I recently created a method that can be called from other classes, this is my code.
In the ViewController1.h
+ (void)updateName:(id)sender;
In the ViewController1.m
+ (void)updateName:(id)sender {
}
The method is calling and working which is good however I have another method in the ViewController1.m file which is
-(void)updateString {
NSLog(#"IT WORKED");
}
However, I try to call it in my updateName method like this:
+ (void)updateName:(id)sender {
[self updateString];
}
But I get an error saying "no known class method for selector 'updateString' " Can anyone tell why is this happening and how I can call this method? Thanks.
The + in front of the method denotes a class method i.e. you don't need to create a new instance of ViewController1 in order to call the method. Where as [self updateString] is an instance method i.e. you need to create a new instance of the class in order to perform it. The problem here is the difference in scope. See below:
Inside another class:
[ViewController1 updateName:SOMETHING];
vs
ViewController1 *newViewController1 = [[ViewController1 alloc] init];
[newViewController1 updateString];
EDIT
If you want to call that method from that class you can do this?
+ (void)updateName:(id)sender {
[ViewController1 updateString];
}
But that won't be able to reference or update any class properties etc.. So from the names of your methods, this is likely not going to solve your problem.
Does that make sense ?
You're doing something odd but to fix your problem simply replace the - with + in front of your method name.
Related
I have been doing some research online and have found that using the ObjectiveC package in Objective C you can get a list of all the methods on a class using class_copyMethodList(), and I see you can get the implementation (IMP) of a method using instanceMethodForSelector:. The Apple documentation here has been helpful so far but I'm stuck and not sure what I'm really looking to find.
I want a list of the methods/functions called in a given method's implementation so I can build a call tree.
Any suggestions? Thanks in advance!
This solution is kind of hard way, and will cause a line of code in every method You can also make use of sqlite and save the tracked methods..
MethodTracker.h
#interface MethodTracker : NSObject
#property (nonatomic) NSMutableArray *methodTrackArr;
+ (MethodTracker *)sharedVariables;
#end
MethodTracker.m
#implementation MethodTracker
static id _instance = nil;
+ (MethodTracker *)sharedVariables
{
if (!_instance)
_instance = [[super allocWithZone:nil] init];
return _instance;
}
// optional
- (void)addMethod:(NSString *)stringedMethod
{
// or maybe filter by: -containObject to avoid reoccurance
[self.methodTrackArr addObject:stringedMethod];
NSLog("current called methods: %#", methodTrackArr);
}
#end
and using it like:
OtherClass.m
- (void)voidDidLoad
{
[super viewDidLoad];
[[MethodTracker sharedVariables] addMethod:[NSString stringWithUTF8String:__FUNCTION__]];
// or directly
[[MethodTracker sharedVariables].methodTrackArr addObject:[NSString stringWithUTF8String:__FUNCTION__]];
}
- (void)someOtherMethod
{
// and you need to add this in every method you have (-_-)..
[[MethodTracker sharedVariables] addMethod:[NSString stringWithUTF8String:__FUNCTION__]];
}
i suggest you import that MethodTracker.h inside [ProjectName]-Prefix.pch file.
Sorry, for the double answer, i deleted the other one and i have no idea how did that happen..
Hope this have helped you or at least gave you an idea.. Happy coding,
Cheers!
I think in the runtime track method is possible, but function not.
I have been build a tool DaiMethodTracing for trace all methods activity in single class for some of my need. This is based on objective-c method swizzling. So, there is an idea to do this
List all Classes in your application.
swizze all the methods in each class.
filter the method you want to trace.
finally, you may got the method call path.
I'm new to iPhone application development, but I seem to have somewhat managed so far (learning as I go).. however, I've run in to an issue I can't figure out. Here's the scenario:
I have an extension class called CoreAPI which I have my network functions inside. I have a function called "Login" inside CoreAPI which makes a request to a server, gets the 0 or 1 response and returns true or false. I had this working perfectly with Synchronous requests, but now I need to make everything asynchronous.
So, below is what I'm trying to do.. this is not working with the error along the lines of "Object of type ID has no method loginCallback"
loginViewController.m
- (void) login {
CoreAPI APIObject = [[CoreAPI alloc] init];
[APIObject login:self];
}
- (void) loginCallback {
NSLog(#"It called back.");
}
CoreAPI.m
- (void)login:(id)sender {
[sender loginCallback];
}
Thanks, and please let me know if I have missed any details needed to help me.
