I have coded this method in a class:
- (NSMutableDictionary *)fetch {
NSMutableDictionary *ret = [[NSMutableDictionary alloc] init];
// filling ret with some data here
return ret;
}
Is the way of returning this NSMUtableDictionary object without release correct ?
Thx for helping,
Stephane
Do the following:
- (NSMutableDictionary *)fetch {
NSMutableDictionary *ret = [[NSMutableDictionary alloc] init];
// filling ret with some data here
return [ret autorelease];
}
To learn more about autoreleaseing, read this Apple document called Memory Management Programming Guide.
use like this
- (NSMutableDictionary *)fetch {
NSMutableDictionary *ret = [[NSMutableDictionary alloc] init];
// filling ret with some data here
return [ret autorelease];
}
Developer Docs
Auto release puts the object into a autorelease pool and release is called later after it has been returned.
Related
I want to fetch JSON data asynchronously. The data is set up in a way that one request will bring only 8 records. I need to send the requests repeatedly until the response becomes empty or returns less than 8 records.
Currently, I have these methods in myviewcontroller.m class:
(void)myCallback:(id)sender {
MyDataRequest *objMyDataRequest = [[[MyDataRequest alloc] init] autorelease];
objMyDataRequest.myRequiredVariableToGetAuthTokenDataResponse = classOfMyCallBack.someVariable;
// Initiate getAuthToken request
[objWishListRequest initiateGetAuthTokenRequest:self requestSelector:#selector(getAuthTokenDataResponse:)];
}
Now here is the definition of getAuthTokenDataResponse:
(void) getAuthTokenDataResponse:(NSData *)data {
NSString *stringResponse = [[NSString alloc] initWithData:data encoding:NSASCIIStringEncoding];
SBJsonParser *parser=[[SBJsonParser alloc]init];
NSDictionary *objDictionaryForStringResponse = [parser objectWithString:stringResponse];
[stringResponse release];
[parser release];
MyListRequest *objMyListRequest = [[[MyListRequest alloc] init] autorelease];
objMyListRequest.myRequiredValueToGetMyDataResponse = [objDictionaryForStringResponse objectForKey:#"Data"];
// Initiate GetMyDataResponse request
[objMyListRequest initiateGetMyDataRequest:self requestSelector:#selector(getMyDataResponse:)];
}
(void) getMyDataResponse:(NSData *)data {
NSString *stringResponse = [[NSString alloc] initWithData:data encoding:NSASCIIStringEncoding];
SBJsonParser *parser=[[SBJsonParser alloc]init];
NSDictionary *objGetMyDataRootDictionary = [parser objectWithString:stringResponse];
[stringResponse release];
[parser release];
NSDictionary *dataElements=[objGetMyDataRootDictionary objectForKey:#"Data"];
Wish *objMyData;
for (NSDictionary* objGetMyDataRootDictionary in dataElements) {
objMyData = [[Wish alloc]init];
//add different elements from dataElements into member variables of object objWish
[self.myDataArray addObject:objMyData];
[objMyData release];
}
[self.myDataTableView reloadData];
}
This method lies in MyDataRequest class:
(void)initiateGetMyDataRequest:(id)requestDelegate requestSelector:(SEL)requestSelector{
// Set the delegate and selector
self.delegate = requestDelegate;
self.callback = requestSelector;
NSString* unescapedUrlString = [NSString stringWithFormat:#"http://test.mytesturl.com/core.svc/alldata/My/get/All/?token=%#&search=&page=1",myRequiredtokenparameter];
[self request:url];
}
I need to send multiple requests to the same url (with different parameter value i.e. value of page number) to fetch the results. How may I achieve it given the above scenario? The calls must be asynchronous.
How should I make the actual flow between all these calls? How may I get the data of "all the pages" asynchronously?
I think you are looking for a operation queue. I use ASIHTTPRequests in my apps and they work.
If you want to use this library, here's the link how to use it: Show UIActivityIndicatorView when loading NSString from Web
I have a method like this
- (NSDictionary *)getCellValuesForRow:(int)row {
NSMutableDictionary *dictValues= [[NSMutableDictionary alloc] init];
Outage *outage = [listOutage objectAtIndex:row];
[dictValues setObject:outage.duration forKey:#"OutageDuration"];
return dictValues;
}
and this value is stored in this way
NSDictionary *dict = [[NSDictionary alloc] initWithDictionary:[self getCellValuesForRow:(indexPath.row-1)]];
how to release memory in this scenario
This is what autorelease is for.
