I create a new thread from a controller like this:
[NSThread detachNewThreadSelector:#selector(makeMovie) toTarget:movieMaker withObject:nil];
What is the best way to call methods on the controller from the new thread/movieMaker object?
In this case, you probably want to use the delegate pattern. In your movie-maker class’s .h file:
#protocol MovieMakerDelegate;
#interface MovieMaker : NSObject
{
id<MovieMakerDelegate> delegate;
...
}
#property (nonatomic, assign) id<MovieMakerDelegate> delegate;
...
#end
#protocol MovieMakerDelegate <NSObject>
- (void)movieMaker:(MovieMaker *)maker didSomething:(id)result;
#end
...and in its .m:
#implementation MovieMaker
#synthesize delegate;
...
- (void)makeMovie
{
NSAutoreleasePool *pool = [[NSAutoreleasePool alloc] init];
...
[self performSelectorOnMainThread:#selector(notifyDelegateOfDoingSomethingWithObject:) withObject:someObject waitUntilDone:YES];
[pool release];
}
- (void)notifyDelegateOfDoingSomethingWithObject:(id)someObject
{
[self.delegate movieMaker:self didSomething:someObject];
}
...
#end
Then in your controller’s header, declare that it supports the MovieMakerDelegate protocol, like this:
#interface MyController : Whatever <MovieMakerDelegate>
and in your .m, before calling your -detachNewThreadSelector:etc:, call movieMaker.delegate = self;. Implement the -movieMaker:didSomething: method on your controller class and you’re good to go.
You may pass the controller instance to your makeMovie method, with the withObject parameter.
[NSThread detachNewThreadSelector:#selector(makeMovie) toTarget:movieMaker withObject:self];
You can also use a singleton-like pattern, if applicable, to retrieve your controller instance from the thread.
Use performSelectorOnMainThread:withObject:waitUntilDone: (or similar performSelector:... methods), it is the easiest way.
Related
I want to provide methods used in several view controllers called in my delegate methods.
For example, I have some CloudKit functionality (I've added this to my own framework, but I don't think thats important), where I want to provide some crash logging.
Previosuly I had a crashLog function in each of my view controllers, which worked fine, but I have a lot of duplicate code.
Therefore I'd like to produce a category with these methods instead.
However I'm having difficulty getting my delegate methods to see these category methods.
Here's my code..
UIViewController+CloudKitDelegates.h
#interface UIViewController (CloudKitDelegates) <iCloudDBDelegate>
#property (weak,nonatomic) id<iCloudDBDelegate>iCloudDBDelegate;
-(void)crashLog:(NSString*)message, ...;
#end
UIViewController+CloudKitDelegates.m
#import "UIViewController+CloudKitDelegates.h"
#implementation UIViewController (CloudKitDelegates)
#dynamic iCloudDBDelegate;
-(void)crashLog:(NSString*)message, ...
{
va_list args;
va_start(args, message);
NSLog(#"%#", [[NSString alloc] initWithFormat:message arguments:args]);
va_end(args);
}
#end
h file - my calling view controller (e.g. My View Controller)
#import "UIViewController+CloudKitDelegates.h"
m file - delegate method
-(NSString*)getDBPath
{
[self.iCloudDBDelegate crashLog: #"testing"];
From this call I'm getting an error ...
'NSInvalidArgumentException', reason: '-[MyViewController crashLog:]:
unrecognized selector sent to instance
The error is showing that my calling view controller called MyViewController doesn't have the crashLog method, which I have in my category.
Any ideas where I'm going wrong ?
