iOS多线程编程NSThread的使用

NSThread是多线程的一种，有两种方法创建子线程

（1）优点：NSThread 比GCD、NSOperation都轻量级

（2）缺点：需要自己管理线程的生命周期，线程同步。线程同步对数据的加锁会有一定的系统开销

第一种是隐藏创建，有以下几种方式：

（1）多用于串行：- (id)performSelector:(SEL)aSelector withObject:(id)object;

（2）后台执行，多用于并行：- (void)performSelectorInBackground:(SEL)aSelector withObject:(nullable id)arg;

（3）延迟执行：- (void)performSelector:(SEL)aSelector withObject:(nullable id)anArgument afterDelay:(NSTimeInterval)delay;

（4）回到主线程执行：- (void)performSelectorOnMainThread:(SEL)aSelector withObject:(nullable id)arg waitUntilDone:(BOOL)wait;

注意：

（1）通过方法" + (void)cancelPreviousPerformRequestsWithTarget:(id)aTarget selector:(SEL)aSelector object:(nullable id)anArgument;

 "，或"+ (void)cancelPreviousPerformRequestsWithTarget:(id)aTarget"停止执行；

 

示例：

//创建子线程-隐式方法

 // 子线程-串行 [self performSelector:@selector(showCount:) withObject:@(11)]; [self performSelector:@selector(showCount:) withObject:@(12)]; [self performSelector:@selector(showCount:) withObject:@(23)];

 // 子线程-并行（后台） [self performSelectorInBackground:@selector(showCount:) withObject:@(41)]; [self performSelectorInBackground:@selector(showCount:) withObject:@(42)];

 // 回到主线程 [self performSelectorOnMainThread:@selector(showCount:) withObject:@(51) waitUntilDone:YES];

 // 子线程延迟执行 [self performSelector:@selector(showCount:) withObject:@(61) afterDelay:5.0];

 // 停止 [NSObject cancelPreviousPerformRequestsWithTarget:self];

 第二种是显示创建，方式如下：

 - (instancetype)initWithTarget:(id)target selector:(SEL)selector object:(nullable id)argument;

 

注意：

 （1）通过方法" - (void)start; "开始执行；

 （2）通过方法" - (void)cancel; "停止执行； 

 

 示例：

 //创建子线程-显示方法

 self.thread = [[NSThread alloc] initWithTarget:self selector:@selector(showCount:) object:@(61)]; self.thread.name = @"计数"; [self.thread start]; [self.thread cancel];

代码示例

- (void)showCount:(NSNumber *)number{    NSInteger count = arc4random() % 1000;    count = 1000;    for (int i = 0; i < count; i++)    {        NSLog(@"第 %@ 个 i = %@", number, @(i));                // 休眠n秒再执行        [NSThread sleepForTimeInterval:0.2];                // 停止//        BOOL isStop = [self.thread isCancelled];//        if (isStop)//        {//            NSLog(@"2 停止");//            break;//        }        if (isCancelThread)        {            NSLog(@"2 停止");            break;        }    }}

bool isCancelThread = NO;- (void)stopClick{    [NSObject cancelPreviousPerformRequestsWithTarget:self];        if (self.thread)    {        BOOL isExecuting = [self.thread isExecuting];        if (isExecuting)        {            NSLog(@"1 停止");//            [self.thread cancel];            isCancelThread = YES;        }    }}

- (void)downloadImage:(NSString *)imageUrl{    NSURL *url = [NSURL URLWithString:imageUrl];    NSData *data = [[NSData alloc] initWithContentsOfURL:url];    UIImage *image = [[UIImage alloc] initWithData:data];    if (image == nil)    {            }    else    {//        [self performSelectorOnMainThread:@selector(updateImage:) withObject:image waitUntilDone:YES];        [self performSelectorInBackground:@selector(updateImage:) withObject:image];    }    //    NSURL *url = [NSURL URLWithString:imageUrl];//    NSURLRequest *request = [NSURLRequest requestWithURL:url];//    NSURLSession *session = [NSURLSession sharedSession];//    NSURLSessionDataTask *dataTask = [session dataTaskWithRequest:request completionHandler: ^(NSData *data, NSURLResponse *response, NSError *error) {//        //        // 输出返回的状态码，请求成功的话为200//        NSHTTPURLResponse *httpResponse = (NSHTTPURLResponse *)response;//        NSInteger responseStatusCode = [httpResponse statusCode];//        NSLog(@"%ld", responseStatusCode);//        //        UIImage *image = [UIImage imageWithData:data];////        [self performSelectorOnMainThread:@selector(updateImage:) withObject:image waitUntilDone:YES];//        [self performSelectorInBackground:@selector(updateImage:) withObject:image];//    }];//    //    // 使用resume方法启动任务//    [dataTask resume];}

- (void)updateImage:(UIImage *)image{    self.imageview.image = image;    //    self.imageview = [[UIImageView alloc] initWithFrame:CGRectMake(10.0, 10.0, (CGRectGetWidth(self.view.bounds) - 10.0 * 2), (CGRectGetWidth(self.view.bounds) - 10.0 * 2))];//    [self.view addSubview:self.imageview];//    self.imageview.backgroundColor = [UIColor colorWithWhite:0.5 alpha:0.2];//    //    self.imageview.image = image;}

NSString *imageUrl = @"http://ww1.sinaimg.cn/crop.0.0.1242.1242.1024/763fb12bjw8empveq3eq8j20yi0yiwhw.jpg";// 隐藏创建// [self performSelectorInBackground:@selector(downloadImage:) withObject:imageUrl];[self performSelectorOnMainThread:@selector(downloadImage:) withObject:imageUrl waitUntilDone:YES];// 创建子线程-显示方法self.thread = [[NSThread alloc] initWithTarget:self selector:@selector(downloadImage:) object:imageUrl];self.thread.name = @"imageDownload";[self.thread start];