IOS多线程编程NSThread的使用方法

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];

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