I'm only new to iPhone development, so my apologies if this is a silly question. I'm building various apps based on a book I'm reading and one of their suggestion was to build a mini web browser. I thought this would be easy, but while most of it is, I'm seriously struggling with the NSDictionary.
I have a UISegmentedControl used to display various bookmarks. The bookmark name that is displayed on the buttons of the UISegmentedControl is going to be my key and the url is the value associated with it.
I first try to declare an NSDictonary as a private (global variable), but since I could not get it to work, I resorted to declare it in my header file as follows:
#property (nonatomic, retain) NSDictionary *bookmarks;
I synthesize it and I initialized it in the viewDidLoad as follows:
- (void)viewDidLoad
{
bookmarks = [NSDictionary
dictionaryWithObjectsAndKeys:#"http://www.microsoft.com",
#"Microsoft",
#"http://www.google.com",
#"Google",
#"http://www.apple.com",
#"Apple",
#"http://msdn.microsoft.com",
#"MSDN", nil];
[super viewDidLoad];
}
I then associated a control with my segmented control and when the event is triggered and the function is called I've got the following code which is called:
- (IBAction) getShortcut:(id)sender
{
NSString *shortcut;
shortcut = [shortcuts titleForSegmentAtIndex:shortcuts.selectedSegmentIndex];
NSString *url = [bookmarks valueForKey:shortcut];
//[self navigateTo: url];
[url release];
}
When a button from the UISegmentedControl is clicked, I extract the value and stored it into shortcut and then I try to use the shortcut variable as a key to extract the associated value from the NSDictionary "bookmarks" but it keeps crashing on NSString *url = [bookmarks valueForKey:shortcut];
and bombs out of my function and displays the usual error EXC_BAD_ACCESS
Any help would be greatly appreciated.
T.
You have two options. one is to deal with the ivar directly as #Matt S. posted. Note that in this case you need to keep you object with enough retain count. You're using and auto released object and causing the error.
The other option is to use the property you already defined:
self.bookmarks = [[NSDictionary ...]];
And the property retains it.
That dictionary is autoreleased.
Try this:
self.bookmarks = [NSDictionary dictionaryWithObjectsAndKeys...]
You didn't retain the NSDictionary.
Do:
bookmarks = [[NSDictionary
dictionaryWithObjectsAndKeys:#"http://www.microsoft.com",
#"Microsoft", nil] retain];
The problem is, that you do not retain "bookmarks" in the viewDidLoad method. There is an naming convention mentioned somewhere in the Apple docs: If an intialisation method starts with "init..." the returned object is retained, if not you have to do it yourself. The "dictionaryWithObjectsAndKeys" returns and object with retain count 0, which means, that after the scope of assignment (your viewDidLoad method) it is immediatly released again.
So just put a
[bookmarks retain];
after your initalisation and you are done. Another solution which does the retaining for you
bookmarks = [[NSDictionary alloc] initWithObjectsAndKeys ...];
And you shouldn't release the url in your action. It gets released, once you release the dictionary
Related
General noob questions:
(1) How can I create an NSMutable array in a buttonClicked action that I can add more entries to during subsequent clicks of the same button? I always seem to start over with a new array at every click (the array prints with only 1 entry which is the most recent button's tag in an NSLog statement).
I have about 100 buttons (one for each character in my string called "list") generated by a for-loop earlier in my code, and each has been assigned a tag. They are in a scrollview within the view of my ViewController.
I wish to keep track of how many (and which ones) of the buttons have been clicked with the option of removing those entries if they are clicked a second time.
This is what I have so far:
-(void) buttonClicked:(UIButton *)sender
NSMutableArray * theseButtonsHaveBeenClicked = [[NSMutableArray alloc] initWithCapacity: list.length];
NSNumber *sendNum = [NSNumber numberWithInt:sender.tag];
[theseButtonsHaveBeenClicked addObject:sendNum at index:sender.tag];
NSLog(#"%#",theseButtonsHaveBeenClicked);
}
(2) I have read that I may be able to use a plist dictionary but I don't really understand how I would accomplish that in code since I cant type out the items in the dictionary manually (since I don't know which buttons the user will click). Would this be easier if I somehow loaded and replaced the dictionary in a plist file? And how would I do that?
(3) I also have no idea how I should memory manage this since I need to keep updating the array. autorelease?
Thanks for any help you can provide!
Okay, firstly you are creating a locally scoped array that is being re-initialised on every call to buttonClicked:. The variable should be part of the class init cycle.
You will also be better off with an NSMutableDictionary instead of an NSMutableArray. With a dictionary we don't have to specify capacity and we can use the button's tags as dictionary keys.
Here's what you need to do, these three steps always go together: property/synthesize/release. A good one to remember.
