一，NSOperation简介
1，NSOperation是一个抽象类，需要使用子类实现具体的功能。
2，NSOperation是基于GCD的面相对象封装。
3，不需要关心线程管理，数据同步的事情，可以把精力放在自己需要执行的操作上。
二，NSOperation优势
1，可以设置最大并发数
2，可以设置线程间的依赖关系
3，可以设置优先级
4，可以暂停、继续、取消
5，可以监听属性的变化
三，两个核心概念
1，Operation（操作）：NSInvocationOperation，NSBlockOperation，自定义子类
2，queue（队列）：NSOperationQueue
四，NSOperation使用：
NSBlockOperation
1，简介
NSBlockOperation类是NSOperation的一个具体子类，用于管理一个或多个块的并发执行。您可以使用这个对象一次执行多个块，而不必为每个块创建单独的操作对象。当执行多个块时，只有当所有块都已完成执行时，才认为操作本身已完成。
添加到block operation的块将以默认优先级分派到适当的工作队列。块本身不应该对其执行环境的配置做出任何假设。
2，方法
//创建并返回一个NSBlockOperation对象，并将指定的块添加到它。
blockOperationWithBlock:
//将指定的块添加到接收者要执行的块列表中。
addExecutionBlock:
3，属性
//与接收器相关联的块
executionBlocks
4，使用方法
blockOperationWithBlock方法：
NSBlockOperation *op1 = [NSBlockOperation blockOperationWithBlock:^{
NSLog(@"---1--%@---", [NSThread currentThread]);
}];
NSBlockOperation *op2 = [NSBlockOperation blockOperationWithBlock:^{
NSLog(@"---2--%@---", [NSThread currentThread]);
}];
NSBlockOperation *op3 = [NSBlockOperation blockOperationWithBlock:^{
NSLog(@"---3--%@---", [NSThread currentThread]);
}];
[op1 start];
[op2 start];
[op3 start];
始终打印：
2021-09-08 13:41:05.836798+0800 OperationTest[35466:17354403] ---1--<NSThread: 0x2807f0900>{number = 1, name = main}---
2021-09-08 13:41:05.836886+0800 OperationTest[35466:17354403] ---2--<NSThread: 0x2807f0900>{number = 1, name = main}---
2021-09-08 13:41:05.836927+0800 OperationTest[35466:17354403] ---3--<NSThread: 0x2807f0900>{number = 1, name = main}---
解析：
使用NSBlockOperation类方法blockOperationWithBlock创建的多个任务，会按照调用实例方法start的顺序，在当前线程同步执行。
addExecutionBlock方法：
NSBlockOperation *op1 = [NSBlockOperation blockOperationWithBlock:^{
NSLog(@"---1--%@---", [NSThread currentThread]);
}];
//NSBlockOperation *op1 = [[NSBlockOperation alloc] init];
[op1 addExecutionBlock:^{
NSLog(@"---1.1--%@---", [NSThread currentThread]);
}];
[op1 addExecutionBlock:^{
NSLog(@"---1.2--%@---", [NSThread currentThread]);
}];
[op1 addExecutionBlock:^{
NSLog(@"---1.3--%@---", [NSThread currentThread]);
}];
[op1 addExecutionBlock:^{
NSLog(@"---1.4--%@---", [NSThread currentThread]);
}];
NSBlockOperation *op2 = [NSBlockOperation blockOperationWithBlock:^{
NSLog(@"---2--%@---", [NSThread currentThread]);
}];
//NSBlockOperation *op2 = [[NSBlockOperation alloc] init];
[op2 addExecutionBlock:^{
NSLog(@"---2.1--%@---", [NSThread currentThread]);
}];
[op2 addExecutionBlock:^{
NSLog(@"---2.2--%@---", [NSThread currentThread]);
}];
NSBlockOperation *op3 = [NSBlockOperation blockOperationWithBlock:^{
NSLog(@"---3--%@---", [NSThread currentThread]);
}];
//NSBlockOperation *op3 = [[NSBlockOperation alloc] init];
[op3 addExecutionBlock:^{
NSLog(@"---3.1--%@---", [NSThread currentThread]);
}];
[op3 addExecutionBlock:^{
NSLog(@"---3.2--%@---", [NSThread currentThread]);
}];
[op1 start];
[op2 start];
[op3 start];
打印：
第一次打印
2021-09-08 14:00:05.085719+0800 OperationTest[35494:17363182] ---1--<NSThread: 0x281074900>{number = 1, name = main}---
2021-09-08 14:00:05.085730+0800 OperationTest[35494:17363382] ---1.1--<NSThread: 0x28103c2c0>{number = 5, name = (null)}---
2021-09-08 14:00:05.085802+0800 OperationTest[35494:17363182] ---1.3--<NSThread: 0x281074900>{number = 1, name = main}---
2021-09-08 14:00:05.085803+0800 OperationTest[35494:17363382] ---1.2--<NSThread: 0x28103c2c0>{number = 5, name = (null)}---
2021-09-08 14:00:05.085850+0800 OperationTest[35494:17363380] ---1.4--<NSThread: 0x28103d940>{number = 3, name = (null)}---
2021-09-08 14:00:05.085901+0800 OperationTest[35494:17363182] ---2--<NSThread: 0x281074900>{number = 1, name = main}---
2021-09-08 14:00:05.085912+0800 OperationTest[35494:17363380] ---2.1--<NSThread: 0x28103d940>{number = 3, name = (null)}---
