hai folks,
i want to create array for user defined class like in java.
eg in java:
ClassA[] obj=new ClassA[10];
like this i want to make a array in objective-c, and also i want to return this object in the method.
eg in java:
ClassA[] method1()
{
ClassA[] classA=new ClassA[10];
return classA;
}
is it possible to do this one, without using NSArray. if it possible, how can i do this one in objective-c.
plz give me some sample code snippet for this.
thanks in advance.
There is rarely a reason to avoid NSArray. However, if you are absolutely certain that you have one of those cases, then use the C idiom, because Obj-C is a superset of C.
You can do it in C style:
ClassA *objCollection[10];
objCollection = (ClassA *)malloc(sizeof(ClassA)*10);
objCollection[0] = [[ClassA alloc] init];
objCollection[1] = [[ClassA alloc] init];
...
In this way you are declaring a array of pointers to ClassA objects of size 10.
Related
I've realized that several of my list view controllers behave in the same way, and now I want to abstract them into a generic one called ListVC. The plan is to create an instance of ListVC when its needed, and pass into it all of the specific things needed for that instance of it.
For example, if I need a list of customers I would do something like:
ListVC *customersVC = [[ListVC alloc] init];
customersVC.tableArray = self.customersList
In ListVC, there are times when I need to know certain object's class type. In my example, the objects in the array self.customersList are from the class CustomerClass. I know I can convert strings to class names but that doesn't help when I have a method inside ListVC that needs to return the object's type. For example, in ListVC, this old non-abstracted method:
- (CustomerClass *)customerAfterFilter
should be something like:
- (self.objectClass *)objectAfterFilter
And I'd set objectClass after it was instantiated like so.
ListVC *customersVC = [[ListVC alloc] init];
customersVC.tableArray = self.customersList
customersVC.objectClass = [CustomerClass class];
How do I do something like this? Or if my approach is just wrong, please suggest the correct approach. I'm a beginner in programming.
You can't change the return type like that. What you can do is return an id, which is a pointer to an object of any class.
- (id)objectAfterFilter
EDIT:
Customer *c = [customersVC objectsAfterFilter];
[c duCustomerStuff];
Alternatively:
[((Customer *)[customersVC objectsAfterFilter]) doCustomerStuff];
I have an iPhone application and I do this in my MyView1Controller:
MyView2Controller *myV2C = [[MyView2Controller alloc] initWithNibName:#"MyView2" bundle:nil];
myV2C.shareObject = self.shareObject;
[self.navigationController pushViewController:myV2C animated:YES];
[myV2C release];
So I push shareObject to the next ViewController. There, in viewDidLoad, I set a property of shareObject like this:
self.shareObject.myText = #"Test String";
So in MyView2Controller, everything is okay, the String is set. But going back to the previous MyView1Controller with the left upper "back" Button, the value of shareObject.myText is not set to Test String.
So, how can I do this? I want to give the View2Controller an object which can be modified, and the modifications I want to have in the View1Controller.
Does anyone know? Thank you in advance & Best Regards, Tim.
OR you can even try using the Singleton pattern
http://www.cocoadev.com/index.pl?SingletonDesignPattern
You can use delegation pattern and/or key value observations
EDIT:
You can achieve this my creating a single object, and then use that object in all classes, wherever you want. For this you can use singleton class, Or you can create a class method. For ex:If I have class A, and I want to push some values in B class, So if I modify the values in B, the newly updated value can be retrieved in a too, or in any other class. In that case, you can create a different class (usually subclass of NSObject),and then write the getter/settor methods in that.