//Add property declaration to .h file
#property (nonatomic, retain) NSMutableDictionary * theseButtonsHaveBeenClicked;
//Add the synthesize directive to the top of .m file
#synthesize theseButtonsHaveBeenClicked;
// Add release call to the dealloc method at the bottom of .m file
- (void) dealloc {
self.theseButtonsHaveBeenClicked = nil; // syntactically equiv to [theseButtonsHaveBeenClicked release] but also nulls the pointer
[super dealloc];
}
Next we create a storage object when the class instance is initialised. Add this to your class's init or viewDidLoad method.
self.theseButtonsHaveBeenClicked = [[NSMutableDictionary alloc] dictionary]; // convenience method for creating a dictionary
And your updated buttonClicked: method should look more like this.
-(void) buttonClicked:(UIButton *)sender {
NSNumber *senderTagAsNum = [NSNumber numberWithInt:sender.tag];
NSString *senderTagAsString = [[NSString alloc] initWithFormat:#"%#",senderTagAsNum];
// this block adds to dict on first click, removes if already in dict
if(![self.theseButtonsHaveBeenClicked objectForKey:senderTagAsString]) {
[self.theseButtonsHaveBeenClicked setValue:senderTagAsNum forKey:senderTagAsString];
} else {
[self.theseButtonsHaveBeenClicked removeObjectForKey:senderTagAsString]; }
[senderTagAsString release];
NSLog(#"%#", self.theseButtonsHaveBeenClicked);
}
I'm new to cocoa / objective-c and i'm struggeling with the releases of my objects. I have the following code:
gastroCategoryList = [[NSMutableArray alloc] init];
for (NSDictionary *gastrocategory in gastrocategories) {
NSString *oid = [gastrocategory objectForKey:#"id"];
GastroCategory *gc = [[GastroCategory alloc] initWithId:[oid intValue] name:[gastrocategory objectForKey:#"name"]];
[gastroCategoryList addObject:gc];
}
The analyzer shows me that the "gastrocategory" defined in the for is a potential memory leak. But i'm not sure if i can release this at the end of the for loop?
Also at the following code:
- (NSArray *)eventsForStage:(int)stageId {
NSMutableArray *result = [[NSMutableArray alloc] init];
for (Event *e in eventList) {
if ([e stageId] == stageId) {
[result addObject:e];
}
}
return result;
}
The Analyzer tells me that my "result" is a potential leak. But where should I release this?
Is there also a simple rule to memorize when i should use assign, copy, retain etc. at the #property ?
Another problem:
- (IBAction)showHungryView:(id)sender {
GastroCategoriesView *gastroCategoriesView = [[GastroCategoriesView alloc] initWithNibName:#"GastroCategoriesView" bundle:nil];
[gastroCategoriesView setDataManager:dataManager];
UIView *currentView = [self view];
UIView *window = [currentView superview];
UIView *gastroView = [gastroCategoriesView view];
[window addSubview:gastroView];
CGRect pageFrame = currentView.frame;
CGFloat pageWidth = pageFrame.size.width;
gastroView.frame = CGRectOffset(pageFrame,pageWidth,0);
[UIView beginAnimations:nil context:NULL];
currentView.frame = CGRectOffset(pageFrame,-pageWidth,0);
gastroView.frame = pageFrame;
[UIView commitAnimations];
//[gastroCategoriesView release];
}
I don't get it, the "gastroCategoriesView" is a potential leak. I tried to release it at the end or with autorelease but neither works fine. Everytime I call the method my app is terminating. Thank you very much again!
In your loop, release each gc after adding it to the list since you won't need it in your loop scope anymore:
gastroCategoryList = [[NSMutableArray alloc] init];
for (NSDictionary *gastrocategory in gastrocategories) {
NSString *oid = [gastrocategory objectForKey:#"id"];
GastroCategory *gc = [[GastroCategory alloc] initWithId:[oid intValue] name:[gastrocategory objectForKey:#"name"]];
[gastroCategoryList addObject:gc];
[gc release];
}
In your method, declare result to be autoreleased to absolve ownership of it from your method:
NSMutableArray *result = [[[NSMutableArray alloc] init] autorelease];
// An alternative to the above, produces an empty autoreleased array
NSMutableArray *result = [NSMutableArray array];
EDIT: in your third issue, you can't release your view controller because its view is being used by the window. Setting it to autorelease also causes the same fate, only delayed.
You'll have to retain your GastroCategoriesView controller somewhere, e.g. in an instance variable of your app delegate.
BoltClock's answer is spot-on as to the first part of your question. I'll try to tackle the rest.
Assign is for simple, non-object types such as int, double, or struct. It generates a setter that does a plain old assignment, as in "foo = newFoo". Copy & retain will, as their names imply, either make a copy of the new value ("foo = [newFoo copy]") or retain it ("foo = [newFoo retain]"). In both cases, the setter will release the old value as appropriate.
