Hi i will try to explain my problem: i'm working with webservices and i need to give variable or label.text to webservice request wich is in another class... I tried in lots ways, but i can't find solution. I know it must be very easy, but i'm new in objective-c so i have problem in primitive situation. Thanks for everyone who will help me :)
Use an instance variable and a property. See here.
In .h:
#interface YourClass : Superclass {
NSString *text;
}
#property (nonatomic, retain) NSString *text;
in .m you have to synthesize it:
#implementation YourClass
#synthesize text;
now you can set this variable like so:
[instanceOfYourClass setText:someText];
get it like so:
someString = [instanceOfYourClass text];
and use it like so (in your implementation):
someString = [self text];
Related
You can declare a variable like this.
Case1:
#interface MyClass : NSObject
{
NSString *str;
}
#end
Also, if you want to set its property, you can do
Case2:
#interface MyClass : NSObject
{
NSString *str;
}
#property (nonatomic, strong) NSString *str;
#end
And in the .m,
#synthesize str;
My understanding with the difference between Case 1 and Case 2 is that synthesized and propertied variables in Case 2 can be accessed from another class when this another class instantiates this class.
What are other differences between Case 1 and 2? Say when these variables are just used only in its .m file. The fact that you are setting 'str' properties probably makes a difference, but how? If you don't set property, how are they going to be released with ARC?
The differences are fairly confusing in this case because of the way it is set up.
Also it is using what is now old practises.
The new suggested way of doing this (suggested by Apple) is to do this...
MyClass.h
#interface MyClass : NSObject
#property (nonatomic, strong) NSString *str;
#end
MyClass.m
#import "MyClass.h"
#implementation MyClass
#end
You no longer need the #synthesize as Xcode (since 4.5) will auto generate these for you.
Doing this sets up the property called str and an iVar called _str.
You now no longer need to worry about defining multiple ivars and properties etc... Just use the property and that's it done.
An example setter method for the property str would look like this...
- (void)setStr:(NSString*)str
{
_str = str;
}
Sorry for the simple question.
When I see a definition of a property inside the h file, but outside of the class #interface scope, what does it mean ?
#property (nonatomic, readonly) RMMapContents *mapContents;
Here is the code:
#class RootViewController;
#class RMMapContents;
#interface MapTestbedAppDelegate : NSObject <UIApplicationDelegate> {
UIWindow *window;
//MAIN VIEW
//==============
RootViewController *rootViewController;
// NETWORK DATA
// =============
NSMutableArray *photoTitles; // Titles of images
NSMutableArray *photoSmallImageData; // Image data (thumbnail)
NSMutableArray *photoURLsLargeImage; // URL to larger image
NSMutableData *receivedData;
NSURLConnection *theConnection;
NSURLRequest *request;
}
#property (nonatomic, retain) IBOutlet UIWindow *window;
#property (nonatomic, retain) IBOutlet RootViewController *rootViewController;
#property (nonatomic, readonly) RMMapContents *mapContents;
#end
Inside a function I see this line:
- (void)foo:(xyz *)abc{
..
RMMapContents *mapContents = [self mapContents];
..
}
So, taking it from C++, the mapContents seem like it is not a global scope var (after all, that's why they call them properties, right?), but isn't defining the same name again inside the function weird a bit?
I hope someone can clarify a little here.
Thanks!
The scope of the #interface block extends upto the #end keyword and is not restricted to the braces {}.
So the #property declaration lies very much inside the scope of the #interface and like cli_hlt rightly answered, it acts like a substitute to setter and getter methods for the mapContents property.
so a property named mapContents, would have setters and getters which look like this :
- (void)setMapContents; //setter
- (RMMapContents *)mapContents; //getter
and would can be accessed from within the class using these methods:
[self setMapContents:newContents];
AND
RMMapContents *contents = [self mapContents];
Well, a property is not just a variable. A property is a variable plus its setter and getter methods. A property is usually said to be backed by a variable, which usually(but not always) has the same name as the property itself.
So there are basically three scenarios:
The developer has redefined the backing variable, look for something like:#synthesize mapContents=mapContents_, at the beginning of the implementation -> no problem here.
The compiler defined the variable to be something you don't now but not equal to mapContents - > no problem.
