从UIImage转换到NSData类型

- (void)requestFinished:(ASIHTTPRequest *)request
{
    NSData *responseData = [request responseData];
    int responseStatusCode = [request responseStatusCode];
    if (responseStatusCode == 404) {
        return;
    }
    UIImage *image = [[UIImage alloc] initWithData:responseData];
    
    /*
    NSString *fileName = [[request.url absoluteString] lastPathComponent];
    NSString *extension = [fileName pathExtension];
    NSFileManager *fm = [NSFileManager defaultManager];
    
    BOOL isDirectory = [fm fileExistsAtPath:_savePath isDirectory:nil];
    NSString *path = [_savePath stringByDeletingLastPathComponent];
    if (!isDirectory) {
        [fm createDirectoryAtPath:path withIntermediateDirectories:YES attributes:nil error:nil];
    }
    
    if([extension isEqual:@"png"]){
        [UIImagePNGRepresentation(image) writeToFile:_savePath atomically:YES];
    }else if([extension isEqual:@"jpg"]){
        [UIImageJPEGRepresentation(image, 1.0) writeToFile:_savePath atomically:YES];
    }*/
    [delegate downloadFinish:image];
    [image release];
    
}

 

 //sdk中提供了方法可以直接调用  
UIImage *img = [UIImage imageNamed:@"some.png"];  
NSData *dataObj = UIImageJPEGRepresentation(img, 1.0);  
  
//下面是sdk中UIImage.h头文件中的内容  
UIKIT_EXTERN NSData *UIImagePNGRepresentation(UIImage *image);                               // return image as PNG. May return nil if image has no CGImageRef or invalid bitmap format  
UIKIT_EXTERN NSData *UIImageJPEGRepresentation(UIImage *image, CGFloat compressionQuality);  // return image as JPEG. May return nil if image has no CGImageRef or invalid bitmap format. compression is 0(most)..1(least)