I think that I am a bit confused about iOS #property getter and setters. I am trying to set an NSString iVar in my AppDelegate.h file from another class so that it can be used by all of the classes in the project?
For example, I am working on an iPhone project that stores an iVar NSString *currentUser in AppDelegate.h. I need to be able to set this through one method in a ViewController.m and then get it through another method in a second ViewController?
Maybe Getter and Setter is the wrong direction of attack all together? I understand that i don't want to alloc init the AppDelegate as the iVar will only exist in that object and I want it accessible to ALL objects in ALL classes?
Please someone set me straight.
All the best,
Darren
Here's the setup for the app delegate.
#interface AppDelegate
{
NSString *__currentUser;
}
#property (monatomic, copy) NSString* currentUser;
#end
#implementation AppDelegate
#synthesize currentUser = __currentUser;
- (void) dealloc
{
[__currentUser release];
[super dealloc];
}
#end
From one view controller, you could set a value for the current user, and from a subsequent view controller, get that value for some nefarious purpose.
#implementation LoginController
- (void) viewDidLoad
{
...
AppDelegate *bob = [[UIApplication sharedApplication] delegate];
[bob setCurrentUser: #"Jim Kirk"];
...
}
#end
In some other view controller that appears later, the value of the current user can be accessed.
#implementation ProfileViewController
- (void) viewDidLoad
{
...
AppDelegate *bob = (AppDelegate *)[[UIApplication sharedApplication] delegate];
NSString * user = [bob currentUser];
// insert nefarious purpose for current user value here
...
}
#end
Related
Code:
[[UIApplication sharedApplication] delegate];
Through this code how to pass data from one to another.
Basically there is only one instance of 'sharedApplication' (it is a singleton), which means that instances of view controllers that are independent of each other can still talk to the same data object. You can therefore write methods in your sharedApplication delegate which can effectively allow these two view controllers to communicate. For more information please see the Apple documentation.
https://developer.apple.com/library/ios/documentation/UIKit/Reference/UIApplication_Class/
You can use the segue destination view controller for transfar data between controllers.Suppose you have one TextField in one View Controller and you want to pass the Textfield text to another viewController.Then use this it might be helpful.
-(void) prepareForSegue:(UIStoryboardSegue *)segue sender:(id)sender{
TargetViewController *tvc; //Second view controller Object
tvc = [segue destinationViewController];
tvc.lonetxt = fname.text; //use properties of another view using . operator
tvc.ltwotxt = lname.text;
tvc.lthreetxt = age.text;
tvc.lfourtxt = college.text;
}
Try following:
Interface in Your AppDelegate:
#interface MyAppDelegate : NSObject {
NSString *myString;
}
#property (nonatomic, retain) NSString *myString;
...
#end
and in the .m file for the App Delegate you would write:
#implementation MyAppDelegate
#synthesize myString;
myString = some string;
#end
Then, in viewcontroller.m file you can fetch:
MyAppDelegate *appDelegate = (MyAppDelegate*)[[UIApplication sharedApplication] delegate];
someString = appDelegate.myString; //..to read
appDelegate.myString = some NSString; //..to write
I have an NSMutableArray declared as property in .h and initialized in viewDidLoad in my SPOCVC .m (UIViewController)...
#property (strong, nonatomic) NSMutableArray* SPOCTrackList;
in viewDidLoad
if ([self SPOCTrackList] == nil) {
self.SPOCTrackList = [[NSMutableArray alloc]init];
NSLog(#"SPOTTrackList INITIALIZED");
}
In a separate VC, I'm trying to pass/addObject to SPOCTracklist...
-(void)tableView:(UITableView *)tableView didSelectRowAtIndexPath:(NSIndexPath *)indexPath {
SCTrack* selectedTrack = self.trackList[indexPath.row];
[[[SPOCVC sharedInstance]SPOCTrackList]addObject:selectedTrack];
NSLog(#"%lu", (unsigned long)[[[SPOCVC sharedInstance]SPOCTrackList]count]);
So my NSMutableArray is initialized and I can add dummy objects, but why can't I pass it from another VC using singleton or anything, such as...
SPOCVC* spocVC = self.tabBarController.viewControllers[2];
[spocVC.SPOCTrackList addObject:selectedTrack];
Thanks for pointing me in the right direction.
