iOS多线程NSOperation的使用

NSOperation是iOS中一种多线程技术的实现，基于GCD，比GCD更加面向对象，和类NSOperationQueue配合使用。NSOperation是一个抽象类，我们不能直接使用它，应该使用它的子类NSInvocationOperation或者NSBlockOperation。

NSInvocationOperation

当我们有需要在子线程中执行的方法时，使用NSInvocationOperation比较方便。

NSInvocationOperation *oper1 = [[NSInvocationOperation alloc] initWithTarget:self selector:@selector(run) object:nil];/* 1.放到队列中的操作都是在子线程中执行 * 2.如果不做特殊操作依赖，队列中的操作都是并发的 */NSOperationQueue *queue = [[NSOperationQueue alloc] init];// 主线程队列NSOperationQueue *mainQueue = [NSOperationQueue mainQueue];// 设置队列最大并发数queue.maxConcurrentOperationCount = 4;// 把Operation添加到队列中，系统会自动取出队列中的Operation放到子线程中执行[queue addOperation:oper1];- (void)run {    NSLog(@"正在下载图片1----%@",[NSThread currentThread]);}// 2015-12-26 23:00:48.854 NSOperation学习[8816:1300341] 正在下载图片1----<NSThread: 0x7fbc50c18270>{number = 2, name = (null)}

NSBlockOperation

把要在子线程中执行的代码放到Block中。

NSBlockOperation *oper2 = [NSBlockOperation blockOperationWithBlock:^{    NSLog(@"正在下载图片2----%@",[NSThread currentThread]);}];NSBlockOperation *oper3 = [NSBlockOperation blockOperationWithBlock:^{    NSLog(@"正在下载图片3----%@",[NSThread currentThread]);}];NSOperationQueue *queue = [[NSOperationQueue alloc] init];queue.maxConcurrentOperationCount = 4;[queue addOperation:oper2];[queue addOperation:oper3];/*2015-12-26 23:17:09.399 NSOperation学习[8838:1309995] 正在下载图片2----<NSThread: 0x7fdeaaf11d30>{number = 2, name = (null)}2015-12-26 23:17:09.399 NSOperation学习[8838:1309994] 正在下载图片3----<NSThread: 0x7fdeaaf2d440>{number = 3, name = (null)}*/

Operation中的依赖关系

NSOperationQueue *queue = [[NSOperationQueue alloc] init];NSBlockOperation *oper1 = [NSBlockOperation blockOperationWithBlock:^{    NSLog(@"正在下载图片1----%@",[NSThread currentThread]);}];[oper1 setCompletionBlock:^{    /*      * 当oper1执行完毕时执行这个block中的代码，这个block所在的线程不是     * 主线程，可能与oper1所在线程一样，也可能不一样。     *     */    NSLog(@"完成下载图片1----%@",[NSThread currentThread]);}];NSBlockOperation *oper2 = [NSBlockOperation blockOperationWithBlock:^{    NSLog(@"正在下载图片2----%@",[NSThread currentThread]);}];NSBlockOperation *oper3 = [NSBlockOperation blockOperationWithBlock:^{    NSLog(@"正在下载图片3----%@",[NSThread currentThread]);}];// oper3依赖oper1，只有1执行完成之后才能执行3[oper3 addDependency:oper1];// oper3依赖oper2[oper3 addDependency:oper2];[queue addOperation:oper1];[queue addOperation:oper2];[queue addOperation:oper3];/*2015-12-27 01:04:10.575 NSOperation学习[9003:1333576] 正在下载图片1----<NSThread: 0x7ff9e1c33970>{number = 2, name = (null)}2015-12-27 01:04:10.575 NSOperation学习[9003:1333577] 正在下载图片2----<NSThread: 0x7ff9e1f1eba0>{number = 3, name = (null)}2015-12-27 01:04:10.576 NSOperation学习[9003:1333579] 完成下载图片1----<NSThread: 0x7ff9e1d3a7b0>{number = 4, name = (null)}2015-12-27 01:04:10.576 NSOperation学习[9003:1333577] 正在下载图片3----<NSThread: 0x7ff9e1f1eba0>{number = 3, name = (null)}*/