Here is a simple one for you guys . I'm defining a class to store variables in so I can reuse those variables in different ViewControllers .
Here is how I do it, it`s obviously not working ( that's why I'm asking a question ... ):
I declare a class :
VariableStore.h
#interface VariableStore : NSObject {
int evTe;
}
#property (nonatomic) int evTe;
+ (VariableStore *)shareInstance;
#end
VariableStore.m
#implementation VariableStore
#synthesize evTe;
+ (VariableStore *)sharedInstance {
static VariableStore *myInstance = nil;
return myInstance;
}
#end
Now in my FirstViewController I want to set the value for evTe :
[[VariableStore sharedInstance] setEvte:2];
NSLog(#"value testing, %i", evTe);
And this keeps on returning 0 unfortunately, Im obviously missing something important here but I can't figure out what it is .
Later on Id like to set the value for evTe here in the FirstViewController and then reuse it back in the SecondViewController ..
You are setting your shared instance to nil and then returning it:
static VariableStore *myInstance = nil;
return myInstance;
A nil instance won't hold your variable. It's nil.
First off you shouldn't be using a singleton to pass around variables. If you're going to do that then you might as well just use global variables instead (don't do that either by, the way). Second, if you insist on using a singleton, you need to read up on how to use them.
Finally, if you want to pass variables between view controllers, you either need another view controller that is a parent to the two to facilitate passing data between them, or one needs to call the other and take the first one or its data as a parameter.
Well, you're asking for the value of evTe without calling the object to which it belongs. Try this:
NSLog(#"value testing, %i", [[VariableStore sharedInstance] evTe]);
If you keep using the singleton for a number of times, you might want to do:
VariableStore *vStore = [VariableStore sharedInstance];
so you can do:
[vStore setEvTe:2];
NSLog(#"value testing, %i", [vStore evTe]);
And look out for what Matt said about nilling your singleton ;)
I think in nslog you should output not just evTe, but [[VariableStore sharedInstance] evTe].
First, you have to declare the static variable outside the function, in a way both controllers can access.
static VariableStore* myInstance = nil;
The singleton sharedInstance should be:
if(myInstance == nil)
{
myInstance = [[VariableStore] alloc] init];
}
return myInstance;
Related
I am setting the value for the string in the viewdidload method and getting the string value in the button action method the app gets crashed. can I know the reason for crashing and how to pass the values to the method.
in .h file
NSString *test;
in .m file
-(void)viewDidLoad
{
test = [NSString stringWithFormat:#"sample"];
}
-(IBAction) buttonPressed:(id)sender
{
NSLog(#"%#", test);
}
When I pressed the button the app crashes.
Please try using this solution, I think this will help you,
Create Property of test in .h file like this,,
#property(nonatomic,retain) NSString *test;
and synthesize it in .m file like this,
#synthesize test;
now use test as self.test in .m file like this,
-(void)viewDidLoad
{
self.test = [NSString stringWithFormat:#"sample"];
}
-(IBAction) buttonPressed:(id)sender
{
NSLog(#"%#", self.test);
}
Another solution for this is just retain that test string in ViewDidLoad also, I think this will also help you..
Hope this will help you..
Let me try to explain it in more detail:
You have a string variable in .h file. In view did load you are assigning it as:
test = [NSString stringWithFormat:#"sample"];
What actually happning in this code is your test is a autoreleased object. When you use this and object without alloc and init this is autoreleased object and will release memory after the method you occupied it.
For avoiding this situation you can use #Mehul's solution by creating property. This is against encapsulation concept. Sometimes you have objects you don't want to access outside of the class or don't want to show with objects. Use following in those conditions:
test = [[NSString stringWithFormat:#"sample"] retain]; // or
test = [[NSString alloc] initWithFormat:#"sample"];
this will keep your string alive till you release it.
There is another way that is not good to use but want to tell you so you can understand it better. Using
test = #"sample";
If you don't want to append string or use it with format you can assign simple string to you NSString object.
using this will have a infinite retainCount of your test variable. You can use this to avoid crash but this is not preferable because as I told this have a infinite retaiCount you can't release it and free your memory after use. So earlier methods are more correct.
This is true with all of your autorelease objects which are created with class methods and not with init.
Hope this will clear you more.
I think simple allocation will solve the problem. Just replace this code in the viewDidLoad method
-(void)viewDidLoad {
test=[[NSString alloc]initWithString:#"Sample"];
}
I have a small function which I want to rewrite, so that function is valid for every class.
At the moment I have 10 of the same functions which all work same but every function is for another class.
I know, that I have to do it with reflections, but I am not so sure how to do it.