Suppose the name of this newly created class is Manager, then in Manager. m create getter/setter methods, like
NSString *strGlobal;
+(void)setString:(NSString *)strTemp
{
if(!strGlobal)
{
strGlobal = [[NSString alloc] init];
}
//point to same location
strGlobal = strTemp;
}
+(NSString *)getMySavedString
{
return strGlobal;
}
Now In you class A , where you want to send the value to Class B controller, call the setter method to set the value, like: -
-(void)navigateto_ClassB
{
//Setting the value, that should be sent to the other controller
[ManagerClass setString:#"Hello"];
[self.navigationController pushViewController:[[[ClassB alloc]init] autorelease] animated:YES];
}
Now In class B (Or wherever you want to get the saved value, use getter method, like:-
NSString *strSavedValue = [ManagerClass getMySavedString];
No you will have the value, If you want to update the value from anywhere, the again call the setter method, with new value. For ex, i want to update the value in class B, then
[ManagerClass setString:#"Hello Upadted"];
Now this value is updated to same memory location, retrieve it from anywhere using getter method created in Manager class.
As I stated earlier, this is the easiest but not the best approach. Alternatively, you can achieve same functionality with delegate patterns, KVOs (Key value observations) and/or singleton class.
tia was right: "You did it right already, so there must be something wrong somewhere".
It was my fault, so the source code in my question is correct.
OK, maybe I'm not seeing clear anymore and hope you can help.
I'm trying to select an Object from a NSMutableArray using:
if([car.seat isEqualToString:#"fancyOne"]){
fancyThings = [[NSMUtableArray]init];
[fancyThings addObjects: car];
}
Now I forgot to tell you I'm new at this Objective-C, so maybe I'm thinking the wrong way.
What I'm basically trying to do is to get an Object from one array by selecting a value of it's components.
This is the way to do it, I am however keep having trouble with my if-statement.
If I leave out the IF-statement it does fill my other NSMutableArray with the exact same object (thisCar) but if I put in the IF-statement it doesn't pick up that the string is the same in thisCar.seat.
I next example it puts everything in the normalThings but there are some aCar.seats which contain the string FANCYONE. I checked the XML file on spaces and that sort of things but everything is in order as far as I can see.
Shall I build it using NSScanner instead of IsEqualToString?
- (void)viewDidLoad {
appDelegate = (XMLAppDelegate *)[[UIApplication sharedApplication] delegate];
appDelegate.fancyThings = [[NSMutableArray alloc]init];
for (CARS *aCar in appDelegate.someCars) {
if ([aCar.seats isEqualToString:#"FANCYONE"]){
[appDelegate.fancyThings addObject:aCar];
}
else {
[appDelegate.normalThings addObject:aCar];
}
}
self.title = #"Cars";
super viewDidLoad];
}
EDIT:
My BAD!! The code supplied was in fact in order!
There was a mistake in my XMLParser, which added blank lines to the strings, so I couldn't get an equal string!
Hopefully this will give you some guidance:
//init new array
NSMutableArray *fancyThings = [[NSMutableArray alloc] init];
//walk your array
for (SomeCarObject *thisCar in arrayOfCars) {
//is thisCar a qualifying object
if ([thisCar.seat isEqualToString:#"fancyOne"]) {
//yes, add thisCar object
[fancyThings addObject:thisCar];
}
}
You'll want to create that NSMutableArray outside of the for loop (assuming you're iterating through a collection). Then you can add to that NSMutableArray like you did.
Hope this helps!
BTW, you should edit your question with the comment you made to elaborate on it..
It's depends from volume of objects, which u deal with. If there is 1000 objects or less, this method looks good. But if there is more objects, u have risk to freeze u application and have a big memory leaks.
Also if u will need concurrency code later, u have to keep in u mind some
other solutions.
U can using not just a string objects in u array, u can try to fill u array after application startup in objects, which response if string is same or not. Or using nsdictionary with appropriate keys.
Please read my post multithread search design
I'm attempting to create an NSArray with a grouping of string literals, however I get the compile error "Initializer element is not constant".
NSArray *currencies = [NSArray arrayWithObjects:#"Dollar", #"Euro", #"Pound", nil];
Could someone point out what I'm doing wrong, and possibly explain the error message?
New syntax for creating an array with string literals:
NSArray *currencies = #[#"Dollar", #"Euro", #"Pound"];
To fix your complication error the code must be in a method. If you want to use it statically then create a class method that follows the singleton pattern.
