NSOperation 的使用(下载相关) 图片和文件都是可以的 断点续传 图片逐渐显示

//
//  ImageDownloader.h
//  NSOperationTest
//
//  Created by ydc on 11-10-29.
//  Copyright 2011年 __MyCompanyName__. All rights reserved.
//

#import <Foundation/Foundation.h>

@protocol imageDownloaderDelegate;

@interface ImageDownloader : NSOperation
{
NSURLRequest* _request;

NSURLConnection* _connection;

NSMutableData* _data;

BOOL _isFinished;

BOOL _cancelled;
}

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

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

@end

@protocol imageDownloaderDelegate

@optional

//图片下载完成的委托
- (void)imageDidFinished:(UIImage *)image para:(NSObject *)obj;

@end

//
//  ImageDownloader.m
//  NSOperationTest
//
//  Created by ydc on 11-10-29.
//  Copyright 2011年 __MyCompanyName__. All rights reserved.
//

#import "ImageDownloader.h"

@implementation ImageDownloader

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

self = [self init];
if (self) {
assert(url != nil);
_request = [[NSURLRequest alloc] initWithURL:[NSURL URLWithString:url]];
_data = [NSMutableData data];
}
return self;
}

- (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];

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
{
[_data appendData:data];
if (self.delegate != nil){
UIImage *img = [[UIImage alloc] initWithData:self.data] ;
[_delegate imageDidFinished:img para:self.delPara];
}
}

- (void)connectionDidFinishLoading:(NSURLConnection*)connection {
if (self.delegate != nil)
{
UIImage *img = [[UIImage alloc] initWithData:self.data] ;
[_delegate imageDidFinished:img para:self.delPara];
}
_connection=nil;
}

-(void)connection: (NSURLConnection *) connection didFailWithError: (NSError *) error
{
_connection=nil;
}
- (void)cancelOnRequestThread
{
[[self cancelledLock] lock];
if ([self isCancelled]) {
[[self cancelledLock] unlock];
return;
}
[self willChangeValueForKey:@"isCancelled"];
_cancelled = YES;
[self didChangeValueForKey:@"isCancelled"];

[[self cancelledLock] unlock];
}
- (BOOL)isCancelled
{
BOOL result;

[[self cancelledLock] lock];
result = _cancelled;
[[self cancelledLock] unlock];

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

@end

NSString *newUrl = [NSString stringWithFormat:@"http://static2.dmcdn.net/static/video/666/645/43546666:jpeg_preview_source.jpg?%d",(int)[NSDate timeIntervalSinceReferenceDate]];
ImageDownloader *imageDownloader = [[ImageDownloader alloc]initWithURLString:newUrl];
imageDownloader.delegate = self;
[self.queue addOperation:imageDownloader];

[[NSOperationQueue mainQueue] addOperationWithBlock:^{
self.urlConnection = [NSURLConnection connectionWithRequest:request delegate:self];
}];

NSMutableURLRequest *fileRequest = [NSMutableURLRequest requestWithURL:self.downloadURL
cachePolicy:NSURLRequestUseProtocolCachePolicy
timeoutInterval:kFileDefaultTimeout];

_startFileSize = [[fm attributesOfItemAtPath:self.pathToFile error:nil] fileSize];
NSString *range = [NSString stringWithFormat:@"bytes=%lld-", _startFileSize];
[fileRequest setValue:range forHTTPHeaderField:@"Range"];

_connection = [[NSURLConnection alloc] initWithRequest:fileRequest
delegate:self
startImmediately:NO];
if (self.connection) {
[self.connection scheduleInRunLoop:[NSRunLoop mainRunLoop]
forMode:NSDefaultRunLoopMode];
[self willChangeValueForKey:@"isExecuting"];
[self.connection start];
[self didChangeValueForKey:@"isExecuting"];
}