如何通過NSInvocation調用類方法？

Question

我們可以通過+ (NSMethodSignature *)instanceMethodSignatureForSelector:(SEL)aSelector NSObject + (NSMethodSignature *)instanceMethodSignatureForSelector:(SEL)aSelector來獲取NSMethodSignature 。 然后通過+ (NSInvocation *)invocationWithMethodSignature:(NSMethodSignature *)signature構造NSInvocation

這是問題所在。 我們只能得到實例的方法簽名，類方法怎么樣？

Answer 1

您可以通過以下方式獲取類方法：

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

片段[YourObject class]返回類對象（singleton）的一個實例，然后您可以使用它來獲取類方法。

添加：以下評論的新信息。 您可以執行以下操作：

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

Answer 2

以下是有關通過顯示methodForSignature:和instanceMethodForSignature: NSInvocation調用類（和實例方法）的其他詳細信息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
}