我已將子類UIImage創建爲UIImageExtra。我在UIImageExtra中有一個名爲adjustForResolution的方法,用於調整UIImage的大小。不過,我希望它返回一個UIImageExtra。我知道我需要轉換它,但不完全確定如何。基本上,如果我調整UIImageExtra的大小,它將成爲UIImage。將父類的實例轉換爲其子類
這裏是我UIImageExtra類:
#import "UIImageExtra.h"
#import <objc/runtime.h>
#import "UIApplication+AppDimensions.h"
#define kOriginData @"originData"
@implementation UIImageExtra
@synthesize originData;
+ (UIImageExtra *)imageNamed:(NSString *)imageName origin:(NSValue *)originData {
NSString *path = [[NSBundle mainBundle] pathForResource:imageName ofType:@""];
UIImageExtra *imageExtra = [[UIImageExtra alloc] initWithContentsOfFile:path];
imageExtra.originData = originData;
return imageExtra;
}
- (id)initWithContentsOfFile:(NSString *)path {
self = [super initWithContentsOfFile:path];
if (self) {
self = [self adjustForResolution];
}
NSLog(@"Image description: %@", [self description]);
return self;
}
- (id)adjustForResolution {
//All images are sized for ipad3 (2048 x 1536), so determine scale factor by ratio
CGSize screenSize = [UIApplication currentSize];
double scalefactor = screenSize.width/2048;
CGSize newSize = CGSizeMake(self.size.width*scalefactor, self.size.height*scalefactor);
UIImage *scaledImage = [self imageByScalingAndCroppingForSize:newSize];
return scaledImage;
}
- (id)imageByScalingAndCroppingForSize:(CGSize)targetSize
{
//returns resized image
}
@end
我認爲你的imageByScalingAndCroppingForSize方法只是返回一個UIImage,所以你的init方法返回一個UIImage。另外我不認爲在init中返回比self更自然的對象是個好主意。 –
imageByScalingAndCroppingForSize:裏面有什麼?你正在創建一個新的'UIImage'實例嗎? –
@JonathanCichon是的,那麼如何確保它返回一個UIImageExtra實例,而不是UIImage? – Smikey