How do we hide private class when using it in Objective-C? - ios

Question

Question
How do we hide private class when using it in Objective-C?
For example, as described below
PrivateFilter is the class I want to hide.
CustomFilter is the class I make, which is open.
GPUImageFilter is the class public on Github, which is open, too.
And CustomFilter actully wraps the functionallity of PrivateFilter.
#interface CustomFilter : GPUImageFilter
#end
#interface PrivateFilter : GPUImageFilter
#end
Possible Solutions
So there are two solutions:
Solution 1: Class cluster
Have a look at the example A Composite Object: An Example in the Apple document.
I followed the steps and make the following code.
// CustomFilter.h
#interface CustomFilter : GPUImageFilter
#end
// CustomFilter.m
#interface CustomFilter()
#property (nonatomic, strong) PrivateFilter *privateFilter;
#end
#implementation CustomFilter
- (instancetype)init
{
self = [super init];
if (self) {
_privateFilter = [[PrivateFilter alloc] init];
}
return self;
}
// and then override the most of GPUImageFilter functions...
#end
But somehow it doesn't work, so I try the solution 2.
Solution 2: Init with PrivateFilter
// CustomFilter.h
#interface CustomFilter : GPUImageFilter
#end
// CustomFilter.m
#implementation CustomFilter
- (CustomFilter *)init
{
self = (CustomFilter *)[[PrivateFilter alloc] init];
return self;
}
#end
This works, but it's very strange to use alloc in init.
So I try the solution 3.
Solution 3: factory class method
// CustomFilter.h
#interface CustomFilter : GPUImageFilter
+ (CustomFilter *)filter;
#end
// CustomFilter.m
#implementation CustomFilter
+ (CustomFilter *)filter
{
CustomFilter *filter = (CustomFilter *)[[PrivateFilter alloc] init];
return filter;
}
#end
This works, but it could not be inherited, just like class cluster.
Repeat Question
SO which is the best solution? Or is there other some good solutions?

Answer 1

I think you need protocol, instead of CustomFilter with factory approach. If you need some GPUImageFilter subclass you can make GPUImageFilter<CustomFilter>
//CustomFilter.h
#protocol CustomFilter
...
#end
typedef GPUImageFilter<CustomFilter> CustomFilter;
//PrivateFilter.h
#import "CustomFilter.h"
#interface PrivateFitler: CustomFilter
...
#end
//GPUImageFilter+CustomFilter.h
#interface GPUImageFilter(CustomFilter)
+ (CustomFilter *)filter;
#end
//GPUImageFilter+CustomFilter.m
#import "PrivateFilter.h"
#implementation GPUImageFilter(CustomFilter)
+ (CustomFilter *)filter
{
return [[PrivateFilter alloc] init;
}
#end
With such approach Xcode even give you warnings if you forget to implement some methods.