1、FPS 监测CADisplayLink

方法一：核心代码如下

@implementation ViewController {
    UILabel *_fpsLbe;
    CADisplayLink *_link;
    NSTimeInterval _lastTime;
    float _fps;
}

- (void)startMonitoring {
    if (_link) {
        [_link removeFromRunLoop:[NSRunLoop mainRunLoop] forMode:NSRunLoopCommonModes];
        [_link invalidate];
        _link = nil;
    }
    _link = [CADisplayLink displayLinkWithTarget:self selector:@selector(fpsDisplayLinkAction:)];
    [_link addToRunLoop:[NSRunLoop mainRunLoop] forMode:NSRunLoopCommonModes];
}

- (void)fpsDisplayLinkAction:(CADisplayLink *)link {
    if (_lastTime == 0) {
        _lastTime = link.timestamp;
        return;
    }
    
    self.count++;
    NSTimeInterval delta = link.timestamp - _lastTime;
    if (delta < 1) return;
    _lastTime = link.timestamp;
    _fps = _count / delta;
    NSLog(@"count = %d, delta = %f,_lastTime = %f, _fps = %.0f",_count, delta, _lastTime, _fps);
    self.count = 0;
    _fpsLbe.text = [NSString stringWithFormat:@"FPS:%.0f",_fps];
}

监听count值的改变:

#pragma mark - observer
- (void)addObserver {
    [self addObserver:self forKeyPath:@"count" 
    options:NSKeyValueObservingOptionNew | NSKeyValueObservingOptionOld context:nil];
}

- (void)observeValueForKeyPath:(NSString *)keyPath ofObject:(id)object 
        change:(NSDictionary<NSKeyValueChangeKey,id> *)change context:(void *)context {
    NSLog(@"count new = %@, old = %@",
    [change valueForKey:@"new"], 
    [change valueForKey:@"old"]);
}

方法二：核心代码如下（运行结果和方法一差不多。）

- (void)startFpsMonitoring {
    _link = [CADisplayLink displayLinkWithTarget: self selector: @selector(displayFps:)];
    [_link addToRunLoop: [NSRunLoop mainRunLoop] forMode: NSRunLoopCommonModes];
}

- (void)displayFps: (CADisplayLink *)fpsDisplay {
    self.count++;
    CFAbsoluteTime threshold = CFAbsoluteTimeGetCurrent() - _lastTime;
    if (threshold >= 1.0) {
        _fps = (_count / threshold);
        _lastTime = CFAbsoluteTimeGetCurrent();
        _fpsLbe.text = [NSString stringWithFormat:@"FPS:%.0f",_fps];
        self.count = 0;
        NSLog(@"count = %d,_lastTime = %f, _fps = %.0f",_count, _lastTime, _fps);
    }
}