iOS 开发多线程 —— NSOperation
本文是根据文顶顶老师的博客学习而来,转载地址:http://www.cnblogs.com/wendingding/p/3809042.html
一、NSOperation简介
1.简单说明
NSOperation的作⽤: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)系统会⾃动将NSOperationQueue中的NSOperation取出来
(4)将取出的NSOperation封装的操作放到⼀条新线程中执⾏
2.NSOperation的子类
NSOperation是个抽象类,并不具备封装操作的能力,必须使⽤它的子类
使用NSOperation⼦类的方式有3种:
(1)NSInvocationOperation
(2)NSBlockOperation
(3)自定义子类继承NSOperation,实现内部相应的⽅法
NSInvocationOperation:
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 = , name = main} currentThread2 = <NSThread: 0x17406d780>{number = , 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:
NSBlockOperation *operation3 = [NSBlockOperation blockOperationWithBlock:^{
NSLog(@"operation = %@",[NSThread currentThread]);
}];
[operation3 start]; 看打印结果:
operation = <NSThread: 0x1700728c0>{number = , 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 = , name = main}
operation2 = <NSThread: 0x170075a40>{number = , name = (null)}
NSOperationQueue:
NSOperationQueue的作⽤:NSOperation可以调⽤start⽅法来执⾏任务,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 = , name = (null)}
currentThread2 = <NSThread: 0x17007d9c0>{number = , name = (null)}
currentThread3_1 = <NSThread: 0x17007d9c0>{number = , name = (null)}
currentThread3 = <NSThread: 0x17006f440>{number = , name = (null)}
currentThread4 = <NSThread: 0x17007d9c0>{number = , name = (null)}
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