4.4 多线程进阶篇<下>（NSOperation）
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本文源码 Demo 详见 Github
https://github.com/shorfng/iOS-4.0-multithreading.git
1.0 NSOperation 的作用
使用 NSOperation 的目的就是为了让开发人员不再关心线程
- 配合使用 NSOperation(任务) 和 NSOperationQueue(队列) 也能实现多线程编程
NSOperation 和 NSOperationQueue 实现多线程的具体步骤：
（1）先将需要执行的操作封装到一个NSOperation对象中
（2）然后将NSOperation对象添加到NSOperationQueue中
（3）系统会自动将NSOperationQueue中的NSOperation取出来
（4）将取出的NSOperation封装的操作放到一条新线程中执行
使用NSOperation子类的方式有3种：
NSOperation是个抽象类，并不具备封装操作的能力，必须使用它的子类
- NSInvocationOperation
- NSBlockOperation
- 自定义子类继承NSOperation，实现内部相应的方法
2.0 NSInvocationOperation
//创建NSInvocationOperation对象
- (id)initWithTarget:(id)target selector:(SEL)sel object:(id)arg;
//调用start方法开始执行操作，一旦执行操作，就会调用target的sel方法
- (void)start;
注意：
- 默认情况下，操作对象在主线程中执行
- 调用了start方法后并不会开一条新线程去执行操作，只有添加到队列中才会开启新的线程
- 即默认情况下，如果操作没有放到队列中queue中，都是同步执行。
- 只有将NSOperation放到一个NSOperationQueue中，才会异步执行操作
代码示例：
#import "ViewController.h"
@interface ViewController ()
@end
@implementation ViewController
- (void)viewDidLoad {
[super viewDidLoad];
// Do any additional setup after loading the view, typically from a nib.
}
- (void)touchesBegan:(NSSet *)touches withEvent:(UIEvent *)event {
//创建操作对象，封装要执行的任务
NSInvocationOperation *op =
[[NSInvocationOperation alloc] initWithTarget:self
selector:@selector(run)
object:nil];
//执行操作
[op start];
}
- (void)run {
NSLog(@"------%@", [NSThread currentThread]);
}
- (void)didReceiveMemoryWarning {
[super didReceiveMemoryWarning];
// Dispose of any resources that can be recreated.
}
@end
打印结果：
NSInvocationOperation[862:29437] ------<NSThread: 0x7f9cea507920>{number = 1, name = main}
3.0 NSBlockOperation
//创建 NSBlockOperation 操作对象
+ (id)blockOperationWithBlock:(void (^)(void))block;
// 添加操作
- (void)addExecutionBlock:(void (^)(void))block;
注意：只要NSBlockOperation封装的操作数 > 1，就会异步执行操作
代码示例：
#import "ViewController.h"
@interface ViewController ()
@end
@implementation ViewController
- (void)viewDidLoad {
[super viewDidLoad];
// Do any additional setup after loading the view, typically from a nib.
}
- (void)touchesBegan:(NSSet *)touches withEvent:(UIEvent *)event {
// 1.创建 NSBlockOperation 操作对象
NSBlockOperation *op = [NSBlockOperation blockOperationWithBlock:^{
// 在主线程
NSLog(@"下载1------%@", [NSThread currentThread]);
}];
// 2.添加操作（额外的任务）（在子线程执行)
[op addExecutionBlock:^{
NSLog(@"下载2------%@", [NSThread currentThread]);
}];
[op addExecutionBlock:^{
[op addExecutionBlock:^{
NSLog(@"下载2------%@", [NSThread currentThread]);
}];
[op addExecutionBlock:^{
NSLog(@"下载3------%@", [NSThread currentThread]);
}];
[op addExecutionBlock:^{
NSLog(@"下载4------%@", [NSThread currentThread]);
}];
// 3.开启执行操作
[op start];
}
- (void)run {
NSLog(@"------%@", [NSThread currentThread]);
}
- (void)didReceiveMemoryWarning {
[super didReceiveMemoryWarning];
// Dispose of any resources that can be recreated.
}
@end
打印结果：
NSBlockOperation[1013:37922] 下载1------<NSThread: 0x7feea1c05460>{number = 1, name = main}
NSBlockOperation[1013:37952] 下载2------<NSThread: 0x7feea1f0b790>{number = 2, name = (null)}
NSBlockOperation[1013:37955] 下载3------<NSThread: 0x7feea1c0f8a0>{number = 3, name = (null)}
NSBlockOperation[1013:37951] 下载4------<NSThread: 0x7feea1e0b520>{number = 4, name = (null)}
4.0 NSOperationQueue
NSOperationQueue的作用：添加操作到NSOperationQueue中，自动执行操作，自动开启线程
- NSOperation 可以调用 start 方法来执行任务，但默认是同步执行的
- 如果将 NSOperation 添加到 NSOperationQueue（操作队列）中，系统会自动异步执行NSOperation中的操作
添加操作到 NSOperationQueue 中：2种方式
- (void)addOperation:(NSOperation *)op;
- (void)addOperationWithBlock:(void (^)(void))block NS_AVAILABLE(10_6, 4_0);
代码示例：
#import "ViewController.h"
@interface ViewController ()
@end
@implementation ViewController
- (void)viewDidLoad {
[super viewDidLoad];
// Do any additional setup after loading the view, typically from a nib.
