iOS中使用UI控件时，修饰符用strong？还是weak好呢？

大部分iOS工程师一般写代码的时候，都会使用strong，这是为了方便、快捷、不易报错，有的时候如果写成weak，会莫名其妙的报错，比如崩溃，但是看代码却没有问题。当然细心的工程师其实在使用Xcode的时候，在一个地方会发现，系统所使用的UI控件修饰符全是weak，当你用xib、view等拖控件关联时，这个时候系统提供的修饰符全部是weak，所以，其实官方推荐在实际开发中尽量用weak，那么怎么验证呢，我们可以通过一个示例程序来进行说明。

#import "ViewController.h"

@interface ViewController ()
@property (nonatomic,strong) UIView *strongView;
@property (nonatomic,strong) UIView *selfStrongView;
@property (nonatomic,weak) UIView *weakView;
@property (nonatomic,weak) UIView *selfWeakView;
@end

@implementation ViewController

- (void)viewDidLoad {
    [super viewDidLoad];
    
    //1、创建selfStrongView
    self.selfStrongView = [[UIView alloc]initWithFrame:CGRectMake(50, 25, 50, 50)];
    printf("self.selfStrongViewretain count = %ld\n",CFGetRetainCount((__bridge CFTypeRef)(self.selfStrongView)));
    [self.view addSubview:self.selfStrongView];
    printf("self.selfStrongView retain count = %ld\n",CFGetRetainCount((__bridge CFTypeRef)(self.selfStrongView)));
    
    _strongView = [[UIView alloc]initWithFrame:CGRectMake(150, 100, 50, 50)];
    printf("_strongView retain count = %ld\n",CFGetRetainCount((__bridge CFTypeRef)(_strongView)));
    [self.view addSubview:self.strongView];
    printf("_strongView retain count = %ld\n",CFGetRetainCount((__bridge CFTypeRef)(_strongView)));
    
    UIView *selfView = [[UIView alloc]initWithFrame:CGRectMake(250, 150, 50, 50)];
    self.selfWeakView = selfView;
    printf("self.selfWeakView retain count = %ld\n",CFGetRetainCount((__bridge CFTypeRef)(self.selfWeakView)));
    [self.view addSubview:self.selfWeakView];
    printf("self.selfWeakView retain count = %ld\n",CFGetRetainCount((__bridge CFTypeRef)(self.selfWeakView)));
    
    UIView *weaksView = [[UIView alloc]initWithFrame:CGRectMake(300, 200, 50, 50)];
    printf("weakView retain count = %ld\n",CFGetRetainCount((__bridge CFTypeRef)(weaksView)));
    _weakView = weaksView;
    printf("_weakView retain count = %ld\n",CFGetRetainCount((__bridge CFTypeRef)(_weakView)));
    [self.view addSubview:_weakView];
    printf("_weakView retain count = %ld\n",CFGetRetainCount((__bridge CFTypeRef)(_weakView)));
}

- (void)viewWillAppear:(BOOL)animated
{
    printf("self.selfStrongView retain count = %ld\n",CFGetRetainCount((__bridge CFTypeRef)(_strongView)));
    printf("_strongView retain count = %ld\n",CFGetRetainCount((__bridge CFTypeRef)(_strongView)));
    printf("self.selfWeakView retain count = %ld\n",CFGetRetainCount((__bridge CFTypeRef)(self.selfWeakView)));
    printf("_weakView retain count = %ld\n",CFGetRetainCount((__bridge CFTypeRef)(_weakView)));
    
    
}

@end

总结

在现在开发中，一般都是在ARC中，对于ARC来说，对象释放的最终根据还是根据引用计数为0时去释放。而weak与strong的根本区别是在set方法中，weak的set方法和strong的set方法都是释放旧值保留新值，但是weak的set方法会对其autorelease，即延迟release一次，而strong的set方法也是释放旧值保留新值，但是其不会延迟release。最终效果是strong会+1，weak不会+1.
要注意，用去赋值的时候是不调用set方法的，也就是说无论weak还是strong，只要用赋值都不会对引用计数加1，区别在于self.语法会调用set方法，strong的self.会调用set方法+1.而weak的_和self.语法都不会+1.

所以，建议用weak，用weak时无论用_和.语法都不会导致+1。用strong时用self.语法会导致+1.建议用weak。同时weak在对象回收以后可以将对象指针置成nil。