[z]使用NSoperation 实现异步加载图片

采用UITableView显示从网络上下载的图片，因为网络图片下载比较耗费时间，一般采用边显示文字，内容，后台下载图片，下载完成后刷新TableViewCell ，本文将演示如何通过自定的UITableViewCell，显示图片。
1。定义ImageTableViewCell

@interface ImageTableViewCell : UITableViewCell {
UILabel *txtLabel;
UIImageView *imageView;
}
@property(nonatomic, retain)IBOutlet UILabel *txtLabel;
@property(nonatomic, retain)IBOutlet UIImageView *imageView;

- (void)setCell:(UIImage *)image text:(NSString *)text;

@end

方法添加如下

- (void)setCell:(UIImage *)image text:(NSString *)text

{
if (image != nil)
{
self.imageView.image = image;
}

self.txtLabel.text = text;

}

具体实现代码，请在源代码里查看

2。定义ImageDownloader ，这个类继承NSOperation，因为需要并发，所以需要实现下面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。

#import <Foundation/Foundation.h>

@protocol imageDownloaderDelegate;

@interface ImageDownloader : NSOperation
{
NSURLRequest* _request;

NSURLConnection* _connection;

NSMutableData* _data;

BOOL _isFinished;

id<imageDownloaderDelegate> delegate;

NSObject *delPara;
}

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

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

@end

@protocol imageDownloaderDelegate

@optional

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

@end

实现文件如下

#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;
}

然后再UITableViewController里每个Cell创建的时候，如果没有图片的话，就通过ImageDownloader去下载，下载完了刷新这个Cell就可以了。

#import <UIKit/UIKit.h>
#import "ImageDownloader.h"
@interface RootViewController : UITableViewController <imageDownloaderDelegate>
{
NSOperationQueue *queue;
NSMutableArray *siteArray;
NSMutableArray *imageArray;
NSMutableDictionary *dic;
}
@property(nonatomic, retain)NSOperationQueue *queue;
@property(nonatomic, retain)NSMutableArray *siteArray;
@property(nonatomic, retain)NSMutableArray *imageArray;

@end

实现文件

//
// RootViewController.m
// NSOperationTest
//
//

#import "RootViewController.h"
#import "ImageDownloader.h"
#import "ImageTableViewCell.h"

@implementation RootViewController
@synthesize queue;
@synthesize siteArray;
@synthesize imageArray;

- (void)dealloc
{
[self.queue release];
[self.siteArray release];
[self.imageArray release];
[super dealloc];
}

- (void)viewDidLoad
{
[super viewDidLoad];
self.queue = [[[NSOperationQueue alloc] init] autorelease];
self.siteArray = [[[NSMutableArray alloc] init] autorelease];
[self.siteArray addObject:@"http://s1.lashouimg.com/zt/201110/27/131972321636938600.jpg"];
[self.siteArray addObject:@"http://s1.lashouimg.com/zt/201110/25/131953930325377400.jpg"];
[self.siteArray addObject:@"http://s1.lashouimg.com/zt/201110/25/131953847613105000.jpg"];
[self.siteArray addObject:@"http://s1.lashouimg.com/zt/201110/27/131972570125915500.jpg"];
[self.siteArray addObject:@"http://s1.lashouimg.com/zt/201110/25/131954190510086200.jpg"];
[self.siteArray addObject:@"http://s1.lashouimg.com/zt/201110/27/131972321636938600.jpg"];
[self.siteArray addObject:@"http://s1.lashouimg.com/zt/201110/25/131953930325377400.jpg"];
[self.siteArray addObject:@"http://s1.lashouimg.com/zt/201110/25/131953847613105000.jpg"];
[self.siteArray addObject:@"http://s1.lashouimg.com/zt/201110/27/131972570125915500.jpg"];
[self.siteArray addObject:@"http://s1.lashouimg.com/zt/201110/25/131954190510086200.jpg"];
[self.siteArray addObject:@"http://s1.lashouimg.com/zt/201110/27/131972321636938600.jpg"];
[self.siteArray addObject:@"http://s1.lashouimg.com/zt/201110/25/131953930325377400.jpg"];
[self.siteArray addObject:@"http://s1.lashouimg.com/zt/201110/25/131953847613105000.jpg"];
[self.siteArray addObject:@"http://s1.lashouimg.com/zt/201110/27/131972570125915500.jpg"];
[self.siteArray addObject:@"http://s1.lashouimg.com/zt/201110/25/131954190510086200.jpg"];
[self.siteArray addObject:@"http://s1.lashouimg.com/zt/201110/27/131972321636938600.jpg"];
[self.siteArray addObject:@"http://s1.lashouimg.com/zt/201110/25/131953930325377400.jpg"];
[self.siteArray addObject:@"http://s1.lashouimg.com/zt/201110/25/131953847613105000.jpg"];
[self.siteArray addObject:@"http://s1.lashouimg.com/zt/201110/27/131972570125915500.jpg"];
[self.siteArray addObject:@"http://s1.lashouimg.com/zt/201110/25/131954190510086200.jpg"];
[self.siteArray addObject:@"http://s1.lashouimg.com/zt/201110/27/131972321636938600.jpg"];
[self.siteArray addObject:@"http://s1.lashouimg.com/zt/201110/25/131953930325377400.jpg"];
[self.siteArray addObject:@"http://s1.lashouimg.com/zt/201110/25/131953847613105000.jpg"];
[self.siteArray addObject:@"http://s1.lashouimg.com/zt/201110/27/131972570125915500.jpg"];
[self.siteArray addObject:@"http://s1.lashouimg.com/zt/201110/25/131954190510086200.jpg"];
[self.siteArray addObject:@"http://s1.lashouimg.com/zt/201110/27/131972321636938600.jpg"];
[self.siteArray addObject:@"http://s1.lashouimg.com/zt/201110/25/131953930325377400.jpg"];
[self.siteArray addObject:@"http://s1.lashouimg.com/zt/201110/25/131953847613105000.jpg"];
[self.siteArray addObject:@"http://s1.lashouimg.com/zt/201110/27/131972570125915500.jpg"];
[self.siteArray addObject:@"http://s1.lashouimg.com/zt/201110/25/131954190510086200.jpg"];

