IOS多线程编程NSThread的使用方法

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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