}
- (void)touchesBegan:(NSSet *)touches withEvent:(UIEvent *)event {
[self operationQueue2];
}
#pragma mark - 把操作添加到队列中,方式1：addOperation
- (void)operationQueue1 {
// 1.创建队列
NSOperationQueue *queue = [[NSOperationQueue alloc] init];
// 2.1 方式1：创建操作（任务）NSInvocationOperation ，封装操作
NSInvocationOperation *op1 =
[[NSInvocationOperation alloc] initWithTarget:self
selector:@selector(download1)
object:nil];
// 2.2 方式2：创建NSBlockOperation ，封装操作
NSBlockOperation *op2 = [NSBlockOperation blockOperationWithBlock:^{
NSLog(@"download2 --- %@", [NSThread currentThread]);
}];
// 添加操作
[op2 addExecutionBlock:^{
NSLog(@"download3 --- %@", [NSThread currentThread]);
}];
// 3.把操作（任务）添加到队列中，并自动调用 start 方法
[queue addOperation:op1];
[queue addOperation:op2];
}
- (void)download1 {
NSLog(@"download1 --- %@", [NSThread currentThread]);
}
#pragma mark - 把操作添加到队列中,方式2：addOperationWithBlock
- (void)operationQueue2 {
// 1.创建队列
NSOperationQueue *queue = [[NSOperationQueue alloc] init];
// 2.添加操作到队列中
[queue addOperationWithBlock:^{
NSLog(@"download1 --- %@", [NSThread currentThread]);
}];
[queue addOperationWithBlock:^{
NSLog(@"download2 --- %@", [NSThread currentThread]);
}];
}
- (void)didReceiveMemoryWarning {
[super didReceiveMemoryWarning];
// Dispose of any resources that can be recreated.
}
@end
打印结果：
NSOperationQueue[1658:89517] download2 --- <NSThread: 0x7f88a9e059d0>{number = 3, name = (null)}
NSOperationQueue[1658:89518] download1 --- <NSThread: 0x7f88a9d901f0>{number = 2, name = (null)}
NSOperationQueue[1658:89521] download3 --- <NSThread: 0x7f88a9d15d30>{number = 4, name = (null)}
NSOperationQueue[1704:92509] download2 --- <NSThread: 0x7fd318f06540>{number = 2, name = (null)}
NSOperationQueue[1704:92513] download1 --- <NSThread: 0x7fd318d0e460>{number = 3, name = (null)}
提示：队列的取出是有顺序的，与打印结果并不矛盾。这就好比，选手A,BC虽然起跑的顺序是先A,后B，然后C，但是到达终点的顺序却不一定是A,B在前，C在后。
4.1 最大并发数
并发数：同时执⾏行的任务数 比如,同时开3个线程执行3个任务,并发数就是3
最大并发数：同一时间最多只能执行的任务的个数
最⼤并发数的相关⽅方法：
//最大并发数，默认为-1
@property NSInteger maxConcurrentOperationCount;
- (void)setMaxConcurrentOperationCount:(NSInteger)cnt;
说明：
- 如果没有设置最大并发数，那么并发的个数是由系统内存和CPU决定的，内存多就开多一点，内存少就开少一点。
- 最⼤并发数的值并不代表线程的个数，仅仅代表线程的ID。
- 最大并发数不要乱写（5以内），不要开太多，一般以2~3为宜，因为虽然任务是在子线程进行处理的，但是cpu处理这些过多的子线程可能会影响UI，让UI变卡。
- 最大并发数的值为1，就变成了串行队列
代码示例：
#import "ViewController.h"
@interface ViewController ()
@end
@implementation ViewController
- (void)viewDidLoad {
[super viewDidLoad];
// Do any additional setup after loading the view, typically from a nib.
}
- (void)touchesBegan:(NSSet *)touches withEvent:(UIEvent *)event {
// 1.创建队列
NSOperationQueue *queue = [[NSOperationQueue alloc] init];
// 2.设置最大并发操作数(大并发操作数 = 1,就变成了串行队列)
queue.maxConcurrentOperationCount = 2;
// 3.添加操作
[queue addOperationWithBlock:^{
NSLog(@"download1 --- %@", [NSThread currentThread]);
[NSThread sleepForTimeInterval:0.01];
}];
[queue addOperationWithBlock:^{
NSLog(@"download2 --- %@", [NSThread currentThread]);
[NSThread sleepForTimeInterval:0.01];
}];
[queue addOperationWithBlock:^{
NSLog(@"download3 --- %@", [NSThread currentThread]);
[NSThread sleepForTimeInterval:0.01];
}];
[queue addOperationWithBlock:^{
NSLog(@"download4 --- %@", [NSThread currentThread]);
[NSThread sleepForTimeInterval:0.01];
}];
[queue addOperationWithBlock:^{
NSLog(@"download5 --- %@", [NSThread currentThread]);
[NSThread sleepForTimeInterval:0.01];
}];
[queue addOperationWithBlock:^{
NSLog(@"download6 --- %@", [NSThread currentThread]);
[NSThread sleepForTimeInterval:0.01];
}];
}
- (void)didReceiveMemoryWarning {
[super didReceiveMemoryWarning];
// Dispose of any resources that can be recreated.
