I am getting confused about how to use shared instance.
This is my set up:
+ (ViewController *)sharedInstance {
static ViewController *_sharedInstance = nil;
if (_sharedInstance == nil) {
_sharedInstance = [[ViewController alloc] init];
}
return _sharedInstance;
}
I also have a property in the ViewController.h file called
#property (nonatomic, retain) CBPeripheral * selectedPeripheral; and under the interface in the ViewController.m file CBPeripheral * _selectedPeripheral; and I make sure to synthesize them
So whenever I do this. It works.
[ViewController sharedInstance].selectedPeripheral = _selectedPeripheral;
NSLog(#"_sharedInstance %#", [[ViewController sharedInstance] selectedPeripheral]);
But if I do this? Without doing the line above. It returns null?
I thought the synthesize would make it so I don't have to assign it again?
NSLog(#"_sharedInstance %#", [[ViewController sharedInstance] selectedPeripheral]);
You are not assigning any value to _selectedPeripheral, thus, is has no value.
Try setting _selectedPeripheral inside your singleton initializer.
I don't know anything about the code, but it implies something needs to be selected. You may have an issue in your selection code as well, but you're class won't magically create objects because it is a singleton ;-)
EDIT
#synthesize only creates the instance variavle (the underscored), so it is available from inside your class. Note this is only necessary, if you overwrite getter and setter as well.
Also note that you posted the getter of the singleton and you have problems with a property. Please poste the code we need to see to help you without guessing.
Related
I have viewController with a global property 'notesArray", and I want to get it from AppDelegate through singleton.
Here is my appViewController.h
#import <UIKit/UIKit.h>
#interface AppViewController : UIViewController <UITableViewDelegate, UITableViewDataSource>
{
NSMutableArray *notesArray;
}
#property (nonatomic, strong) NSMutableArray *notesArray;
+ (AppViewController*)sharedManager;
#end
Here is my AppViewController.m
#implementation AppViewController
#synthesize notesArray;
+ (AppViewController*)sharedManager {
static AppViewController *sharedManager;
static dispatch_once_t onceToken;
dispatch_once(&onceToken, ^{
sharedManager = [[self alloc] init];
});
return sharedManager;
}
...
#end
My app works fine, but I need to save it's state in NSUserDefaults, so in AppDelegate/applicationDidEnterBackground: I make
- (void)applicationDidEnterBackground:(UIApplication *)application {
[[NSUserDefaults standardUserDefaults] setObject:[AppViewController sharedManager].notesArray forKey:#"savedNotes"];
[[NSUserDefaults standardUserDefaults] synchronize];
}
But the problem is that [AppViewController sharedManager].notesArray = nil.
I tried to set breakpoint to applicationDidEnterBackground: and all data from [AppViewController sharedManager] = nil.
Few observations:
notesArray is not a global property. It is a property on instances of AppViewController. Now in #2 we see that you intend it to be a singleton, but since ObjC doesn't really have a good way to prevent someone else from creating a second object of this type, are you sure you're not creating a second copy e.g. by creating an object of that type in a XIB? This is probably not your problem (see #3), but I just wanted to cover all the bases.
Your sharedManager method implies that you're seeing AppViewController as a singleton. That's an unusual thing to do with a view controller. Usually you would have several view controllers, and the singleton would be part of the model they share. Even better, you'd just give each view controller a pointer to the model object that has this array, and if you ever need a second list, everything will just work. Also, why is it called "manager"? It's a view controller.
Have you stepped through your code in the debugger to see what is going on? What value does notesArray have while you're trying to use it in applicationDidEnterBackground:? I do not see anywhere in your code that you initialize notesArray. So you just have an empty pointer to an object (i.e. notesArray is likely nil). You probably meant to add an init method to your singleton's class that creates an NSMutableArray instance and remembers its address in notesArray?
A very common, generic question but it seems that everybody has it's own opinion about accessing variables that belong in another class. What I want is to use boolean variable in class2 to perform a statement. Example of what I want is:
Class1.h
#Interface Class1{
bool boolean;
}
#Property (nonatomic, retain) bool boolean;
Class1.m
#synthesize boolean;
Class2.m
if(class1.boolean == YES){
Do Something
}
The if statement is class2 doesn't seem to work, as I tried to print the boolean value in class2 and all it returns is false. I want to get the current value of class1 boolean variable and use it in class 2 without initialising it.
Looking at your question, it seems you want to create an instance of 'Class1' in another class, get the properties value to be presented there.