I already read this link:
http://developer.apple.com/library/mac/#documentation/Cocoa/Reference/ObjCRuntimeRef/Reference/reference.html
The functions I am talking about are:
-(NSCountedSet *)MissionGetReferecedNested:(id)modelObject
{
setOfObjects = [[NSCountedSet alloc]initWithArray:modelObject.MissionSectionList];
return setOfObjects;
}
-(NSCountedSet *)MissionGetSectionReferecedNested:(id)modelObject
{
setOfObjects = [[NSCountedSet alloc]initWithArray:modelObject.DamageAccountList];
return setOfObjects;
}
MissionSectionList and DamageAccountList are both NSMutableArrays from two different classes.
Is it possible to see if a class consists a NSMutableArray and if yes then it should call the .... modelObject.MyMutableArray?
You can use reflection like this:
- (NSCountedSet *)MissionGet:(id)modelObject
{
SEL propertySelector = NULL;
if ([modelObject respondsToSelector:#selector(MissionSectionList)]) {
propertySelector = #selector(MissionSectionList);
} else if ([modelObject respondsToSelector:#selector(DamageAccountList)]) {
propertySelector = #selector(DamageAccountList);
}
if (!propertySelector) {
[NSException raise:#"Invalid modelObject value" format:#"Model object %# does not contain any recognised selectors", modelObject];
}
return [[NSCountedSet alloc] initWithArray:[modelObject performSelector:propertySelector]];
}
But a more common technique among cocoa programmers would be:
- (NSCountedSet *)MissionGet:(id <MyCustomProtocol>)modelObject
{
return [[NSCountedSet alloc] initWithArray:[modelObject missionArray]];
}
Where you would accept any object which confirms to the protocol MyCustomProtocol. The protocol is defined in a header files somewhere, using:
#protocol MyCustomProtocol
#property (readonly) NSArray *missionArray;
#end
And then in each of your classes, declare it as implementing the protocol:
#interface MissionSectionListClass <MyCustomProtocol>
And add a method implementation:
#implementation MissionSectionListClass <MyCustomProtocol>
- (NSArray *)missionArray
{
return self.MissionSectionList;
}
#end
Using protocols is a bit more code, but it's the "right" way to go. It allows you to add support for new classes, without any change to your MissiongGet... method.
More info about protocols: http://developer.apple.com/library/mac/#documentation/Cocoa/Conceptual/ObjectiveC/Chapters/ocProtocols.html
EDIT : Cleared all my answer to this :
I think it's not possible to check if a class has a member variable of specified type. You can only check if a class has a specified method.
So, in this case it will be best if you make all your NSMutableArray list the same name, and then create a declared property for this list, and then do a respondsToSelector in your ...GetReferencedNested method.
So, for example, in all of your class create this property :
#property (nonatomic, retain) NSMutableArray * list;
and then in the ..MissionGetReferencedNested method :
if ([modelObject respondsToSelector:#selector(list)])
...
Correct me if i'm wrong...
In terms of style I'd also follow Abhi's suggestion.
But if you really want to inspect a class that you are stuck with and, for example build a NSCountedSet with the first NSMutableArray variable you can find, you could do it like this:
#import "Utilities.h"
#import <Foundation/Foundation.h>
#import <objc/objc-runtime.h>
#implementation Utilities
+ (NSCountedSet*)initCountedSetWithFirstArrayinObject:(id)someObject {
unsigned int c;
Ivar *ivar_arr = class_copyIvarList([someObject class], &c);
for (unsigned int i = 0; i < c; i++) {
if ([#"#\"NSMutableArray\"" isEqualToString:
[NSString stringWithCString:ivar_getTypeEncoding(ivar_arr[i]) encoding:NSUTF8StringEncoding]
]) {
return [[NSCountedSet alloc] initWithArray:object_getIvar(someObject, ivar_arr[i])];
}
}
return nil;
}
#end
Of course this has very limited real world use because it depends on you knowing that the first array will be the one you're interested in.
I think I have to go with the runtime type editing.(http://developer.apple.com/library/mac/#documentation/Cocoa/Reference/ObjCRuntimeRef/Reference/reference.html)
The idea with the protocols was good but there I have to change a lot of things in the classes.(which is not possible/allowed) for me. My intension was only to change the functions so that I have only one function for all classes.
I think with the runtime type editing I can check what classes and attributes I have (?) Am I right?
Did somebody already work with runtime type editing?