The problem: identical method crashLog: in multiple classes, for example
#interface ViewController : UIViewController
#end
#implementation ViewController
- (void)someMethod {
[self crashLog:#"error"];
}
-(void)crashLog:(NSString *)message {
NSLog(#"%#", message);
}
#end
Solution A: move crashLog: to a common superclass (or a category on superclass UIViewController)
#interface CommonViewController : UIViewController
-(void)crashLog:(NSString *)message;
#end
#implementation CommonViewController
-(void)crashLog:(NSString *)message {
NSLog(#"%#", message);
}
#end
#interface ViewController : CommonViewController
#end
#implementation ViewController
- (void)someMethod {
[self crashLog:#"error"];
}
#end
Solution B: move crashLog: to a delegate and protocol
#protocol ICloudDBDelegate
-(void)crashLog:(NSString *)message;
#end
#interface DelegateClass : AnyClass <ICloudDBDelegate>
#end
#implementation DelegateClass
-(void)crashLog:(NSString *)message {
NSLog(#"%#", message);
}
#end
#interface ViewController : UIViewController
#end
#implementation ViewController
#property (weak, nonatomic) id <ICloudDBDelegate> iCloudDBDelegate;
- (void)viewDidLoad
{
[super viewDidLoad];
AppDelegate *appDel = (AppDelegate *)[[UIApplication sharedApplication] delegate];
self.iCloudDBDelegate = appDel.iCloudDBDelegate;
}
- (void)someMethod {
[self.iCloudDBDelegate crashLog:#"error"];
}
#end
#interface AppDelegate : UIResponder <UIApplicationDelegate, AppDelProtocolDelegate, iCloudDBDelegate>
#property (strong, nonatomic) id<iCloudDBDelegate>iCloudDBDelegate;
#end
#implementation AppDelegate
- (id<iCloudDBDelegate>)iCloudDBDelegate {
if (!_iCloudDBDelegate) {
_iCloudDBDelegate = [[DelegateClass alloc] init];
}
return _iCloudDBDelegate;
}
#end
Now we have new problem: property iCloudDBDelegate in multiple classes
Solution B + A: move crashLog to a delegate, move iCloudDBDelegate property to a superclass
#protocol ICloudDBDelegate
-(void)crashLog:(NSString *)message;
#end
#interface DelegateClass : AnyClass <ICloudDBDelegate>
#end
#implementation DelegateClass
-(void)crashLog:(NSString *)message {
NSLog(#"%#", message);
}
#end
#interface CommonViewController : UIViewController
#property (weak, nonatomic) id <ICloudDBDelegate> iCloudDBDelegate;
#end
#implementation CommonViewController
#end
#interface ViewController : CommonViewController
#end
#implementation ViewController
- (void)someMethod {
[self.iCloudDBDelegate crashLog:#"error"];
}
#end
Solution C:
Another approach is a singleton object like NSUserDefaults.standardUserDefaults or NSFontManager.sharedFontManager: CloudDBManager.sharedCloudDBManager. No category or protocol required, just include CloudDBManager.h and use CloudDBManager.sharedCloudDBManager from everywhere.
#interface CloudDBManager : NSObject
#property(class, readonly, strong) CloudDBManager *sharedCloudDBManager;
-(void)crashLog:(NSString *)message;
#end
#implementation CloudDBManager
+ (CloudDBManager *)sharedCloudDBManager {
static CloudDBManager *sharedInstance = nil;
static dispatch_once_t onceToken = 0;
dispatch_once(&onceToken, ^{
sharedInstance = [[CloudDBManager alloc] init];
// Do any other initialisation stuff here
});
return sharedInstance;
}
-(void)crashLog:(NSString *)message {
NSLog(#"%#", message);
}
#end
#interface ViewController : CommonViewController
#end
#implementation ViewController
- (void)someMethod {
[CloudDBManager.sharedCloudDBManager crashLog:#"error"];
}
#end
(I've added this to my own framework, but I don't think thats important)
Yep, that's the typical problem. You've failed to include -ObjC in the link flags.
See Building Objective-C static libraries with categories. This applies to frameworks as well.
ObjC does not create linker symbols for methods. It can't, they're not resolved until runtime. So the category methods aren't seen by the linker as "missing" and it doesn't bother linking the relevant compile unit. This is an important optimization that keeps you from linking all of a massive C library just because you use one function in it, but Objective-C categories break some of the linker's assumptions. The compiler saw the definition (via the header), but the linker didn't care, so there's no error until runtime.
The -ObjC flag says "this C-looking compile unit is actually Objective-C; link all of it even if you don't think you need to."
I'm developing an app in Objective-C using ARC.
