相关资料:http://stackoverflow.com/questions/14489071/nsdictionary-release-triggers-valueforkey-return-value-release
NSString *path = [self.dataPath stringByAppendingPathComponent:@"dummy.plist"]; NSMutableDictionary *dict = [[NSMutableDictionary alloc] initWithContentsOfFile:path]; NSString *dummyKeyValue = [dict valueForKey:@"dummyKey"]; // NSLog(@"%@",[NSString stringWithString:dummyKeyValue]); [dict release]; NSString *anotherString = [dummyKeyValue lowercaseString];
当使用到dummyKeyValue时 挂掉。
背景:
NSDictionary在获得里面的值后, 对Dict进行释放。此时value也全部释放了。 当有引用在使用该value时,就会野指针。
解决办法:
NSString *dummyKeyValue = [[[dict valueForKey:@"dummyKey"] retain] autorelease];
进一步:
写分类来代替valueForKey方法。该分类实现下面功能
1. 类型转换保护
2. 数据内存计数保护(如上面所说)
例子:
- (NSString *)stringAtPath:(NSString *)path { NSObject * obj = [[[self objectAtPath:path]retain]autorelease]; if ( [obj isKindOfClass:[NSNull class]] ) { return nil; } else if ( [obj isKindOfClass:[NSNumber class]] ) { return [NSString stringWithFormat:@"%lld", [(NSNumber *)obj longLongValue]]; } else if ( [obj isKindOfClass:[NSString class]] ) { return (NSString *)obj; } return nil; }