NSMutableDictionary *dictValues= [[[NSMutableDictionary alloc] init] autorelease];
You should autorelease dictValues in getCellValuesForRow, or just don't alloc it. This will keep it autoreleased:
NSMutableDictionary *dictValues= [NSMutableDictionary dictionary];
In most cases it should be the responsibility of whatever calls it to alloc it (if it needs to be kept around after the autorelease pool is cleared), then dealloc it later.
If whatever calls it doesn't need it kept around, it can just leave it autoreleased.
An alternative is to simply use
NSMutableDictionary *dictValues= [NSMutableDictionary dictionary];
That's effectively the same thing as what Dan suggested. Just less typing.
It applies to your next line, too:
NSDictionary *dict = [NSDictionary dictionaryWithDictionary:[self getCellValuesForRow:(indexPath.row-1)];
There are multiple memory leaks in this section of my code. Specifically with these arrays: PlaylistItem, PlaylistItemID and PlaylistItemLength. The problem is that I can't successfully release the arrays. When I attempt to use insert [xxxx release]; anywhere in this code, the app locks up. It's driving me absolutely nurtz!
-(void)configureCueSet {
MPMediaQuery *myPlaylistsQuery = [MPMediaQuery playlistsQuery];
NSArray *playlists = [myPlaylistsQuery collections];
//Get # of items in a playlist and names -------------------------------------
NSArray *songs;
for (MPMediaPlaylist *playlist in playlists) {
NSString *playListItem = [playlist valueForProperty: MPMediaPlaylistPropertyName];
if ([playListItem isEqualToString: savedLastSelectedPlaylist]){
songs = [playlist items];
}
}
PlaylistItem = [[NSMutableArray alloc] init];
PlaylistItemID = [[NSMutableArray alloc] init];
PlaylistItemLength = [[NSMutableArray alloc] init];
for (MPMediaItem *song in songs) {
[PlaylistItem addObject:[song valueForProperty: MPMediaItemPropertyTitle]];
[PlaylistItemID addObject:[song valueForProperty: MPMediaItemPropertyPersistentID]];
[PlaylistItemLength addObject:[song valueForProperty: MPMediaItemPropertyPlaybackDuration]];
}
}
Does that method get called multiple times? If so, your leak likely occurs on that assignment. You'd want:
[PlayListItem release];
PlaylistItem = [[NSMutableArray alloc] init];
[PlayListItemID release];
PlaylistItemID = [[NSMutableArray alloc] init];
[PlaylistItemLength release];
PlaylistItemLength = [[NSMutableArray alloc] init];
If you don't release what was there before, then you'll get a leak.
Attempting to insert [xxx release] would release the contents, not the arrays. The application crashes because with that you are deallocating the object which you are about to add to the array. According to the documentation (here), the values in an NSArray are automatically retained, and will be released as soon as the array is dealloc'ed. So, if you want to release any of those arrays, simply type [PlaylistItem release].
I have an NSMutableArray called playlist. This is in a method called getAllPlaylists. The code is something like this:
-(NSMutableArray *)getAllPlaylists
{
//playlist is an instance variable
playlist = [[NSMutableArray alloc] init]; //memory leak here
...
//some code here which populates the playlist array
[playlist addObject: object1];
...
return playlist;
}
The array allocation step of playlist is causing a memory leak. In such a scenario where can i release this array? Or can i avoid allocation n initialization of playlist here by doing something else? Any help will be greatly appreciated!!
2 solutions:
Use autorelease:
- (NSMutableArray*)getAllPlaylists
{
playlist = [[NSMutableArray alloc] init];
...
return [playlist autorelease];
}
or instead of using [[NSMutableArray alloc] init] to create your NSMutableArray object, use [NSMutableArray array] which is equivalent to [[[NSMutableArray alloc] init] autorelease]:
- (NSMutableArray*)getAllPlaylists
{
playlist = [NSMutableArray array];
...
return playlist;
}
You should autorelease newly created objects that you want to return that are not owned by the object (local variables, not instance variables).
playlist = [[[NSMutableArray alloc] init] autorelease];
Alternatively, you can use the convenience method to do that more easily:
playlist = [NSMutableArray array];
For items the object owns (instance variables), you should make sure you release the old value first and implement a dealloc method that also releases the value.
