本文转载至 http://blog.csdn.net/enuola/article/details/8639404
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:
[cpp] view plaincopy
- #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:
[cpp] view plaincopy
- #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")
[cpp] view plaincopy
- 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。
时间: 2024-09-29 01:59:28