}
@end
打印结果：
最大并发数[1909:113433] download2 --- <NSThread: 0x7ffef240ba70>{number = 3, name = (null)}
最大并发数[1909:113432] download1 --- <NSThread: 0x7ffef24aee50>{number = 2, name = (null)}
最大并发数[1909:113432] download4 --- <NSThread: 0x7ffef24aee50>{number = 2, name = (null)}
最大并发数[1909:113431] download3 --- <NSThread: 0x7ffef251aa80>{number = 4, name = (null)}
最大并发数[1909:113428] download5 --- <NSThread: 0x7ffef2603d90>{number = 5, name = (null)}
最大并发数[1909:113432] download6 --- <NSThread: 0x7ffef24aee50>{number = 2, name = (null)}
4.2 队列的暂停和恢复
队列的暂停：当前任务结束后，暂停执行下一个任务，而非当前任务
//暂停和恢复队列（YES代表暂停队列，NO代表恢复队列）
- (void)setSuspended:(BOOL)b;
//当前状态
- (BOOL)isSuspended;
暂停和恢复的使用场合：
在tableview界面，开线程下载远程的网络界面，对UI会有影响，使用户体验变差。那么这种情况，就可以设置在用户操作UI（如滚动屏幕）的时候，暂停队列（不是取消队列），停止滚动的时候，恢复队列。
代码示例：
#import "ViewController.h"
@interface ViewController ()
@property(nonatomic, strong) NSOperationQueue *queue; //队列
@end
@implementation ViewController
- (void)viewDidLoad {
[super viewDidLoad];
// 1.创建队列
NSOperationQueue *queue = [[NSOperationQueue alloc] init];
// 2.设置最大并发操作数(大并发操作数 = 1,就变成了串行队列)
queue.maxConcurrentOperationCount = 1;
// 3.添加操作
[queue addOperationWithBlock:^{
NSLog(@"download1 --- %@", [NSThread currentThread]);
[NSThread sleepForTimeInterval:3];
}];
[queue addOperationWithBlock:^{
NSLog(@"download2 --- %@", [NSThread currentThread]);
[NSThread sleepForTimeInterval:3];
}];
[queue addOperationWithBlock:^{
NSLog(@"download3 --- %@", [NSThread currentThread]);
[NSThread sleepForTimeInterval:3];
}];
[queue addOperationWithBlock:^{
NSLog(@"download4 --- %@", [NSThread currentThread]);
[NSThread sleepForTimeInterval:3];
}];
self.queue = queue;
}
#pragma mark - 暂停和恢复
- (void)touchesBegan:(NSSet *)touches withEvent:(UIEvent *)event {
if (self.queue.isSuspended) {
self.queue.suspended = NO; // 恢复队列，继续执行
} else {
self.queue.suspended = YES; // 暂停（挂起）队列，暂停执行
}
}
- (void)didReceiveMemoryWarning {
[super didReceiveMemoryWarning];
// Dispose of any resources that can be recreated.
}
@end
打印结果：
队列的暂停和恢复[2650:156206] download1 --- <NSThread: 0x7fd689f552b0>{number = 3, name = (null)}
队列的暂停和恢复[2650:156205] download2 --- <NSThread: 0x7fd689c02e70>{number = 2, name = (null)}
队列的暂停和恢复[2650:156206] download3 --- <NSThread: 0x7fd689f552b0>{number = 3, name = (null)}
队列的暂停和恢复[2650:156385] download4 --- <NSThread: 0x7fd689ea11c0>{number = 4, name = (null)}
4.3 队列的取消
取消队列的所有操作：相等于调用了所有 NSOperation 的 -(void)cancel 方法，
当前任务结束后，取消执行下面的所有任务，而非当前任务
// 也可调用NSOperation的 -(void)cancel 方法取消单个操作
- (void)cancelAllOperations;
代码示例：
#import "ViewController.h"
@interface ViewController ()
@property(nonatomic, strong) NSOperationQueue *queue; //队列
@end
@implementation ViewController
- (void)viewDidLoad {
[super viewDidLoad];
// 1.创建队列
NSOperationQueue *queue = [[NSOperationQueue alloc] init];
// 2.设置最大并发操作数(大并发操作数 = 1,就变成了串行队列)
queue.maxConcurrentOperationCount = 1;
// 3.添加操作
[queue addOperationWithBlock:^{
NSLog(@"download1 --- %@", [NSThread currentThread]);
[NSThread sleepForTimeInterval:3];
}];
[queue addOperationWithBlock:^{
NSLog(@"download2 --- %@", [NSThread currentThread]);
[NSThread sleepForTimeInterval:3];
}];
[queue addOperationWithBlock:^{
NSLog(@"download3 --- %@", [NSThread currentThread]);
[NSThread sleepForTimeInterval:3];
}];
[queue addOperationWithBlock:^{
NSLog(@"download4 --- %@", [NSThread currentThread]);
[NSThread sleepForTimeInterval:3];
}];
self.queue = queue;
}
#pragma mark - 取消队列的所有操作
- (void)touchesBegan:(NSSet *)touches withEvent:(UIEvent *)event {
// 取消队列的所有操作（相等于调用了所有NSOperation的-(void)cancel方法）
[self.queue cancelAllOperations];
}
- (void)didReceiveMemoryWarning {
[super didReceiveMemoryWarning];
// Dispose of any resources that can be recreated.