My simplified code looks like this:
ClassA (.m)
MyCustomClass *obj = [[MyCustomClass alloc] initWithValue1:#"abc" value2:1000];
MyViewController *vc = [[MyViewController alloc] initWithObject:obj];
// "vc" will become the first item of a UITabBarController
MyViewController (.h)
- (id)initWithObject:(MyCustomClass *)obj {
...
localReferenceToOjbect = obj;
...
}
- (void)viewWillAppear:(BOOL)animated {
// do something with "localRefernceToObject" <---
}
launching the app will result in a call to a zombie: when the ViewController is shown, the "obj" will be already deallocated and so i can't use it anymore.
my workaround is:
ClassA (.h)
#interface ClassA : UIViewController {
MyCustomClass *obj;
}
ClassA (.m)
obj = [[MyCustomClass alloc] initWithValue1:#"abc" value2:1000];
MyViewController *vc = [[MyViewController alloc] initWithObject:obj];
// "vc" will become the first item of a UITabBarController
is this the right way?! i don't think so: why i've to store an istance of an object that is useless for ClassA?
i can't get an explanation on what's actually happening. could you help me?
You're right in the fact that it is not logical to keep around a reference to obj in ClassA.
But if you need to keep around the reference to obj for MyViewController to use it, retain it in MyViewController, not in ClassA, because that's MyViewController that will use it.
The easiest way to do this is to transform your localReferenceToObject you use in MyViewController into a #property(retain) propertyToObject; (or #property(strong) propertyToObject if you use ARC) and access it in your MyViewController.m with self.propertyToObject (instead of localReferenceToObject, to be sure to call the property's setter and thus really retain the object).
This way, the object will be retained and kept around while your MyViewController instance is still alive.
[EDIT] If you want this property to be private, you can declare it in the class extension so that it is not accessible from other classes, as in the below example. See here in Apple's documentation for more details.
In your MyViewController.h header file
#interface MyViewController : UIViewController
// Here you write the public API in the .h / public header
// If you don't want your property to be visible, don't declare it there
#end
In your MyViewController.m file
#interface MyViewController ()
// This is the private API, only visible inside the MyViewController.m file and not from other classes
// Note the "()" to declare the class extension, as explained in Apple doc
#property(nonatomic, retain) MyCustomClass* referenceToObject; // Note: use strong (which is a synonym of retain) if you use ARC
#end
#implementation MyViewController
#synthesize referenceToObject = _referenceToObject; // not even needed with modern ObjC and latest LLVM compiler
- (id)initWithObject:(MyCustomClass *)obj
{
self = [super init];
if (self) {
...
self.referenceToOjbect = obj;
...
}
return self;
}
- (void)viewWillAppear:(BOOL)animated {
[super viewWillAppear:animated];
// do something with "self.refernceToObject"
}
// This memory management code is only needed if you don't use ARC
-(void)dealloc
{
self.referenceToObject = nil; // release memory
[super dealloc];
}
Personally, as suggested by Apple in some WWDC sessions, I now really rarely use instance variables and prefer the use of properties instead, either public in the .h or private in the .m.
If you use ARC, you can still use an instance variable instead of a property as ARC will retain it for you, but as long as you make sure your instance variable is declared as strong and not weak.
So i have a question .
Can someone Tell me the Problem with this line of code for calling(protocol) a Method
[self.delegate poplogin];
poplogin is method name , its not working for some reason.
its not calling the method poplogin
for reference :
#property(nonatomic,retain) id<loginAuthDelegate> delegate;
So let me Explain the Case
so lets say i have a Class abc.h
#protocol loginAuthDelegate <NSObject>
-(void)poplogin;
#end
After interface
#property(nonatomic,retain) id<loginAuthDelegate> delegate;
in .m i am just calling the Delegate and #synthesize it
[self.delegate poplogin];
not i have another files
let say def.h
i am importing the Class abc.h
#interface def : UIViewController<loginAuthDelegate>
def.m
-(void)poplogin
{
NSLog(#"Delegate doesn't respond to here");
vmpaSecureLogin *ivc = [[vmpaSecureLogin alloc] init];
ivc.modalPresentationStyle = UIModalPresentationFormSheet;
[self presentModalViewController:ivc animated:YES];
}
This is probably because self.delegate is nil.
