使用NSoperation多线程异步加载图片数据

转：http://blog.csdn.net/likendsl/article/details/7553716

NSoperation是ios封装好的的实现多线程的很简单的一种方法。

定义ImageDownloader ，这个类继承NSOperation，因为需要并发，需要实现下面4个方法 ：

//是否允许并发，
-(BOOL)isConcurrent ；
-(BOOL)isExecuting；

//是否已经完成，这个必须要重载，不然放在NSOperationQueue里的NSOpertaion不能正常释放。
- (BOOL)isFinished

//具体下载的方法在这里执行。

- (void)start

而对应于非并发的情况下，只需要重载main方法就好了。

头文件

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ImageDownloader.h

定义如下：

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#import <Foundation/Foundation.h>

@protocol imageDownloaderDelegate;

@interface ImageDownloader : NSOperation
{
NSURLRequest* _request;

NSURLConnection* _connection;

NSMutableData* _data;//请求的数据

BOOL _isFinished;

id<imageDownloaderDelegate> delegate;

NSObject *delPara;//可携带额外的参数
}

- (id)initWithURLString:(NSString *)url;

@property (readonly) NSData *data;
@property(nonatomic, assign) id<imageDownloaderDelegate> delegate;
@property(nonatomic, retain) NSObject *delPara;

@end

@protocol imageDownloaderDelegate

@optional

//图片下载完成的代理方法
- (void)imageDidFinished:(UIImage *)image para:(NSObject *)obj;

@end

实现文件

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ImageDownloader.m

定义如下：

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#import "ImageDownloader.h"

@implementation ImageDownloader

@synthesize data=_data;
@synthesize delegate;
@synthesize delPara;

- (void)dealloc
{

[_request release];
_request=nil;

[_data release];
_data=nil;

[_connection release];
_connection=nil;

[delPara release];

[super dealloc];

}
- (id)initWithURLString:(NSString *)url
{

self = [self init];
if (self) {

_request = [[NSURLRequest alloc] initWithURL:[NSURL URLWithString:url]];

_data = [[NSMutableData data] retain];

}

return self;

}

// 开始处理-本类的主方法

- (void)start {

if (![self isCancelled]) {

[NSThread sleepForTimeInterval:3];
// 以异步方式处理事件，并设置代理

_connection=[[NSURLConnection connectionWithRequest:_request delegate:self]retain];

while(_connection != nil) {

[[NSRunLoop currentRunLoop] runMode:NSDefaultRunLoopMode beforeDate:[NSDate distantFuture]];

}

}

}

#pragma mark NSURLConnection delegate Method

// 接收到数据（增量）时

- (void)connection:(NSURLConnection*)connection

didReceiveData:(NSData*)data
{
// 添加数据
[_data appendData:data];

}

- (void)connectionDidFinishLoading:(NSURLConnection*)connection {

[_connection release],
_connection=nil;
NSLog(@"%s", __func__);

UIImage *img = [[[UIImage alloc] initWithData:self.data] autorelease];

if (self.delegate != nil)
{
[delegate imageDidFinished:img para:self.delPara];
}

}

-(void)connection: (NSURLConnection *) connection didFailWithError: (NSError *) error
{
[_connection release],
_connection=nil;
}

-(BOOL)isConcurrent
{
//返回yes表示支持异步调用，否则为支持同步调用
return YES;

}
- (BOOL)isExecuting
{
return _connection == nil;
}
- (BOOL)isFinished
{
return _connection == nil;
}

应用举例：

NSString *url =@”xxxxxxx“；

NSString*param=@”额外参数“；

ImageDownloader *downloader = [[[ImageDownloader alloc] initWithURLString:url] autorelease];

downloader.delegate = self;

downloader.delPara = param;

NSOperationQueue* queue = [[[NSOperationQueue alloc] init] autorelease];

[queue addOperation:downloader];

#pragma delegate

- (void)imageDidFinished:(UIImage *)image para:(NSObject *)obj

{

//image,下载下来的图片；

NSString*param = (NSString *)obj;//附带的参数；

}