iOS学习笔记-119.多线程18——NSOperationQueue自定义NSOperation执行一个操作的取消

多线程18——NSOperationQueue自定义NSOperation执行一个操作的取消

一、场景说明

我们创建自定义了一个 NSOperation 它里面执行多个耗时任务，根据我们前面的知识，只有这个操作执行完了，我们才能取消。现在我希望是有三个耗时的任务，任务1执行完了能够取消，任务2执行完了也能取消。那么我们需要怎么实现呢？？？

其实很简单啦。我们只需要在任务1执行完了判断一下，当前的任务是否已经取消了，取消了那么返回，没有取消那么继续。

---

二、代码示例

2.1 QWMOperation2.m

////  QWMOperation2.m//  03_UIview85多线程_NSOperation////  Created by 杞文明 on 17/9/4.//  Copyright © 2017年 杞文明. All rights reserved.//#import "QWMOperation2.h"@implementation QWMOperation2-(void)main{    //3个耗时操作    //耗时任务 1    for (NSInteger i = 0; i<1000;i++ ) {        NSLog(@"download1---%zd--%@",i,[NSThread currentThread]);    }    //苹果官方的建议:每执行完一小段耗时操作的时候判断当前操作时候被取消    if(self.isCancelled)return;    NSLog(@"+++++++++++++++");    //耗时任务 2    for (NSInteger i = 0; i<1000;i++ ) {        NSLog(@"download2---%zd--%@",i,[NSThread currentThread]);    }    if(self.isCancelled)return;    NSLog(@"+++++++++++++++");    //耗时任务 3    for (NSInteger i = 0; i<1000;i++ ) {        NSLog(@"download3---%zd--%@",i,[NSThread currentThread]);    }}@end

2.2 代码示例

- (IBAction)startClick:(id)sender {    if(_queue==nil){        _queue = [[NSOperationQueue alloc]init];        _queue.maxConcurrentOperationCount = 1;    }    [self test2];}- (IBAction)cancelClick:(id)sender {    //取消,不可以恢复    //该方法内部调用了所有操作的cancel方法    [self.queue cancelAllOperations];}-(void)test2{    QWMOperation2 *op = [[QWMOperation2 alloc]init];    [self.queue addOperation:op];}

---

三、运行结果

[26503:132215] download1---0--<NSThread: 0x608000071880>{number = 5, name = (null)}[26503:132215] download1---1--<NSThread: 0x608000071880>{number = 5, name = (null)}[26503:132215] download1---2--<NSThread: 0x608000071880>{number = 5, name = (null)}......[26503:132215] download1---997--<NSThread: 0x608000071880>{number = 5, name = (null)}[26503:132215] download1---998--<NSThread: 0x608000071880>{number = 5, name = (null)}[26503:132215] download1---999--<NSThread: 0x608000071880>{number = 5, name = (null)}[26503:132215] +++++++++++++++[26503:132215] download2---0--<NSThread: 0x608000071880>{number = 5, name = (null)}[26503:132215] download2---1--<NSThread: 0x608000071880>{number = 5, name = (null)}[26503:132215] download2---2--<NSThread: 0x608000071880>{number = 5, name = (null)}......[26503:132215] download2---997--<NSThread: 0x608000071880>{number = 5, name = (null)}[26503:132215] download2---998--<NSThread: 0x608000071880>{number = 5, name = (null)}[26503:132215] download2---999--<NSThread: 0x608000071880>{number = 5, name = (null)}