NSOperation常见用法

一提到多线程，脑海中大致会出现三种常用的方法NSThread,NSOperation,GCD。可是...你还在用GCD吗？看看基于GCD封装的NSOperation吧，更加的面相对象，方便阅读。
然鹅...... NSOperation是抽象基类。
老爹难使唤，只能使唤他的俩儿子NSInvocationOperation和NSBlockOperation。来来来，上demo。

NSInvocationOperation

-(void)InvocationOperation
{
    NSInvocationOperation *invo = [[NSInvocationOperation alloc]initWithTarget:self selector:@selector(testInvocation) object:nil];
    //记得手动start啊！
    [invo start];
}

-(void)testInvocation
{
    NSLog(@"%@",[NSThread currentThread]);
}

运行结果：可以看到，默认是在主线程的

19:05:38.346 [2689:142129] <NSThread: 0x600000071200>{number = 1, name = main}

NSBlockOperation

为了效果好一点，多来几个block试试看

-(void)BlockOperation
{
    NSBlockOperation *blockOperation = [NSBlockOperation blockOperationWithBlock:^{
        NSLog(@"1---%@",[NSThread currentThread]);
    }];
    [blockOperation addExecutionBlock:^{
        NSLog(@"2---%@",[NSThread currentThread]);
    }];
    [blockOperation addExecutionBlock:^{
        NSLog(@"3---%@",[NSThread currentThread]);
    }];
    [blockOperation addExecutionBlock:^{
        NSLog(@"4---%@",[NSThread currentThread]);
    }];
    [blockOperation addExecutionBlock:^{
        NSLog(@"5---%@",[NSThread currentThread]);
    }];
    [blockOperation addExecutionBlock:^{
        NSLog(@"6---%@",[NSThread currentThread]);
    }];
    //你手动start了嘛？！
    [blockOperation start];
}

运行结果

19:00:35.899 [2656:140762] 4---<NSThread: 0x608000078000>{number = 5, name = (null)}
19:00:35.899 [2656:140730] 1---<NSThread: 0x60800006dc00>{number = 1, name = main}
19:00:35.899 [2656:140763] 3---<NSThread: 0x608000070380>{number = 4, name = (null)}
19:00:35.899 [2656:140765] 2---<NSThread: 0x60000007ca40>{number = 3, name = (null)}
19:00:35.899 [2656:140762] 5---<NSThread: 0x608000078000>{number = 5, name = (null)}
19:00:35.899 [2656:140730] 6---<NSThread: 0x60800006dc00>{number = 1, name = main}

总结一下：
1.NSBlockOperation确实实现了多线程。但是！并非是将所有的block都放到放到了子线程中，主线程和子线程都有啊。怎么回事？
辣么，再观察线程id号：
[2656:140762]和[2656:140730]出现过两次。它会优先将block放到主线程中执行，若主线程已有待执行的代码，就开辟新的线程。
2.相同blockOperation中的代码是同步执行的。这个可以在打印的运行时间看出来19:00:35.899。

NSInvocationOperation和NSBlockOperation挺厉害啊......于是NSOperationQueue表示不服。

NSOperationQueue

-(void)OpertationQueue
{
    //invocation添加到queue的写法
    NSOperationQueue *queue = [[NSOperationQueue alloc]init];
    NSInvocationOperation *invo = [[NSInvocationOperation alloc]initWithTarget:self selector:@selector(testInvocation) object:nil];
    [queue addOperation:invo];
    
    //block添加到queue的方法
    NSBlockOperation *blockOperation = [NSBlockOperation blockOperationWithBlock:^{
        NSLog(@"blockOperation---%@",[NSThread currentThread]);
    }];
    [queue addOperation:blockOperation];
    
    //更简单的方法，直接添加
    [queue addOperationWithBlock:^{
        NSLog(@"addOperationWithBlock---%@",[NSThread currentThread]);
    }];
}

运行结果：可以看到三个线程异步执行
1.直接add到NSOperationQueue就可以，不需要手动startNSOperationQueue会在合适的时机自动调用。
2.add到NSOperationQueue之后，会自动到子线程中。

20:20:25.095 [2971:164505] <NSThread: 0x60800007de00>{number = 3, name = (null)}
20:20:25.095 [2971:164519] blockOperation---<NSThread: 0x60800007de40>{number = 4, name = (null)}
20:20:25.095 [2971:164504] addOperationWithBlock---<NSThread: 0x600000079500>{number = 5, name = (null)}

......看黑板啊！
这个NSOperation还能添加依赖，控制线程的执行顺序，一句话的事儿

addDependency

-(void)addDependency{
    NSInvocationOperation *invo1 = [[NSInvocationOperation alloc]initWithTarget:self selector:@selector(test1) object:nil];
    NSInvocationOperation *invo2 = [[NSInvocationOperation alloc]initWithTarget:self selector:@selector(test2) object:nil];
    NSOperationQueue *queue = [[NSOperationQueue alloc]init];
    [invo1 addDependency:invo2];
    [queue addOperation:invo1];
    [queue addOperation:invo2];
}

-(void)test1
{
    NSLog(@"invo1---%@",[NSThread currentThread]);
}

-(void)test2
{
    NSLog(@"invo2---%@",[NSThread currentThread]);
}

运行结果：设置了invo1依赖于invo2，运行几遍都是这个顺序了

20:40:14.201 [3207:175388] invo2---<NSThread: 0x60800006fe00>{number = 3, name = (null)}
20:40:14.202 [3207:175389] invo1---<NSThread: 0x608000070640>{number = 4, name = (null)}

⚠️warning
1.不要循环依赖，不然会循环引用。
2.如果想混合使用invocaiton和block，多上点心。
3.依赖无国界，不同队列的NSOperation对象设置的依赖关系。

优先级和依赖关系的区别

看看Foundation---NSOperation.h你会发现可以直接设置优先级。Bu t！优先级和依赖关系是有区别的：优先级不能替代依赖关系,优先级只是对已经准备好的 operations确定执行顺序。先满足依赖关系,然后再根据优先级从所有准备好的操作中选择优先级最高的那个执行。

typedef NS_ENUM(NSInteger, NSOperationQueuePriority) {
    NSOperationQueuePriorityVeryLow = -8L,
    NSOperationQueuePriorityLow = -4L,
    NSOperationQueuePriorityNormal = 0,
    NSOperationQueuePriorityHigh = 4,
    NSOperationQueuePriorityVeryHigh = 8
};

其他可能用到的属性

setMaxConcurrentOperationCount; //设置最大并发数
[queue setSuspended:YES]; //暂停队列
[queue setSuspended:NO]; //继续队列
[operation waitUntilFinished]; //会阻塞当前线程，等到某个operation执行完毕
[queue waitUntilAllOperationsAreFinished]; //阻塞当前线程，等待queue的所有操作执行完毕
所以。。。有木有发现是基于GCD封装的