}
@end
打印结果：
队列的取消[3041:167756] download1 --- <NSThread: 0x7fcc09543b40>{number = 3, name = (null)}
队列的取消[3041:167749] download2 --- <NSThread: 0x7fcc094505f0>{number = 2, name = (null)}
4.4 操作优先级
设置NSOperation在queue中的优先级，可以改变操作的执行优先级：
@property NSOperationQueuePriority queuePriority;
- (void)setQueuePriority:(NSOperationQueuePriority)p;
优先级的取值：优先级高的任务，调用的几率会更大
typedef NS_ENUM(NSInteger, NSOperationQueuePriority) {
NSOperationQueuePriorityVeryLow = -8L,
NSOperationQueuePriorityLow = -4L,
NSOperationQueuePriorityNormal = 0,
NSOperationQueuePriorityHigh = 4,
NSOperationQueuePriorityVeryHigh = 8
};
4.5 操作依赖
NSOperation之间可以设置依赖来保证执行顺序：不能循环依赖（不能A依赖于B，B又依赖于A）
// 操作B依赖于操作A（一定要让操作A执行完后，才能执行操作B）
[operationB addDependency:operationA];
可以在不同queue的NSOperation之间创建依赖关系（跨队列依赖）：
注意：
- 一定要在把操作添加到队列之前，进行设置操作依赖。
- 任务添加的顺序并不能够决定执行顺序，执行的顺序取决于依赖。
代码示例：
#import "ViewController.h"
@interface ViewController ()
@end
@implementation ViewController
- (void)viewDidLoad {
[super viewDidLoad];
// Do any additional setup after loading the view, typically from a nib.
}
- (void)touchesBegan:(NSSet *)touches withEvent:(UIEvent *)event {
NSOperationQueue *queue = [[NSOperationQueue alloc] init];
//创建对象，封装操作
NSBlockOperation *op1 = [NSBlockOperation blockOperationWithBlock:^{
NSLog(@"download1----%@", [NSThread currentThread]);
}];
NSBlockOperation *op2 = [NSBlockOperation blockOperationWithBlock:^{
NSLog(@"download2----%@", [NSThread currentThread]);
}];
NSBlockOperation *op3 = [NSBlockOperation blockOperationWithBlock:^{
NSLog(@"download3----%@", [NSThread currentThread]);
}];
NSBlockOperation *op4 = [NSBlockOperation blockOperationWithBlock:^{
for (NSInteger i = 0; i < 5; i++) {
NSLog(@"download4----%@", [NSThread currentThread]);
}
}];
NSBlockOperation *op5 = [NSBlockOperation blockOperationWithBlock:^{
NSLog(@"download5----%@", [NSThread currentThread]);
}];
//操作的监听
op5.completionBlock = ^{
NSLog(@"op5执行完毕---%@", [NSThread currentThread]);
};
//设置操作依赖（op4执行完，才执行 op3）
[op3 addDependency:op1];
[op3 addDependency:op2];
[op3 addDependency:op4];
//把操作添加到队列中
[queue addOperation:op1];
[queue addOperation:op2];
[queue addOperation:op3];
[queue addOperation:op4];
[queue addOperation:op5];
}
- (void)didReceiveMemoryWarning {
[super didReceiveMemoryWarning];
// Dispose of any resources that can be recreated.
}
@end
打印结果：
操作依赖[4196:150518] download5----<NSThread: 0x7ffa61d177d0>{number = 3, name = (null)}
操作依赖[4196:150506] download1----<NSThread: 0x7ffa61ca6b90>{number = 4, name = (null)}
操作依赖[4196:150509] download4----<NSThread: 0x7ffa61f0e470>{number = 2, name = (null)}
操作依赖[4196:150510] download2----<NSThread: 0x7ffa61f0e800>{number = 5, name = (null)}
操作依赖[4196:150518] op5执行完毕---<NSThread: 0x7ffa61d177d0>{number = 3, name = (null)}
操作依赖[4196:150509] download4----<NSThread: 0x7ffa61f0e470>{number = 2, name = (null)}
操作依赖[4196:150509] download4----<NSThread: 0x7ffa61f0e470>{number = 2, name = (null)}
操作依赖[4196:150509] download4----<NSThread: 0x7ffa61f0e470>{number = 2, name = (null)}
操作依赖[4196:150509] download4----<NSThread: 0x7ffa61f0e470>{number = 2, name = (null)}
操作依赖[4196:150509] download3----<NSThread: 0x7ffa61f0e470>{number = 2, name = (null)}
操作的监听
可以监听一个操作的执行完毕：
@property (nullable, copy) void (^completionBlock)(void);
- (void)setCompletionBlock:(void (^)(void))block;
代码详见4.5 操作依赖 示例代码
5.0 线程间通信（图片下载示例）
#import "ViewController.h"
@interface ViewController ()
@property(weak, nonatomic) IBOutlet UIImageView *imageView;
@end
@implementation ViewController
- (void)viewDidLoad {
[super viewDidLoad];
// Do any additional setup after loading the view, typically from a nib.
