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"];
}
Related
How can i lazily initialize a NSMutableArray of Buttons ? I do something like this :
-(NSMutableArray *)roasteryButtons
{
if(!roasteryButtons)
{
roasteryButtons = [ NSMutableArray new];
//other code
}
return roasteryButtons;
}
And don't know what to do to call this lazy initializer ? i.e. I need to initialize the array so that i may set the frame for every button in the array
What u have done is correct. Instead of allocating the array in the init method of class, u are allocating the array only when required. Thus it serves the purpose of lazily allocating.
In the class, Wherever you want the array, you just call,
NSMutableArray *arr = [self roasteryButtons];
Also declare the method in header file as, -(NSMutableArray*)roasteryButtons;.
If you want the reference of the array in other classes, the call like,
[classObj roasteryButtons];
I have shown it as instance method. You can also declare that as class method, if you want like that.
And release that in -(void)dealloc method.
I guess you know when to call this method, right ?
The first thing is that you shouldn't use "new" method, but [[NSMutableArray alloc] init] instead : You should have a look at all existing [Init] methods available for NSArray : there are a bunch of them (with capacity, with objects, etc...)
Anyway, you should add some parameters to your method [roasteryButtons] : parameters that will help the method to know, for instance how many buttons to create, what is the frame where they have to show, etc. So this will look a bit like
-(NSMutableArray *)roasteryButtonsWithFrame:(*Frame) andNumbersOfButtons:(int)
for example...
or instead of parameters, you can pass a reference to a delegate that will be able to give answers to those questions (How many buttons, what's my frame and bounds, etc.) So in this case, the method will look like :
-(NSMutableArray *)roasteryButtonsWithDelegate:(id)
(This delegate should implement a protocol that you will create, containing the different methods that the delegate will have to respond to. ie methods like [howManyButtons]...)
The Perfect Way to Lazy initialize is as follow
in .h file declare your NSMUtableArray as property as follow
#property (nonatomic,strong) NSMutableArray *array;
Now in .m file synthesize it and do lazy initialize in getter like as follow:
#synthesize array=_array;
(NSMutableArray *) array
{
(!_array) _array=[[NSMutableArray alloc]init];
//this line is called lazy intialization..this line will create MutableArray at program //run time.
return _array
}
Now answer why we need this is that it take care about that if no NSMutableArray is created then it create it at programme run time and like this your app will not crash.
You could make your method a class method:
+(NSMutableArray *)roasteryButtons {
in this way you will be able to call it like this:
[MyRoasteryButtonClass roasteryButtons];
and this will return you your object.
Hope this helps.
i have a tableview controller like so,
NSString *selectedindex;
#interface ContactsController : UITableViewController<ABPeoplePickerNavigationControllerDelegate> {
NSMutableArray *names;
NSMutableArray *phonenumbers;
NSMutableArray *contacts;
DatabaseCRUD *sampledatabase;
}
+(NSString *) returnselectedindex;
#end
in the implementation file i have
+(NSString *) returnselectedindex
{
return selectedindex;
}
when a row is selected in the tableview i put have the following code.
selectedindex = [NSString stringWithFormat:#"%d", indexPath.row];
NSLog(#"selected row is %#",selectedindex);
in a different class i am trying to access the selectedindex. like so
selected = [ContactsController returnselectedindex];
NSLog(#"selected is %#",selected);
it gives me a warning: 'ContactsController' may not respond to '+returnselectedindex'
and crashes. i am not sure why. i have used class methods previously lot of times , and never had a problem. any help please. Thank You.
The reason you're crashing is that you're assigning a value to a global variable (selectedindex), but you're never taking ownership of it by calling -retain. As a result, the string doesn't know you need it to stay around, so the system deallocates it. Later, when you try to access it, it's already deallocated.
In order to avoid the crash, you need to add a retain call when you assign the value. Of course, since a selected index is something that's likely to be changing often, you'd want to release the previous value before overwriting it and retaining the new one. Thus, you should have this code:
[selectedindex release];
selectedindex = [[NSString stringWithFormat:#"%d", indexPath.row] retain];
That will fix your crash.