This isn't a problem with the NSArray creation itself (you would get the same error if you wrote [NSArray array] instead), but with where you've written it. I'm guessing this is a global or file-static NSArray. In C, that kind of variable has to have a constant initializer — meaning not a function call (or, by extension, a method call). The solution is to put the actual creation and assignment of the array into a method that will be called before you need the array, such as initialize.
It sounds like Chuck has spotted the problem. One thing you want to be aware of though in coding your solution is that you'll want to avoid storing an autoreleased instance of NSArray in a static variable. Also, a common pattern for these situations is to write a class method that creates and returns the value stored in the static variable, like so:
+ (NSArray *)currencies
{
static NSArray *_currencies;
// This will only be true the first time the method is called...
//
if (_currencies == nil)
{
_currencies = [[NSArray alloc] initWithObjects:#"Dollar", #"Euro", #"Pound", nil];
}
return _currencies;
}
Although this is old, please notice that Apple committed a new patch to the llvm project adding support for new Objective-C literal syntax for NSArray, NSDictionary and NSNumber.
See here and here
I'm a newbie in objective-c, but I think that the correct code is:
NSArray *currencies = [[NSArray alloc] initWithObjects:#"Dollar", #"Euro", #"Pound", nil];
I am not sure tho.
There's nothing wrong with that code. Are you sure the error is being produced at that line?
Example:
I have 10 view controllers, which are all allocated and initialized in the same way:
UIViewController *controller = [[MyViewController alloc] initWithNib];
(note that -initWithNib is a custom method of a UIViewController subclass)
The next view controller class is OtherViewController, and so on. I want to load the view controllers lazily, just when I need them. But to do that, I need to have some kind of "array" that will give me the corresponding class for a given index, so that I can initialize it.
I ended up creating a method with a big switch-statement, that will just do that nasty allocation and initialization separately for every single view controller. I'm not happy with that. There it would be much better if I could assign the appropriate class to a variable, and then at the end of the switch statement just allocate and initialize that class from the variable.
Is there a way to achieve that?
EDIT: I've found a function
id class_createInstance(Class cls, size_t extraBytes)
and every class seems to have a property "class". But I can't assign it to an instance variable. This doesn't work:
Class cls = [UIImage class];
cls *image = [cls imageNamed:#"avatar.png"];
The first line compiles. But the second one gives an error: "image undeclared".
If you know the names of the classes at compile time, you can assign the classes to Class variables. For example:
static Class factory[2];
factory[0] = [MyViewController1 class];
factory[1] = [MyViewController2 class];
...
Then you could have (classid would be a constant known at compile time that would map to a desired class:
-(UIViewController*)createViewController:(int)classid
{
return [[factory[classid] alloc] init];
}
Assuming that method is defined in a class named MyFactory, you can then do:
MyFactory * fac = [[MyFactory alloc] init];
UIViewController * v1 = [fac createViewController: 0]; // typed
id v2 = [fac createViewController: 1]; // untyped
If you don't have the compile time name of the class, you can simply do the following:
#include <objc/objc-runtime.h>
id object = [[NSClassFromString(#"TheClassName") alloc] init];
Since your original question involves a set of UIViewControllers though, there's no reason to lose type safety with the latter method.
You want to use reflection:
id controller = class_createInstance(NSClassFromString(#"your class name"), 0/*extra bytes*/);
Objective-C Runtime Reference
I blogged about this last month at:
http://igotosoft.blogspot.com/2009/05/dynamically-creating-viewscontrollers.html
Essentially, it involves a new class I call the ClassConstructor, which takes a class name, init method name, and comma separated arguments. When you need to create an instance of that class, just use your [myClassConstructor create];
What you want is Reflection. No idea of objective-c has it though - but the term might help you Google for your answer better.
The Objective C Reference also will be a good place to look to get the calls. Try searching for Objective-C 2.0 Runtime Reference since I cant add links