10 iPhone Memory Management Tips

Transcript

1. 10 iPhone Memory Management Tips Adrian Kosmaczewski January 28th, 2009 1
2. http://kosmaczewski.net/ 2009/01/28/ 10-iphone-memory-management-tips/ 2
4. Facts 4
6. 128 MB RAM 6
7. 128 MB RAM 6
8. 128 MB RAM ~ 40 MB for you! 6
9. Garbage Collection 7
10. Garbage Collection 7
11. [ alloc | copy | retain] [ release ] 8
12. [ alloc | copy | retain] [ release ] 8
14. http://cocoadevcentral.com/d/learn_objectivec/ 9
15. Objects on the heap 10
16. // C++ automatic object on the stack // Memory freed when out of scope std::string name(“Adrian”); // C++ object on the heap std::string *name = NULL; name = new std::string(“Adrian”); delete name; 11
17. ... autorelease]; 12
18. Virtual Memory 13
19. Virtual Memory 13
21. Tips 15
23. 1) Respond to Memory Warnings 17
24. - (void)didReceiveMemoryWarning { [super didReceiveMemoryWarning]; } 18
25. - (void)applicationDidReceiveMemoryWarning:(UIApplication *)app { [[ImageCache sharedImageCache] removeAllImagesInMemory]; } 19
26. NSNotificationCenter *center = [NSNotificationCenter defaultCenter]; [center addObserver:self selector:@selector(whatever:) name:UIApplicationDidReceiveMemoryWarningNotification object:nil]; 20
28. 2) Avoid Autoreleased Objects 22
29. (when possible) 23
30. // Instead of NSString *string = [NSString stringWithFormat:@"value = %d", var]; // use NSString *string = [[NSString alloc] initWithFormat:@"value = %d", var]; ... [string release]; 24
31. NSAutoreleasePool *pool = [[NSAutoreleasePool alloc] init]; for (id item in array) { id anotherItem = [item create]; [anotherItem doSomethingWithIt]; } [pool release]; 25
33. 3) Load Lazily and Reuse 27
34. - (void)tableView:(UITableView *)tableView didSelectRowAtIndexPath:(NSIndexPath *)indexPath { Item *item = [items objectAtIndex:indexPath.row]; if (detailController == nil) { detailController = [[DetailController alloc] init]; } detailController.item = item; [self.navigationController pushViewController:detailController animated:YES]; } 28
35. viewWillAppear: viewDidDisappear: 29
36. tabBarController:didSelectViewController: 30
38. 4) Avoid UIImage’s imageNamed: 32
39. http://www.alexcurylo.com/blog/2009/01/13/ imagenamed-is-evil/ 33
40. @implementation UIImage (AKLoadingExtension) + (UIImage *)newImageFromResource:(NSString *)filename { NSString *imageFile = [[NSString alloc] initWithFormat:@"%@/%@", [[NSBundle mainBundle] resourcePath], filename]; UIImage *image = nil; image = [[UIImage alloc] initWithContentsOfFile:imageFile]; [imageFile release]; return image; } @end 34
41. #import <Foundation/Foundation.h> @interface ImageCache : NSObject { @private NSMutableArray *keyArray; NSMutableDictionary *memoryCache; NSFileManager *fileManager; } + (ImageCache *)sharedImageCache; - (UIImage *)imageForKey:(NSString *)key; - (BOOL)hasImageWithKey:(NSString *)key; - (void)storeImage:(UIImage *)image withKey:(NSString *)key; - (BOOL)imageExistsInMemory:(NSString *)key; - (BOOL)imageExistsInDisk:(NSString *)key; - (NSUInteger)countImagesInMemory; - (NSUInteger)countImagesInDisk; - (void)removeImageWithKey:(NSString *)key; - (void)removeAllImages; - (void)removeAllImagesInMemory; - (void)removeOldImages; @end 35
42. - (void)applicationDidReceiveMemoryWarning:(UIApplication *)app { [[ImageCache sharedImageCache] removeAllImagesInMemory]; } 36
43. http://kosmaczewski.net/projects/iphone-image-cache/ 37
45. 5) Build Custom Table Cells and Reuse Them Properly 39
46. - (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath { Item *item = [items objectAtIndex:indexPath.row]; static NSString *identifier = @"ItemCell"; ItemCell *cell = (ItemCell *)[tableView dequeueReusableCellWithIdentifier:identifier]; if (cell == nil) { cell = [[[ItemCell alloc] initWithIdentifier:identifier] autorelease]; } cell.item = item; return cell; } 40
48. 6) Override Setters Properly 42
49. @interface SomeClass { @private NSArray *items; NSString *name; id<SomeProtocol> delegate; } @property (nonatomic, retain) NSArray *items; @property (nonatomic, copy) NSString *name; @property (nonatomic, assign) id<SomeProtocol> delegate; @end 43
50. - (void)setItems:(NSArray *)obj { if (obj == items) { return; // (merci Marco! :) } [items release]; items = nil; items = [obj retain]; if (items != nil) { // create the internal // structure of the cell // if not present, // and change the // widget values } } 44
51. - (void)setName:(NSString *)obj { [name release]; name = nil; // I always copy NSStrings! name = [obj copy]; if (name != nil) { // create the internal // structure of the cell // if not present, // and change the // widget values } } 45
52. - (void)setDelegate:(id<SomeProtocol>)obj { // do not retain! // This is an "assign" property delegate = obj; if (delegate != nil) { // create the internal // structure of the cell // if not present, // and change the // widget values } } 46
54. 7) Beware of Delegation 48
55. @interface SomeClass <WidgetDelegate> { @private Widget *widget; } @end 49
56. @implementation SomeClass - (id)init { if (id = [super init]) { widget = [[Widget alloc] init]; widget.delegate = self; } return self; } 50
57. - (void)dealloc { // widget might be retained by someone else! widget.delegate = nil; [widget release]; widget = nil; } #pragma mark - #pragma mark WidgetDelegate methods - (void)widget:(Widget *)obj method:(BOOL)value { // and here something happens... } @end 51
59. 8) Use Instruments 53
62. 9) Use a Static Analysis Tool 56
63. http://clang.llvm.org/StaticAnalysis.html 57
64. scan-build -k -V xcodebuild -configuration Debug 58
69. 10) Use NSZombieEnabled 63
73. Thanks! 67
74. Questions? 68