View controllers are only intended to be around while they are on screen. They are not a place to store data. Generally when one view controller talks directly to another view controller that it didn't create, you're doing something wrong.
Move SPOCTrackList to your model and have both view controllers talk to it rather than to each other.
There should never be a "sharedInstance" on a view controller. That's a sure sign that you're abusing the view controller as the model.
What's probably happening in your particular case is that viewDidLoad is running on a completely different SPOCVC than your sharedInstance.
why not use appdelegate to handle this
appdelegate.h
//add property to hold the reference
#property (nonatomic, copy) NSMutableArray *referenceArray;
//share the app delegate
+(AppDelegate *)sharedAppDelegate;
#end
in appdelegate.m
//synthesize the property
#synthesize referenceArray;
//return the actual delegate
+(AppDelegate *)sharedAppDelegate {return (AppDelegate *)[UIApplication sharedApplication].delegate;}
in viewdidload method
//add the delegate
import "appdelegate.h"
//init the array
self.SPOCTrackList = [[NSMutableArray alloc]init];
//Add reference
[AppDelegate sharedAppDelegate].referenceArray = self.SPOCTrackList;
and add anywhere like this
import "appdelegate.h"
[[AppDelegate sharedAppDelegate].referenceArray addobject:object];
I have the NSMutableArray property in ViewController.h Now i want to get this Array value from appdelegate.
Is it possible can anyone help me to do that.
In viewcontroller.h
#property (nonatomic, retain) NSMutableArray *fullImg;
In viewcontroller.m
#synthesis fullImg;
I also assigned values for fullImg. Now i want to get that value in app delegate.
Thanks in advance.
Move the array declaration from viewController to AppDelegate
In viewController.m do:
top file:
#import "AppDelegate.h"
in place you want to use the array:
AppDelegate *ap = [[UIApplication sharedApplication] delegate];
ap.fullImg // -> USE IT HOW YOU WANT
...
You can put the whole NSMutableArray into NSUserDefaults with a key e.g.
In app delegate:
NSUserDefaults *def=[NSUserDefaults StanderUserDefaults];
[def setObject:fulImg forKey:#"ImageArray"];
In ViewController class:
NSUserDefaults *def=[NSUserDefaults StanderUserDefaults];
NSMutableArray *yourimgarry=[def valueForKey:#"ImageArray"];
When you create the object for viewController class, you can pass the array reference to the viewController by creating new custom constructor. i.e,
//in appdidFinishLaunchingWithOptions
ViewController *viewController = [[ViewController alloc] initWithArray:fullImgArray];
self.window.rootViewController = viewController;
// In ViewController.h
- (id)initWithArray:(NSMutableArray *)fullImgArray;
// In ViewController.m
- (id)initWithArray:(NSMutableArray *)fullImgArray
{
self = [super init];
if (self)
{
self.fulImg = fullImgArray;
}
return self;
}
There are two possibilities.
Using appDelegate. Use a property in app delegate to pass data between ViewContriollers
and AppDelegate.
in first controller
MyAppdeleagte appDelegate=[[UIApplication sharedApplication]delegate];
appDelegate.fullImg=dataToPass;
in the second controller
MyAppdeleagte appDelegate=[[UIApplication sharedApplication]delegate];
data=appDelegate.fullImg;
in AppDelegate
self.fullImg=data;
2.Specifying object Instance.
in your ViewController after allocating the AppDelegate , specify that the object instance in the current viewController is same as the one in AppDelegate. For this declare a NSMutableArray property in AppDelegate.
in AppDelegate.h
#property NSMutableArray *fullImg;
in ViewController.h
MyAppdeleagte appDelegate=[[UIApplication sharedApplication]delegate];
appDeleagte.fullImg=self.fullImg;
So I've declared this in my appDelegate.h
#property(nonatomic,strong) NSMutableArray *featured;
I've synthesized it like so in my appDelegate.m
#synthesize featured;
When I log that out in the appDelegate with the object stored in there, I get the value it's supposed to have
In a viewController.h file I have declared this
#property(nonatomic,strong) NSMutableArray *featured;
In the viewController.m file I've synthesized it like this
#synthesize featured;
I then print out this line and get a null value
NSLog(#"HERE %#", featured);
That same line prints out the correct value in my appDelegate.m file. I'm completely lost. I've set it up in the way I've done it for a previous class exercise. Thanks in advance!
