objective-c - 如何通过 NSInvocation 调用类方法？

Question

我们可以NSMethodSignature过+ (NSMethodSignature *)instanceMethodSignatureForSelector:(SEL)aSelector的NSObject。然后NSInvocation由+ (NSInvocation *)invocationWithMethodSignature:(NSMethodSignature *)signature

这是问题所在。我们只能获取实例的方法签名，那么类方法呢？

Answer 1

您可以通过以下方式获取类方法：

NSMethodSignature *pMS = [[YourObject class] methodSignatureForSelector: (SEL)aSelector];

该片段[YourObject class]返回一个类对象的实例（单例），然后您可以使用它来获取类方法。

添加：来自以下评论的新信息。您可以执行以下操作：

NSMethodSignature *pMS = [YourObject methodSignatureForSelector: (SEL)aSelector];

Answer 2

methodForSignature:这是有关通过 NSInvocation 显示和调用类（和实例方法）的其他详细信息instanceMethodForSignature:

@interface SomeObject : NSObject
+ (void)instanceAndClass;
- (void)instanceAndClass;
+ (void)classOnly;
- (void)instanceOnly;
@end

@implementation SomeObject
+ (void)instanceAndClass { NSLog(@"Class version"); }
- (void)instanceAndClass { NSLog(@"Instance version"); }    
+ (void)classOnly { NSLog(@"Class only"); }
- (void)instanceOnly { NSLog(@"Instance only"); }
@end

@implementation Foo

- (void)invoke:(id)receiver signature:(NSMethodSignature *)signature selector:(SEL)selector {
    if (!signature) {
        NSLog(@"method signature is nil");
        return;
    }        
    NSInvocation *invocation = [NSInvocation invocationWithMethodSignature:signature];
    invocation.selector = selector;
    invocation.target = receiver;
    [invocation invoke];
}

- (void)foo {
    NSMethodSignature *signature;
    SomeObject *someObject = [SomeObject new];

    signature = [someObject methodSignatureForSelector:@selector(instanceAndClass)];
    [self invoke:someObject signature:signature selector:@selector(instanceAndClass)];
    // 2015-07-10 11:01:10.227 FooBar[65312:3097866] Instance version
    [self invoke:[someObject class] signature:signature selector:@selector(instanceAndClass)];
    // 2015-07-10 11:01:10.227 FooBar[65312:3097866] Class version

    signature = [someObject methodSignatureForSelector:@selector(classOnly)];
    [self invoke:someObject signature:signature selector:@selector(classOnly)];
    // 2015-07-10 11:01:10.227 FooBar[65312:3097866] method signature is nil

    signature = [[someObject class] methodSignatureForSelector:@selector(classOnly)];
    [self invoke:[someObject class] signature:signature selector:@selector(classOnly)];
    // 2015-07-10 11:01:10.228 FooBar[65312:3097866] Class only

    signature = [someObject methodSignatureForSelector:@selector(instanceOnly)];
    [self invoke:someObject signature:signature selector:@selector(instanceOnly)];
    // 2015-07-10 11:01:10.228 FooBar[65312:3097866] Instance only

    signature = [[someObject class] methodSignatureForSelector:@selector(instanceOnly)];
    [self invoke:[someObject class] signature:signature selector:@selector(instanceOnly)];
    2015-07-10 11:01:10.228 FooBar[65312:3097866] method signature is nil

    signature = [[someObject class] instanceMethodSignatureForSelector:@selector(instanceOnly)];
    [self invoke:someObject signature:signature selector:@selector(instanceOnly)];
    // 2015-07-10 11:01:10.228 FooBar[65312:3097866] Instance only
}