In that case, whenever you instantiate 'Class1', it comes with the initial values. That means the values will be 'null' for sure. If you want to get the changed value, you need to create 'Class1' as Singleton class, where, this class will be instantiated once in the whole application. Means change the value of 'boolean1' in any class, and get the same value in another, whenever or wherever you want.
But again, it totally depends on how you want to use the whole thing.
Singleton example:
// Class1.h
#interface Class1 : NSObject
/**
* A boolean property
*/
#property (nonatomic, strong) BOOL *boolean;
// Class1.m
#implementation Class1
// This is actual initialisation of the class instance.
+ (Class1 *)sharedInstance {
static Class1 *sharedInstance = nil; //static property, so that it can hold the changed value
// Check if the class instance is nil.
if (!sharedInstance) {
static dispatch_once_t onceToken;
dispatch_once(&onceToken, ^{
// If nil, create the instance, using dispatch_once, so that this instance never be created again. So, if needed, app will use the existing instance.
sharedInstance = [[super allocWithZone:NULL] init];
// custom initialisation if needed
});
}
return sharedInstance;
}
// So that, if somebody uses alloc and init, a new instance not created always.
// Rather use existing instance
+ (id)allocWithZone:(NSZone *)zone {
return [self sharedInstance];
}
// So that, if somebody uses alloc and init, a new instance not created always.
// Rather use existing instance
- (id)copyWithZone:(NSZone *)zone {
return self;
}
#end
Now updating and using the value.
//Class2.m
#import "Class1.h"
Class1 *myinstance = [[Class1 alloc] init];
myinstance.boolean = YES;
Getting the value on another class
//Class3.m
#import "Class1.h"
Class1 *myinstance = [[Class1 alloc] init];
if(myinstance.boolean == YES){
Do Something
}
I am developing an ARC enabled project. From a view controller I am pushing MyClass,
- (void)pushMyClass {
MyClass *myClass = [[MyClass alloc] init];
[self.navigationController pushViewController:myClass animated:YES];
}
After doing some operations I am popping MyClass. The problem here is that MyClass is not getting deallocated. Following is how the classes look.
/* MyHelperClassDelegate */
#protocol MyHelperClassDelegate <NSObject>
- (void)helperDidFinishHelping:(MyHelperClass *)helper;
#end
/* MyHelperClass Interface */
#interface MyHelperClass : NSObject {
__weak id <MyHelperDelegate> delegate;
}
#property(nonatomic, weak) id<MyHelperDelegate> delegate;
- (void)startHelping;
#end
/* MyHelperClass Implementation */
#implementation MyHelperClass
#synthesize delegate;
- (void)dealloc {
delegate = nil;
}
/* MyClass */
#interface MyClass : UIViewController <MyHelperClassDelegate> {
MyHelperClass *helper;
}
#implementation MyClass {
- (void)dealloc {
helper.delegate = nil;
}
- (void)getHelp {
helper = [MyHelperClass new];
helper.delegate = self;
[helper startHelping];
}
- (void)helperDidFinishHelping:(MyHelperClass *)helper {
}
}
MyHelperClass calls a web service using NSMutalbleURLRequest & NSURLConnection to fetch some data and saves it to user defaults.
One thing to notice here is, if I comment the line helper.delegate = self;, then MyClass gets deallocated.
What to do to make MyClass get deallocated when it is popped out of navigation controller?
Thanks.
Your delegate code looks correct (except your use of an ivar, you don't show a #synthesize so you may have _delegate and delegate both). Its quite likely that something else is retaining MyClass. What I suggest you do is add a NSLog to your MyClass dealloc. Then push it, and immediately hit the back button and see if its dealloc'd or not. If not, then take a hard look at what you do in viewDidLoad et al and start commenting out sections of that code until you can get the dealloc.
Also, I assume you don't keep a strong reference in the class that pushes the MyClass object.
I agree with Chuck that one cannot say much from the code provided. But one reason why the MyClass object is not deallocated might be that it is retained by your helper object since delegate is declared as strong, and the MyClass object has the property helper also declared as strong. In this case you had a retain cycle, and none of them can be released.
The trick could possibly lie within the fact that you use NSURLConnection. It is not specified how you use this class with the code that you've provided, but please note the special considerations referenced in the NSURLConnection class reference:
Special Considerations: During the download the connection maintains a
strong reference to the delegate. It releases that strong reference
when the connection finishes loading, fails, or is canceled.
I was wondering how can I share a NSDictionary objects among several view controllers which basically are tabs in my application.
I tried using a protocol, like in Java, so that I can cast to the protocol and access the property. That doesn't seem to work.