Edit:
I created the array in appDelegate.m file like so in a method I called loadFeatured
featured = [NSMutableArray array];
for (id dict in tempArray)
{
//NSLog(#"dict=%#",dict);
NSString *shopName = [dict objectForKey:#"shopName"];
NSString *drinkName = [dict objectForKey:#"drinkName"];
NSNumber *likes = [dict objectForKey:#"likes"];
NSNumber *dislikes = [dict objectForKey:#"dislikes"];
NSString *review = [dict objectForKey:#"review"];
Featured *feat = [[Featured alloc] initWithName:shopName drinkName:drinkName likes:likes dislikes:dislikes review:review];
NSLog(#"feat=%#\n\n",feat);
[featured addObject:feat];
}
NSLog(#"there is %d featured",[featured count]);
NSLog(#"HERE %#", featured);
Here is the way, how to access the data stored in the app delegate from your viewcontroller.
You need not synthesize the object in the viewcontroller. Just import your appdelegate file and copy the following code wherever necessary.
NSMutableArray * nArray =[ (AppDelegate*) [[UIApplication sharedApplication] delegate] featured];
The above code gives you the required array from the app delegate.Now you can make use of the nArray object to display the details in the console.
NSLog(#"%#",nArray.description);
It's hard to say how to do this without knowing the structure of your app. You could pass a pointer to the array to your view controller, if you have access to that view controller from the app delegate. The other way is to get a reference to the app delegate in your view controller, and then access its array. That can be done like this:
AppDelegate *appDel = [UIApplication shared application].delegate;
NSArray *myControllerArray = appDel.featured;
You'll need to import your app delegate into your controller's .m file to use this approach.
Since you already declared a property in appDelegate.h you can access it in the other viewController like this:
#import "appDelegate.h"
and you can access the value it by using something like this:
((AppDelegate *)[[UIApplication sharedApplication]delegate]).featured
If you need to access an NSArray or any other object in any class, via AppDelegate, just create a property to access your ViewController, like so, in your AppDelegate class:
#import "ViewController.h"
#property (nonatomic, strong) AppDelegate *appDelegate;
#property (nonatomic, strong) ViewController *viewController;
In your ViewController class:
#import "AppDelegate.h"
AppDelegate *appDelegate = (AppDelegate *)[[UIApplication sharedApplication] delegate];
ViewController *viewControllerREFERENCE = [appDelegate viewController];
Then you'll have access to any value on your ViewController, via AppDelegate.
I hope that helps you.
This question already has answers here:
How do I create delegates in Objective-C?
(20 answers)
Closed 9 years ago.
What is a "delegate" in Objective C's iPhone development?
A delegate is a pointer to an object with a set of methods the delegate-holder knows how to call. In other words, it's a mechanism to enable specific callbacks from a later-created object.
A good example is UIAlertView. You create a UIAlertView object to show a short message box to users, possibly giving them a choice with two buttons like "OK" and "Cancel". The UIAlertView needs a way to call you back, but it has no information of which object to call back and what method to call.
To solve this problem, you can send your self pointer to UIAlertView as a delegate object, and in exchange you agree (by declaring the UIAlertViewDelegate in your object's header file) to implement some methods that UIAlertView can call, such as alertView:clickedButtonAtIndex:.
Check out this post for a quick high-level intro to the delegate design pattern and other callback techniques.
References:
UIAlertView class reference
UIAlertViewDelegate class reference
Apple's guide to Delegates and Data sources
See this discussion
A delegate allows one object to send messages to another object when an event happens. For example, if you're downloading data from a web site asynchronously using the NSURLConnection class. NSURLConnection has three common delegates:
- (void)connection:(NSURLConnection *)connection didFailWithError:(NSError *)error
- (void)connectionDidFinishLoading:(NSURLConnection *)connection
- (void)connection:(NSURLConnection *)connection didReceiveResponse:(NSURLResponse *)response
One or more of these delegates will get called when NSURLConnection encounters a failure, finishes successfully, or received a response from the web site, respectively.
Delegates are a design pattern; there is no special syntax or language support.
A delegate is just an object that another object sends messages to when certain things happen, so that the delegate can handle app-specific details the original object wasn't designed for. It's a way of customizing behavior without subclassing.