}
- (void)touchesBegan:(NSSet *)touches withEvent:(UIEvent *)event {
[self test2];
}
#pragma mark - 线程间通信（图片合成）
- (void)test1 {
// 1.队列
NSOperationQueue *queue = [[NSOperationQueue alloc] init];
__block UIImage *image1 = nil;
// 2.下载图片1
NSBlockOperation *download1 = [NSBlockOperation blockOperationWithBlock:^{
// 图片的网络路径
NSURL *url =
[NSURL URLWithString:@"http://img.pconline.com.cn/images/photoblog/9/9/"
@"8/1/9981681/200910/11/1255259355826.jpg"];
// 加载图片
NSData *data = [NSData dataWithContentsOfURL:url];
// 生成图片
image1 = [UIImage imageWithData:data];
}];
__block UIImage *image2 = nil;
// 3.下载图片2
NSBlockOperation *download2 = [NSBlockOperation blockOperationWithBlock:^{
// 图片的网络路径
NSURL *url = [NSURL
URLWithString:
@"http://pic38.nipic.com/20140228/5571398_215900721128_2.jpg"];
// 加载图片
NSData *data = [NSData dataWithContentsOfURL:url];
// 生成图片
image2 = [UIImage imageWithData:data];
}];
// 4.合成图片
NSBlockOperation *combine = [NSBlockOperation blockOperationWithBlock:^{
// 开启新的图形上下文
UIGraphicsBeginImageContext(CGSizeMake(100, 100));
// 绘制图片1
[image1 drawInRect:CGRectMake(0, 0, 50, 100)];
image1 = nil;
// 绘制图片2
[image2 drawInRect:CGRectMake(50, 0, 50, 100)];
image2 = nil;
// 取得上下文中的图片
UIImage *image = UIGraphicsGetImageFromCurrentImageContext();
// 结束上下文
UIGraphicsEndImageContext();
// 5.回到主线程
[[NSOperationQueue mainQueue] addOperationWithBlock:^{
self.imageView.image = image;
}];
}];
// 设置依赖操作
[combine addDependency:download1];
[combine addDependency:download2];
//把操作添加到队列中
[queue addOperation:download1];
[queue addOperation:download2];
[queue addOperation:combine];
}
#pragma mark - 线程间通信（图片下载）
- (void)test2 {
[[[NSOperationQueue alloc] init] addOperationWithBlock:^{
// 图片的网络路径
NSURL *url =
[NSURL URLWithString:@"http://img.pconline.com.cn/images/photoblog/9/9/"
@"8/1/9981681/200910/11/1255259355826.jpg"];
// 加载图片
NSData *data = [NSData dataWithContentsOfURL:url];
// 生成图片
UIImage *image = [UIImage imageWithData:data];
// 回到主线程
[[NSOperationQueue mainQueue] addOperationWithBlock:^{
self.imageView.image = image;
}];
}];
}
- (void)didReceiveMemoryWarning {
[super didReceiveMemoryWarning];
// Dispose of any resources that can be recreated.
}
@end
6.0 自定义NSOperation
自定义NSOperation的步骤很简单：
- 重写- (void)main方法，在里面实现想执行的任务
重写- (void)main方法的注意点：
- 自己创建自动释放池（因为如果是异步操作，无法访问主线程的自动释放池）
- 经常通过- (BOOL)isCancelled方法检测操作是否被取消，对取消做出响应
ViewController.m
#import "TDOperation.h"
#import "ViewController.h"
@interface ViewController ()
@end
@implementation ViewController
- (void)viewDidLoad {
[super viewDidLoad];
// Do any additional setup after loading the view, typically from a nib.
}
- (void)touchesBegan:(NSSet *)touches withEvent:(UIEvent *)event {
// 1.创建队列
NSOperationQueue *queue = [[NSOperationQueue alloc] init];
// 2.创建自定义 TDGOperation
TDOperation *op = [[TDOperation alloc] init];
// 3.把操作（任务）添加到队列中，并自动调用 start 方法
[queue addOperation:op];
}
- (void)didReceiveMemoryWarning {
[super didReceiveMemoryWarning];
// Dispose of any resources that can be recreated.
