NSOperation的使用细节 [3]

NSOperation的使用细节 [3]

这一节我们来写自定义concurrent的operation，自定义concurrent的operation稍微有点复杂，需要按照某些既定的步骤编写才可以完成线程的操作。

Methods to override for concurrent operations （concurrent operation需要重写的一些方法）

Method	Description
start	(Required) All concurrent operations must override this method and replace the default behavior with their own custom implementation. To execute an operation manually, you call its start method. Therefore, your implementation of this method is the starting point for your operation and is where you set up the thread or other execution environment in which to execute your task. Your implementation must not call super at any time.
main	(Optional) This method is typically used to implement the task associated with the operation object. Although you could perform the task in the start method, implementing the task using this method can result in a cleaner separation of your setup and task code.
isExecuting isFinished	(Required) Concurrent operations are responsible for setting up their execution environment and reporting the status of that environment to outside clients. Therefore, a concurrent operation must maintain some state information to know when it is executing its task and when it has finished that task. It must then report that state using these methods. Your implementations of these methods must be safe to call from other threads simultaneously. You must also generate the appropriate KVO notifications for the expected key paths when changing the values reported by these methods.
isConcurrent	(Required) To identify an operation as a concurrent operation, override this method and return YES.

接下来就是写类了，如下所示：

//
//  ConcurrentOperation.h
//  NSOperationExample
//
//  Created by YouXianMing on 15/9/5.
//  Copyright (c) 2015年 YouXianMing. All rights reserved.
//

#import <Foundation/Foundation.h>

@interface ConcurrentOperation : NSOperation {

    BOOL  _executing;
    BOOL  _finished;
}

@end

//
//  ConcurrentOperation.m
//  NSOperationExample
//
//  Created by YouXianMing on 15/9/5.
//  Copyright (c) 2015年 YouXianMing. All rights reserved.
//

#import "ConcurrentOperation.h"

@implementation ConcurrentOperation

- (void)main {

    // do tasks
    NSLog(@"%@", self.name);
    
    // at last, you should run this method.
    [self completeOperation];
}

- (void)completeOperation {
    
    [self willChangeValueForKey:@"isFinished"];
    [self willChangeValueForKey:@"isExecuting"];
    _executing = NO;
    _finished  = YES;
    [self didChangeValueForKey:@"isExecuting"];
    [self didChangeValueForKey:@"isFinished"];
}

- (void)start {
    
    // Always check for cancellation before launching the task.
    if ([self isCancelled]) {
        
        // Must move the operation to the finished state if it is canceled.
        [self willChangeValueForKey:@"isFinished"];
        _finished = YES;
        [self didChangeValueForKey:@"isFinished"];
        
        return;
    }
    
    // If the operation is not canceled, begin executing the task.
    [self willChangeValueForKey:@"isExecuting"];
    [NSThread detachNewThreadSelector:@selector(main) toTarget:self withObject:nil];
    _executing = YES;
    [self didChangeValueForKey:@"isExecuting"];
}

- (BOOL)isExecuting {
    
    return _executing;
}

- (BOOL)isFinished {
    
    return _finished;
}

- (BOOL)isConcurrent {
    
    return YES;
}

@end

以下是必须携带的内容：

自定义concurrent的operation可以说是nonconcurrent的operation的复杂版本。

完整项目：

https://github.com/YouXianMing/NSOperationExample