use the autorelease to release,the app will crash - ios

Question

I write an app (using no-arc)named Album which as the iPhone's native "Photo".
My Question:
1.
(please look the attached file name:1)when clicking the button of "+",then inputing some string and clicking the button of "save",the app will crash.But if change the code from "NSMutableArray *albumArr = [[[NSMutableArray alloc] init] autorelease];" to "NSMutableArray *albumArr = [[NSMutableArray alloc] init]", the app can work fine.But I think I should use the autorelease to release.
The related code:
// AlbumDB.m
+ (NSMutableArray *)fetchAlbumData
{
#warning why autorelease crash?
NSMutableArray *albumArr = [[[NSMutableArray alloc] init] autorelease];
FMDatabase *db = [FMDatabase databaseWithPath:[self dataBasePath]];
if ([db open]) {
NSString *sqlSelect = #"SELECT * FROM ALBUM";
FMResultSet *result = [db executeQuery:sqlSelect];
while ([result next]) {
AlbumModel *albumModel = [[AlbumModel alloc] init];
albumModel.albumid = [result intForColumn:#"albumid"];
albumModel.albumName = [result stringForColumn:#"albumName"];
[albumArr addObject:albumModel];
[albumModel release];
}
[db close];
}
return albumArr;
}
(please look the attached file name:2)when analyzing the code,I find the potential leak of an object.But in the dealloc,I had released.Why happen?
The related code:
//MainViewController.h
#property (nonatomic, retain) AlbumModel *editingAlbum;
// MainViewController.m
- (void)dealloc
{
[_albumArr release], _albumArr = nil;
self.editingAlbum = nil;
self.detailViewController = nil;
[super dealloc];
}

Answer 1

I think you should learn more about mrc.
In your first case, the albumArr if it is autorelease , it means when the runloop end ,it will be release, so the _albumArr will be nil when you use, you must retain it ,when you set the value to _albumArr.
In the second case, self.editingAlbum = [[AlbumModel alloc] init]; It will casuse the editingAlbum retain cout ==2 .You must change the code to like this:
AlbumModel *temp = [[AlbumModel alloc] init];
self.editingAlbum = temp;
[temp release];