ASIHttpRequest中Block代码块的使用和注意事项

使用ASIHttpRequest的setCompletionBlock、setFailedBlock时碰到一些诡异的内存泄漏和莫名其妙的行为（如：无法release对象）。

1. 声明ASIHttpRequest时一定要使用__block关键字
  __block关键字告诉block不要retain request，这对于防止循环retain非常重要！！因为request总是会retain block
2. 谨慎处理block与对象的关系
  当setCompletionBlock/setFailedBlock内部使用对象的instance var时，self会被retain（If you access an instance variable by reference, self is retained;）。所以在request结束前向对象发送release消息不会导致对象的释放（dealloc），亦即：该对象依然可进行所有操作，这将导致诸多你意想不到的结果。
3. 解决第2点的问题
  3.1 仔细拿捏block与对象的关系 + 按值的方式访问instance var（If you access an instance variable by value, the variable is retained.）
  3.2 不使用block，而使用ASIHttpRequestDelegate
4. 参考资料
  4.1 http://allseeing-i.com/ASIHTTPRequest/How-to-use - Using blocks
  4.2 Blocks Programming Topics - Object and Block Variables

接口部分:

//

//  LYHASIRequestBlock.h

//  ASIBlockTest

//

//  Created by Charles Leo on 14-7-23.

//  Copyright (c) 2014年 Charles Leo. All rights reserved.

//

 

#import <Foundation/Foundation.h>

#import "ASIHTTPRequest.h"

#import "ASIFormDataRequest.h"

typedef void (^RequestBlock) ( void );

@interface LYHASIRequestBlock : NSObject <ASIHTTPRequestDelegate>

{

     ASIHTTPRequest * getRequest;

     ASIFormDataRequest * postRequest;

     NSURL * url;

     RequestBlock finishBlock;

     RequestBlock failBlock;

     RequestBlock startBlock;

     NSString * requestType;

}

 

//接收到的数据

@property (strong, nonatomic ) NSData * receiveData;

//请求完成的block

- ( void )didFinishBlock:(RequestBlock)block;

//请求失败的block

- ( void )didFailedBlock:(RequestBlock)block;

//请求开始的block

- ( void )didStartBlock:(RequestBlock)block;

//取消请求

- ( void )cancelRequst;

//get请求方法

- ( void )getRequest:( NSString *)getUrl;

//post请求方法

- ( void )postRequest:( NSString *)postUrl andKeys :( NSArray *)keyArray andValues :( NSArray *)valueArray;

@end

 

实现部分:

//

//  LYHASIRequestBlock.m

//  ASIBlockTest

//

//  Created by Charles Leo on 14-7-23.

//  Copyright (c) 2014年 Charles Leo. All rights reserved.

//

 

#import "LYHASIRequestBlock.h"

 

@implementation LYHASIRequestBlock

 

- ( void )getRequest:( NSString *)getUrl

{

     requestType = @"GET" ;

     getRequest  = [[ ASIHTTPRequest alloc ]initWithURL:[ NSURL URLWithString :getUrl]];

     getRequest .delegate = self ;

     getRequest .timeOutSeconds = 1 5 ;

     [getRequest startAsynchronous ];

}

#pragma mark -GET请求的代理方法

//开始请求

- ( void )requestStarted:( ASIHTTPRequest *)request

{

     startBlock();

}

//请求完成

- ( void )requestFinished:( ASIHTTPRequest *)request

{

     self .receiveData = request .responseData ;

     finishBlock();

}

//请求失败

- ( void )requestFailed:( ASIHTTPRequest *)request

{

     failBlock();

}

//post请求

-( void )postRequest:( NSString *)postUrl andKeys :( NSArray *)keyArray andValues :( NSArray *)valueArray

{

     postRequest = [[ ASIFormDataRequest alloc ]initWithURL:[ NSURL URLWithString :postUrl]];

     postRequest .timeOutSeconds = 1 5 ;

     postRequest .delegate = self ;

     for ( int i = 0 ; i<keyArray .count ; i++) {

         [postRequest setPostValue :[valueArray objectAtIndex :i] forKey :[keyArray objectAtIndex :i]];

     }

     [postRequest setDidFinishSelector : @selector (didFinishPostRequest:)];

     [postRequest setDidStartSelector : @selector (didStartPostRequest:)];

     [postRequest setDidFailSelector : @selector (didFailPostRequest:)];

     [postRequest startAsynchronous ];

}

 

#pragma mark - POST请求的代理方法

//请求开始

- ( void )didStartPostRequest:( ASIFormDataRequest *)request

{

     startBlock();

}

//请求完成

- ( void )didFinishPostRequest:( ASIFormDataRequest *)request

{

     finishBlock();

}

//请求失败

- ( void )didFailPostRequest:( ASIFormDataRequest *)request

{

     failBlock();

}

 

//设置Blocks

//设置开始块

- ( void )didStartBlock:(RequestBlock)block

{

     [startBlock release ];

     startBlock = [block copy ];

}

//设置完成块

-( void )didFinishBlock:(RequestBlock)block

{

     [finishBlock release ];

     finishBlock = [block copy ];

}

//设置失败块

-( void )didFailedBlock:(RequestBlock)block

{

     [failBlock release ];

     failBlock = [block copy ];

}

//取消请求

- ( void )cancelRequst{

     if ([requestType isEqualToString : @"GET" ])

     {

         [getRequest cancel ];

     }

     else if ([requestType isEqualToString : @"POST" ])

     {

         [postRequest cancel ];

     }

}

 

-( void )dealloc

{

     [getRequest release ];

     [postRequest release ];

     [startBlock release ];

     [finishBlock release ];

     [failBlock release ];

     [ super dealloc ];

}

@end

参考：http://www.cocoachina.com/bbs/read.php?tid=95100

http://code4app.com/snippets/one/%E7%94%A8Block%E5%B0%81%E8%A3%85ASIHttpRequest/5428f5b8933bf0bf118b51d8