10、修改RootViewController.m：
打开RootViewController.m文件，在@implementation之前添加代码：
#import "FirstViewController.h"
#import "SecondViewController.h"
在@implementation之后添加代码：
@synthesize firstViewController;
@synthesize secondViewController;
接下来修改viewDidLoad方法，这个方法默认是被注释掉的，先去掉其周围的注释符，然后修改其代码如下：
- (void)viewDidLoad
{
self.firstViewController = [[FirstViewController alloc] initWithNibName:@"FirstView" bundle:nil];
[self.view insertSubview: firstViewController.view atIndex:0];
[super viewDidLoad];
}
添加switchViews方法：
- (IBAction)switchViews:(id)sender {
if (self.secondViewController.view.superview == nil) {
if (self.secondViewController == nil) {
self.secondViewController = [[SecondViewController alloc] initWithNibName:@"SecondView" bundle:nil];
}
[firstViewController.view removeFromSuperview];
[self.view insertSubview:self.secondViewController.view atIndex:0];
} else {
if (self.firstViewController == nil) {
self.firstViewController =
[[FirstViewController alloc] initWithNibName:@"FirstView" bundle:nil];
}
[secondViewController.view removeFromSuperview];
[self.view insertSubview:self.firstViewController.view atIndex:0];
}
}
修改didReceiveMemoryWarning方法：
- (void)didReceiveMemoryWarning
{
[super didReceiveMemoryWarning];
if (self.firstViewController.view.superview == nil) {
self.firstViewController = nil;
} else {
self.secondViewController = nil;
}
}
11、打开FirstView.xib文件，选择左边的File's Owner，然后在Identity Inspector中选择Class为FirstViewController；然后按住Control键从File's Owner图标拖到View，在弹出的菜单选择view。为SecondView.xib进行同样的操作，不过Class选择为SecondViewController。
12、打开FirstView.xib文件，选择View，打开Attribute Inspector，进行如下设置：
