ACM_Someone like you

         iOS圖片的下載緩存全部在此
分類： iOS編程 2012-11-03 21:15 2075人閱讀 評論(2) 收藏 舉報
注意: 我的文章只寫給自己看
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(一)這部分(感覺out了), 但是還是保留,  算是學習的痕跡.
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(1)最簡單的下載,顯示圖片的方法: 
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   UIImageView *imageView = [[UIImageView alloc] initWithFrame:[self.view bounds]];  
   imageView.image = [self loadImageFromUrl:@"http://storage.live.com/items/72A00BF5A838647C!1616?filename=meinv004.jpg"];  
   [self.view addSubview:imageView];  
     
   -(UIImage*)loadImageFromUrl: (NSString*)url  
{  
    NSURL  *imageUrl = [NSURL URLWithString:url];  
    NSData *imageData = [NSData dataWithContentsOfURL:imageUrl];  
    UIImage *image = [UIImage imageWithData:imageData];  
    return image;  
}  
    
這種最簡單的圖片加載方式阻塞了main線程. 使得流程不能流暢進行.


(2)開辟線程來解決這個問題.

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   // set imageview  
   UIImageView *imageView = [[UIImageView alloc] initWithFrame:[self.view bounds]];  
   imageView.backgroundColor = [UIColor yellowColor];  
   imageView.tag = imageView_tag;  
   [self.view addSubview:imageView];  
     
   // load image in background  
   NSString *url = IMAGE_URL;  
   [self performSelectorInBackground:@selector(loadImageFromUrl:) withObject:url];  
     
  
  
-(void)loadImageFromUrl: (NSString*)url {  
    NSURL  *imageUrl = [NSURL URLWithString:url];  
    NSData *imageData = [NSData dataWithContentsOfURL:imageUrl];  
    [self performSelectorOnMainThread:@selector(updateImageView:) withObject:imageData waitUntilDone:NO];  
}  
-(void) updateImageView:(NSData*) data {  
    UIImageView *imageView = (UIImageView *)[self.view viewWithTag:imageView_tag];  
    imageView.image = [UIImage imageWithData:data];  
}  


并且只能在main線程中設置UI的內容, 所以代碼量增加了較多. 代碼量暫且不管, 這里還有一個比較嚴重的問題就是每次都要加載圖片, 


使用SDWebImage: 
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#import <SDWebImage/UIImageView+WebCache.h>  
[imageView setImageWithURL:[NSURL URLWithString:[_objects objectAtIndex:indexPath.row]]  
                  placeholderImage:[UIImage imageNamed:@"placeholder.png"]];  
SDWebImage可以實現: 
*下載和緩存圖片.
*相同的url不會被重復下載.
*壞的url不會一直請求.

使用HJCache:
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// 目前HJCache不支持ARC, 所以這是個問題.  

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(二)多線程初步實現TableView的圖片顯示(之前用第三庫老是不穩定) 這個算是比較滿意的.
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@interface c:NSOperation  
  
@property NSString *url;  
@property NSString *imageName;  
@property UIImage *image;  
@property UIImageView *delegate;  
  
-(void) main;  
-(id) initWith:(NSString *)url imageName:(NSString *)imageName delegate:(UIImageView *)delegate;  
  
@end  
  
@implementation c:NSOperation  
@synthesize url = _url,imageName=_imageName, image=_image, delegate=_delegate;  
  
-(id) initWith:(NSString *)url imageName:(NSString *)imageName delegate:(UIImageView *)delegate{  
    if (self = [super init]) {  
        self.url = url;  
        self.imageName = imageName;  
        self.delegate = delegate;  
    }  
    return self;  
}  
  
-(void) main{  
    //  
    NSString *cachefile = [NSTemporaryDirectory() stringByAppendingPathComponent: self.imageName];  
    NSData *data = [NSData dataWithContentsOfURL:[NSURL URLWithString:self.url]];  
    [data writeToFile:cachefile atomically:YES];  
      
    //  
    self.image = [UIImage imageWithData:data];  
    [self performSelectorOnMainThread:@selector(u) withObject:nil waitUntilDone:NO];  
}  
-(void)u{  
    [self.delegate setImage:self.image];  
}  

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queue = [[NSOperationQueue alloc] init];//這是成員隊列的實例化  
設置TableView cell中的圖片:
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NSString *filename = [NSString stringWithFormat:@"%d", indexPath.row];  
NSString *cachefile = [NSTemporaryDirectory() stringByAppendingPathComponent: filename];  
UIImage *image = [UIImage imageWithContentsOfFile:cachefile];  
if (image) {  
    cell.imageView.image = image;  
} else {  
    c *o = [[c alloc] initWith:[_objects objectAtIndex:indexPath.row] imageName:[NSString stringWithFormat:@"%d",indexPath.row] delegate:cell.imageView];  
    [queue addOperation:o];  
    cell.imageView.image= [UIImage imageNamed:@"placeholder.png"];  
}  

注: 保存一下測試圖片  urls