使用NSoperation多线程异步加载图…

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

ImageDownloader.h

定义如下：

#import

@protocol imageDownloaderDelegate;

@interface ImageDownloader : NSOperation

{

NSURLRequest* _request;

NSURLConnection*_connection;

NSMutableData*_data;//请求的数据

BOOL_isFinished;

id delegate;

NSObject*delPara;//可携带额外的参数

}

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

@property (readonly) NSData *data;

@property(nonatomic, assign) id 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

ImageDownloader.m

定义如下：

#import "ImageDownloader.h"

@implementation ImageDownloader

@synthesize data=_data;

@synthesize delegate;

@synthesize delPara;

- (void)dealloc

{

[_requestrelease];

_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=[[NSURLConnectionconnectionWithRequest:_request delegate:self]retain];

while(_connection != nil) {

[[NSRunLoop currentRunLoop] runMode:NSDefaultRunLoopModebeforeDate:[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 = [[[UIImagealloc] initWithData:self.data] autorelease];

if (self.delegate != nil)

{

[delegate imageDidFinished:imgpara: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；
}