1.简单说明
NSOperation的作?：配合使用NSOperation和NSOperationQueue也能实现多线程编程
NSOperation和NSOperationQueue实现多线程的具体步骤：
（1）先将需要执行的操作封装到一个NSOperation对象中
（2）然后将NSOperation对象添加到NSOperationQueue中
（3）系统会?动将NSOperationQueue中的NSOperation取出来
（4）将取出的NSOperation封装的操作放到?条新线程中执?
2.NSOperation的子类
NSOperation是个抽象类,并不具备封装操作的能力,必须使?它的子类
使用NSOperation?类的方式有3种：
（1）NSInvocationOperation
（2）NSBlockOperation
（3）自定义子类继承NSOperation,实现内部相应的?法
示例代码：
- (void)viewDidLoad { [super viewDidLoad]; NSInvocationOperation *operation = [[NSInvocationOperation alloc]initWithTarget:self selector:@selector(thread1) object:nil]; [operation start]; NSInvocationOperation *operation2 = [[NSInvocationOperation alloc]initWithTarget:self selector:@selector(thread2) object:nil]; [operation2 start]; }-(void)thread1{ NSLog(@"currentThread = %@",[NSThread currentThread]);}-(void)thread2{ NSLog(@"currentThread2 = %@",[NSThread currentThread]);}
currentThread = <NSThread: 0x17406d780>{number = 1, name = main}currentThread2 = <NSThread: 0x17406d780>{number = 1, name = main}
可以看见，并没有开启新的线程.
注意：操作对象默认在主线程中执行，只有添加到队列中才会开启新的线程。即默认情况下，如果操作没有放到队列中queue中，都是同步执行。只有将NSOperation放到一个NSOperationQueue中,才会异步执行操作
NSBlockOperation *operation3 = [NSBlockOperation blockOperationWithBlock:^{ NSLog(@"operation = %@",[NSThread currentThread]); }]; [operation3 start];看打印结果：operation = <NSThread: 0x1700728c0>{number = 1, name = main}
注意：只要NSBlockOperation封装的操作数 > 1,就会异步执行操作
例如：
NSBlockOperation *operation3 = [NSBlockOperation blockOperationWithBlock:^{ NSLog(@"operation = %@",[NSThread currentThread]); }]; [operation3 addExecutionBlock:^{ NSLog(@"operation2 = %@",[NSThread currentThread]); }]; [operation3 start];然后看打印结果：operation = <NSThread: 0x1700706c0>{number = 1, name = main}operation2 = <NSThread: 0x170075a40>{number = 4, name = (null)}
NSOperationQueue的作?：NSOperation可以调?start?法来执?任务,但默认是同步执行的
如果将NSOperation添加到NSOperationQueue(操作队列)中,系统会自动异步执行NSOperation中的操作
添加操作到NSOperationQueue中，自动执行操作，自动开启线程
示例：
- (void)viewDidLoad { [super viewDidLoad]; NSInvocationOperation *operation1 = [[NSInvocationOperation alloc]initWithTarget:self selector:@selector(thread1) object:nil]; NSInvocationOperation *operation2 = [[NSInvocationOperation alloc]initWithTarget:self selector:@selector(thread2) object:nil]; NSBlockOperation *operation3 = [NSBlockOperation blockOperationWithBlock:^{ NSLog(@"currentThread3 = %@",[NSThread currentThread]); }]; [operation3 addExecutionBlock:^{ NSLog(@"currentThread3_1 = %@",[NSThread currentThread]); }]; NSOperationQueue *queue = [[NSOperationQueue alloc]init]; //把操作添加到队列中 //第一种方式 [queue addOperation:operation1]; [queue addOperation:operation2]; [queue addOperation:operation3]; //第二种方式 [queue addOperationWithBlock:^{ NSLog(@"currentThread4 = %@",[NSThread currentThread]); }]; }-(void)thread1{ NSLog(@"currentThread1 = %@",[NSThread currentThread]);}-(void)thread2{ NSLog(@"currentThread2 = %@",[NSThread currentThread]);}
查看结果：
currentThread1 = <NSThread: 0x17006f440>{number = 4, name = (null)}currentThread2 = <NSThread: 0x17007d9c0>{number = 5, name = (null)}currentThread3_1 = <NSThread: 0x17007d9c0>{number = 5, name = (null)}currentThread3 = <NSThread: 0x17006f440>{number = 4, name = (null)}currentThread4 = <NSThread: 0x17007d9c0>{number = 5, name = (null)}
