iOS NSOperation 子类实现及并发执行

浏览数：23 / 时间：2015年06月11日

上一节《iOS NSOperation 非并发执行》中已经讲了NSOperation中系统提供的子类NSBlockOperation和NSInvocationOperation的任务的非并发执行，以及添加到NSOperationQueue中进行并发执行。这节将NSOperation 子类实现以及并发执行。

NSOperation非并发子类实现，只需重盖main方法，将要执行的任务放到main方法中，在main方法中要做cancel判断的，如下例：

@interface MyNonConcurrentOperation : NSOperation
@property (strong) id myData;
- (id)initWithData:(id)data;

@end

@implementation MyNonConcurrentOperation
- (id)initWithData:(id)data
{
    if (self = [super init])
    {
        _myData = data;
    }
    return self;
}

- (void)main
{
    @try {
        BOOL isDone = NO;

        while (![self isCancelled] && !isDone) {
            // Do some work and set isDone to YES when finished
        }
    }
    @catch(...) {
        // Do not rethrow exceptions.
    }
}

@end

NSOperation 并发子类实现，必须覆盖 start、isConcurrent、isExecuting和isFinished四个方法，main方法可选

@interface MyOperation : NSOperation {
BOOL executing;
BOOL finished;
}
- (void)completeOperation;

@end

@implementation MyOperation
- (id)init {
    self = [super init];
    if (self) {
        executing = NO;
        finished = NO;
    }
    return self;
}

- (BOOL)isConcurrent {
    return YES;
}

- (BOOL)isExecuting {
    return executing;
}

- (BOOL)isFinished {
    return finished;
}

- (void)start {
    // Always check for cancellation before launching the task.
    if ([self isCancelled])
    {
        // Must move the operation to the finished state if it is canceled.
        [self willChangeValueForKey:@"isFinished"];
        finished = YES;
        [self didChangeValueForKey:@"isFinished"];
        return;
    }

    // If the operation is not canceled, begin executing the task.
    [self willChangeValueForKey:@"isExecuting"];
    [NSThread detachNewThreadSelector:@selector(main) toTarget:self withObject:nil];
    executing = YES;
    [self didChangeValueForKey:@"isExecuting"];
}

- (void)main {
    @try {

        // Do the main work of the operation here.

        [self completeOperation];
    }
    @catch(...) {
        // Do not rethrow exceptions.
    }
}

- (void)completeOperation {
    [self willChangeValueForKey:@"isFinished"];
    [self willChangeValueForKey:@"isExecuting"];

    executing = NO;
    finished = YES;

    [self didChangeValueForKey:@"isExecuting"];
    [self didChangeValueForKey:@"isFinished"];
}

@end

NSOperation 的属性添加了KVO机制，当我们覆盖属性的getter方法，按我们指定的状态返回，所以在状态改变时要发起KVO通知，通知监听次属性的对象。在start方法中使用NSThread 开启了新线程实现并发执行。

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iOS NSOperation 子类实现及并发执行