object c 循环引用计数问题，非常重要。

头文件：@interface ObjA : NSObject@property (nonatomic, strong) ObjB * objB;@end@interface ObjB : NSObject@property (nonatomic, strong) ObjA * objA;@end源文件：@implementation ObjA@synthesize objB;-(void) dealloc{ NSLog(@"ObjA");}@end@implementation ObjB@synthesize objA;-(void) dealloc{ NSLog(@"ObjB");}@end错误用法：-(void) retainCycleTest{ /** 以下代码将导致死锁而内存泄露,ObjA，ObjB都无法释放，观察ObjA，ObjB的dealloc函数即可 */ ObjA * a = [[ObjA alloc] init]; ObjB * b = [[ObjB alloc] init]; a.objB = b; b.objA = a;}解救方法：@interface ObjB : NSObject@property (nonatomic, weak) ObjA * objA;@end