CADisplayLink、NSTimer使用注意

CADisplayLink、NSTimer會(huì)對(duì)target產(chǎn)生強(qiáng)引用，如果target又對(duì)它們產(chǎn)生強(qiáng)引用，那么就會(huì)引發(fā)循環(huán)引用，舉例如下

@interface ViewController ()
@property (strong, nonatomic) CADisplayLink *link;
@property (strong, nonatomic) NSTimer *timer;
@end

@implementation ViewController

- (void)viewDidLoad {
    [super viewDidLoad];
    
    self.timer = [NSTimer scheduledTimerWithTimeInterval:1.0 target:self selector:@selector(timerTest) userInfo:nil repeats:YES];
    // 保證調(diào)用頻率和屏幕的刷幀頻率一致，60FPS
    self.link = [CADisplayLink displayLinkWithTarget:self selector:@selector(linkTest)];
    [self.link addToRunLoop:[NSRunLoop mainRunLoop] forMode:NSDefaultRunLoopMode];

}
- (void)timerTest
{
    NSLog(@"%s", __func__);
}
- (void)linkTest
{
    NSLog(@"%s", __func__);
}

• 解決方法1：使用 block , __weak self

__weak typeof(self) weakSelf = self;
self.timer = [NSTimer scheduledTimerWithTimeInterval:1.0 repeats:YES block:^(NSTimer * _Nonnull timer) {
    [weakSelf timerTest];
}];

• 解決方法2：利用 Runtime 機(jī)制消息轉(zhuǎn)發(fā)，使用代理對(duì)象

@interface KJProxy : NSObject
+ (instancetype)proxyWithTarget:(id)target;
// 使用 weak 不會(huì)對(duì) target 造成強(qiáng)引用
@property (weak, nonatomic) id target;
@end

@implementation KJProxy

+ (instancetype)proxyWithTarget:(id)target
{
    KJProxy *proxy = [[KJProxy alloc] init];
    proxy.target = target;
    return proxy;
}
// 將方法調(diào)用轉(zhuǎn)發(fā)給proxy.target
- (id)forwardingTargetForSelector:(SEL)aSelector
{
    return self.target;
}
@end

self.link = [CADisplayLink displayLinkWithTarget:[KJProxy proxyWithTarget:self] selector:@selector(linkTest)];
[self.link addToRunLoop:[NSRunLoop mainRunLoop] forMode:NSDefaultRunLoopMode];
    
self.timer = [NSTimer scheduledTimerWithTimeInterval:1.0 target:[KJProxy proxyWithTarget:self] selector:@selector(timerTest) userInfo:nil repeats:YES];

可以將方法2中的代理對(duì)象替換成NSProxy

@interface KJProxy : NSProxy
+ (instancetype)proxyWithTarget:(id)target;
@property (weak, nonatomic) id target;
@end

@implementation KJProxy

+ (instancetype)proxyWithTarget:(id)target
{
    // NSProxy對(duì)象不需要調(diào)用init，因?yàn)樗緛?lái)就沒(méi)有init方法
    KJProxy *proxy = [KJProxy alloc];
    proxy.target = target;
    return proxy;
}
// 返回proxy.target中的方法簽名
- (NSMethodSignature *)methodSignatureForSelector:(SEL)sel
{
    return [self.target methodSignatureForSelector:sel];
}
// 轉(zhuǎn)發(fā)給proxy.target處理
- (void)forwardInvocation:(NSInvocation *)invocation
{
    if(self.target){
      [invocation invokeWithTarget:self.target];
    }
}
@end