How to swizzle a class method on iOS?

Method swizzling works great for instance methods. Now, I need to swizzle a c开发者_如何学编程lass method. Any idea how to do it?

Tried this but it doesn't work:

void SwizzleClassMethod(Class c, SEL orig, SEL new) {

Method origMethod = class_getClassMethod(c, orig);
Method newMethod = class_getClassMethod(c, new);

if(class_addMethod(c, orig, method_getImplementation(newMethod), method_getTypeEncoding(newMethod)))
    class_replaceMethod(c, new, method_getImplementation(origMethod), method_getTypeEncoding(origMethod));
else
    method_exchangeImplementations(origMethod, newMethod);
}

Turns out, I wasn't far away. This implementation works for me:

void SwizzleClassMethod(Class c, SEL orig, SEL new) {

    Method origMethod = class_getClassMethod(c, orig);
    Method newMethod = class_getClassMethod(c, new);

    c = object_getClass((id)c);

    if(class_addMethod(c, orig, method_getImplementation(newMethod), method_getTypeEncoding(newMethod)))
        class_replaceMethod(c, new, method_getImplementation(origMethod), method_getTypeEncoding(origMethod));
    else
        method_exchangeImplementations(origMethod, newMethod);
}

Objective-C swizzling using category

@interface cA : NSObject {

}
@end

@implementation cA

+(NSString*) cClassFooA {
    return @"class fooA";
}

-(NSString*) cFooA {
    return @"fooA";
}

@end


@interface cB : NSObject {

}
@end

@implementation cB

+(NSString*) cClassFooB {
    return @"class fooB";
}

-(NSString*) cFooB {
    return @"fooB";
}

@end

NSObject+Swizzling.h

#import <Foundation/Foundation.h>

@interface NSObject (Swizzling)

+ (void)cExchangeClassWithCls1:(Class)cls1 Sel1:(SEL)sel1 Cls2:(Class)cls2 Sel2:(SEL)sel2;
+ (void)cExchangeInstanceWithCls1:(Class)cls1 Sel1:(SEL)sel1 Cls2:(Class)cls2 Sel2:(SEL)sel2;

@end

NSObject+Swizzling.m

#import "NSObject+Swizzling.h"
#import <objc/runtime.h>

@implementation NSObject (Swizzling)

+ (void)cExchangeClassWithCls1:(Class)cls1 Sel1:(SEL)sel1 Cls2:(Class)cls2 Sel2:(SEL)sel2 {

    Method originalMethod = class_getClassMethod(cls1, sel1);
    Method swizzledMethod = class_getClassMethod(cls2, sel2);

    method_exchangeImplementations(originalMethod, swizzledMethod);
}

+ (void)cExchangeInstanceWithCls1:(Class)cls1 Sel1:(SEL)sel1 Cls2:(Class)cls2 Sel2:(SEL)sel2 {

    Method originalMethod = class_getInstanceMethod(cls1, sel1);
    Method swizzledMethod = class_getInstanceMethod(cls2, sel2);

    method_exchangeImplementations(originalMethod, swizzledMethod);
}
@end

using via Objective-C

- (void)testCExchangeClass {
    [NSObject cExchangeClassWithCls1:[cA class] Sel1:@selector(cClassFooA) Cls2:[cB class] Sel2:@selector(cClassFooB)];

    XCTAssertEqual(@"class fooB", [cA cClassFooA]);
}

- (void)testCExchangeInstance {
    [NSObject cExchangeInstanceWithCls1:[cA class] Sel1:@selector(cFooA) Cls2:[cB class] Sel2:@selector(cFooB)];

    XCTAssertEqual(@"fooB", [[[cA alloc] init] cFooA]);
}

[Add Swift as an consumer]

using via Swift

func testCExchangeClass() {
    NSObject.cExchangeClass(withCls1: sA.self, sel1: #selector(sA.sClassFooA), cls2: sB.self, sel2: #selector(sB.sClassFooB))

    XCTAssertEqual("class fooB", sA.sClassFooA())
}

func testCExchangeInstance() {
    NSObject.cExchangeInstance(withCls1: sA.self, sel1: #selector(sA.sFooA), cls2: sB.self, sel2: #selector(sB.sFooB))

    XCTAssertEqual("fooB", sA().sFooA())
}

[Swift swizzling]