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 |
方法添加如下
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- (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。
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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 |
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 |
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.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