self.imageArray = [[[NSMutableArray alloc] init] autorelease];
for ( int i = 0; i < [self.siteArray count]; i++)
{
[self.imageArray addObject: [NSNull null]];
}
dic = [NSDictionary dictionary];

}

// Customize the number of sections in the table view.
- (NSInteger)numberOfSectionsInTableView:(UITableView *)tableView
{
return 1;
}

- (NSInteger)tableView:(UITableView *)tableView numberOfRowsInSection:(NSInteger)section
{
return [siteArray count];
}

// Customize the appearance of table view cells.
- (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath
{
static NSString *CellIdentifier = @"Cell";

ImageTableViewCell *cell = (ImageTableViewCell *)[tableView dequeueReusableCellWithIdentifier:CellIdentifier];
if (cell == nil)
{
NSArray *bundle = [[NSBundle mainBundle] loadNibNamed:@"ImageTableViewCell" owner:self options:nil];
cell = (ImageTableViewCell *)[bundle objectAtIndex:0];
}

NSString *text = [NSString stringWithFormat:@"%d", indexPath.row];

NSNull *null = (NSNull *)[self.imageArray objectAtIndex:indexPath.row];

if (![null isKindOfClass:[NSNull class]])
{
[cell setCell:[imageArray objectAtIndex:indexPath.row] text:text];

}
else
{
[cell setCell:nil text:text];
NSString *url = [self.siteArray objectAtIndex:indexPath.row];
ImageDownloader *downloader = [[[ImageDownloader alloc] initWithURLString:url] autorelease];
downloader.delegate = self;
downloader.delPara = indexPath;
[self.queue addOperation:downloader];
}

// Configure the cell.
return cell;
}

- (CGFloat)tableView:(UITableView *)tableView heightForRowAtIndexPath:(NSIndexPath *)indexPath
{
return 112;
}

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

NSIndexPath *indexPath = (NSIndexPath *)obj;
[self.imageArray replaceObjectAtIndex:indexPath.row withObject:image];
ImageTableViewCell *cell = (ImageTableViewCell *)[self.tableView cellForRowAtIndexPath:indexPath];
NSString *text = [NSString stringWithFormat:@"%d", indexPath.row];
[cell setCell:image text:text];
[cell setNeedsDisplay];

}

@end

本文是通过委托实现的刷新Cell，你也可以通过一个Observer，观察图片是否下载完成，完成后就刷新图片所再Cell。通过Observer如何实现请参考这个网址http://blog.csdn.net/kmyhy/article/details/6050345

本文地址：http://www.cnblogs.com/likwo/archive/2011/10/30/2229582.html

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