iOS并发编程：操作队列、依赖关系与定时器的运用

### iOS并发编程：操作队列、依赖关系与定时器的运用 在iOS开发中，实现并发操作、创建操作之间的依赖关系以及使用定时器是常见的需求。下面将详细介绍如何使用操作队列异步执行任务、创建操作之间的依赖关系以及创建定时器。 #### 1. 异步执行任务 当需要并发执行操作时，有两种主要的解决方案：使用操作队列或子类化`NSOperation`并在`main`方法中分离新线程。 ##### 1.1 使用操作队列 操作队列是管理并发操作的有效方式。以下是一个使用操作队列和两个简单调用操作的示例： ```objc // 声明文件（.h） #import <UIKit/UIKit.h> @interface Running_Tasks_Asynchronously_with_OperationsAppDelegate : UIResponder <UIApplicationDelegate> @property (nonatomic, strong) UIWindow *window; @property (nonatomic, strong) NSOperationQueue *operationQueue; @property (nonatomic, strong) NSInvocationOperation *firstOperation; @property (nonatomic, strong) NSInvocationOperation *secondOperation; @end // 实现文件（.m） #import "Running_Tasks_Asynchronously_with_OperationsAppDelegate.h" @implementation Running_Tasks_Asynchronously_with_OperationsAppDelegate - (void) firstOperationEntry:(id)paramObject{ NSLog(@"%s", __FUNCTION__); NSLog(@"Parameter Object = %@", paramObject); NSLog(@"Main Thread = %@", [NSThread mainThread]); NSLog(@"Current Thread = %@", [NSThread currentThread]); } - (void) secondOperationEntry:(id)paramObject{ NSLog(@"%s", __FUNCTION__); NSLog(@"Parameter Object = %@", paramObject); NSLog(@"Main Thread = %@", [NSThread mainThread]); NSLog(@"Current Thread = %@", [NSThread currentThread]); } - (BOOL) application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions{ NSNumber *firstNumber = [NSNumber numberWithInteger:111]; NSNumber *secondNumber = [NSNumber numberWithInteger:222]; self.firstOperation = [[NSInvocationOperation alloc] initWithTarget:self selector:@selector(firstOperationEntry:) object:firstNumber]; self.secondOperation = [[NSInvocationOperation alloc] initWithTarget:self selector:@selector(secondOperationEntry:) object:secondNumber]; self.operationQueue = [[NSOperationQueue alloc] init]; [self.operationQueue addOperation:self.firstOperation]; [self.operationQueue addOperation:self.secondOperation]; NSLog(@"Main thread is here"); self.window = [[UIWindow alloc] initWithFrame:[[UIScreen mainScreen] bounds]]; self.window.backgroundColor = [UIColor whiteColor]; [self.window makeKeyAndVisible]; return YES; } @end ``` 上述代码的执行步骤如下： 1. 定义两个方法`firstOperationEntry:`和`secondOperationEntry:`，用于打印当前线程、主线程和参数信息。 2. 初始化两个`NSInvocationOperation`对象，并设置目标选择器。 3. 初始化一个`NSOperationQueue`对象，用于管理操作的并发执行。 4. 将两个调用操作添加到操作队列中。 运行代码后，会发现调用操作在各自的线程上并行运行，不会阻塞主线程。 ##### 1.2 子类化`NSOperation` 如果需要更精细地控制操作，可以子类化`NSOperation`。以下是一个简单的示例： ```objc // 声明文件（.h） #import <Foundation/Foundation.h> @interface SimpleOperation : NSOperation - (id) initWithObject:(NSObject *)paramObject; @end // 实现文件（.m） #import "SimpleOperation.h" @implementation SimpleOperation NSObject *givenObject; BOOL finished; BOOL executing; - (id) init { NSNumber *dummyObject = [NSNumber numberWithInteger:123]; return([self initWithObject:dummyObject]); } - (id) initWithObject:(NSObject *)paramObject{ self = [super init]; if (self != nil){ givenObject = paramObject; } return(self); } - (void) start { if ([self isCancelled]){ [self willChangeValueForKey:@"isFinished"]; finished = YES; [self didChangeValueForKey:@"isFinished"]; return; } else { [self willChangeValueForKey:@"isExecuting"]; executing = YES; [self didChangeValueForKey:@"isExecuting"]; [self main]; } } - (void) main { @try { @autoreleasepool { BOOL taskIsFinished = NO; while (taskIsFinished == NO && [self isCancelled] == NO){ NSLog(@"%s", __FUNCTION__); NSLog(@"Parameter Object = %@", givenObject); NSLog(@"Main Thread = %@", [NSThread mainThread]); NSLog(@"Current Thread = %@", [NSThread currentThread]); taskIsFinished = YES; } [self willChangeValueForKey:@"isFinished"]; [self willChangeValueForKey:@"isExecuting"]; finished = YES; executing = NO; [self didChangeValueForKey:@"isFinished"]; [self didChangeValueForKey:@"isExecuting"]; } } @catch (NSException * e) { NSLog(@"Exception %@", e); } } - (BOOL) isConcurrent{ return YES; } - (BOOL) isFinished{ return finished; } - (BOOL) isExecuting{ return executing; } @end ``` 使用这个自定义操作类的示例代码如下： ```objc // 声明文件（.h） #import <UIKit/UIKit.h> @class ```