}
@end
TDOperation.h(继承自：NSOperation)
#import <Foundation/Foundation.h>
@interface TDOperation : NSOperation
@end
TDOperation.m
#import "TDOperation.h"
@implementation TDOperation
//需要执行的任务
- (void)main {
for (NSInteger i = 0; i < 3; i++) {
NSLog(@"download1 -%zd-- %@", i, [NSThread currentThread]);
}
// 人为的判断是否执行取消操作，如果执行取消操作，就直接 return 不往下执行
if (self.isCancelled)
return;
for (NSInteger i = 0; i < 3; i++) {
NSLog(@"download2 -%zd-- %@", i, [NSThread currentThread]);
}
// 人为的判断是否执行取消操作，如果执行取消操作，就直接 return 不往下执行
if (self.isCancelled)
return;
for (NSInteger i = 0; i < 3; i++) {
NSLog(@"download3 -%zd-- %@", i, [NSThread currentThread]);
}
// 人为的判断是否执行取消操作，如果执行取消操作，就直接 return 不往下执行
if (self.isCancelled)
return;
}
@end
运行结果：
自定义NSOperation[1567:84075] download1 -0-- <NSThread: 0x7fb6ba4109b0>{number = 2, name = (null)}
自定义NSOperation[1567:84075] download1 -1-- <NSThread: 0x7fb6ba4109b0>{number = 2, name = (null)}
自定义NSOperation[1567:84075] download1 -2-- <NSThread: 0x7fb6ba4109b0>{number = 2, name = (null)}
自定义NSOperation[1567:84075] download2 -0-- <NSThread: 0x7fb6ba4109b0>{number = 2, name = (null)}
自定义NSOperation[1567:84075] download2 -1-- <NSThread: 0x7fb6ba4109b0>{number = 2, name = (null)}
自定义NSOperation[1567:84075] download2 -2-- <NSThread: 0x7fb6ba4109b0>{number = 2, name = (null)}
自定义NSOperation[1567:84075] download3 -0-- <NSThread: 0x7fb6ba4109b0>{number = 2, name = (null)}
自定义NSOperation[1567:84075] download3 -1-- <NSThread: 0x7fb6ba4109b0>{number = 2, name = (null)}
自定义NSOperation[1567:84075] download3 -2-- <NSThread: 0x7fb6ba4109b0>{number = 2, name = (null)}
6.1 自定义NSOperation队列的取消操作
代码示例：
ViewController.m
#import "TDOperation.h"
#import "ViewController.h"
@interface ViewController ()
@property(nonatomic, strong) NSOperationQueue *queue; //队列
@end
@implementation ViewController
- (void)viewDidLoad {
[super viewDidLoad];
// 1.创建队列
NSOperationQueue *queue = [[NSOperationQueue alloc] init];
// 2.设置最大并发操作数(大并发操作数 = 1,就变成了串行队列)
queue.maxConcurrentOperationCount = 2;
// 3.添加操作 - 自定义 NSOperation
[queue addOperation:[[TDOperation alloc] init]];
self.queue = queue;
}
#pragma mark - 取消队列的所有操作
- (void)touchesBegan:(NSSet *)touches withEvent:(UIEvent *)event {
// 取消队列的所有操作（相等于调用了所有NSOperation的-(void)cancel方法）
[self.queue cancelAllOperations];
}
- (void)didReceiveMemoryWarning {
[super didReceiveMemoryWarning];
// Dispose of any resources that can be recreated.
}
@end
TDOperation.h
#import <Foundation/Foundation.h>
@interface TDOperation : NSOperation
@end
TDOperation.m
#import "TDOperation.h"
@implementation TDOperation
//需要执行的任务
- (void)main {
for (NSInteger i = 0; i < 1000; i++) {
NSLog(@"download1 -%zd-- %@", i, [NSThread currentThread]);
}
// 人为的判断是否执行取消操作，如果执行取消操作，就直接 return 不往下执行
if (self.isCancelled)
return;
for (NSInteger i = 0; i < 1000; i++) {
NSLog(@"download2 -%zd-- %@", i, [NSThread currentThread]);
}
// 人为的判断是否执行取消操作，如果执行取消操作，就直接 return 不往下执行
if (self.isCancelled)
return;
for (NSInteger i = 0; i < 1000; i++) {
NSLog(@"download3 -%zd-- %@", i, [NSThread currentThread]);
}
// 人为的判断是否执行取消操作，如果执行取消操作，就直接 return 不往下执行
if (self.isCancelled)
return;
}
@end
6.2 多图下载
沙盒结构：
Documents
Library
- Caches
- Preference
tmp
自定义NSOperation下载图片思路 – 有沙盒缓存
代码示例：
ViewController.m
#import "TDApp.h"
#import "ViewController.h"
@interface ViewController ()
@property(nonatomic, strong) NSArray *apps; //所有数据
@property(nonatomic, strong) NSMutableDictionary *imageCache; //内存缓存的图片
@property(nonatomic, strong) NSOperationQueue *queue; //队列对象
@property(nonatomic, strong) NSMutableDictionary *operations; //所有的操作对象
@end
@implementation ViewController
- (void)viewDidLoad {
[super viewDidLoad];
// Do any additional setup after loading the view, typically from a nib.
