NSUserDefaults正确使用并检测更改

如何解决NSUserDefaults正确使用并检测更改

| 我是一个初学者，正在构建一个iOS Universal应用程序，该应用程序在应用程序生命周期的各个阶段都使用NSUserDefaults-包括用于设置这些变量的应用程序内页面。我发现我的UserDefaults通常与UI不同步，并且编写代码来检查这些首选项很繁琐。 正如您在下面看到的那样，我正在检查“使用相机”偏好设置是否设置过高；一定有更简单的方法...？ 当加载允许在应用程序中编辑用户首选项的viewController时，Get \更糟糕： 是否有某种方法可以消除一些代码量（从而最大程度地减少调试/对内存优化的工作量），而不必经常检查首选项的值是多少？我是否应该使用NSUserDefaultsDidChangeNotification检测到更改，并在此通知方法内设置AppDelegate变量一次？ 示例（明显的省略假定存在这些方法...与我的偏好无关： 在我的AppDelegate中：

#progma mark Application Lifecycle
- (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions {
    NSUserDefaults *prefs = [NSUserDefaults standardUserDefaults];

    // check values; if not present,set some defaults.
    if (![prefs stringForKey:@\"pfUseCamera\"]) {
        [prefs setValue:@\"NO\" forKey:@\"pfUseCamera\"];
    }

    if (![prefs stringForKey:@\"pfWorkInBackground\"]) {
        [prefs setValue:@\"NO\" forKey:@\"pfWorkInBackground\"];
    }

    [prefs synchronize];

    self.backgroundTasksTimer = [NSString stringWithString:[prefs stringForKey:@\"pfWorkInBackground\"]];
    self.shouldUseCamera = [NSString stringWithString:[prefs stringForKey:@\"pfUseCamera\"]];

    // start our timer
    // chose to run this timer ALL-the-time,dispite the user-preference; instead,see below that the timer method returns based on the user preference.
    [NSTimer scheduledTimerWithTimeInterval:10.0 target:self selector:@selector(backgroundTasks:) userInfo:nil repeats:YES];
}

- (void)applicationDidBecomeActive:(UIApplication *)application {
    // pretty much the same as above
    // except NSTimer,which is controlled elsewhere
}

#progma mark AppDelegate-controlled Methods
- (void)backgroundTasks:(NSTimer *)timer { 
    if (![self.backgroundTasksTimer boolValue]) {
        return;
    } else {
        // do stuff in a timer begun in AppDelegate only if this preference is NOT NO
    }
}

我的主要ViewController：

#progma mark ViewController Lifecycle
- (void)viewDidLoad {
    [super viewDidLoad];
    MyAppDelegate *app = [MyAppDelegate sharedAppDelegate]; // I have this set up in the AppDelegate to allow this
    if ([app.shouldUseCamera boolValue]) {
        // init the camera and have it ready for use
    }
}

- (void)viewDidAppear:(BOOL)animated {
    MyAppDelegate *app = [MyAppDelegate sharedAppDelegate]; // I have this set up in the AppDelegate to allow this
    if ([app.shouldUseCamera boolValue]) {
        // resume the camera capture
    }
}

- (void)viewDidDisappear:(BOOL)animated {
    [super viewDidDisappear:animated];

    MyAppDelegate *app = [MyAppDelegate sharedAppDelegate]; 
    if ([app.shouldUseCamera boolValue]) {
        // suspend the camera capture
    }
}

- (void)viewDidUnload {
    MyAppDelegate *app = [MyAppDelegate sharedAppDelegate]; 
    if ([app.shouldUseCamera boolValue]) {
        // unload the camera
    }
}

#progma mark User/IBAction Methods
-(IBAction)doStuff:(id)sender {
    MyAppDelegate *app = [MyAppDelegate *app = [MyAppDelegate sharedAppDelegate]; sharedAppDelegate];   

    // take a picture
    if ([app.shouldUseCamera boolValue]) {
        [NSThread detachNewThreadSelector:@selector(takePicture:) toTarget:self withObject:fileName];  // take a photo and do stuff to it in a separate thread
    }   
}

SettingsViewController：

- (void)viewDidLoad {
    NSUserDefaults *prefs = [NSUserDefaults standardUserDefaults];
    MyAppDelegate *app = [MyAppDelegate sharedAppDelegate];

    // set UITextField to value of String Preference
    someUITextField.text = [prefs stringForKey:@\"pfSomeOtherValue\"];

    // set UISwitch to value of PSToggleSwitchSpecifier
    if ([app.backgroundTasksTimer boolValue]) {
        [shouldExecuteBackgroundTasks setOn:YES];
    } else {
        [shouldExecuteBackgroundTasks setOn:NO];
    }

    // set UISwitch to value of PSToggleSwitchSpecifier
    if ([app.shouldUseCamera boolValue]) {
        [shouldUseCamera setOn:YES];
    } else {
        [shouldUseCamera setOn:NO];
    }

- (IBAction)done:(id)sender {
    NSUserDefaults *prefs = [NSUserDefaults standardUserDefaults];
    MyAppDelegate *app = [MyAppDelegate sharedAppDelegate];
    [prefs setObject:companyID.text forKey:@\"pfCompanyID\"];

    if ([shouldUseCamera isOn]) {
        [prefs setObject:@\"YES\" forKey:@\"pfUseCamera\"];
        app.backgroundTasksTimer = @\"YES\";
    } else {
        [prefs setObject:@\"NO\" forKey:@\"pfUseCamera\"];
        app.backgroundTasksTimer = @\"NO\";
    }

    if ([shouldExecuteBackgroundTasks isOn]) {
        [prefs setObject:@\"YES\" forKey:@\"pfWorkInBackground\"];
        app.shouldUseCamera = @\"YES\";
    } else {
        [prefs setObject:@\"NO\" forKey:@\"pfWorkInBackground\"];
        app.shouldUseCamera = @\"NO\";
    }
    [prefs synchronize];

    [self.delegate settingsControllerDidFinish:self];
}

    

解决方法

一种方法是摆脱应用程序委托中的字段，而仅使用NSUserDefaults。我不确定这样做的开销，但是有一个带有静态访问器的“ Config \”类。另外，您可以考虑使用bool（和其他）访问器，例如：

@implementation Config

    +(BOOL)shouldUseCamera {
       NSUserDefaults *defaults = [NSUserDefaults standardUserDefaults];
       return [defaults boolForKey:@\"shouldUseCamera\"];
    }

    +(void)setShouldUseCamera:(BOOL)should {
       NSUserDefaults *defaults = [NSUserDefaults standardUserDefaults];
       [defaults setBool:should forKey:@\"shouldUseCamera\"];
    }

然后从任何地方访问这些都是很重要的。我将在同一Config类中使用NSBundle和NSProcessInfo，然后我的应用程序将所有配置放在一个位置。 另外，根据我所读的内容，您通常不必调用同步。     ,看一下该主题，该主题通过注册默认更改的更改通知来进行。 Nsuserdefaultschange 如果需要多个视图来检查此值，则可以将该值作为应用程序委托的属性公开，并在需要时检查该属性。应用程序委托将订阅通知，并在触发时重新加载属性值。