2021-09-08 14:00:05.085955+0800 OperationTest[35494:17363383] ---2.2--<NSThread: 0x281038280>{number = 7, name = (null)}---
2021-09-08 14:00:05.086049+0800 OperationTest[35494:17363182] ---3--<NSThread: 0x281074900>{number = 1, name = main}---
2021-09-08 14:00:05.086052+0800 OperationTest[35494:17363383] ---3.1--<NSThread: 0x281038280>{number = 7, name = (null)}---
2021-09-08 14:00:05.086082+0800 OperationTest[35494:17363380] ---3.2--<NSThread: 0x28103d940>{number = 3, name = (null)}---
第n次打印
2021-09-08 14:05:55.583552+0800 OperationTest[35504:17365839] ---1.1--<NSThread: 0x28350cc40>{number = 6, name = (null)}---
2021-09-08 14:05:55.583598+0800 OperationTest[35504:17365837] ---1.2--<NSThread: 0x28350cf40>{number = 5, name = (null)}---
2021-09-08 14:05:55.583545+0800 OperationTest[35504:17365827] ---1--<NSThread: 0x28354c900>{number = 1, name = main}---
2021-09-08 14:05:55.583660+0800 OperationTest[35504:17365842] ---1.4--<NSThread: 0x28350d100>{number = 3, name = (null)}---
2021-09-08 14:05:55.583671+0800 OperationTest[35504:17365838] ---1.3--<NSThread: 0x283500240>{number = 7, name = (null)}---
2021-09-08 14:05:55.583723+0800 OperationTest[35504:17365827] ---2--<NSThread: 0x28354c900>{number = 1, name = main}---
2021-09-08 14:05:55.583734+0800 OperationTest[35504:17365838] ---2.1--<NSThread: 0x283500240>{number = 7, name = (null)}---
2021-09-08 14:05:55.583759+0800 OperationTest[35504:17365827] ---2.2--<NSThread: 0x28354c900>{number = 1, name = main}---
2021-09-08 14:05:55.583897+0800 OperationTest[35504:17365827] ---3--<NSThread: 0x28354c900>{number = 1, name = main}---
2021-09-08 14:05:55.583916+0800 OperationTest[35504:17365838] ---3.1--<NSThread: 0x283500240>{number = 7, name = (null)}---
2021-09-08 14:05:55.583933+0800 OperationTest[35504:17365842] ---3.2--<NSThread: 0x28350d100>{number = 3, name = (null)}---
解析：
1，使用方法blockOperationWithBlock添加的任务都在当前线程中执行。
2，使用方法addExecutionBlock追加的任务可能在当前线程中执行，也可能在新开的线程中执行。
3，单个NSBlockOperation中有多个任务的话会开启新线程并发执行。
4，多个NSBlockOperation会按照调用start方法的顺序同步执行。(op1中任务执行完，才开始执行op2的任务，以此类推)。
NSInvocationOperation
1，简介
NSInvocationOperation类是NSOperation的一个具体子类，管理指定为调用的单个封装任务的执行的操作。可以初始化一个调用指定对象上的选择器的操作。NSInvocationOperation实现了一个非并发操作。
2，方法
//返回使用指定目标和选择器初始化的NSInvocationOperation对象。
initWithTarget:selector:object:
//返回一个由指定的调用对象初始化的NSInvocationOperation对象。
initWithInvocation:
3，使用方法
NSInvocationOperation *op1 = [[NSInvocationOperation alloc] initWithTarget:self selector:@selector(operation1:) object:@"first"];
NSInvocationOperation *op2 = [[NSInvocationOperation alloc] initWithTarget:self selector:@selector(operation2:) object:@"second"];
NSInvocationOperation *op3 = [[NSInvocationOperation alloc] initWithTarget:self selector:@selector(operation3:) object:@"third"];
[op1 start];
[op2 start];
[op3 start];
- (void)operation1:(id)obj {
NSLog(@"---1--%@--%@---", obj, [NSThread currentThread]);
}
- (void)operation2:(id)obj {
NSLog(@"---2--%@--%@---", obj, [NSThread currentThread]);
}
- (void)operation3:(id)obj {
NSLog(@"---3--%@--%@---", obj, [NSThread currentThread]);
}
打印：
2021-09-08 14:41:41.399288+0800 OperationTest[35516:17375314] ---1--first--<NSThread: 0x281c78900>{number = 1, name = main}---
2021-09-08 14:41:41.399381+0800 OperationTest[35516:17375314] ---2--second--<NSThread: 0x281c78900>{number = 1, name = main}---
2021-09-08 14:41:41.399427+0800 OperationTest[35516:17375314] ---3--third--<NSThread: 0x281c78900>{number = 1, name = main}---
解析：
NSInvocationOperation不会开启新线程，默认在当前线程（执行该方法的线程）中同步执行。
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