IOS多線程編程NSThread的使用方法

2020-07-26 02:39:51

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IOS多線程編程NSThread的使用方法

NSThread是多線程的一種，有兩種方法創建子線程

（1）優點：NSThread 比GCD、NSOperation都輕量級

（2）缺點：需要自己管理線程的生命周期，線程同步。線程同步對數據的加鎖會有一定的系統開銷

第一種是隱藏創建，有以下幾種方式：

（1）多用于串行：- (id)performSelector:(SEL)aSelector withObject:(id)object;
（2）后臺執行，多用于并行：- (void)performSelectorInBackground:(SEL)aSelector withObject:(nullable id)arg;
（3）延遲執行：- (void)performSelector:(SEL)aSelector withObject:(nullable id)anArgument afterDelay:(NSTimeInterval)delay;
（4）回到主線程執行：- (void)performSelectorOnMainThread:(SEL)aSelector withObject:(nullable id)arg waitUntilDone:(BOOL)wait;
注意：
（1）通過方法" + (void)cancelPreviousPerformRequestsWithTarget:(id)aTarget selector:(SEL)aSelector object:(nullable id)anArgument; "，或"+ (void)cancelPreviousPerformRequestsWithTarget:(id)aTarget"停止執行；

示例：

//創建子線程-隱式方法

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

// 子線程-并行（后臺）  [self performSelectorInBackground:@selector(showCount:) withObject:@(41)]; [self performSelectorInBackground:@selector(showCount:) withObject:@(42)];

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

// 子線程延遲執行 [self performSelector:@selector(showCount:) withObject:@(61) afterDelay:5.0];

// 停止 [NSObject cancelPreviousPerformRequestsWithTarget:self];

第二種是顯示創建，方式如下：

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

注意：

（1）通過方法" - (void)start; "開始執行；
（2）通過方法" - (void)cancel; "停止執行；

示例：

//創建子線程-顯示方法

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

代碼示例

- (void)showCount:(NSNumber *)number {  NSInteger count = arc4random() % 1000;  count = 1000;  for (int i = 0; i < count; i++)  {   NSLog(@"第 %@ 個 i = %@", number, @(i));      // 休眠n秒再執行   [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) { //   //  // 輸出返回的狀態碼，請求成功的話為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方法啟動任務 // [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"; // 隱藏創建 // [self performSelectorInBackground:@selector(downloadImage:) withObject:imageUrl]; [self performSelectorOnMainThread:@selector(downloadImage:) withObject:imageUrl waitUntilDone:YES]; // 創建子線程-顯示方法 self.thread = [[NSThread alloc] initWithTarget:self selector:@selector(downloadImage:) object:imageUrl]; self.thread.name = @"imageDownload"; [self.thread start];