是否可以在addObject: in NSMutableArray中使用swizzle？

Question

是否可以对addObject: NSMutableArray方法进行分步处理？

这是我正在尝试的。

#import <Foundation/Foundation.h>
#import <objc/runtime.h>

@implementation NSMutableArray (LoggingAddObject)


+ (void)load {
Method addObject = class_getInstanceMethod(self, @selector(addObject:));
Method logAddObject = class_getInstanceMethod(self, @selector(logAddObject:));
method_exchangeImplementations(addObject, logAddObject);

Method original = class_getInstanceMethod(self, @selector(setObject:atIndexedSubscript:));
Method swizzled = class_getInstanceMethod(self, @selector(swizzled_setObject:atIndexedSubscript:));
method_exchangeImplementations(original, swizzled);
}


- (void)logAddObject:(id)anObject {
[self logAddObject:anObject];
NSLog(@"Added object %@ to array %@", anObject, self);
}

-(void)swizzled_setObject:(id)obj atIndexedSubscript:(NSUInteger)idx
{
NSLog(@"This gets called as expected!!-----");
[self swizzled_setObject:obj atIndexedSubscript:idx];  
}

我可以使用一些方法，如setObject:atIndexedSubscript:但我担心我不能这样做，比如addObject:和其他方法。我想下面的话不可以被挥霍吗？谁能解释一下原因吗？我做错了什么或者绕过这件事？

/****************   Mutable Array       ****************/

@interface NSMutableArray : NSArray

- (void)addObject:(id)anObject;
- (void)insertObject:(id)anObject atIndex:(NSUInteger)index;
- (void)removeLastObject;
- (void)removeObjectAtIndex:(NSUInteger)index;
- (void)replaceObjectAtIndex:(NSUInteger)index withObject:(id)anObject;

@end

Answer 1

您可以在NSProxy中尝试这一点，但我不建议您在生产代码中使用它，因为：

• 它会破坏某些东西(某些框架可能要求NSMutableArray在向其中添加nil时抛出异常，以防止以后发生更严重的错误。即Fail fast)
• 太慢了

如果您真的想避免nil检查，我建议您创建一个NSMutableArray子类，并在代码中的任何地方使用它。但真的吗？使用ObjC的NSMutableArray代码太多，其中大多数不需要这个特性。那你为什么这么特别？

#import <objc/runtime.h>

@interface XLCProxy : NSProxy

+ (id)proxyWithObject:(id)obj;

@end

@implementation XLCProxy
{
    id _obj;
}

+ (void)load
{
    Method method = class_getClassMethod([NSMutableArray class], @selector(allocWithZone:));
    IMP originalImp = method_getImplementation(method);

    IMP imp = imp_implementationWithBlock(^id(id me, NSZone * zone) {
        id obj = ((id (*)(id,SEL,NSZone *))originalImp)(me, @selector(allocWithZone:), zone);
        return [XLCProxy proxyWithObject:obj];
    });

    method_setImplementation(method, imp);
}

+ (id)proxyWithObject:(id)obj
{
    XLCProxy *proxy = [self alloc];
    proxy->_obj = obj;
    return proxy;
}

- (void)forwardInvocation:(NSInvocation *)invocation
{
    [invocation setTarget:_obj];
    [invocation invoke];
    const char *selname = sel_getName([invocation selector]);
    if ([@(selname) hasPrefix:@"init"] && [[invocation methodSignature] methodReturnType][0] == '@') {
        const void * ret;
        [invocation getReturnValue:&ret];
        ret = CFBridgingRetain([XLCProxy proxyWithObject:CFBridgingRelease(ret)]);
        [invocation setReturnValue:&ret];
    }
}

-(NSMethodSignature *)methodSignatureForSelector:(SEL)sel
{
    return [_obj methodSignatureForSelector:sel];
}

- (Class)class
{
    return [_obj class];
}

- (void)addObject:(id)obj
{
    [_obj addObject:obj ?: [NSNull null]];
}

- (BOOL)isEqual:(id)object
{
    return [_obj isEqual:object];
}

- (NSUInteger)hash {
    return [_obj hash];
}

// you can add more methods to "override" methods in `NSMutableArray` 

@end

@interface NSMutableArrayTests : XCTestCase

@end

@implementation NSMutableArrayTests

- (void)testExample
{
    NSMutableArray *array = [NSMutableArray array];
    [array addObject:nil];
    [array addObject:@1];
    [array addObject:nil];
    XCTAssertEqualObjects(array, (@[[NSNull null], @1, [NSNull null]]));
}

@end

Answer 2

您可以迭代所有已注册的类，检查当前类是否是NSMutableArray的子类，如果是，请检查swizzle。

我建议您不要这样做，而是在逐个案例的基础上采取行动，以便具有更可预测的行为--您永远不知道在这种特定行为中其他系统框架依赖哪个系统框架(例如，我可以看到CoreData如何依赖于这种特定行为)。

Answer 3

您可以以以下方式对任何NSMutableArray方法进行分步操作：

@implementation NSMutableArray (Swizzled)

+ (void)load
{
    Method orig = class_getInstanceMethod(NSClassFromString(@"__NSArrayM"), NSSelectorFromString(@"addObject:"));
    Method override = class_getInstanceMethod(NSClassFromString(@"__NSArrayM"), @selector(addObject_override:));

    method_exchangeImplementations(orig, override);
}

- (void)addObject_override:(id)anObject
{
   [self addObject_override:anObject];

   NSLog(@"addObject called!");
}