iPhoneGeek 爱疯极客

// UIImage+Extras.h
@interface UIImage (Extras)

- (id)initWithContentsOfResolutionIndependentFile:(NSString *)path;
+ (UIImage*)imageWithContentsOfResolutionIndependentFile:(NSString *)path;

@end

// UIImage+Extras.m
- (id)initWithContentsOfResolutionIndependentFile:(NSString *)path {
    if ( [[[UIDevice currentDevice] systemVersion] intValue] >= 4 && [[UIScreen mainScreen] scale] == 2.0 ) {
        NSString *path2x = [[path stringByDeletingLastPathComponent]
                            stringByAppendingPathComponent:[NSString stringWithFormat:@"%@@2x.%@",
                                                            [[path lastPathComponent] stringByDeletingPathExtension],
                                                            [path pathExtension]]];
       
        if ( [[NSFileManager defaultManager] fileExistsAtPath:path2x] ) {
            return [self initWithCGImage:[[UIImage imageWithData:[NSData dataWithContentsOfFile:path2x]] CGImage] scale:2.0 orientation:UIImageOrientationUp];
        }
    }
   
    return [self initWithData:[NSData dataWithContentsOfFile:path]];
}

+ (UIImage*)imageWithContentsOfResolutionIndependentFile:(NSString *)path {
    return [[[UIImage alloc] initWithContentsOfResolutionIndependentFile:path] autorelease];
}

- (void)viewDidLoad
{
    [super viewDidLoad];

    UIGraphicsBeginImageContext(CGSizeMake(20,20));
    CGContextRef ctx = UIGraphicsGetCurrentContext();
    CGContextBeginPath(ctx);
    CGContextAddArc(ctx, 10, 10, 10, 0, 2*M_PI, 1);
    CGContextSetRGBFillColor(ctx, 1,0, 0, 1);
    CGContextFillPath(ctx);
    UIImage *redBall = UIGraphicsGetImageFromCurrentImageContext();
    UIGraphicsEndImageContext();
    UIImageView *redBallView = [[UIImageView alloc] initWithImage:redBall];
    redBallView.center = CGPointMake(160,330);
    [self.view addSubview:redBallView];
}