我已经查看了苹果的“PageControl”示例项目(请点击这里),并在代码中看到了以下函数:
然后就在这之后:
- (void)loadScrollViewWithPage:(int)page
{
if (page < 0)
return;
if (page >= kNumberOfPages)
return;
// replace the placeholder if necessary
MyViewController *controller = [viewControllers objectAtIndex:page];
if ((NSNull *)controller == [NSNull null])
{
controller = [[MyViewController alloc] initWithPageNumber:page];
[viewControllers replaceObjectAtIndex:page withObject:controller];
[controller release];
}
// add the controller's view to the scroll view
if (controller.view.superview == nil)
{
CGRect frame = scrollView.frame;
frame.origin.x = frame.size.width * page;
frame.origin.y = 0;
controller.view.frame = frame;
[scrollView addSubview:controller.view];
NSDictionary *numberItem = [self.contentList objectAtIndex:page];
controller.numberImage.image = [UIImage imageNamed:[numberItem valueForKey:ImageKey]];
controller.numberTitle.text = [numberItem valueForKey:NameKey];
}
}
有些事情我不太明白。
如果测试部分 if ((NSNull *)controller == [NSNull null])
为真,则我们有
controller = [[MyViewController alloc] initWithPageNumber:page];
[viewControllers replaceObjectAtIndex:page withObject:controller];
[controller release];
然后就在这之后:
if (controller.view.superview == nil)
但是,控制器刚刚发布。我认为它可能有效,因为控制器仍然在内存中,但这不是编写代码的正确方式吗?