The property backing variable is indeed called "mapContents", so then the local definition hides the global definition (look for a compiler warning here). But by calling [self mapContents] you will not access the global variable but call the getter, which in turn will access the class variable (because then the local mapContents is out of scope)
Hope this helps.
global var mapContents is readonly,in foo function , create a new pointer,then you can change the value of inner var.
Look for a method in your class with a name mapContents that will return a initialization to your RMMapContents class.
Basically this line RMMapContents *mapContents = [self mapContents]; says that initializing an instance of RMMapContents called mapContens using the method mapContents.
So what is actually the difference between these two versions:
#interface Foo : NSObject
// A guy walks into a bar.
#property(nonatomic, copy) NSString *bar;
#end
// Implementation file
#interface Foo ()
#property(nonatomic, retain) NSArray *baz;
#end
and
#interface Foo : NSObject
// A guy walks into a bar.
#public
#property(nonatomic, copy) NSString *bar;
#private
#property(nonatomic, retain) NSArray *baz;
#end
As far as my understanding goes, putting the #property in the .m basically means that it is private. Correct me if I am wrong? Also which is the best implementation then? Is it just a coding style/practice?
The compiler can warn you about things that it knows about.
When I import your header the compiler can see that Foo has a method called bar and setBar:. This means I can use them both
[instanceOfFoo setBar:#"some string"];
NSLog(#"%#", [instanceOfFoo bar]);
whereas because I only imported the header - the compiler can only see the header it is not aware that there are also methods baz and setBaz: available, so doing the following will cause the compiler to barf
[instanceOfFoo setBaz:#"some string"];
NSLog(#"%#", [instanceOfFoo baz]);
I can however still access these properties if I know they exist by using KVC like this without the compiler barfing
[instanceOfFoo setValue:#"some string" forKey:#"baz"];
NSLog(#"%#", [instanceOfFoo valueForKey:#"baz"]);
You are correct in your understanding. Putting the #property in an #interface in the .m is making it "private". What that means is you'll get compiler warnings if you try to access that property from another class that includes the .h that doesn't include the #property declaration. This doesn't mean that you can't access the property, just that the compiler will yell at you.
As for best, neither one is best. You should implement the one that makes sense for you object, which could include items in both the .h and .m (read only proper in .h with full property in .m). Basically if the #property shouldn't ever be accessed outside of your class put it in the .m.
If I have a class/object like this
#import <Foundation/Foundation.h>
#interface anObject : NSObject {
NSString *aProp;
}
#property NSString aProp;
#end
and in the cellForRowAtIndexPath method i want to assign one of the string values from its properties to a uilabel of a tableviewcell, how do i do it?
I've tried this but it doesn't work
[[cell topLabel] setText:(NSString *)anObject.aProp];
Putting a breakpoint on the above line and inspecting it, the debugger says "variable is not a CFString
Casting the property to a CFString doesnt work
Modifying the class and declaring the property as a CFStringRef doesnt work either
cell.textLabel.text = #"Foo";
This is the proper way to declare the property:
#property (nonatomic, copy) NSString * aProp;
note: the issue was with your "NSString aProp" not being a pointer.
and, yes, as frog suggested, copy is more appropriate.
Hey all i have been trying to figure out why i am getting this warning:
'TxtAppDelegate' may not respond to '-TCN'
'TxtAppDelegate' may not respond to '-TID'
when i try to use this code:
// .h file
#interface RootViewController : UITableViewController <UIActionSheetDelegate> {
NSString *theCompanyName;
NSString *theID;
}
#property (nonatomic, retain)NSString *theCompanyName;
#property (nonatomic, retain)NSString *theID;
// .m
NSString *theCompanyName;
NSString *theID;
#synthesize theCompanyName;
#synthesize theID;
TxtAppDelegate *customObjInstance = [[TxtAppDelegate alloc] init];
theCompanyName = [customObjInstance TCN];
theID = [customObjInstance TID];
I've added the header for the .h file that has the two functions in them. The code works but i really would like to solve the warning problem.
Any help would be great to solve this problem of mine :)
David
While it would have been more helpful to see the header file where TxtAppDelegate is declared, I'm guessing the method declarations must be off. They should look like this:
- (NSString *)TCN;
- (NSString *)TID;
If this is not the cause of the problem, please post the header file here so we can examine it.
How are declared these two functions in your header?
They should belong to a category of TxtAppDelegate class or to a protocol. If you choose the protocol, TxtAppDelegate interface should mention that it conforms to that protocol.