I'm seeing a couple problems. First, I'm guessing you don't provide visibility of the loginCallback function to CoreAPI.m. You should be able to send any message to an id type, so long as it's defined for a known type.
However, I'd recommend using a completion block in this case. Here's what that could look like:
(in CoreAPI.h)
- (void)login:(void (^)(void))completed;
(in CoreAPI.m)
- (void)login:(void (^)(void))completed {
// Login code
if (completed) completed();
}
Calling it would look like:
CoreAPI APIObject = [[CoreAPI alloc] init];
[APIObject login:^{
NSLog(#"It called back.");
}];
They have really goofy syntax, but blocks are really nice for this sort of thing. Hope this helped! Let me know if I didn't explain something clearly.
this should do the trick for you:
first, import loginViewController header inside CoreApi.m
#import "loginViewController.h"
Then, change login method to this:
- (void)login:(id)sender {
[(loginViewController*)sender loginCallback];
}
Or this:
- (void)login:(loginViewController*)sender {
[sender loginCallback];
}
Explanation: notice that your login method is receiving by parameter one object of type id . In objective C, id type means a reference to any Objective-C of unknow class. So, inside your login method, the compiler doesn't know that the sender is a instance of your loginViewController class, so it won't recognize loginViewController's methods.
To informations about this, please read: Objective-C: difference between id and void *
Notice that I only focused in remove your actual error. You should have to do more things in order to accomplish your code to run asynchronous.
In order to perform a better callback, please look for delegates or blocks (like in oltman's answer).
To run things in background, look for CDG : http://developer.apple.com/library/ios/#DOCUMENTATION/General/Conceptual/ConcurrencyProgrammingGuide/OperationQueues/OperationQueues.html
Mehul has defined this method.
+(BOOL)isCameraDeviceAvailable
{
BOOL isCameraAvailable=NO;
if([UIImagePickerController isSourceTypeAvailable:UIImagePickerControllerSourceTypeCamera])
{
if([UIImagePickerController isCameraDeviceAvailable:UIImagePickerControllerCameraDeviceFront] || [UIImagePickerController isCameraDeviceAvailable:UIImagePickerControllerCameraDeviceRear])
isCameraAvailable = YES;
}
return isCameraAvailable;
}
But I cannot declare it properly and am getting the error
Instance method '-isCameraDeviceAvailable' not found (return type defaults to 'id')
when I declare it as follows.
+ (BOOL)isCameraDeviceAvailable;
and then use it this way
if([self isCameraDeviceAvailable]){
}
I suppose I need to declare it in a different place or in a different way. Can you tell me how to do this?
[self isCameraDeviceAvailable]
is an instance method call, not a class method call.
You have to use it like this:
[MyClass isCameraDeviceAvailable]
+(BOOL)isCameraDeviceAvailable
The + at the beginning of the line makes this a class method, which means that you can only send isCameraDeviceAvailable to the class. If you want to use the method with an instance of that class, you'll need to declare it that way by using a - instead of +:
-(BOOL)isCameraDeviceAvailable
Or, as Kashiv explains, you can use the method as you have it by sending isCameraDeviceAvailable to the class instead. See Objective-C Classes Are also Objects for more information.
So I have this custom class with just a test method that does nslog. I am going to reuse this method many times in my app. The interface looks like this.
#interface TestViewController: UIViewController { CMImageMover * imageMover }
Then in the view did load I:
imageMover = [[CmImageMover alloc] init];
If I do:
[imageMover testMethod];
Right after the alloc and init it works in the viewDidLoad function but if I call it again from another function in the view controller nothing works and the class method does not get called.
What am I doing wrong here. Every other var I declare like NSArray/NSTimer, I do the say way and I am able to access and use it throughout my controller.
When you say "if I call it again from another function in the view controller nothing works" then first thing to check is what you are sending the testMethod. It could be nil, in which case nothing will happen. In objective C sending a message to nil does nothing. Add an NSLog to find out, e.g.
NSLog(#"imageMover object is: %#", imageOver);
[imageMover testMethod];
If the NSLog shows it is nil - or something crazy - then follow up what you are doing with the imageMover ivar.