Now that your crash is fixed, though, you should really rethink your design. There's no reason for selectedindex to be a global variable; since the selected index is very likely specific to that instance of your ContactsController, it should be an instance variable of that class. Instead, you've declared it as a global variable, which means that there is only one selectedIndex shared between ALL instances of ContactsController. Then, in turn, your +returnselectedindex method should be an instance method, not a class method. (It should also be renamed in order to follow Cocoa naming conventions, but that's well off topic.)
I think You didn't allocated the selectedindex NSString.Thats why it will not crash on the same class and it crashes in the new Class.
So You allocate it in the setter method of "returnselectedindex"
Otherwise, Copy or retain the receive value of returnselectedindex value like this,
selected = [[ContactsController returnselectedindex]copy];
Hopefully I can make this clear, but I am new to Objective-C and to be honest not great with Arrays in the first place.
So, I have a Singleton class (called SingletonState) that I am using to pass variables around my app (please can we leave the whether I should use Singleton classes out of this - I will fix that later). In this class, I have an NSMutableArray (called arrayMyEvents). I have also created a class that I am going to store a list of events (called EventClass). When the user logs in, I call a web service and get back 3 strings. The 3rd string is a comma separated list of value. I parse the data and populate the custom class EventClass. I then add this class to the SingletonState.arrayMyEvents.
I have all of this working. I can go to another ViewController and access the "count" of items in arrayMyEvents.
PROBLEM: I now want to edit one of the ScheduledEventsClass"es" in my array. How do I get access to it and edit some of the properties and update the one in my SingletonState class?
Here is some of the code, that I've tried:
NSString *sWebServiceEvents = [[NSString alloc] initWithFormat:#"%#", [result objectAtIndex:2]];
if ( [ sWebServiceEvents isEqualToString:#"NULL" ] != true ) {
NSArray *arrayEvents = [sWebServiceEvents componentsSeparatedByString:#","];
// If the array has not been initialized they initialize it.
if (sharedState.arrayMyEvents == nil) {
sharedState.arrayMyEvents = [[NSMutableArray alloc ] init ];
}
for (NSString * sEvent in arrayEvents) {
// Set equal to the value of the array (the Event Number) at the same
// position as the row that we are being asked to return a cell/row for.
EventClass *eventClass = [[EventClass alloc] retain];
eventClass.sEvent = sEvent;
[ sharedState.arrayEvents addObject:eventClass ];
}
NSLog(#"LoginView - sharedState.arrayMyEvents Count: %d", [sharedState.arrayMyEvents count]);
}
Here is me trying to access it in another ViewController:
EventClass *eventClass =
[sharedState.arrayMyEvents objectAtIndex:row ];
NSLog(#"eventClass.sEventNumber: ", eventClass.sEventNumber);
eventClass.sLocation = #"Jason's Big Location";
You're going to have some memory leaks from the sEvent loop. [[EventClass alloc]retain] leaves you an uninitialized EventClass object with a reference count of 2. You'll need to change that to [[[EventClass alloc] init] autorelease] to keep it from leaking. The arrayEvents NSMutableArray will retain it during the addObject: call. (Shouldn't that be [sharedState.arrayMyEvents addObject: eventClass] in the loop?)
After that, all you have to do to edit the EventClass object in the second block of code is edit it. The eventClass variable is a pointer to an object in the array. Anything done to that object doesn't affect the pointer referencing it, it affects data referenced by it. The code you have in the second block should change the sLocation of the selected object as you intend.
You have a few more memory leaks in there, too. Use Cmd-Shift-A to build with the static analyzer and it'll tell you where.
Maybe the problem is that you put them in sharedState.arrayEvents but try to take them out of sharedState.arrayMyEvents. Different variables.
Also, lots of memory leaks.
Thanks John and St3fan, your answers and time are appreciated!!!
