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转：iOS4.1之前无法正确加载@2x的解决办法——扩展UIImage类

2011-12-24 16:51  张智清  阅读(766)  评论(0)  编辑  收藏  举报

为使用retina显示，我们一般把图片的高分辨率版本存为@2x的形式，但是iOS 4.1以前的版本，如果使用imageWithContentsOfFile是无法保证@2x文件正确加载的。我使用如下方法解决此问题：

View Code 
 1 // UIImage+Extras.h
 2 @interface UIImage (Extras)
 3 
 4 - (id)initWithContentsOfResolutionIndependentFile:(NSString *)path;
 5 + (UIImage*)imageWithContentsOfResolutionIndependentFile:(NSString *)path;
 6 
 7 @end
 8 
 9 // UIImage+Extras.m
10 - (id)initWithContentsOfResolutionIndependentFile:(NSString *)path {
11     if ( [[[UIDevice currentDevice] systemVersion] intValue] >= 4 && [[UIScreen mainScreen] scale] == 2.0 ) {
12         NSString *path2x = [[path stringByDeletingLastPathComponent] 
13                             stringByAppendingPathComponent:[NSString stringWithFormat:@"%@@2x.%@", 
14                                                             [[path lastPathComponent] stringByDeletingPathExtension], 
15                                                             [path pathExtension]]];
16         
17         if ( [[NSFileManager defaultManager] fileExistsAtPath:path2x] ) {
18             return [self initWithCGImage:[[UIImage imageWithData:[NSData dataWithContentsOfFile:path2x]] CGImage] scale:2.0 orientation:UIImageOrientationUp];
19         }
20     }
21     
22     return [self initWithData:[NSData dataWithContentsOfFile:path]];
23 }
24 
25 + (UIImage*)imageWithContentsOfResolutionIndependentFile:(NSString *)path {
26     return [[[UIImage alloc] initWithContentsOfResolutionIndependentFile:path] autorelease];
27 }