I have implemented Opencv in one of my project. In an opencv .mm file, I need to access the appdelegate object for global access of an array but it is giving Linker Error all the time (When I am trying to import the AppDelegate Class). So I have created an NSObject Class, still I can not access the Global Array which is created as the #property of the NSObject (I have imported the NSObject class in the .mm file). Array is giving the NULL value.
So where do I create the Array by which I can access the array in my whole project?
I can not use the NSUSerDefaults and DocumentDirectory. Because I want to save a lots of images and video links in that array, So I can not use NSUserDefaults and I don't want to use again the phone memory for the temp file as because I am picking the images from the Photolibrary, so DocumentDirectory is discarded, So Is there any way by which I can create the global array and access them from the openCV files i.e objective CPP files?
you can make class as UserdataSingleton which overrides NSObject. which you can use all over your application to share data globally (for your case array). this code template may help you:
#import <Foundation/Foundation.h>
#interface UserDataSingleton : NSObject
{
#private
NSArray *globalArray;
}
+(UserDataSingleton *) getInstance;
-(void)saveInUserDatasingletonWithArray:(NSArray *)array;
-(NSDictionary *)getGlobalArray;
#end
and implementation file will be some thing like:
#import "UserDataSingleton.h"
#implementation UserDataSingleton
static UserDataSingleton *userDataSingletonInstance;
+(UserDataSingleton *) getInstance
{
if (userDataSingletonInstance == nil) {
userDataSingletonInstance = [[UserDataSingleton alloc] init];
}
return userDataSingletonInstance;
}
-(void)saveInUserDatasingletonWithArray:(NSArray *)array
{
globalArray = array;
}
-(NSDictionary *)getGlobalDictionary
{
return globalArray;
}
#end
================== usage:
#import "UserDataSingleton.h"
#define USERDATASINGLETON (UserDataSingleton *)[UserDataSingleton getInstance]
......................your code...
NSArray *this_IS_Array_Populated_here_For_Global_Access = [NSArray alloc] initWith....];
[USERDATASINGLETON saveInUserDatasingletonWithArray:this_IS_Array_Populated_here_For_Global_Access];//you put your array for global access.
later some where in any other view or view controller you can get that global array for example lets say you have YourViewController class:
NSMutableArray *yourArrayFromWebResponse = [USERDATASINGLETON getGlobalArray];
thanks
Note that Objective C is a superset of C. Thus, you can have regular C variables in your program. My favorite is to make a global variable for my appDelegate. Put this in your app delegate's .h file:
MyAppDelegateClass * appDelegate;
(change "MyAppDelegateClass" to your appDelegate's class name) and put this in application: didFinishLaunchingWithOption: method in your app delegate's .m file:
appDelegate = self; // set universal global variable
Now just #import your app delegate's .h file and have access to your appDelegate from anywhere.
You may try to create a singleton objet like and access it from everywhere
you could define a macro in your delegate like so:
#define sharedAppDelegate ((AppDelegate *)[UIApplication sharedApplication].delegate)
and then in the class which you want to access your array import your AppDelegate class, boiler plate would be:
#import AppDelegate.h
and then just use:
NSArray *arrayYouWanted = [AppDelegate sharedAppDelegate].yourPropertyArrayName;
You can also store it in NSUserDefaults if you want to persist it.
Related
In Objective c, what is the differences between instance variables var1 and var2 showing below?
(This code is in one .m file, does it make any difference if the #interface is in a header file & #implementation is in implementation file? I mean any difference comparing with that in one file regarding to the two instance variables.)
#interface MyService {
NSString *var1;
}
#end
#implementation MyService {
NSString *var2;
}
#end
The difference between them is visibility. The variable defined in the #interface section is visible to any code which imports the interface. The variable declared in the #implementation section is only visible to code within the class implementation.
If the #interface is declared in the implementation file, it will act, for all practical purposes, the same as declaring it in the #implementation section.
Instance variables declared in the implementation are implicitly
hidden (effectively private) and the visibility cannot be changed -
#public, #protected and #private do not produce compiler errors (with
the current Clang at least) but are ignored.
you can found it here
I have deep searched for your question.Well asked Leem.fin brother.I tried sample one
#import "SecondViewController.h"
#interface SecondViewController ()
{
NSString *variableOne;
}
#end
#implementation SecondViewController
{
NSString *variableTwo;
}
- (void)viewDidLoad
{
[super viewDidLoad];
// Do any additional setup after loading the view.
