如果同时覆盖setter和getter，编译器将不再为你自动创建实例变量。您可以将其添加到类实现中，如下所示：

If you override both the setter and the getter, the compiler will not automatically create the instance variable for you anymore. You can add it to your class implementation like so:

@implementation ClassName {
    ViewFrameModel *_viewFrameModel;
}
...
@end