So the question is, when to copy and when to retain. The answer is... it depends. How does your class use the new value? Will your class break if some other code modifies the incoming object? Say, for example, you have an NSString* property imaginatively named "theString." Other code can assign an NSMutableString instance to theString - that's legal, because it's an NSString subclass. But that other code might also keep its own reference to the mutable string object, and change its value - is your code prepared to deal with that possibility? If not, it should make its own copy, which the other code can't change.
On the other hand, if your own code makes no assumptions about whether theString might have been changed, and works just as well whether or not it was, then you'd save memory by retaining the incoming object instead of unnecessarily making a copy of it.
Basically, the rule, which is unfortunately not so simple sometimes, is to think carefully about whether your own code needs its own private copy, or can correctly deal with a shared object whose value might be changed by other code.
The reason you can release gc after it is added to the gastroCategoryList is that when an object is added to an array, the array retains that object. So, even though you release your gc, it will still be around; retained by the gastroCategoryList.
When you are returning a newly created object from a method, you need to call autorelease. This will cause the object to be released only after the runtime leaves the scope of the calling method, thereby giving the calling method a chance to do something with the returned value.
Note that if your method starts with the word copy or new, then you should not autorelease your object; you should leave it for the calling method to release.
As for copy vs retain vs assign... as a general rule, copy objects that have a mutable version, such as NSArray, NSSet, NSDictionary, and NSString. This will ensure that the object you have a pointer to is not mutable when you don't want it to be.
Otherwise, use retain whenever you want your class to be ensured that an object is still in memory. This will apply to almost every object except for objects that are considered parents of your object, in which case you would use assign. (See the section on retain cycles here).
Also note that you have to use assign for non-object types such as int.
Read through the Memory Management Programming Guide a bit; it's quite helpful.
I just did a search for my particular question and although the answers are close, I can't get my head around the answer...so I need some assistance.
I'd like to populate an array (NSMutableArray I suppose) with a group of dictionary objects that are parsed from JSON strings...the dictionary part I got, the JSON parsing I got, but when I try to put these objects into the NSMutableArray and NSLog it I get (null)... here are my steps (in a general way)
edit 1:
-The array I am creating is called NewFinalArray. it is an NSMutableArray, declared at the .h file and synthesized (and now alloc'd and init'd) as noted in the viewDidLoad method of the DetailViewController. It's contents are to be displayed in a UITableView.
-In DetailViewController, I have been successful in creating a plain NSArray/NSMutableArray and populating it with values that display in my UITableView.
-In the new scenario, I am receiving the information to be displayed through JSON strings which are retrievable through dictionary objects. I am using the Stig JSON libraries for iPHone/iPad. I have no problems there.
-All I wanted to do is getting the existing dictionary objects (which I can loop through from the existing array and see) and add them to a new Array to be used for displaying menu items in my UITableview.
I declared my mutableArray in my .h file
#interface blah : ...,...,...{
NSMutableArray *newFinalArray;
// other vars and IBOutlets
}
#property (nonatomic, retain) NSMutableArray *newFinalArray;
// other #property and (IBAction) stuff
#end
I then synthesize it in my .m file... I even alloc/inited it at viewDidLoad (it's a DetailViewController)
#synthesize this,that, newFinalArray; // keep track of newFinalArray, that's the one I want
- (void)viewDidLoad {
// other code
[[newFinalArray alloc] init]; // ya returns a warning, about not responding to alloc, but whatever (for now)
// I also tested of course without having to do that.
in my method that uses newFinalArray, the method is a recursive function that calls itself. each time it calls, it should add the dictionary object to the array (or does it?)
-(void)digTree:(NSArray *)array{
for (NSDictionary *dictionary in array){
// looping through the array
[self newFinalArray addObject:[dictionary]];
// more other code, and somewhere along the way I recurse
[self digTree:anotherArray];
}
}
when I try to NSLog (#"my final array is %#", newFinalArray) I get (null).
I am probably missing something here. I tried to add "nil" at the end. I am a little new/green to this , so if someone can lend a hand and let me know how to populate my newFinalArray with these dictionary objects it would be most appreciated.
[[newFinalArray alloc] init];
should be:
newFinalArray = [[NSMutableArray alloc] init];
This line is wrong too:
[self newFinalArray addObject:[dictionary]];
it should be:
[newFinalArray addObject:dictionary];
The first thing I notice that is wrong, is it should be:
newFinalArray = [[NSMutableArray alloc] init];
in viewDidLoad. See if that fixes it. It looks like there are other things wrong as well, so turn on warnings and see what else the compiler warns you about for hints.
How are the dictionaries stored? An alternative/probably easier way to do this would probably be to use arrayWithObjects:. Also, when using addObject:, there is no need to add nil (in fact, you can't add nil).
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;