iphone中使用NSoperation实现图片异步加载
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
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@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
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- (
void
)setCell:(UIImage *)image text:(NSString *)text
{
if
(image != nil)
{
self.imageView.image = image;
}
self.txtLabel.text = text;
}
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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。
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#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
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实现文件如下
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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;
}
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
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实现文件
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//
// 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
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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