2020-09-15 技术回顾

屏幕监测帧率如何实现

A CADisplayLink object is a timer object that allows your application to synchronize its drawing to the refresh rate of the display.这是官方文档对于CADisplayLink的定义，意思就是说CADisplayLink是一个定时器（但并不继承自NSTimer），它能够让你的应用以屏幕刷新的帧率来同步更新UI，所以我们可以通过它1s内调用指定target的指定方法的次数来获得屏幕刷新的帧率，从而来判断CPU的运行状态。

使用

-(BOOL)application:(UIApplication*)application didFinishLaunchingWithOptions:(NSDictionary*)launchOptions{[CPUFpsLabel setupOnView:[[application windows]firstObject].rootViewController.view];returnYES;}

CPUFpsLabel

@interface CPUFpsLabel: UILabel

+(void)setupOnView:(UIView*)view;

-(void)start;

@end

@implementation CPUFpsLabel {

CADisplayLink*_link;

NSUInteger _count;

NSTimeInterval _lastTime;

}

+(void)setupOnView:(UIView*)view{

CGSize screenSize=[UIScreen mainScreen].bounds.size;

CPUFpsLabel*fpsLabel=[[CPUFpsLabel alloc]initWithFrame:CGRectMake(screenSize.width/2.0+25,0,50,20)];

[fpsLabel start];

[view addSubview:fpsLabel];

}

-(instancetype)initWithFrame:(CGRect)frame{

    self=[superinitWithFrame:frame];

    if(self){self.font=[UIFont boldSystemFontOfSize:12];

    self.textColor=[UIColor colorWithRed:0.33green:0.84blue:0.43alpha:1.00];

    self.backgroundColor=[UIColor clearColor];

    self.textAlignment=NSTextAlignmentCenter;

    _link=[CADisplayLink displayLinkWithTarget:selfselector:@selector(tick:)];

    [_link addToRunLoop:[NSRunLoop mainRunLoop]forMode:NSRunLoopCommonModes];

    _link.paused=YES;

    [[NSNotificationCenter     defaultCenter]addObserver:selfselector:@selector(applicationDidBecomeActiveNotification) name:UIApplicationDidBecomeActiveNotification object:nil];

    [[NSNotificationCenter     defaultCenter]addObserver:selfselector:@selector(applicationWillResignActiveNotification)name:UIAppli    cationWillResignActiveNotification object:nil];

    }

    returnself;

}

- (void)dealloc{

    [_link invalidate];

    [_link removeFromRunLoop:[NSRunLoop mainRunLoop]forMode:NSRunLoopCommonModes];

}

- (void)applicationDidBecomeActiveNotification{

    [_link setPaused:NO];

}

- (void)applicationWillResignActiveNotification{

    [_link setPaused:YES];

}

- (void)start {

    [_link setPaused:NO];

}

- (void)tick:(CADisplayLink*)link{

    if(_lastTime==0){

        _lastTime=link.timestamp;

        return;

    }

    _count++;

    NSTimeInterval delta=link.timestamp-_lastTime;

    if(delta<1)return;

    _lastTime=link.timestamp;

    floatfps=_count/delta;

    _count=0;

    NSString*fpsString=[NSString stringWithFormat:@"%zd fps",(int)round(fps)];

    self.text=fpsString;

}

@end