iOS开发之异步加载图片

比较原始的方法：

AsyncImageView.h:

#import <UIKit/UIKit.h>
@interface AsyncImageView : UIView
{
    NSURLConnection* connection;
    NSMutableData* data;
}
- (void)loadImageFromURL:(NSURL*)url;
@end

AsyncImageView.m:

#import "AsyncImageView.h"
@implementation AsyncImageView

- (id)initWithFrame:(CGRect)frame
{
    self = [super initWithFrame:frame];
    if(self) {
        // Initialization code
    }
    returnself;
}

- (void)loadImageFromURL:(NSURL*)url {
    if(connection!=nil) { [connection release]; }
    if(data!=nil) { [data release]; }
    NSURLRequest* request = [NSURLRequest requestWithURL:url
                                             cachePolicy:NSURLRequestUseProtocolCachePolicy
                                         timeoutInterval:60.0];
    connection = [[NSURLConnection alloc]
                  initWithRequest:request delegate:self];
}

- (void)connection:(NSURLConnection *)theConnection
    didReceiveData:(NSData *)incrementalData {
    if(data==nil) {
        data =
        [[NSMutableData alloc] initWithCapacity:2048];
    }
    [data appendData:incrementalData];
}

- (void)connectionDidFinishLoading:(NSURLConnection*)theConnection {

    [connection release];
    connection=nil;

    if([[self subviews] count] > 0) {
        [[[self subviews] objectAtIndex:0] removeFromSuperview];
    }

    UIImageView *imageView = [[[UIImageView alloc] initWithImage:[UIImage imageWithData:data]] autorelease];

    imageView.contentMode = UIViewContentModeScaleAspectFit;
    imageView.autoresizingMask = ( UIViewAutoresizingFlexibleWidth | UIViewAutoresizingFlexibleHeight );

    [self addSubview:imageView];
    imageView.frame = self.bounds;
    [imageView setNeedsLayout];
    [self setNeedsLayout];
    [data release];
    data=nil;
}

- (UIImage*) image {
    UIImageView* iv = [[self subviews] objectAtIndex:0];
    return[iv image];
}

- (void)dealloc {
    [connection cancel];
    [connection release];
    [data release];
    [super dealloc];
}
@end

使用：

AsyncImageView *asyncImage = [[AsyncImageView alloc] init];
asyncImage.frame = CGRectMake(100, point_y, 95, 95)
//圆角
[asyncImage.layer setMasksToBounds:YES];
[asyncImage.layer setCornerRadius:15];
[asyncImage loadImageFromURL:[NSURL URLWithString:@"www.istar.name/...."]];

不过发现一个好东东， SDWebImage， 这个实在是太方便了
主页：https://github.com/rs/SDWebImage
1.下载下来放到project里面
2. 添加：MapKit.framework
3. #import “UIImageView+WebCache.h”
4. 使用：

UIImageView *asyncImage = [[UIImageView alloc] init];
[asyncImage setImageWithURL:[NSURL URLWithString:@www.istar.name/....]];

 

使用第三方库

EGOImageLoading是我在项目中用的比较多的一个第三方图片异步加载类，你们可以在git上找到并下载它，链接如下。另外提一下，
广为人知的下拉刷新EGORefreshTableHeaderView也是就是这个人写的。

https://github.com/enormego/EGOImageLoading
(下载后运行demo程序XCode会提示找不到EGOCache.h头文件，可以在这个地方下载https://github.com/enormego/EGOCache)

使用方法可以参照里面的demo程序，很简单，只要把ImageUrl告诉它，剩下的就什么都不用管了，它会帮你异步加载，还会做缓存处理...

?1234     // 设置默认占位图片     myEgoimageView.placeholderImage = [UIImage imageNamed:@"placeholder.png"];     // 告诉它图片的url地址, done     myEgoimageView.imageURL = [NSURL URLWithString:@"http://simg.cocoachina.com/201111220746561330.jpg"];