I'm new to objective-c and I searched and read several posts here on how to create "global variable" but I just can't get it to work right, so far I can create it and check it but the values are not persisting on another views, my global var is an array of a custom object called "profile", I would like to be able to read and write that array from any view of my iphone app (tabbarapplication delegate);
Helper.h
#interface Helper : NSObject {
int globalInteger;
NSMutableArray *profiles;
}
#property (nonatomic, retain) NSMutableArray *profiles;
// message from which our instance is obtained
+ (Helper *)sharedInstance;
Helper.m
#import "Helper.h"
#implementation Helper
#synthesize profiles, globalInteger;
+ (Helper *)sharedInstance
{
// the instance of this class is stored here
static Helper *myInstance = nil;
// check to see if an instance already exists
if (nil == myInstance) {
myInstance = [[[self class] alloc] init];
// initialize variables here
}
// return the instance of this class
return myInstance;
}
ACertainViewController.m
//Initialize Policies Array
NSMutableArray *profs = [[Helper instance] profiles];
profs = [[NSMutableArray alloc] init];
//Sample Data
Profile *prof1 = [[Profile alloc] init];
prof1.name = #"John";
//add
[profs addObject:prof1];
[[[Helper instance] profiles] addObject:prof1];
After this point if I check the global var "profiles" contents again it returns count == 0;
As of the globalInteger var I don't even know how to set its value to be able to read somewhere else in the app.
Any help is much appreciated!
Thanks!!!
You need to move "static Helper *myInstance = nil" outside the class method. Now, you're setting it to nil each time and so each time you access the sharedInstance it gets reallocated.
Declare your NSMutableArray in your AppDelegate (i.e. MyAppDelegate) class. Then from another class (like your view controller), you can do this:
#import "MyAppDelegate.h"
MyAppDelegate *aDelegate = (MyAppDelegate *)[UIApplication sharedApplication].delegate;
aDelegate.profiles = .... // or do whatever you need to do with the profiles property.
hope that helps.
You need to alloc/initialize the profiles array. try this:
// the instance of this class is stored here: thanks #onnoweb for pointing this out
static Helper *myInstance = nil;
+ (Helper *)sharedInstance
{
// check to see if an instance already exists
if (nil == myInstance) {
myInstance = [[[self class] alloc] init];
// initialize variables here
profiles=[[NSMutableArray alloc] init];
}
// return the instance of this class
return myInstance;
}
Also take a look here: http://cocoawithlove.com/2008/11/singletons-appdelegates-and-top-level.html
"instance variable 'profiles' accessed in class method"
Where the code you posted has the comment // initialize variables here, are you actually accessing the variable profiles? Instead use myInstance.profiles.
"warning: incomplete implementation of class 'Helper' warning: method definition for '+instance' not found"
There some code you're not showing us, or the code you posted is different from your real code. There is no method declared or defined in the code you posted called 'instance', but you are attempting to call a method called 'instance'. There is one by a different name called 'sharedInstance'. Most likely in your real code you mixed up the names and declared 'instance' but defined 'sharedInstance'. Pick one name and stick with it.
I want to make a singleton containing information "title, comments, Two picture" and it saves all the information in an array
I want to do is these objects in my application I use it All The Time
#interface CarteManager : NSObject {
NSMutableArray *carteMan ;
}
#property(nonatomic,retain) NSMutableArray *carteMan;
+(CarteManager*)sharedInstance;
-(void)ajouttitre:(NSString*)txt;
-(void)ajoutcom:(NSString*)com;
-(void)ajoutimage1:(UIImage*)img;
-(void)ajoutimage2:(UIImage*)img;
#end
In order to create a Singleton you will need a static instance.
#implementation CarteManager
static CarteManager *_carteManager = nil;
+(CarteManager*)sharedInstance {
if (!_carteManager) {
_carteManager = [[CarteManager alloc] init];
}
return _carteManager;
}
// your other codes
#end
And before creating a Singleton, make sure that you really need a Singleton. Please pay special attention to Singleton: How should it be used.
You didn't state your problem. If it's how to make the object a singleton, you can find several possible implementations in the question What does your Objective-C singleton look like?.
I'm trying to understand how strategies some folks use to distinguish instance vars vs. properties. A common pattern is the following:
#interface MyClass : NSObject {
NSString *_myVar;
}
#property (nonatomic, retain) NSString *myVar;
#end
#implementation MyClass
#synthesize myVar = _myVar;
Now, I thought the entire premise behind this strategy is so that one can easily distinguish the difference between an ivar and property. So, if I want to use the memory management inherited by a synthesized property, I'd use something such as:
myVar = #"Foo";
The other way would be referencing it via self.[ivar/property here].
The problem with using the #synthesize myVar = _myVar strategy, is I figured that writing code such as:
myVar = some_other_object; // doesn't work.
The compiler complains that myVar is undeclared. Why is that the case?
Thanks.
Properties are just setters and getters for ivars and should (almost) always be used instead of direct access.
