Question

I have these two methods. How do I call them?

 //to base 64 string
-(NSString *)getStringFromImage:(UIImage *)image{
    if(image){
        NSData *dataObj = UIImagePNGRepresentation(image);
        return [dataObj base64Encoding];
    } else {
        return @"";
    }
}

//Convert back 
//    NSData *dataObj = [NSData dataWithBase64EncodedString:beforeStringImage];
//  UIImage *beforeImage = [UIImage imageWithData:dataObj];

Answer 1

If you want to call the method from same class, you could call like as follows:

UIImage *image = [UIImage imageNamed:@"someimg.png"];
NSString *str = [self getStringFromImage:image];

Else, if you want call the method from different class, then do as follows:
Assume clInstance be the instance of the class having that method, then

UIImage *image = [UIImage imageNamed:@"someimg.png"];
NSString *str = [clInstance getStringFromImage:image];