[self setValueToString];
NSLog(#"The variable One is - %#",variableOne);
NSLog(#"The variable Two is - %#",variableTwo);
}
-(void)setValueToString
{
variableOne = #"iOS";
variableTwo = #"iPhone";
}
The printed results are
The variable One is - iOS
The variable Two is - iPhone
But when I tried to access these in Class method
+(void)changeStrings
{
variableOne = #"iPad"; //I get error here
variableTwo = #"iMac"; //I get error here
}
The error shows
Instance variable 'variableOne' accessed in class method
Instance variable 'variableTwo' accessed in class method
From above code I understood
Both are instance variables
That can be accessed only in instance methods
There is no difference between them
So Where to put
Difference between them
Difference between putting variable inside interface and implementation
I know how to implement UISearchController for a table view. But can anyone help me in implementing search bar for complete app.
In my app i have 3 view controllers
a)students VC
b)teachers VC
c)parents VC
and I have a search button. Here i want to implement complete in app search functionality. If we type in a name it should appear in a table view either it is in students/parents/teachers. I am not getting any idea how to start this. Please give some KT.
I just try to create singleton class that store value and use as a global. So first you need to create a Singleton-class using following code:
#import <Foundation/Foundation.h>
#interface GlobalData : NSObject
{
NSMutableArray *ClassArray;
}
+(GlobalData *) getInstance;
-(void)saveClassARray:(NSArray *)array;
-(NSMutableArray *)getGlobalArray;
#end
It's .M Class
#import "GlobalData.h"
#implementation GlobalData
static GlobalData *instanceGlobalData;
+(GlobalData *) getInstance
{
static dispatch_once_t onceToken;
dispatch_once(&onceToken, ^{
instanceGlobalData = [[GlobalData alloc] init];
instanceGlobalData->ClassArray = [[NSMutableArray alloc]init];;
});
return instanceGlobalData;
}
-(void)saveClassARray:(NSArray *)array
{
[ClassArray addObjectsFromArray:array];
}
-(NSMutableArray *)getGlobalArray
{
return ClassArray;
}
#end
Now you need to store your Students, Teachers and Parents data by following code.
First you need to import #import "GlobalData.h" in your ViewController and create define variable that like following:
#import "GlobalData.h"
#define USERDATASINGLETON (GlobalData *)[GlobalData getInstance]
And in Web services Call back Success you need to store your data in globle array using following code:
NSArray *array =[[NSArray alloc]initWithObjects:#"Nitin",#"Nit", nil];
[USERDATASINGLETON saveClassARray:array];
Above array is just for your referance do same things for all your 3 ViewController and store the result using saveClassARray. now finally you need to get full array by following code:
NSMutableArray *FinalGlobalArray = [USERDATASINGLETON getGlobalArray];
NSLog(#"==%#",FinalGlobalArray);
That will be NSlog allof the data that have you stored. but make sure use some check that once you add teacher,student,parents data and if saveClassARray calling again that old data wont be overtire that will be create duplicate entry so take care about.
Now you have finalArray you can do your search code that you have did for individual.
Hope that help
I'm having issues with dictionary, i want a dictionary create only once to save data to plist file. So how to create singleton dictionary ? Thank in advance
You can create one instance of NSDictionary in AppDelegate, make this dictionary as a public property of class.
#property (nonatomic, strong) NSMutableDictionary *myDict;
Initialize this in - (BOOL)application:(UIApplication *)application willFinishLaunchingWithOptions:(NSDictionary *)launchOptions method.
Now access it through out the app -
((AppDelegate *) [UIApplication sharedApplication].delegate).myDict
Only one instance will be created for your use.
As you responded in comments, you need a global variable. Bellow is the receipt.
Here is what you can do:
Add variable extern definition at the top of your AppDelegate.h file:
extern NSMutableDictionary *MyGlobalDictionary;
Add variable definition at the top of your AppDelegate.m file:
NSMutableDictionary *MyGlobalDictionary;
Now you need to initialize the dictionary, can be done in initialize method of you AppDelegate. In AppDelegate.m add this somewhere in #implemetaion of AppDelegate:
+ (void)initialize {
MyGlobalDictionary = [[NSMutableDictionary alloc] init];
}
How to use:
Whenever you need it, just #import your AppDelegate.h file. Bellow is an example how to use:
NSLog(#"%#", [MyGlobalDictionary objectForKey:#"someKey"]);
Important:
While creating singleton is extremely easy it is considered to be a bad practice. Think about passing your dictionary to objects that can be interested in it. Or may be define some global class singleton if it is unavoidable.
A "token" will be given upon authentication in a form of xml file with some other elements.
I managed to extract the token, and display it in the calling class, let's say parser.m.
However, I need to make the content of that variable available globally, so that I can reuse the same token. How do I do that?
Please note that a different token will be given upon the next authentication.