I think this Wikipedia article describes it best: http://en.wikipedia.org/wiki/Delegation_pattern
It is "just" an implementation of a design pattern and very common in Objective-C
I think all these answers make a lot of sense once you understand delegates. Personally I came from the land of C/C++ and before that procedural languages like Fortran etc so here is my 2 min take on finding similar analogues in C++ paradigm.
If I were to explain delegates to a C++/Java programmer I would say
What are delegates ? These are static pointers to classes within another class. Once you assign a pointer, you can call functions/methods in that class. Hence some functions of your class are "delegated" (In C++ world - pointer to by a class object pointer) to another class.
What are protocols ? Conceptually it serves as similar purpose as to the header file of the class you are assigning as a delegate class. A protocol is a explicit way of defining what methods needs to be implemented in the class who's pointer was set as a delegate within a class.
How can I do something similar in C++? If you tried to do this in C++, you would by defining pointers to classes (objects) in the class definition and then wiring them up to other classes that will provide additional functions as delegates to your base class. But this wiring needs to be maitained within the code and will be clumsy and error prone. Objective C just assumes that programmers are not best at maintaining this decipline and provides compiler restrictions to enforce a clean implementation.
I try to elaborate it through simple program
Two Classes
Student.h
#import <Foundation/Foundation.h>
#interface Student : NSObject
#property (weak) id delegate;
- (void) studentInfo;
#end
Student.m
#import "Student.h"
#implementation Student
- (void) studentInfo
{
NSString *teacherName;
if ([self.delegate respondsToSelector:#selector(teacherName)]) {
teacherName = [self.delegate performSelector:#selector(teacherName)];
}
NSLog(#"\n Student name is XYZ\n Teacher name is %#",teacherName);
}
#end
Teacher.h
#import <Foundation/Foundation.h>
#import "Student.h>
#interface Teacher: NSObject
#property (strong,nonatomic) Student *student;
- (NSString *) teacherName;
- (id) initWithStudent:(Student *)student;
#end
Teacher.m
#import "Teacher.h"
#implementation Teacher
- (NSString *) teacherName
{
return #"ABC";
}
- (id) initWithStudent:(Student *)student
{
self = [ super init];
if (self) {
self.student = student;
self.student.delegate = self;
}
return self;
}
#end
main.m
#import <Foundation/Foundation.h>
#import "Teacher.h"
int main ( int argc, const char* argv[])
{
#autoreleasepool {
Student *student = [[Student alloc] init];
Teacher *teacher = [[Teacher alloc] initWithStudent:student];
[student studentInfo];
}
return 0;
}
EXPLANATION :::
From main method when initWithStudent:student will execute
1.1 Teacher's object's property 'student' will be assigned with student object.
1.2 self.student.delegate = self
means student object's delegate will points to teacher object
From main method when [student studentInfo] will be called
2.1 [self.delegate respondToSelector:#selector(teacherName)]
Here delegate already points to teacher object so it can invoke
'teacherName' instance method.
2.2 so [self.delegate performSelector:#selector(teacherName)]
will execute easily.
It looks like Teacher object assign delegate to student object to call it's own method.
It is a relative idea, where we see that student object called 'teacherName' method but it is basically done by teacher object itself.
Please! check below simple step by step tutorial to understand how Delegates works in iOS.
Delegate in iOS
I have created two ViewControllers (for sending data from one to another)
FirstViewController implement delegate (which provides data).
SecondViewController declare the delegate (which will receive data).
Here is the sample code may help you.
AppDelegate.h
#import <UIKit/UIKit.h>
#class FirstViewController;
#interface AppDelegate : UIResponder <UIApplicationDelegate>
#property (strong, nonatomic) UIWindow *window;
#property (strong, nonatomic) FirstViewController *firstViewController;
#end
AppDelegate.m
#import "AppDelegate.h"
#import "FirstViewController.h"
#implementation AppDelegate
#synthesize firstViewController;
- (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions
{
self.window = [[UIWindow alloc] initWithFrame:[[UIScreen mainScreen] bounds]];
// Override point for customization after application launch.
