I am attempting to simply call a method within the same class, e.g.
-(void) createRequest: (NSString*)urlFormatted {
...
}
-(void) sendData {
...
[createRequest request]; <- Error occurs here.
}
Error: 'createRequest undeclared'
Whether is was necessary or not, I also defined createRequest in associated header file, e.g.
-(void) createRequest: (NSString*)urlFormatted;
I'm very new to objective-c. Where am I going wrong?
You call the function like this
[self createRequest:request];
You can call it with:
[self createRequest:request];
It helps to think in terms of objects sending each other messages. In this case, your object is sending itself a message to perform a request on an NSString.
Related
I'm trying to declare a function within another function. So here's part of my code:
ViewController.m
- (void)updatedisplay{
[_displayText setText:[NSString stringWithFormat:#"%d", counter]];
}
- (IBAction)minus1:(id)sender {
counter--;
updatedisplay();
}
ViewController.h
- (IBAction)minus1:(id)sender;
- (void)updatedisplay;
Which returned me the error of "Implicit declaration of function "..." is invalid in C99".
Result: http://i.imgur.com/rsIt6r2.png
I've found that people have encountered similar problem, but as a newbie I didn't really know what to do next. Thanks for your help! :)
Implicit declaration of function '...' is invalid on C99
You are not declaring a function; but a instance method, so to call it you must send it as a message to self;
[self updatedisplay];
EDIT
As #rmaddy pointed out (thanks for that) it is declared as instance method not class method. To make the things clear;
- (return_type)instance_method_name.... is called via 'self' or pointer to object instance.
+ (return_type)class_method_name.... is called directly on the class (static).
Problem
updatedisplay();
solution
[self updatedisplay];
cause
- (void)updatedisplay;
is a class method available for that class.So you have to call from the class to have the method available for you.
That is because you defined your function as a instance method, not a function.
So use it like
- (IBAction)minus1:(id)sender {
counter--;
[self updatedisplay]; // Change this line
}
write this way :
[self updatedisplay];
I have a class, which has a delegate based system for sending different type of requests. it uses delegate to tell the object when the request is complete and also if it was a success o an error.
Now, I also have to check what type of request was it in response to take appropriate action.
I have wrapper class that should give me a block based interface for the same.
I pass a completion-block and an error-block to a request method which should internally use this delegate based class.
And when the response comes, should automatically call the appropriate handler for that request type and depending on success and error as well.
I saw a similar question on SO, but it was a little unclear to me, So please give a general idea of how to go about it instead of marking it as duplicate straight away.
Here is one way to do it. Use this RAExpendable class to dynamically build a delegate with a block based implementation.
Let's say your delegate is:
#protocol XDelegate
-(void) foo:(id)response;
#end
Add RAExpendable.h, RAExpendable.m from https://github.com/evadne/RAExpendable to your project. Dynamically add the delegate method:
RAExpendable *expendable = [RAExpendable new];
[expendable addMethodForSelector:#selector(foo:) types:"v#:#" block:^(id x, SEL sel, id response){
NSLog(#"response is %#", response);
}];
And set the expendable class as your delegate:
someObject.delegate = expendable;
Now, if you do this:
[expendable performSelector:#selector(foo:) withObject:#"OK"];
You get the string response is OK. Replace NSLog with whatever success/failure implementation you see fit. From now on, when you call foo:, the block executes instead.
If you want to modify this for your use case, note that the parameters for this example were v#:#, which according to the Type Encoding guide of the runtime means: void return, self, SEL, object. self and SEL are the two hidden parameters present on every Objective-C methods, the third parameter is the first non hidden parameter of the method. The signature of the block has to match the signature of the method.
With REKit, you can make a delegate dynamically like below:
id dynamicDelegate;
dynamicDelegate = [[NSObject alloc] init];
[dynamicDelegate respondsToSelector:#selector(foo:) withKey:nil usingBlock:^(id receiver, id response) {
NSLog(#"response is %#", response);
}];
someObject.delegate = dynamicDelegate;
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 must be doing something wrong, but the Automatic Reference Counting docs don't give me a hint on what it might be. What I'm doing is calling a method with a block callback from inside a delegate method. Accessing that same delegate from inside the block results in a bad access. The problem is the object I'm passing - loginController which is sending the message to its delegate - is clearly not released, when I don't access it inside the block I can call the method multiple times without an issue. Here's my code:
- (void)loginViewDidSubmit:(MyLoginViewController *)loginController
{
NSString *user = loginController.usernameLabel.text;
NSString *pass = loginController.passwordLabel.text;
__block MyLoginViewController *theController = loginController;
[self loginUser:user withPassword:pass callback:^(NSString *errorMessage) {
DLog(#"error: %#", errorMessage);
DLog(#"View Controller: %#", theController); // omit this: all good
theController = nil;
}];
}
NSZombieEnabled does not log anything and there is no usable stack trace from gdb. What am I doing wrong here? Thanks for any pointers!
Edit:
I figured the problem has a bigger scope - the callback above is called from an NSURLConnectionDelegate method (the block itself is a strong property for that delegate so ARC should call Block_copy()). Do I need to take special measurements in this scenario?
Flow (the loginController stays visible all the time):
loginController
[delegate loginViewDidSubmit:self];
View Delegate
(method shown above calls the loginUser: method, which does something like:)
httpDelegate.currentCallback = callback;
httpDelegate.currentConnection = // linebreak for readability
[[NSURLConnection alloc] initWithRequest:req
delegate:httpDelegate
startImmediately:YES];
NSURLConnectionDelegate
- (void)connection:(NSURLConnection *)aConnection
didFailWithError:(NSError *)error
{
if (NULL != currentCallback) {
currentCallback([error localizedDescription]);
self.currentCallback = NULL;
}
}
And this is where I get the bad access, but ONLY if I access that loginController variable...