.h:
#interface Parser : NSObject <NSXMLParserDelegate>{
NSXMLParser *parser;
NSMutableString *element;
NSMutableString *token;}
#property (nonatomic, retain) NSMutableString *token;
#end
.m:
#import "Parser.h"
NSLog(#"tOKEn called from main: %#", parser->token);
It is not able to access the "token" that was declared under parser.m
How do I go around this?
Update 1:
I found out that using #public serves the purpose too. Not sure whether its a good move or not since I will be needing the token in all my API calls.
create a singleton class for global variable in objective c
in .h file
#import <Foundation/Foundation.h>
#interface Singleton : NSObject
{
///......
}
+ (Singleton *)sharedSingleton;
in .m file
#import "Singleton.h"
#implementation Singleton
static Singleton *singletonObj = NULL;
+ (Singleton *)sharedSingleton
{
#synchronized(self)
{
if (singletonObj == NULL)
singletonObj = [[self alloc] init];
}
return(singletonObj);
}
and use this in another file
#import "Singleton.h"
//.....
Singleton *sinObj = [Singleton sharedSingleton];
and create variables inside that and also write setter and getter method for that variable in singleton class. Access this method and variable using sinObj object of singleton class
IMO singletons are a overused curse.
Your (every) application should have a layers structure, and this token variable shouldn't leave communication layer. If it does this means that something is wrong with your application design. Note that token is needed only to do posts and every other part of code doesn't need it.
For temporary variables, consider using a singleton instance, such as the MySingleton class illustrated in this answer. How to create a singleton: What should my Objective-C singleton look like?.
You can access the variable like this: [MySingleton sharedSingleton].variable; Singleton is a good choice if you have a lot of global variables, but if only one better to use NSUserDefaults.
NSUserDefaults are for things that require persistance, i.e. you are planning on storing them between app starts. Good starter: http://mobile.tutsplus.com/tutorials/iphone/nsuserdefaults_iphone-sdk/
Also please read: Are global variables bad?
Try this:
[[NSUserDefaults standardUserDefaults]setObject:_YourObject_ forKey:#"token"];
NSString *str = [[NSUserDefaults standardUserDefaults] stringForKey:#"token"];
Or You can use singleton.
Try to Declare that varible into Appdelegate as a property and syntesize it in .m .
Or aceess that varible in any class using this.
AppDelegate * appdelegate=(AppDelegate *)[[UIApplication sharedApplication]delegate];
AppDelegate.yourvarible;
or either you used NSUserDefault.
[[NSUserDefaults standardUserDefaults]setObject:token forKey:#"tokan"];
You can create a property in ur appdelegate and set the property when u get the token.
//getter
NSString *token=[(MyAppDelegate *)[[UIApplication sharedApplication] delegate].recievedToken;
//setter
[(MyAppDelegate *)[[UIApplication sharedApplication] delegate].recievedToken=token;
I used to declare variale in appdelegate and make it as sharable in all the classes (If the variable is global ) .
appDelegate = (StoryAppDelegate*)[[UIApplication sharedApplication]delegate];
this was the code am using normally to access appdelegate variable. Now am trying a story board application and its not working for me . while declaring appdelegate it shows an error "Unknown type name StoryAppDelegate".
StoryAppDelegate*ss;
this is the code am using .
Any help appreciated .
Just don't use the app delegate. That isn't what it's for.
Instead, create a specific class to own the responsibility + knowledge, make it a singleton and have all classes that require it get it via it's 'sharedController' (or whatever you call it) class method.
Or use a 'constants' file with a static variable or something (just not the app delegate).
Storyboard is used only for design, not changes to the code.
For that, you'd use:
AppDelegate *app;
in the header file of the view's controller.
And in the implementation file,
app=(AppDelegate *)[[UIApplication sharedApplication]delegate];
Then you can just use app.yourVariable
I would recommend using a singleton instance of your global variable as they have bailed me out of your exact situation multiple times. Here is an example I'm currently using to implement a singleton. This methodology is also ARC-safe as well
mySingleton.h
#import <Foundation/Foundation.h>
#interface mySingleton : NSObject {
}
+ (NSMutableDictionary *) myMutableDict;
#end
mySingleton.m
#import "mySingleton.h"
#implementation mySingleton
+ (NSMutableDictionary *)myMutableDict
{
static NSMutableDictionary *singletonInstance = nil;
static dispatch_once_t onceToken;
dispatch_once(&onceToken, ^{
singletonInstance = [[NSMutableDictionary alloc]init];
});
return singletonInstance;
}
#end
As long as you include mySingleton.h in all of your view controllers you can access the data via [mySingleton myMutableDict]. For example: [[mySingleton myMutableDict] setObject:myObject forKey:myKey]; This will of course work with any object type.
It seems the case of circular dependency.
use #class StoryAppDelegate;
instead of
#import "StoryAppDelegate.h"
in your header file.