IOS中UITableView异步加载图片的实现
最近做一个项目，需要用到UITableView异步加载图片的例子，看到网上有一个EGOImageView的很好的例子。
但是由于，EGOImageView的实现比较复杂，于是自己就动手做了一个AsynImageView，同样可以实现EGOImageView的效果。
而且自己写的代码比较清晰，容易理解，同样可以实现指定placehoderImage以及指定imageURL，来进行图片的异步加载。
同时，如果图片已经请求过，则不会再重复请求网络，会直接读取本地缓存文件。
效果如下：
具体实现思路如下：
AsynImageView.h的文件内容：
#import <UIKit/UIKit.h>
@interface AsynImageView : UIImageView
{
NSURLConnection *connection;
NSMutableData *loadData;
}
//图片对应的缓存在沙河中的路径
@property (nonatomic, retain) NSString *fileName;
//指定默认未加载时，显示的默认图片
@property (nonatomic, retain) UIImage *placeholderImage;
//请求网络图片的URL
@property (nonatomic, retain) NSString *imageURL;
@end
AsynImageView.m中的文件内容：
#import "AsynImageView.h"
#import <QuartzCore/QuartzCore.h>
@implementation AsynImageView
@synthesize imageURL = _imageURL;
@synthesize placeholderImage = _placeholderImage;
@synthesize fileName = _fileName;
- (id)initWithFrame:(CGRect)frame
{
self = [super initWithFrame:frame];
if (self) {
// Initialization code
self.layer.borderColor = [[UIColor whiteColor] CGColor];
self.layer.borderWidth = 2.0;
self.backgroundColor = [UIColor grayColor];
}
return self;
}
//重写placeholderImage的Setter方法
-(void)setPlaceholderImage:(UIImage *)placeholderImage
{
if(placeholderImage != _placeholderImage)
{
[_placeholderImage release];
_placeholderImage = placeholderImage;
self.image = _placeholderImage; //指定默认图片
}
}
//重写imageURL的Setter方法
-(void)setImageURL:(NSString *)imageURL
{
if(imageURL != _imageURL)
{
self.image = _placeholderImage; //指定默认图片
[_imageURL release];
_imageURL = [imageURL retain];
}
if(self.imageURL)
{
//确定图片的缓存地址
NSArray *path=NSSearchPathForDirectoriesInDomains(NSDocumentationDirectory, NSUserDomainMask, YES);
NSString *docDir=[path objectAtIndex:0];
NSString *tmpPath=[docDir stringByAppendingPathComponent:@"AsynImage"];
NSFileManager *fm = [NSFileManager defaultManager];
if(![fm fileExistsAtPath:tmpPath])
{
[fm createDirectoryAtPath:tmpPath withIntermediateDirectories:YES attributes:nil error:nil];
}
NSArray *lineArray = [self.imageURL componentsSeparatedByString:@"/"];
self.fileName = [NSString stringWithFormat:@"%@/%@", tmpPath, [lineArray objectAtIndex:[lineArray count] - 1]];
//判断图片是否已经下载过，如果已经下载到本地缓存，则不用重新下载。如果没有，请求网络进行下载。
if(![[NSFileManager defaultManager] fileExistsAtPath:_fileName])
{
//下载图片，保存到本地缓存中
[self loadImage];
}
else
{
//本地缓存中已经存在，直接指定请求的网络图片
self.image = [UIImage imageWithContentsOfFile:_fileName];
}
}
}
//网络请求图片，缓存到本地沙河中
-(void)loadImage
{
//对路径进行编码
@try {
//请求图片的下载路径
//定义一个缓存cache
NSURLCache *urlCache = [NSURLCache sharedURLCache];
/*设置缓存大小为1M*/
[urlCache setMemoryCapacity:1*124*1024];
//设子请求超时时间为30s
NSMutableURLRequest *request = [NSMutableURLRequest requestWithURL:[NSURL URLWithString:self.imageURL] cachePolicy:NSURLRequestReloadIgnoringCacheData timeoutInterval:60.0];
//从请求中获取缓存输出
NSCachedURLResponse *response = [urlCache cachedResponseForRequest:request];
if(response != nil)
{
// NSLog(@"如果又缓存输出，从缓存中获取数据");
[request setCachePolicy:NSURLRequestReturnCacheDataDontLoad];
}
/*创建NSURLConnection*/
if(!connection)
connection = [[NSURLConnection alloc] initWithRequest:request delegate:self startImmediately:YES];
//开启一个runloop，使它始终处于运行状态
UIApplication *app = [UIApplication sharedApplication];
app.networkActivityIndicatorVisible = YES;
[[NSRunLoop currentRunLoop] runMode:NSDefaultRunLoopMode beforeDate:[NSDate distantFuture]];
}
@catch (NSException *exception) {
// NSLog(@"没有相关资源或者网络异常");
}
@finally {
;//.....
}
}
#pragma mark - NSURLConnection Delegate Methods
//请求成功，且接收数据(每接收一次调用一次函数)
-(void)connection:(NSURLConnection *)connection didReceiveData:(NSData *)data
{
if(loadData==nil)
{
loadData=[[NSMutableData alloc]initWithCapacity:2048];
}
[loadData appendData:data];
}
-(void)connection:(NSURLConnection *)connection didReceiveResponse:(NSURLResponse *)response
{
}
-(NSCachedURLResponse *)connection:(NSURLConnection *)connection willCacheResponse:(NSCachedURLResponse *)cachedResponse
{
return cachedResponse;
// NSLog(@"将缓存输出");
}
-(NSURLRequest *)connection:(NSURLConnection *)connection willSendRequest:(NSURLRequest *)request redirectResponse:(NSURLResponse *)response
{
// NSLog(@"即将发送请求");
return request;
}
//下载完成，将文件保存到沙河里面
-(void)connectionDidFinishLoading:(NSURLConnection *)theConnection
{
UIApplication *app = [UIApplication sharedApplication];
app.networkActivityIndicatorVisible = NO;
//图片已经成功下载到本地缓存，指定图片
if([loadData writeToFile:_fileName atomically:YES])
{
self.image = [UIImage imageWithContentsOfFile:_fileName];
}
connection = nil;
loadData = nil;
}
//网络连接错误或者请求成功但是加载数据异常
-(void)connection:(NSURLConnection *)theConnection didFailWithError:(NSError *)error
{
UIApplication *app = [UIApplication sharedApplication];
app.networkActivityIndicatorVisible = NO;
//如果发生错误，则重新加载
connection = nil;
loadData = nil;
[self loadImage];
}
-(void)dealloc
{
[_fileName release];
[loadData release];
[connection release];
[_placeholderImage release];
[_imageURL release];
[super dealloc];
}
@end
上面的AsynImageView的.h和.m文件，就是所要实现的核心代码。如果想要调用AsynImageView，则只需执行如下代码即可：（需导入 #import"AsynImageView.h"）
asynImgView = [[AsynImageView alloc] initWithFrame:CGRectMake(0, 5, 200, 100)];
asynImgView.placeholderImage = [UIImage imageNamed:@"place.png"];
asynImgView.imageURL = [NSString stringWithFormat:@"http://images.17173.com/2012/news/2012/10/10/lj1010sb10ds.jpg"];
[self.view addSubView:asynImgView];
下面是我实现的UITableView异步加载图片的程序链接，就是上面的效果图的程序完整代码，大家可以参考一下：
http://download.csdn.net/detail/enuola/5112070
如有不恰当的地方，还望指点。
另外，图片的缓存可以定期进行清理，在此处没有写出清理代码，可以自行添加。