给NSMutableArray创建独立实例

需要一份NSMutableArray的复制，所以我用mutableCopy方法。但是我发现如果修改了复制品中的数据，原版也会跟着改变。不知道其他创建NSMutableArray的方法是什么？

delegate = (AppDelegate *)[[UIApplication sharedApplication]delegate];
 self.mainImagesArray = [[NSMutableArray alloc]initWithArray:[delegate.arrayForCarCaptureImages mutableCopy]];

修改代码：

UIImage *filteredImage =[[[[self.mainImagesArray objectAtIndex:i]valueForKey:valueVheck] objectAtIndex:j]  copy];
filteredImage =[filteredImage brightness:(1+sliderValue-0.5)];
[[[self.mainImagesArray objectAtIndex:i]valueForKey:valueVheck]removeObjectAtIndex:j];
[[[self.mainImagesArray objectAtIndex:i] valueForKey:valueVheck]insertObject:filteredImage atIndex:j];

一旦执行arrayForCarCaptureImages也会自动改变。