UIImage，检查是否包含图像

Question

If I instantiate a UIImage like this :

UIImage *image = [[UIImage alloc] init];

The object is created but it doesn't contain any image.

How I can check if my object contains an image or not?

Answer 1

You can check if it has any image data.

UIImage* image = [[UIImage alloc] init];

CGImageRef cgref = [image CGImage];
CIImage *cim = [image CIImage];

if (cim == nil && cgref == NULL)
{
    NSLog(@"no underlying data");
}
[image release];

Swift Version

let image = UIImage()

let cgref = image.cgImage
let cim = image.ciImage

if cim == nil && cgref == nil {
    print("no underlying data")
}

Answer 2

Check for cgImage or ciImage , in Swift 3

public extension UIImage {

  public var hasContent: Bool {
    return cgImage != nil || ciImage != nil
  }
}

CGImage: If the UIImage object was initialized using a CIImage object, the value of the property is NULL.

CIImage: If the UIImage object was initialized using a CGImageRef, the value of the property is nil.

Answer 3

检查 CGImageRef 本身是否包含空值意味着 UIImage 对象不包含图像......

Answer 4

This is updated version of @Kreiri, I put in a method and fixed logic error:

- (BOOL)containsImage:(UIImage*)image {
    BOOL result = NO;

    CGImageRef cgref = [image CGImage];
    CIImage *cim = [image CIImage];

    if (cim != nil || cgref != NULL) { // contains image
        result = YES;
    }

    return result;
}

An UIImage could only based on CGImageRef or CIImage. If both is nil means there is no image. Example use of giving method:

if (![self containsImage:imageview.image]) {
    [self setImageWithYourMethod];
}

hope it will help someone.