[NSObject mutableArrayValueForKey:<#(nonnull NSString *)#>]
通过上面的方法获取到mutableArray并进行操作则可以对数组进行监听
@property (nonatomic, strong) NSMutableArray *mtbArray;
[[self mutableArrayValueForKey:@"mtbArray"] removeObjectAtIndex:0];
[[self mutableArrayValueForKey:@"mtbArray"] insertObject:@"" atIndex:1];