如何保存窗口状态

在iPhone手机客户端开发过程中经常会涉及到一些问题，如：如何保存窗口状态等等。

      当应用别切到后台后，很难保证应用不被杀掉（用户主动杀掉或被系统杀掉），如果被杀掉，当程序

再次启动时就需要恢复前一次状态。ios sdk 6.0提供了一些接口让我们很容易实现对应用状态的保存，具体做法如下：

      首先在AppDelegate中要实现如下几个方法：

1. - (BOOL)application:(UIApplication *)application shouldSaveApplicationState:(NSCoder *)coder {
   
2. return YES;
   
3. }
   
4. - (BOOL)application:(UIApplication *)application shouldRestoreApplicationState:(NSCoder *)coder {
   
5. return YES;
   
6. }
   
7. - (void)application:(UIApplication *)application willEncodeRestorableStateWithCoder:(NSCoder *)coder {
   
8. [coder encodeObject:self.window.rootViewController forKey:PDAppDelegateRootViewCTLKey];
   
9. }
   
10. - (void)application:(UIApplication *)application didDecodeRestorableStateWithCoder:(NSCoder *)coder {
    
11. UIViewController * ctl = [coder decodeObjectForKey:PDAppDelegateRootViewCTLKey];
    
12. if (ctl) {
    
13. UIWindow * window = [[UIWindow alloc] initWithFrame:[[UIScreen mainScreen] bounds]];
    
14. window.rootViewController = ctl; 
    
15. self.window = window;
    
16. }
    
17. }

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程序启动时会先调用

shouldRestoreApplicationState方法，因为方法返回YES，表明恢复应用状态，这时会顺序调用

didDecodeRestorableStateWithCoder方法，最后调用

didFinishLaunchingWithOptions, 该方法实现如下：

1. - (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions {
   
2. if (_window == nil) {
   
3. self.window = [[[UIWindow alloc] initWithFrame:[[UIScreen mainScreen] bounds]] autorelease];
   
4. // Override point for customization after application launch.
   
5. PDViewController *viewController = [[[PDViewController alloc] initWithNibName:nil bundle:nil] autorelease];
   
6. self.window.rootViewController = viewController;
   
7. }
   
8. [self.window makeKeyAndVisible];
   
9. return YES;
   
10. }

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这里还涉及到一个ViewController的写法，该程序主要是为了保存ViewCtronller中的状态，所以ViewCtronller必须要支持状态恢复，如下：

1. @interface PDViewController : UIViewController<UIViewControllerRestoration> {
   
2. int _sliderValue;
   
3. }
   
4. 
   
5. @end
   

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为了支持状态恢复必须实现UIViewControllerRestoration接口，同时还有几个方法需要实现：

1. - (void)encodeRestorableStateWithCoder:(NSCoder *)coder {
   
2. [super encodeRestorableStateWithCoder:coder];
   
3. [coder encodeInt:_sliderValue forKey:@"sliderValue"];
   
4. }
   
5. - (void)decodeRestorableStateWithCoder:(NSCoder *)coder {
   
6. [super decodeRestorableStateWithCoder:coder];
   
7. _sliderValue = [coder decodeIntForKey:@"sliderValue"];
   
8. UISlider *slider = (UISlider*)[self.view viewWithTag:SliderTag];
   
9. slider.value = _sliderValue;
   
10. UITextField *textField = (UITextField*)[self.view viewWithTag:TextFieldTag];
    
11. textField.text = [NSString stringWithFormat:@"%d", _sliderValue]; 
    
12. }
    
13. + (UIViewController *) viewControllerWithRestorationIdentifierPath:(NSArray *)identifierComponents coder:(NSCoder *)coder {
    
14. UIViewController *retViewController = [[[PDViewController alloc] initWithNibName:nil bundle:nil] autorelease];
    
15. return retViewController;
    
16. }

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通过以上基本既可实现窗口状态的保存

参考：http://www.apkbus.com/android-130188-1-1.html