You mention a class method in your question, but don't refer to it in your code snippets.
If you have defined testMethod as a class method it will, of course, fail if you send that message to an instance. (And it will fail noisily.) A class method would be introduced like this:
+ (void) testMethod
{
NSLog(#"CMImageMover testMethod called on Class");
}
An instance method would be introduced like this:
- (void) testMethod
{
NSLog(#"testMethod called on an instance of CMImageMover");
}
Apologies if this is all screamingly obvious to you and missing the point of the question. It's not that clear from your question where the issue lies.
I'm creating a game that uses cards.
I have an AppController class with one instance in the nib.
The AppController instance has an NSArray instance variable called wordList.
On init, the nib's instance of AppController generates a new GameCard.
Every gamecard has an array of words containing 5 words selected at random from the the list in AppController.
Because the list is large, I'd like to read it into memory only once. Therefore, I want only one instance of AppController, as a singleton class. Every time a new GameCard is created from within AppController, it should access that same singleton instance to retrieve the wordlist.
So basically, I need a singleton AppController that creates GameCards, where each GameCard has a reference to the original AppController.
I'm not sure how to implement this. Sorry if the explanation was confusing.
A code example I found online follows (http://numbergrinder.com/node/29)
+ (AppController *)instance
{
static AppController *instance;
#synchronized(self) {
if(!instance) {
instance = [[AppController alloc] init];
}
}
return instance;
}
But when I tried to do something with it in a GameCard instance through the code below, my application took forever to launch and Xcode told me it was loading 99797 stack frames.
AppController *controller = [AppController instance];
It sounds like an infinite loop. Make sure that -[AppController init] isn't calling +[AppController instance].
Why does every card need a reference to the app controller?
If it's just to access its words, it's simpler to let each card own its words directly. Make a new method named initWithWords: the designated initializer for the GameCard class. Initialize each card with the array of its five words, and have the card own that array for its lifetime.
Removing the cards' references to the app controller would resolve the infinite loop that Tom astutely detected.
Also, if no word should appear on two cards at once, remember to take that into account when drawing from the app controller's Great Big Array Of Words, and when destroying cards (you may or may not want the words to go back into the pile for future cards).
It sounds like you're on the right track. I've never tried to put a reference to a singleton in a nib file, though. You may want to create a separate singleton class that maintains a copy of the data (DataManager, maybe?), and then call it from within your instance of AppController to fetch the words.
You may find that putting a singleton within a nib (using the code for a singleton in Stu's post) works just fine, though. Good luck!
It looks like you may be calling your class instance method from within your init method. Try something like this:
static AppController* _instance = nil;
- (id)init
{
// depending on your requirements, this may need locking
if( _instance ) {
[self release];
return _instance;
}
if( (self = [super init]) ) {
_instance = [self retain];
// do your initialization
}
return self;
}
+ (AppController*)instance
{
if( _instance ) return _instance;
else return [[AppController alloc] init];
}
This makes sure that only one instance of AppController is ever available and also that it's safe to allocate it as well as getting a copy through the instance class method. It's not thread safe, so if it's going to be accessed by multiple threads, you should add some locking around the checks to _instance.
The normal way to create an AppController/AppDelegate is to add a custom NSObject to your MainMenu/MainWindow.xib file. Set the class to be AppController. Link your UIApplication/NSApplication delegate reference to your AppController object. Then you can get your single AppController with either
(AppController*)[NSApp delegate];
or
(AppController*)[[UIApplication sharedApplication] delegate];
You never have to create it with alloc/init because it will be created when your application is launched. You don't have to worry about making it a singleton because no one will ever try to create another one. And you don't have to worry about how to access it because it will be the delegate of the UIApplication/NSApplication object.
All that said, if you need a global variable holding an array of words, then forget about the AppController and make a new singleton object which holds/reads the array. In which case you just need:
+ (NSArray *)sharedWordListArray
{
static NSArray *wordList;
if( !wordList ) {
wordList = [[NSMutableArray alloc] init];
// read array
}
return wordList;
}
If you really need thread safety, then simply call [WordList sharedWordListArray] from your app delegate's applicationDidFinishLaunching: method before starting any threads, or add an NSLock if you really want to defer the loading to later, but often its better to take the load time hit at the start of the program rather than unexpectedly when the user takes some later action.