//create instance of FirstViewController
firstViewController = [[FirstViewController alloc] init];
//create UINavigationController instance using firstViewController
UINavigationController *firstView = [[UINavigationController alloc] initWithRootViewController:firstViewController];
//added navigation controller to window as a rootViewController
self.window.rootViewController = firstView;
[self.window makeKeyAndVisible];
return YES;
}
- (void)applicationWillResignActive:(UIApplication *)application
{
// Sent when the application is about to move from active to inactive state. This can occur for certain types of temporary interruptions (such as an incoming phone call or SMS message) or when the user quits the application and it begins the transition to the background state.
// Use this method to pause ongoing tasks, disable timers, and throttle down OpenGL ES frame rates. Games should use this method to pause the game.
}
- (void)applicationDidEnterBackground:(UIApplication *)application
{
// Use this method to release shared resources, save user data, invalidate timers, and store enough application state information to restore your application to its current state in case it is terminated later.
// If your application supports background execution, this method is called instead of applicationWillTerminate: when the user quits.
}
- (void)applicationWillEnterForeground:(UIApplication *)application
{
// Called as part of the transition from the background to the active state; here you can undo many of the changes made on entering the background.
}
- (void)applicationDidBecomeActive:(UIApplication *)application
{
// Restart any tasks that were paused (or not yet started) while the application was inactive. If the application was previously in the background, optionally refresh the user interface.
}
- (void)applicationWillTerminate:(UIApplication *)application
{
// Called when the application is about to terminate. Save data if appropriate. See also applicationDidEnterBackground:.
}
#end
FirstViewController.h
#import <UIKit/UIKit.h>
#import "SecondViewController.h"
#interface FirstViewController : UIViewController<MyDelegate>
#property (nonatomic, retain) NSString *mesasgeData;
#property (weak, nonatomic) IBOutlet UITextField *textField;
#property (weak, nonatomic) IBOutlet UIButton *nextButton;
- (IBAction)buttonPressed:(id)sender;
#property (nonatomic, strong) SecondViewController *secondViewController;
#end
FirstViewController.m
#import "FirstViewController.h"
#interface FirstViewController ()
#end
#implementation FirstViewController
#synthesize mesasgeData;
#synthesize textField;
#synthesize secondViewController;
#pragma mark - View Controller's Life Cycle methods
- (void)viewDidLoad
{
[super viewDidLoad];
}
- (void)didReceiveMemoryWarning
{
[super didReceiveMemoryWarning];
}
#pragma mark - Button Click event handling method
- (IBAction)buttonPressed:(id)sender {
//get the input data from text feild and store into string
mesasgeData = textField.text;
//go keypad back when button clicked from textfield
[textField resignFirstResponder];
//crating instance of second view controller
secondViewController = [[SecondViewController alloc]init];
//it says SecondViewController is implementing MyDelegate
secondViewController.myDelegate = self;
//loading new view via navigation controller
[self.navigationController pushViewController:secondViewController animated:YES];
}
#pragma mark - MyDelegate's method implementation
-(NSString *) getMessageString{
return mesasgeData;
}
#end
SecondViewController.h
//declare our own delegate
#protocol MyDelegate <NSObject>
-(NSString *) getMessageString;
#end
#import <UIKit/UIKit.h>
#interface SecondViewController : UIViewController
#property (weak, nonatomic) IBOutlet UILabel *messageLabel;
#property (nonatomic, retain) id <MyDelegate> myDelegate;
#end
SecondViewController.m
#import "SecondViewController.h"
#interface SecondViewController ()
#end
#implementation SecondViewController
#synthesize messageLabel;
#synthesize myDelegate;
- (void)viewDidLoad
{
[super viewDidLoad];
messageLabel.text = [myDelegate getMessageString];
}
- (void)didReceiveMemoryWarning
{
[super didReceiveMemoryWarning];
}
#end
The delegate fires the automatic events in Objects C. If you set the delegate to Object, it sends the message to another object through the delegate methods.
It's a way to modify the behavior of a class without requiring subclassing.
Each Objects having the delegate methods.These delegate methods fires, when the particular Objects take part in user interaction and Program flow cycle.
Simply stated: delegation is a way of allowing objects to interact with each other without creating strong interdependencies between them.
A delegate captures the taping actions of an user and performs particular Action according to the user Taping Action.
Delegate is nothing but instance of Object which we can call methods behalf of that Objects. and also helps to create methods in rumtime of that Objects.