}
#pragma mark - 数据源方法
- (NSInteger)tableView:(UITableView *)tableView
numberOfRowsInSection:(NSInteger)section {
return self.apps.count;
}
#pragma mark - Cell
- (UITableViewCell *)tableView:(UITableView *)tableView
cellForRowAtIndexPath:(NSIndexPath *)indexPath {
// 重用标识
static NSString *ID = @"app";
UITableViewCell *cell = [tableView dequeueReusableCellWithIdentifier:ID];
TDApp *app = self.apps[indexPath.row];
#pragma mark - app 名称
cell.textLabel.text = app.name;
#pragma mark - 下载量
cell.detailTextLabel.text = app.download;
#pragma mark - 图片
// 1.先从内存缓存中取出图片
UIImage *image = self.imageCache[app.icon];
// 2.判断内存中是否有图片
if (image) {
// 2.1 内存中有图片，直接设置图片
cell.imageView.image = image;
} else {
// 2.2 内存中没有图片，将图片文件数据写入沙盒中
//（1）获得Library/Caches文件夹
NSString *cachesPath = [NSSearchPathForDirectoriesInDomains(
NSCachesDirectory, NSUserDomainMask, YES) firstObject];
//（2）获得文件名
NSString *filename = [app.icon lastPathComponent];
//（3）计算出文件的全路径
NSString *file = [cachesPath stringByAppendingPathComponent:filename];
//（4）加载沙盒的文件数据
NSData *data = [NSData dataWithContentsOfFile:file];
// 2.3 判断沙盒中是否有图片
if (data) {
// 有图片，直接利用沙盒中图片，设置图片
UIImage *image = [UIImage imageWithData:data];
cell.imageView.image = image;
// 并将图片存到字典中
self.imageCache[app.icon] = image;
} else {
// 没有图片,先设置一个占位图
cell.imageView.image = [UIImage imageNamed:@"placeholder"];
// 取出图片，并判断这张图片是否有下载操作
NSOperation *operation = self.operations[app.icon];
if (operation == nil) {
// 如果这张图片暂时没有下载操作，则需要创建一个下载操作
// 下载图片是耗时操作，放到子线程
operation = [NSBlockOperation blockOperationWithBlock:^{
// 下载图片
NSData *data =
[NSData dataWithContentsOfURL:[NSURL URLWithString:app.icon]];
// 如果数据下载失败
if (data == nil) {
// 下载失败，移除操作
[self.operations removeObjectForKey:app.icon];
return;
}
// 下载成功，将图片放在 image 中
UIImage *image = [UIImage imageWithData:data];
// 存到字典中
self.imageCache[app.icon] = image;
//回到主线程显示图片
[[NSOperationQueue mainQueue] addOperationWithBlock:^{
[tableView reloadRowsAtIndexPaths:@[ indexPath ]
withRowAnimation:UITableViewRowAnimationNone];
}];
// 将图片文件数据写入沙盒中
[data writeToFile:file atomically:YES];
// 下载完毕，移除操作
[self.operations removeObjectForKey:app.icon];
}];
// 添加到队列中（队列的操作不需要移除，会自动移除）
[self.queue addOperation:operation];
// 并将图片存到字典中
self.operations[app.icon] = operation;
}
}
}
return cell;
}
#pragma mark - 数据懒加载
- (NSArray *)apps {
if (!_apps) {
NSArray *dictArray =
[NSArray arrayWithContentsOfFile:[[NSBundle mainBundle]
pathForResource:@"apps.plist"
ofType:nil]];
NSMutableArray *appArray = [NSMutableArray array];
for (NSDictionary *dict in dictArray) {
[appArray addObject:[TDApp appWithDict:dict]];
}
_apps = appArray;
}
return _apps;
}
#pragma mark - 懒加载
- (NSMutableDictionary *)imageCache {
if (!_imageCache) {
_imageCache = [NSMutableDictionary dictionary];
}
return _imageCache;
}
#pragma mark - 懒加载
- (NSOperationQueue *)queue {
if (!_queue) {
_queue = [[NSOperationQueue alloc] init];
_queue.maxConcurrentOperationCount = 3;
}
return _queue;
}
#pragma mark - 懒加载
- (NSMutableDictionary *)operations {
if (!_operations) {
_operations = [NSMutableDictionary dictionary];
}
return _operations;
}
- (void)didReceiveMemoryWarning {
[super didReceiveMemoryWarning];
// Dispose of any resources that can be recreated.
