多线程技术：NSOperation 与 NSOperationQ

重写start方法来自定义NSOpeartion

1. 子类化视图控制器

@interface MyOperation : NSOperation

@end

2. 子类为原来的executing属性和finished属性添加setter方法和设置属性名

@interface MyOperation()
@property (assign, readonly, getter=isExecuting) BOOL executing;
@property (assign, readonly, getter=isFinished) BOOL finished;
@end

@implementation MyOperation
@synthesize executing = _executing;
@synthesize finished = _finished;
@end

3. 重写setter方法,手动发送kvo监听executing的getter方法isExecuting和finished的isFinished。

- (void)setFinished:(BOOL)finished {
    [self willChangeValueForKey:@"isFinished"];
    _finished = finished;
    [self didChangeValueForKey:@"isFinished"];
}

- (void)setExecuting:(BOOL)executing {
    [self willChangeValueForKey:@"isExecuting"];
    _executing = executing;
    [self didChangeValueForKey:@"isExecuting"];


}

4.开始执行的时候设置 self.finished = NO; self.executing = YES; 结束的时候设置 self.finished = YES; self.executing = NO

5.和main方法一样，添加self.isCanceled判断

Demo

#import "MyOperation.h"
@interface MyOperation()
@property (assign, readonly, getter=isExecuting) BOOL executing;
@property (assign, readonly, getter=isFinished) BOOL finished;
@end

@implementation MyOperation

@synthesize executing = _executing;
@synthesize finished = _finished;

- (void)start {
    if (self.isCancelled) {
        self.finished = YES;
        self.executing = NO;
    }
    self.finished = NO;
    self.executing = YES;
    [self doSomething];

}

- (void)doSomething {
    for (NSInteger i = 0; i < 100; i++) {
        NSLog(@"%ld", i);
    }
    self.finished = YES;
    self.executing = NO;

}

- (void)setFinished:(BOOL)finished {
    [self willChangeValueForKey:@"isFinished"];
    _finished = finished;
    [self didChangeValueForKey:@"isFinished"];
}

- (void)setExecuting:(BOOL)executing {
    [self willChangeValueForKey:@"isExecuting"];
    _executing = executing;
    [self didChangeValueForKey:@"isExecuting"];


}
@end

start与main方法区别

前者比后者更加灵活，通过operation标记状态来告知queue是否要将自己移除，在start中开了新线程后，可以在新线程的方法中标记状态。而main一定是main```执行完后自动从队列中移除。