Also I had a look at similar question at
How to share data globally among multiple view controllers
But I observed that the appDelegate method is not safe and may lead to memory leak.
Similarly injection on class A into class B will create the same problem.
So can anyone suggest me any method which i should study or implement in my code?
If you wants to share only Dictionary, why don't you go for class method using from helper class.
+(NSDictionary *)shareMethod
{
return dict;
}
You can use singleton class for sharing the data
Check this Singleton class
MyManger.h
#import <foundation/Foundation.h>
#interface MyManager : NSObject {
NSMutableDictionary *_dict
}
#property (nonatomic, retain) NSMutableDictionary *dict;
+ (id)sharedManager;
#end
MyManger.m
#import "MyManager.h"
static MyManager *sharedMyManager = nil;
#implementation MyManager
#synthesize dict = _dict;
#pragma mark Singleton Methods
+ (id)sharedManager {
#synchronized(self) {
if(sharedMyManager == nil)
sharedMyManager = [[super allocWithZone:NULL] init];
}
return sharedMyManager;
}
- (id)init {
if (self = [super init]) {
dict = [[NSMutableDictionary alloc] init];
}
return self;
}
You can access your dictionary from everywhere like this
[MyManager sharedManager].dict
I found a way out. Since I want a dictionary to be shared across, I declared a method in my protocol
- (void) setSingleHouse:(NSDictionary*) singleHouse;
In each of my controller I implemented the method in a appropriate manner. Hence I was able to share across them for now.
Also I figured out that I was casting in a wrong way earlier i.e (#protocol(protocol name)). Now changed it into NSObject .
Sorry for the fuss.
I advise you not to use a property in your appDelegate instance. This pattern doesn't improve code reusability.
Basicly your shared NSDictionnary is your model. So, if you want your code to follow the MVC design parttern, you should create a class with a shared instance that would contain your NDDictionnary in a public property.
This is well explained in this post
This way, you will access your shared NSDictionnary this way
:
NSDictionary* sharedDictionnary = [MyModel sharedInstance].sharedDictionary;
I´m having problems declarating my own delegate. Well...thats not exactly true: i have it declarated and, when i build the project, the compiler reports no issues. I declarated it in this way:
I made a file (enviarDatos.h) for declare the protocol:
#protocol enviarDatos <NSObject>
- (void)addItemViewController:(NSMutableArray *)item;
#end
In the Vista2.h (ViewController) file I imported the file enviarDatos.h and declared a property:
#property (nonatomic, weak) id <enviarDatos> delegare;
In the Vista2.m (ViewController) file I use the protocol method:
#interface ViewController : UIViewController <enviarDatos> {
And, finally, in the ViewController.m file I implement the delegates method:
- (void)addItemViewController:(NSMutableArray *)ar {
origen = ar;
}
Does anyone see something wrong? the code of the last function its never executing.
Thanks for your help.
EDIT:
What i need is to change an array in ViewController from Vista2 (another viewcontroller)
Then create delegate property in next view(child view) & set it to self in parent view while pushing or showing child view.
ParentView.m
1.Implement protocol methods
- (void)addItemViewController:(NSMutableArray *)ar
{
origen = ar;
}
2.While showing child view
ChildViewController *child = [[ChildViewController alloc] init];
child.delegate = self;
//present child view
ChildView.h
#property (nonatomic, weak) id <enviarDatos> delegare;
ChildView.m
-(void) anyMethod
{
if([self.delegate respondsToSelector:#selector(addItemViewController:)])
{
[self.delegate addItemViewController:mutableArray];
}
}
Ah, it looks like you are declaring the delegate property in the wrong place.
You should declare the property delegate in enviarDatos.h.
#property (nonatomic, weak) id <enviarDatos> delegate;
Then in Vista2.m you will do something like this...
EnviarDatos *myObject = [[EnviarDatos alloc] init];
myObject.delegate = self;
This then sets up the EnviarDatos object and assigns the Vista2 object as the delegate.
Now, in EnviarDatos.m you can run...
[self.delegate addItemViewController:someObjectArray];
And this will then run that code in the Vista2 object.
Delegates are used for calling back to objects that create them (or some other objects). If you create an object and then want to run a method in it then you won't need a delegate.
Can you say at what condition addItemViewController is invoked?
You seem to be on the right track, but are you sure you are setting the delegate as
[yourObject setDelegate: self];
Have you tried debugging it? Does the debugger pause at addItemViewController if you set a breakpoint there? Can you confirm the delegate is not null inside the method? I may post some code but your seems to be right except for the assigning of delegate, I think you should check it.