[z]使用NSoperation 实现异步加载图片

最新推荐文章于 2021-09-22 14:27:14 发布

转载最新推荐文章于 2021-09-22 14:27:14 发布 · 69 阅读

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原文链接：http://www.cnblogs.com/aBigRoybot/archive/2011/11/25/2263168.html

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.youkuaiyun.com/kmyhy/article/details/6050345

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

demo下载

转载于:https://www.cnblogs.com/aBigRoybot/archive/2011/11/25/2263168.html