I think that I figured out my issue:
Basically, the class that I created (EventClass) had the properties setup like this:
#property (nonatomic, assign) NSString *sStudyNumber;
#property (nonatomic, assign) NSString *sTheater;
but, they should be (or at least I got it to work like this):
#property (nonatomic, retain) NSString *sStudyNumber;
#property (nonatomic, retain) NSString *sTheater;
Then, in my second view I was able to do this:
EventClass *eventClass = [sharedState.arrayMyEvents objectAtIndex:row ];
NSLog(#"MyEvents: %#", eventClass.sEventNumber);
eventClass.sLocation = #"Jason's Big Location";
I then checked it in another method of the view using this and it was still there:
EventClass *eventClass = [sharedState.arrayMyEvents objectAtIndex:row ];
NSLog(#"MyEvents: %#", eventClass.sEventNumber);
NSLog(#"MyEvents: %#", eventClass.sLocation);
I also, checked it in yet another view and the value was maintained in the SharedState.arrayMyEvents without issue. :)
In the end, I believe that I boiled down to the difference between "assign" and "retain".
Now, on to the memory leaks :(
Please, let me know if you see any other issues with this.
Thanks,
Jason
I have a NSXMLParser that parses YT's API. It then turns all the videos into a class I wrote called video. Then the class is put into an array. Then back at my rootviewcontroller I access xmlParser.allVideos (xmlParser is a class I wrote that is the delegate for the xml parser.
Here is what I do with it in the viewDidLoad:
arrayFromXML = xmlParser.allVideos;
Then in the drawing of the tableView I do this:
tempVideo = [arrayFromXML objectAtIndex:indexPath.row];
cell.textLabel.text = tempVideo.videoTitle; //crashes here and says NSString has been deallocated.
How can I fix this?
If arrayFromXML is an instance variable you have to retain or copy (to be safe from later manipulation) the array as xmlParser simply might not be alive anymore when other methods are called later:
arrayFromXML = [xmlParser.allVideos copy];
Or better yet using a copy or retain property:
self.arrayFromXML = xmlParser.allVideos;
I declared
NSString *dayinfield[43];
and fill it in
-(void)DrawDemo {
dayinfield[2] = #"hallo";
dayinfield[3] = #"test";
// also i can read it
NSLog (#"show: %#",dayinfield[2]);
//works fine
}
but when i like to read its content in another function (same class)
-(void)ReadData
{
NSLog (#"show: %#",dayinfield[2]);
// I get random infos or “EXC_BAD_ACCESS
}
How do I initialize the NSString Array correct so I can reach its content in each of my functions??
Thanks
chris
If you only assign literals to the array elements, this should not be a problem. But if you use other strings, you have to retain the instances manually when using a C array.
By the way: Objective-C methods start with a lowercase letter.
This would happen if you never initialized the array (or the parts of it you are accessing) - if you haven't called -DrawDemo before -ReadData or used different indices than the ones posted here, the array would simply contain garbage values.
Try to initialize the array contents to nil or #"" in your initializer method and see if the problem persists.
Alternatively consider using a suitable Cocoa container.
It's memory is probably being released before your second call. Assuming you have declared dayinfield as an ivar (and the fact that you don't get bad access all the time) your string aren't properly retained.
Initialise the strings like this:
dayinfield[2] = [[NSString alloc] initWithString:#"hallo"];
dayinfield[3] = [[NSString alloc] initWithString:#"test"];
and you should release them after you're class is being deallocated (See Memory Management Guide).
Also, obviously it depends on what you want to do, but it might be easier if you use NSArray instead of C arrays.
What you have in the OP should work although it is an exercise in sheer masochism to use old school C arrays with objects.
I ran this code:
#interface TestClass : NSObject {
NSString *a[1];
}
- (void) drawDemo;
- (void) readData;
#end
#implementation TestClass
- (void) drawDemo{
a[0]=#"A Zero";
a[1]=#"A One";
}//------------------------------------- (void) drawDemo------------------------------------
- (void) readData{
NSLog(#"a[0]=%#,a[1]=%#",a[0],a[1]);
}//------------------------------------- (void) readData------------------------------------
#end
TestClass *tc=[[TestClass alloc] init];
[tc drawDemo];
[tc readData];
... and got this output:
a[0]=A Zero,a[1]=A One
Your problem is elsewhere in your code. There is no compelling reason to use C arrays with objects. You gain nothing and you have to watch them like a hawk to prevent errors.