Set copy attribute to the property, or just call 'copy' method for the block.
- (void)loginUser:(NSString *)user withPassword:(NSString *)pass callback:(void (^callback)(NSString *))
{
callback = [callback copy];
The actual solution was that I had the block as a strong property, but it should have been a copy property! D'oh!
First "Solution":
I just found a way to prevent the bad access. As shown in my Edit above, the View Delegate forwards the block to the httpDelegate (an instance of another class), which in turn keeps a strong reference to the block. Assigning the block to a temporary variable and forwarding the temporary block variable solves the problem, for whatever reason. So:
This crashes on block execution, as described
httpDelegate.currentCallback = callback;
This works
MyCallbackType aCallback = callback;
httpDelegate.currentCallback = aCallback;
I'll accept this as the answer, if anybody has more insights I'm happy to revise my decision. :)
I figure what is happening there is that the loginController is dead right after calling its delegate. Therefore a crash occurs. Without more information I can think of possible scenarios only:
The block do not retains the loginController object (__block type modifier). If the block is executed asynchronously, the loginController might no longer be available if it was killed elsewere. Therefore, no matter what you want to do with it, you wont be able to access it inside the block and the app will crash. This could happen if the controller is killed after sending loginViewDidSubmit.
I think most likely this could be your situation: The loginController calls its delegate object. The delegate method ends up synchronously invoking the callback block that kills the controller. The controller is expected to be alive after invoking the delegate method. Killing it inside the delegate method, most likely will cause crashes to happen. To make sure this is the problem, simply nil the loginController in the delegate method and put an NSLog statement in the controller after calling the delegate, never mind the block, you will get a crash there.
Perhaps if you paste some code we could help more.
My best.
I have a method in an objective-C class. It has 2 callback functions written in C. The class pointer i.e. self is passed to these functions as void *. In the C functions I create a pointer of type class and assign the void * parameter.
The first callback function executes successfully. But the void * pointer becomes nil in the 2nd callback function. Note that I haven't tweaked pointer in the first callback but still I get nil in 2nd callback.
Any ideas what might be going wrong?
For example:
kr = IOServiceAddMatchingNotification(gNotifyPort, kIOFirstMatchNotification,
matchingDict, RawDeviceAdded, NULL,
&gRawAddedIter);
RawDeviceAdded(NULL, gRawAddedIter, self);
This works fine. But below function receives self as nil.
kr = IOServiceAddMatchingNotification(gNotifyPort, kIOFirstMatchNotification,
matchingDict, BulkTestDeviceAdded, NULL,
&gBulkTestAddedIter);
BulkTestDeviceAdded(NULL, gBulkTestAddedIter, self);
Are your problems specifically with the IOKit callback routines? The problem with the specific example you gave is that the IOServiceMatchingCallback takes only 2 parameters, not 3. You need your RawDeviceAdded() and BulkTestDeviceAdded() callback functions to match the IOServiceMatchingCallback prototype and to accept self as the first parameter (refCon), not the 3rd. Also, you need to pass in self as the second-to-last parameter of IOServiceAddMatchingNotification() to get it passed back to you by the callback.
A common method for handling C callbacks in Objective-C code is just to have a static function that forwards the callback to your instance. So, your example callback code would look like this:
static RawDeviceAdded(void* refcon, io_iterator_t iterator)
{
[(MyClass*)refcon rawDeviceAdded:iterator];
}
#implementation MyClass
- (void)setupCallbacks
{
// ... all preceding setup snipped
kr = IOServiceAddMatchingNotification(gNotifyPort,kIOFirstMatchNotification, matchingDict,RawDeviceAdded,(void*)self,&gRawAddedIter );
// call the callback method once to 'arm' the iterator
[self rawDeviceAdded:gRawAddedIterator];
}
- (void)rawDeviceAdded:(io_iterator_t)iterator
{
// take care of the iterator here, making sure to complete iteration to re-arm it
}
#end
Generally, callbacks in Objective-C are handled by passing a delegate object and a selector to perform on that delegate. For example, this method will call a method on its delegate after logging a message, passing both itself and the message that was logged.
- (void)logMessage:(NSString *)message
delegate:(id)delegate
didLogSelector:(SEL)didLogSelector
{
NSLog(#"%#", message);
if (delegate && didLogSelector && [delegate respondsToSelector:didLogSelector]) {
(void) [delegate performSelector:didLogSelector
withObject:self
withObject:message];
}
}
You might call it in code like this:
- (void)sayHello
{
[logger logMessage:#"Hello, world"
delegate:self
didLogSelector:#selector(messageLogger:didLogMessage:)];
}
- (void)messageLogger:(id)logger
didLogMessage:(NSString *)message
{
NSLog(#"Message logger %# logged message '%#'", logger, message);
}
You can also use objc_msgSend() directly instead, though you need to understand the Objective-C runtime enough to choose which variant to use and how to construct the prototype and function pointer through which to call it. (It's the mechanism by which message sends are actually implemented in Objective-C — what the compiler normally generates calls to in order to represent [] expressions.)
This is what Objective-C's selector is for:
http://developer.apple.com/iphone/library/documentation/Cocoa/Reference/NSInvocationOperation_Class
The API isn't very intuitive, but its fine once you understand it
You might need to do some refactoring as well, now there might be a better way, but when I had this problem my solution was to refactor and use InvoationOperation.