is.
From the evidence posted, it sounds like theVCardN.FirstName is either set to garbage or the underlying string has been over-released. Turn on zombie detection mode and see if that is the case. Since it is crashing on FirstName, then show the code related to creating/storing the FirstName.
Also, instance variables and methods should always start with a lowercase letter; PersonName should be personName & FirstName should be firstName.
Maybe i'm reading the code wrong or misunderstanding your class structure, but it looks like you logging:
NSLog(#"Save to Adressbook: %#", theVCardN.FirstName);
Above, where you say it is still working, you are logging:
theVCard.PersonName.FirstName
Are you missing the "PersonName"? Meaning you should be logging:
NSLog(#"Save to Adressbook: %#", theVCardN.PersonName.FirstName);