在ios开发中经常用到NSURLRequest类来进行url请求，通常有以下步骤

1.实例化NSURL;

2.实例化NSURLRequest；

3.连接[NSURLConnection connectionWithRequest:request delegate:self];

4.实现NSURLConnectionDataDelegate协议;

这样的话比较繁琐，可以对其进行封装

1.新建一个MyUrlRequest类

MyUrlRequest.h文件

    @interface MyUrlRequest : NSObject <NSURLConnectionDataDelegate> {  
        NSMutableData *_mData;//接收数据  
    }    
      
    @property (nonatomic, copy) NSString *urlStr;  
    @property (nonatomic, copy) void (^finishBlock)(NSData *data);//请求成功回调block  
    @property (nonatomic, copy) void (^failedBlick)();//请求失败回调block  
    @property (nonatomic, assign) BOOL isCache;//是否缓存  
      
    - (void)startRequest;//开始请求  
      
    @end  

MyUrlRequest.m文件

    #import "MyUrlRequest.h"  
    #import "NSString+Hashing.h"  
      
    @implementation QFURLRequest  
      
    @synthesize urlStr;  
    @synthesize finishBlock;  
    @synthesize failedBlick;  
    @synthesize isCache;  
      
    - (id)init {  
        if (self = [super init]) {  
            _mData = [[NSMutableData alloc] init];  
        }  
        return self;  
    }  
      
    - (void)startRequest {  
        //MyRequestManager里边autorelease掉，在这里可能出错，所以需要retain  
        [self retain];  
        if (self.isCache) {  
            //如果有缓存，则使用缓存  
            NSString *path = [NSHomeDirectory() stringByAppendingFormat:@"/tmp/%@", [self.urlStr MD5Hash]];  
            NSFileManager *manager = [NSFileManager defaultManager];  
            if ([manager fileExistsAtPath:path]) {  
                NSData *data = [NSData dataWithContentsOfFile:path];  
                self.finishBlock(data);  
                return;  
            }  
        }  
          
        NSURL *url = [NSURL URLWithString:self.urlStr];  
        NSURLRequest *request = [NSURLRequest requestWithURL:url];  
        [NSURLConnection connectionWithRequest:request delegate:self];  
    }  
    //实现NSURLConnectionDataDelegate协议  
    - (void)connection:(NSURLConnection *)connection didReceiveResponse:(NSURLResponse *)response {  
        [[UIApplication sharedApplication] setNetworkActivityIndicatorVisible:YES];  
    }  
      
    - (void)connection:(NSURLConnection *)connection didReceiveData:(NSData *)data {  
        [_mData appendData:data];  
    }  
      
    - (void)connectionDidFinishLoading:(NSURLConnection *)connection {  
        [self release];  
        [[UIApplication sharedApplication] setNetworkActivityIndicatorVisible:NO];  
        //写缓存  
        if (self.isCache) {  
            NSString *path = [NSHomeDirectory() stringByAppendingFormat:@"/tmp/%@", [self.urlStr MD5Hash]];  
            [_mData writeToFile:path atomically:YES];  
        }  
          
        self.finishBlock(_mData);  
    }  
      
    - (void)connection:(NSURLConnection *)connection didFailWithError:(NSError *)error {  
        [self release];  
        [[UIApplication sharedApplication] setNetworkActivityIndicatorVisible:NO];  
        self.failedBlick();  
    }  
      
    - (void)dealloc {  
        [_mData release];  
        self.finishBlock = nil;  
        self.failedBlick = nil;  
        [super dealloc];  
    }  
      
    @end  

2.新建一个MyRequestManager类

.h文件

    #import <Foundation/Foundation.h>  
    #import "MyUrlRequest.h"  
      
    @interface MyRequestManager : NSObject  
      
    + (void)requestWithUrl:(NSString *)urlString andIsCache:(BOOL)isCache finish:(void(^)(NSData *data))finishBlock failed:(void(^)())failedBlock;  
      
    @end  

.m文件

    #import "MyRequestManager.h"  
      
    @implementation MyRequestManager  
      
    + (void)requestWithUrl:(NSString *)urlString andIsCache:(BOOL)isCache finish:(void(^)(NSData *data))finishBlock failed:(void(^)())failedBlock  
    {  
        MyUrlRequest *request = [[[MyUrlRequest alloc] init] autorelease];  
        request.urlStr = urlString;  
        request.isCache = isCache;  
        request.finishBlock = finishBlock;  
        request.failedBlick =  failedBlock;  
        //在发送startRequest消息之后，该类方法结束，可能会对request发送autorelease消息，这样的话在request的startRequest方法中就可能会产生错误，所以要在startRequest方法中retain一下  
        [request startRequest];  
    }  
      
    @end  

这样的话，以后再发送请求就可以直接调用

[MyRequestManager requestWithUrl:(NSString *)urlString andIsCache:(BOOL)isCache finish:(void(^)(NSData *data))finishBlock failed:(void(^)())failedBlock ];