- (NSMutableArray*)getAllPlaylists {
[playlist release];
playlist = [[NSMutableArray alloc] init];
return playlist;
}
- (void)dealloc {
[playlist release];
[super dealloc];
}
For more info, see the memory management guide.
This question discusses encrypting data on the iPhone using the crypt() function. As an alternative, is there a keychain on the iPhone and if so, what code would I use to access it in order to store login details and then retrieve them for us in an application?
One other thing to note: the keychain APIs don't work in the simulator when using older versions (2.x, 3.x) of the iPhone SDK. This could save you a lot of frustration when testing!
There is a keychain you can use - for code, the best bet is to check out the GenericKeychain sample application from Apple:
GenericKeychain sample
I really like Buzz Anderson's Keychain abstraction layer and I eagerly await Jens Alfke's MYCrypto to reach a usable state. The latter does a competent job of allowing use on Mac OS X and the iPhone using the same code, though its features only mimic a small subset of the Keychain's.
Here is what i use to store Key/Value pairs in the keychain. Make sure to add Security.framework to your project
#import <Security/Security.h>
// -------------------------------------------------------------------------
-(NSString *)getSecureValueForKey:(NSString *)key {
/*
Return a value from the keychain
*/
// Retrieve a value from the keychain
NSDictionary *result;
NSArray *keys = [[[NSArray alloc] initWithObjects: (NSString *) kSecClass, kSecAttrAccount, kSecReturnAttributes, nil] autorelease];
NSArray *objects = [[[NSArray alloc] initWithObjects: (NSString *) kSecClassGenericPassword, key, kCFBooleanTrue, nil] autorelease];
NSDictionary *query = [[NSDictionary alloc] initWithObjects: objects forKeys: keys];
// Check if the value was found
OSStatus status = SecItemCopyMatching((CFDictionaryRef) query, (CFTypeRef *) &result);
[query release];
if (status != noErr) {
// Value not found
return nil;
} else {
// Value was found so return it
NSString *value = (NSString *) [result objectForKey: (NSString *) kSecAttrGeneric];
return value;
}
}
// -------------------------------------------------------------------------
-(bool)storeSecureValue:(NSString *)value forKey:(NSString *)key {
/*
Store a value in the keychain
*/
// Get the existing value for the key
NSString *existingValue = [self getSecureValueForKey:key];
// Check if a value already exists for this key
OSStatus status;
if (existingValue) {
// Value already exists, so update it
NSArray *keys = [[[NSArray alloc] initWithObjects: (NSString *) kSecClass, kSecAttrAccount, nil] autorelease];
NSArray *objects = [[[NSArray alloc] initWithObjects: (NSString *) kSecClassGenericPassword, key, nil] autorelease];
NSDictionary *query = [[[NSDictionary alloc] initWithObjects: objects forKeys: keys] autorelease];
status = SecItemUpdate((CFDictionaryRef) query, (CFDictionaryRef) [NSDictionary dictionaryWithObject:value forKey: (NSString *) kSecAttrGeneric]);
} else {
// Value does not exist, so add it
NSArray *keys = [[[NSArray alloc] initWithObjects: (NSString *) kSecClass, kSecAttrAccount, kSecAttrGeneric, nil] autorelease];
NSArray *objects = [[[NSArray alloc] initWithObjects: (NSString *) kSecClassGenericPassword, key, value, nil] autorelease];
NSDictionary *query = [[[NSDictionary alloc] initWithObjects: objects forKeys: keys] autorelease];
status = SecItemAdd((CFDictionaryRef) query, NULL);
}
// Check if the value was stored
if (status != noErr) {
// Value was not stored
return false;
} else {
// Value was stored
return true;
}
}
It is worth noting that these key/values will not get deleted if the user deletes your app. If a user deletes your app, then reinstalls it, the key/values will still be accessible.
Also remember that when generating an AppID, if you want more than one application to access the same Keychain information, you have to generate a wild card AppID (#####.com.prefix.*)...
With the latest version 1.2 of the GenericKeychain sample Apple provides a keychain wrapper that also runs on the iPhone Simulator. Check out at this article for details: http://dev-metal.blogspot.com/2010/08/howto-use-keychain-in-iphone-sdk-to.html
Here is one more good wrapper class from Mr.Granoff
https://github.com/granoff/Lockbox
Thanks