使用NSoperation 实现异步加载图片

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wx5acf76b593c6d 2022-05-05 22:04:50

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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"];