#interface APerson : NSObject {
// NSString *_name; // necessary for legacy runtime
}
#property(readwrite) NSString *name;
#end
#implementation APerson
#synthesize name; // use name = _name for legacy runtime
#end
#synthesize creates in this case those two methods (not 100% accurate):
- (NSString *)name {
return [[_name copy] autorelease];
}
- (void)setName:(NSString *)value {
[value retain];
[_name release];
_name = value;
}
It's easy now to distinguish between ivars and getters/setters. The accessors have got the self. prefix. You shouldn't access the variables directly anyway.
Your sample code doesn't work as it should be:
_myVar = some_other_object; // _myVar is the ivar, not myVar.
self.myVar = some_other_object; // works too, uses the accessors
A synthesized property named prop is actually represented by two methods prop (returning the current value of the property) and setProp: (setting a new value for prop).
The self.prop syntax is syntactic sugar for calling one of these accessors. In your example, you can do any one of the following to set the property myVar:
self.myVar = #"foo"; // handles retain/release as specified by your property declaration
[self setMyVar: #"foo"]; // handle retain/release
_myVar = #"Foo"; // does not release old object and does not retain the new object
To access properties, use self.propname. To access instance variables use just the instance variable's name.
The problem with using the #synthesize myVar = _myVar strategy, is I figured that writing code such as:
myVar = some_other_object; // doesn't work.
The compiler complains that myVar is undeclared. Why is that the case?
Because the variable myVar is undeclared.
That statement uses the syntax to access a variable, be it an instance variable or some other kind. As rincewind told you, to access a property, you must use either the property-access syntax (self.myVar = someOtherObject) or an explicit message to the accessor method ([self setMyVar:someOtherObject]).
Otherwise, you're attempting to access a variable, and since you don't have a variable named myVar, you're attempting to access a variable that doesn't exist.
In general, I name my properties the same as my instance variables; this is the default assumption that the #property syntax makes. If you find you're fighting the defaults, you're doing it wrong (or your framework sux, which is not the case for Cocoa/Cocoa-touch in my opinion).
The compiler error you're getting is because property use always has to have an object reference, even inside your own class implementation:
self.stuff = #"foo"; // property setter
[stuff release]; // instance variable
stuff = #"bar"; // instance variable
return self.stuff; // property getter
I know that many Cocoa programmers disagree, but I think it's bad practice to use properties inside your class implementation. I'd rather see something like this:
-(void) someActionWithStuff: (NSString*) theStuff {
// do something
[stuff release];
stuff = [theStuff copy];
// do something else
}
than this:
-(void) someActionWithStuff: (NSString*) theStuff {
// do something
self.stuff = theStuff;
// do something else
}
I prefer to do memory management as explicitly as possible. But even if you disagree, using the self.stuff form will clue in any experienced Objective-C programmer that you're calling a property rather than accessing an instance variable. It's a subtle point that's easy for beginners to gloss over, but after you've worked with Objective-C 2.0 for a while, it's pretty clear.
Don,
According to the "rules", you should call Release for every Copy, Alloc, and Retain. So why are you calling Release on stuff? Is this assuming it was created using Alloc, Copy, or Retain?
This brings up another question: Is it harmful to call Release on a reference to an object if it's already been released?
Since Apple reserves the _ prefix for itself, and since I prefer to make it more obvious when I am using the setter and when I am using the ivar, I have adopted the practive of using a prefix of i_ on my ivars, so for example:
#interface MyClass : NSObject {
NSString *i_myVar;
}
#property (nonatomic, retain) NSString *myVar;
#synthesize myVar = i_myVar;
i_myVar = [input retain];
self.myVar = anotherInput;
[i_myVar release]
Since it is quite important to know when you are using the setter and when you are using the ivar, I find the explicitly different name is safer.
In your question, it should be:
self.myVar = #"Foo"; // with setter, equivalent to [self setMyVar:#"Foo"]
and
_myVar = some_other_object; // direct ivar access - no memory management!
Remember that you should not use setters/getters in init/dealloc, so you need to do your direct ivar access (and careful memory management) iin those methods.
what's wrong with simply using
#interface MyClass : NSObject
#property NSString *prop;
#end
nonatomic and retain are not required, retain is the default, and atomic/nonatomic isn\t important unless XCode tells you with a warning.
it is NOT necessary to declare the iVar, one will be created for you named _prop, if you really want to use one (i don't see why to be honest)
#synthesize is NOT required.
when (and you should) using ARC you don't have to bother with retain and release either.
keep it simple !
furthermore, if you have a method like this one
- (void)aMethod:(NSString*)string
{
self.prop = string;
// shows very clearly that we are setting the property of our object
_aName = string;
// what is _aName ? the _ is a convention, not a real visual help
}
i would always use properties, more flexible, easier to read.