使用NSAlerts和NSNotifications和可達性2.2

Question

我已經在新的iOS 4.2項目中實現了Apple的Reachability 2.2類。我只想在設備失去網絡連接時顯示警報視圖。 （因此符合App Store的界面可用性要求。）我用this previous SO question作爲我的出發點。該應用程序似乎正確通知（當連接中斷或恢復），但我得到循環與我的NS警報視圖。我認爲我的錯誤一定是基本的，但我無法理解。如果有沒有NS AlertView的更清潔的方法，我也可以這樣做。我在下面的代碼中留下了一些方法，但該應用程序非常簡單，只有一個ViewController。

ViewController.h：

#import <UIKit/UIKit.h> 
#import "Reachability.h" 

@class Reachability; 

@interface ViewController : UIViewController { 

IBOutlet UITextView *liveOutputTextView; 
IBOutlet UITextView *textView; 
Reachability* internetReachable; 
    Reachability* hostReachable; 

} 

-(IBAction)action1:(id)sender; 
-(IBAction)action2:(id)sender; 

-(void)textFieldDidUpdate:(id)sender; 
-(void)checkNetworkStatus:(NSNotification *)notice; 

@end 

ViewController.m

#import "ViewController.h" 
#import "Reachability.h" 

@implementation ViewController 

@synthesize liveOutputTextField; 

- (void)checkNetworkStatus:(NSNotification *)notice 

{ 
// called after network status changes 

NetworkStatus internetStatus = [internetReachable currentReachabilityStatus]; 

switch (internetStatus) 

case NotReachable: 
    { 
     NSLog(@"The internet is inaccessible."); 


     UIAlertView * alert = [[UIAlertView alloc] initWithTitle:@"Internet inaccessible." 
                 message:@"Internet inaccessible." 
                 delegate:self 
               cancelButtonTitle:@"Ok" 
     otherButtonTitles:nil]; 

     [alert show]; 
     [alert release]; 

     break; 

    } 
    case ReachableViaWiFi: 

    { 
     NSLog(@"Internet Connetion is UP."); 


     UIAlertView * alert = [[UIAlertView alloc] initWithTitle:@"Internet is Up" 
                 message:@"Internet Up" 
                 delegate:self 
               cancelButtonTitle:@"Ok" 
               otherButtonTitles:nil]; 
     [alert show]; 
     [alert release]; 

     break; 
    } 


    case ReachableViaWWAN: 
    { 
     NSLog(@"The internet is working via WWAN."); 

     break; 
    } 

} 


NetworkStatus hostStatus = [hostReachable currentReachabilityStatus]; 
switch (hostStatus) 

{ 
    case NotReachable: 
    { 
     NSLog(@"A gateway to the host server is down."); 


     UIAlertView * alert = [[UIAlertView alloc] initWithTitle:@"Host is Down" 
                 message:@"Host Down" 
                 delegate:self 
               cancelButtonTitle:@"Ok" 
               otherButtonTitles:nil]; 
     [alert show]; 
     [alert release]; 

     break; 

    } 
    case ReachableViaWiFi: 
    { 
     NSLog(@"A gateway to the host server is working via WIFI."); 

     break; 

    } 
    case ReachableViaWWAN: 
    { 
     NSLog(@"A gateway to the host server is working via WWAN."); 

     break; 
    } 
} 

} 



- (void)viewDidLoad { 

// check for internet connection 
[[NSNotificationCenter defaultCenter] addObserver:self 
                 selector:@selector(checkNetworkStatus:) 
              name:kReachabilityChangedNotification 
                object:nil]; 

internetReachable = [[Reachability reachabilityForInternetConnection] retain ]; 
[internetReachable startNotifier]; 


// check if a pathway to a random host exists 

hostReachable = [[Reachability reachabilityWithHostName: @"www.apple.com"]retain ]; 
[hostReachable startNotifier]; 

// now patiently wait for the notification 


} 

- (void)viewDidAppear:(BOOL)animated { 

// check for internet connection 
[[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(checkNetworkStatus:) name:kReachabilityChangedNotification object:nil]; 


internetReachable = [[Reachability reachabilityForInternetConnection] retain]; 
[internetReachable startNotifier]; 

// check if a pathway to a random host exists 
hostReachable = [[Reachability reachabilityWithHostName: @"www.apple.com"] retain]; 
[hostReachable startNotifier]; 

// now patiently wait for the notification 

} 


-(IBAction) action1:(id)sender { 

// check for internet connection 
[[NSNotificationCenter defaultCenter] addObserver:self 
              selector:@selector(checkNetworkStatus:) 
              name:kReachabilityChangedNotification 
              object:nil]; 

internetReachable = [[Reachability reachabilityForInternetConnection] retain]; 
[internetReachable startNotifier]; 

// check if a pathway to a random host exists 
hostReachable = [[Reachability reachabilityWithHostName: @"www.apple.com"] retain]; 
[hostReachable startNotifier]; 

// now patiently wait for the notification 

// ** LEFT OUT ACTUAL CODE FOR BREVITY ** 

} 

-(IBAction) action2:(id)sender { 

// check for internet connection 
[[NSNotificationCenter defaultCenter] addObserver:self 
              selector:@selector(checkNetworkStatus:) 
              name:kReachabilityChangedNotification 
               object:nil]; 

internetReachable = [[Reachability reachabilityForInternetConnection] retain]; 
[internetReachable startNotifier]; 

// check if a pathway to a random host exists 
hostReachable = [[Reachability reachabilityWithHostName: @"www.apple.com"] retain]; 
[hostReachable startNotifier]; 

// now patiently wait for the notification 

// ** LEFT OUT ACTUAL CODE FOR BREVITY ** 

} 

- (void)viewDidUnload { 

// Release any retained subviews of the main view. 
// e.g. self.myOutlet = nil; 


    [[NSNotificationCenter defaultCenter] removeObserver:self]; 
} 


- (void)dealloc { 

[super dealloc]; 

} 

Answer 1

請記住，通知已發送和處理後，即通知需要從通知中心移除。否則，只要您的可訪問性狀態發生變化，您就會收到警報。

例如，對於刪除的通知，你可以這樣做：

[[NSNotificationCenter defaultCenter] removeObserver:self 
name:kReachabilityChangedNotification 
object:nil]; 

請記住，如果你需要重新添加它。

Answer 2

添加通知視圖確實出現足以處理響應。如果添加更多次，則多次呼叫回叫。