You probably forgot to affect your object's delegate to some other object in which you implemented the delegate methods, like your ViewController or something.
I have a class ApiClient which gets some data from a server using NSURLConnection and sends it back to its delegate
I have another class called Fetcher.h that calls some function on ApiClient and implements the delegate method in it.
I have a third class (View Controller) that calls the Fetcher.h executeCall() and triggers the whole process.
Fetcher *fetcher = [[Fetcher alloc] init];
[fetcher getData];
If I call the ApiClient code directly in the View controller, it works fine. Why wont it work from the Fetcher class? What am I doing wrong?
Within the Fetcher getData I have this code
APIClient* client = [APIClient sharedInstance];
[client setDelegate:self];
[client getData];
Thanks in advance.
It is possible that since you are not assigning the Fetcher object you are creating in the viewcontroller to any property or anything, it is getting released at the end of whatever method you are allocating it in. Try adding this to your viewcontroller:
.h
#interface ViewController
#property (strong, nonatomic) Fetcher *myFetcher; //Add this line in your view controller's interface
...
.m
#implementation ViewController
#synthesize myFetcher;
...
Fetcher *fetcher = [[Fetcher alloc] init];
[fetcher getData];
self.myFetcher = fetcher;//Add this line in your code as well
Try this...
#protocol APIClientProtocol <NSObject>
#optional
- (void) handleMessage;
#end
#interface APIClient : NSObject
#property (readwrite, nonatomic, strong) id<APIClientProtocol> delegate;
#end
#implementation APIClient
#synthesize delegate;
- (void) someAPIClientWork
{
// Do some client work here
if ( [self.delegate respondsToSelector:#selector(handleMessage)] )
[self.delegate performSelector:#selector(handleMessage)];
}
#end
.h of Fetcher
#interface Fetcher : NSObject <APIClientProtocol>
#end
.m of Fetcher
#implementation Fetcher
- (void) someInit
{
APIClient *client = [APIClient sharedInstance];
client.delegate = self;
}
- (void) handleMessage
{
// Something in APIClient was called
}
#end
Here is my code:
//ECHOAppDelegate.m
#implementation ECHOAppDelegate
...
#end
//PtyView.m
#interface PtyView (PtyPrivate)
-(void)startTask;
-(void) didRead: (NSNotification *)fileNoty;
#end
#implementation PtyView
...
-(void)startTask {
//starts task
}
#end
Now, how do I trigger "startTask" from ECHOAppDelegate.m? I need to create an instance? I'm a total beginner :D
Any example code would be awesome!
Thanks,
Elijah
-(void)startTask; appears to be private implementation and in theory should not be called from external classes.
To answer your question, you can call it something like this:
PtyView *v = [[PtyView alloc] init];
[v startTask];
[v release];
Though you will get a warning saying, PtyView might not respond to startTask. Since it is not in public interface of class.
Update: Above code assumes that when startTask returns, you are done with this object. But something tells me that you might be using async callbacks. If that is the case then startTask might return immediately and you won't release it then and there. Normally in this case, you will be notified by PtyView about the completion of task. So you release it when the task is complete.
Update2:
Making a method public is easy. You just declare it in the public interface (the header file of class):
//in PtyView.h
#interface PtyView
-(void)startTask;
#end
//in PtyView.m
#implementation PtyView
...
-(void)startTask {
//starts task
}
#end
Notice that there is no category defined in the interface declaration.
self represent the current object.
You just need to call the method like that.
[self startTask];
How about subclassing ECHOAppDelegate? (Then make sure PtyView inherits from NSObject?)
// cf. http://amath.colorado.edu/pub/mac/programs/PseudoTTY.zip
#interface ECHOAppDelegate : PtyView
...
#end
#implementation ECHOAppDelegate
- (id) init
{
self = [super init];
if (!self) return nil;
...
return self;
}
...
[self startTask];
...
#end