Proxy Pattern in iOS - Swift - ios

Question

I need to create proxy pattern in iOS using swift
I have tried it using Objective C and here is the code
MyProtocol.h
#import <Foundation/Foundation.h>
#protocol MyProtocol <NSObject>
#required
-(void)testMessage;
#end
TestBO.h
#import <Foundation/Foundation.h>
#import "MyProtocol.h"
#interface TestBO : NSObject <MyProtocol>
#end
TestBO.m
#import "TestBO.h"
#implementation TestBO
-(void)testMessage{
NSLog(#"Test Message");
}
#end
TestProxyHandler.h
#import <Foundation/Foundation.h>
#interface TestProxyHandler : NSProxy
#property (nonatomic, strong) id object;
- (instancetype)initWithProtocol:(Protocol *)protocol andObject:(Class)clazz;
- (void)forwardInvocation:(NSInvocation *)invocation;
- (NSMethodSignature *)methodSignatureForSelector:(SEL)selector;
#end
TestProxyHandler.m
#import "TestProxyHandler.h"
#import "TestBO.h"
#implementation TestProxyHandler
- (instancetype)initWithProtocol:(Protocol *)protocol andObject:(Class)clazz{
if ([clazz conformsToProtocol:#protocol(MyProtocol)]) {
self.object = [[clazz alloc] init];
}else{
NSLog(#"Error it does not conform to protocol");
}
return self;
}
- (void)forwardInvocation:(NSInvocation *)invocation{
NSString *selString = NSStringFromSelector(invocation.selector);
NSLog(#"Called %#",selString);
[invocation invokeWithTarget:self.object];
}
- (NSMethodSignature *)methodSignatureForSelector:(SEL)selector {
return [self.object methodSignatureForSelector:selector];
}
#end
I have invoked it using
id <MyProtocol> delegate = (TestBO *)[[TestProxyHandler alloc] initWithProtocol:#protocol(MyProtocol) andObject:[TestBO class]];
[delegate testMessage];
But I am not able to make it work in Swift even the initialzier is showing that the message
TestHandler.swift
import Foundation
class TestHandler: NSProxy {
var object: AnyObject
convenience override init(`protocol`: Protocol, andObject clazz: AnyClass) {
if clazz.conformsToProtocol() {
self.object = clazz()
}
else {
NSLog("Error it does not conform to protocol")
}
}
}
Does anyone have any clue to do this in swift ??
EDIT:
In java you can create runtime implementation of a method using the Proxy.newProxyInstance call but can this be achieved in iOS ? using swift ? Any clue ?

Answer 1

Comparing with Objective C and Swift, Swift offers extremely limited access to runtime language access . So based on my research till now it can’t be done :(
I even tried subclassing the NSProxy class in swift but just couldn’t call the super.init and code never compiles but however same thing works in objective C
So I ended up doing this approach
I created a protocol using
#objc protocol SomeProt {
// Some method
}
Note the keyword #objc before protocol is essential else you would not be able to pass it as a variable, also adding #objc limits the usage of protocol to objective c runtime features so don’t expect to get full features of protocols in swift
public func someMethod(`protocol` : Protocol, implementation : AnyClass) {
let isImplemented : Bool = implementation.conformsToProtocol(`protocol`)
// some code
}
If you need to use it in some dictionary or places where it should conform to NSCopying class then use
NSStringFromProtocol
and
NSProtocolFromString
methods
Now I have wrote a objective c helper class to do the initialization
ObjcHelper.h
#import <Foundation/Foundation.h>
#interface ObjcHelper : NSObject
+(NSObject *)objectForClass:(Class)clazz;
#end
ObjcHelper.m
#import "ObjcHelper.h"
#implementation ObjcHelper
+ (NSObject *)objectForClass:(Class)clazz{
return [[clazz alloc] init];
}
#end
Now to use it
let prot : SomeProt = ObjcHelper.objectForClass(NSClassFromString("PROT_HANDLER_CLASS_NAME")) as! SomeProt
However in future if anyone can offer a better answer then please be sure to post it here