Runtime使用场景

#import "NSMutableArray+Extension.h"
#import <objc/runtime.h>

@implementation NSMutableArray (Extension)

+ (void)load {
    Class cls = NSClassFromString(@"__NSArrayM");
    Method method1 = class_getInstanceMethod(cls, @selector(insertObject:atIndex:));
    Method method2 = class_getInstanceMethod(cls, @selector(dn_insertObject:atIndex:));
    method_exchangeImplementations(method1, method2);
    
    Method method3 = class_getInstanceMethod(cls, @selector(objectAtIndex:));
    Method method4 = class_getInstanceMethod(cls, @selector(dn_objectAtIndex:));
    method_exchangeImplementations(method3, method4);
}
- (void)dn_insertObject:(id)anObject atIndex:(NSUInteger)index {
    if (anObject == nil) {
        return;
    }
    [self dn_insertObject:anObject atIndex:index];
}
- (id)dn_objectAtIndex:(NSUInteger)index {
    if (self.count == 0) {
        return nil;
    }
    return [self dn_objectAtIndex:index];
}

@end

#import "NSMutableDictionary+Extension.h"
#import <objc/runtime.h>

@implementation NSMutableDictionary (Extension)

+ (void)load {
    Class cls = NSClassFromString(@"__NSDictionaryM");
    Method method1 = class_getInstanceMethod(cls, @selector(setObject:forKeyedSubscript:));
    Method method2 = class_getInstanceMethod(cls, @selector(dn_setObject:forKeyedSubscript:));
    method_exchangeImplementations(method1, method2);
    
    Method method3 = class_getInstanceMethod(cls, @selector(setObject:forKey:));
    Method method4 = class_getInstanceMethod(cls, @selector(dn_setObject:forKey:));
    method_exchangeImplementations(method3, method4);
}

- (void)dn_setObject:(id)obj forKeyedSubscript:(id<NSCopying>)key {
    if (key == nil) {
        return;
    }
    [self dn_setObject:obj forKeyedSubscript:key];
}
- (void)dn_setObject:(id)anObject forKey:(id<NSCopying>)aKey {
    if (anObject == nil || aKey == nil) {
        return;
    }
    [self dn_setObject:anObject forKey:aKey];
}

@end