}
@end
TDApp.h
#import <Foundation/Foundation.h>
@interface TDApp : NSObject
@property(nonatomic, strong) NSString *icon; // 图片
@property(nonatomic, strong) NSString *download; //下载量
@property(nonatomic, strong) NSString *name; // 名字
+ (instancetype)appWithDict:(NSDictionary *)dict;
@end
TDApp.m
#import "TDApp.h"
@implementation TDApp
+ (instancetype)appWithDict:(NSDictionary *)dict {
TDApp *app = [[self alloc] init];
[app setValuesForKeysWithDictionary:dict];
return app;
}
@end
6.3 多图下载 - SDWebImage
SDWebImage：
-
iOS中著名的网络图片处理框架
-
包含的功能：图片下载、图片缓存、下载进度监听、gif处理等等
-
SDWebImage的图片缓存周期是:1周
代码示例：
ViewController.m
#import "TDApp.h"
#import "UIImageView+WebCache.h"
#import "ViewController.h"
@interface ViewController ()
@property(nonatomic, strong) NSArray *apps; //所有数据
@property(nonatomic, strong) NSMutableDictionary *imageCache; //内存缓存的图片
@property(nonatomic, strong) NSOperationQueue *queue; //队列对象
@property(nonatomic, strong) NSMutableDictionary *operations; //所有的操作对象
@end
@implementation ViewController
- (void)viewDidLoad {
[super viewDidLoad];
// Do any additional setup after loading the view, typically from a nib.
}
#pragma mark - 数据源方法
- (NSInteger)tableView:(UITableView *)tableView
numberOfRowsInSection:(NSInteger)section {
return self.apps.count;
}
#pragma mark - Cell
- (UITableViewCell *)tableView:(UITableView *)tableView
cellForRowAtIndexPath:(NSIndexPath *)indexPath {
// 重用标识
static NSString *ID = @"app";
UITableViewCell *cell = [tableView dequeueReusableCellWithIdentifier:ID];
TDApp *app = self.apps[indexPath.row];
#pragma mark - app 名称
cell.textLabel.text = app.name;
#pragma mark - 下载量
cell.detailTextLabel.text = app.download;
#pragma mark - 图片
// expectedSize: 图片的总字节数 receivedSize: 已经接收的图片字节数
[cell.imageView sd_setImageWithURL:[NSURL URLWithString:app.icon]
placeholderImage:[UIImage imageNamed:@"placeholder"]
options:0 // 0 表示什么都不做
progress:^(NSInteger receivedSize, NSInteger expectedSize) {
NSLog(@"下载进度：%f", 1.0 * receivedSize / expectedSize);
}
completed:^(UIImage *image, NSError *error, SDImageCacheType cacheType,
NSURL *imageURL) {
NSLog(@"下载完图片");
}];
return cell;
}
#pragma mark - 数据懒加载
- (NSArray *)apps {
if (!_apps) {
NSArray *dictArray =
[NSArray arrayWithContentsOfFile:[[NSBundle mainBundle]
pathForResource:@"apps.plist"
ofType:nil]];
NSMutableArray *appArray = [NSMutableArray array];
for (NSDictionary *dict in dictArray) {
[appArray addObject:[TDApp appWithDict:dict]];
}
_apps = appArray;
}
return _apps;
}
#pragma mark - 懒加载
- (NSMutableDictionary *)imageCache {
if (!_imageCache) {
_imageCache = [NSMutableDictionary dictionary];
}
return _imageCache;
}
#pragma mark - 懒加载
- (NSOperationQueue *)queue {
if (!_queue) {
_queue = [[NSOperationQueue alloc] init];
_queue.maxConcurrentOperationCount = 3;
}
return _queue;
}
#pragma mark - 懒加载
- (NSMutableDictionary *)operations {
if (!_operations) {
_operations = [NSMutableDictionary dictionary];
}
return _operations;
}
#pragma mark - 设置控制器的内存警告
- (void)didReceiveMemoryWarning {
[super didReceiveMemoryWarning];
self.imageCache = nil;
self.operations = nil;
[self.queue cancelAllOperations];
}
@end
TDApp.h
#import <Foundation/Foundation.h>
@interface TDApp : NSObject
@property(nonatomic, strong) NSString *icon; // 图片
@property(nonatomic, strong) NSString *download; //下载量
@property(nonatomic, strong) NSString *name; // 名字
+ (instancetype)appWithDict:(NSDictionary *)dict;
@end
TDApp.m
#import "TDApp.h"
@implementation TDApp
+ (instancetype)appWithDict:(NSDictionary *)dict {
TDApp *app = [[self alloc] init];
[app setValuesForKeysWithDictionary:dict];
return app;
}
@end
7.0【区别】GCD & NSOperationQueue 队列类型的创建方式
GCD 队列类型的创建方式：
（1）并发队列：手动创建、全局
（2）串行队列：手动创建、主队列
NSOperationQueue的队列类型的创建方法：
（1）主队列：[NSOperationQueue mainQueue]
- 凡是添加到主队列中的任务（NSOperation），都会放到主线程中执行
（2）其他队列（同时包含了串行、并发功能）：[NSOperationQueue alloc]init]
- 添加到这种队列中的任务（NSOperation），就会自动放到子线程中执行
注：关于SDWebImage框架的详解会另外再写博客
如果你觉得本篇文章对你有所帮助，请点击文章末尾右下角“推荐”，^_^
作者：蓝田（Loto）
出处：http://www.cnblogs.com/shorfng/
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