尝试让网络错误警报显示在 iPhone 应用程序上？

好的，我正在尝试让这个应用程序显示网络错误警报代码。我添加了 SystemConfiguration.framework 框架和 Apple 的“Reachability”示例代码。

这是 viewcontroller.h 文件：

#import <UIKit/UIKit.h>

@class Reachability;

@interface Test_Internet_ConnectionViewController : UIViewController {

    Reachability* internetReachable;
    Reachability* hostReachable;
}

@property BOOL internetActive;
@property BOOL hostActive;

- (void) checkNetworkStatus:(NSNotification *)notice;

@end

这是 viewcontroller.m 文件：

#import "Test_Internet_ConnectionViewController.h"
#import "Reachability.h";

@implementation Test_Internet_ConnectionViewController

@synthesize internetActive;
@synthesize hostActive;

/*
// The designated initializer. Override to perform setup that is required before the view is loaded.
- (id)initWithNibName:(NSString *)nibNameOrNil bundle:(NSBundle *)nibBundleOrNil {
    self = [super initWithNibName:nibNameOrNil bundle:nibBundleOrNil];
    if (self) {
        // Custom initialization
    }
    return self;
}
*/

/*
// Implement loadView to create a view hierarchy programmatically, without using a nib.
- (void)loadView {
}
*/


// Implement viewDidLoad to do additional setup after loading the view, typically from a nib.
- (void)viewDidLoad {
    [super 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
    }

/*
// Override to allow orientations other than the default portrait orientation.
- (BOOL)shouldAutorotateToInterfaceOrientation:(UIInterfaceOrientation)interfaceOrientation {
    // Return YES for supported orientations
    return (interfaceOrientation == UIInterfaceOrientationPortrait);
}
*/

- (void)didReceiveMemoryWarning {
    // Releases the view if it doesn't have a superview.
    [super didReceiveMemoryWarning];

    // Release any cached data, images, etc that aren't in use.
}

- (void)viewDidUnload {
    // Release any retained subviews of the main view.
    // e.g. self.myOutlet = nil;
}

- (void) checkNetworkStatus:(NSNotification *)notice
{
    // called after network status changes

    NetworkStatus internetStatus = [internetReachable currentReachabilityStatus];
    switch (internetStatus)

    {
        case NotReachable:
        {
            NSLog(@"The internet is down.");
            self.internetActive = NO;

            break;

        }
        case ReachableViaWiFi:
        {
            NSLog(@"The internet is working via WIFI.");
            self.internetActive = YES;

            break;

        }
        case ReachableViaWWAN:
        {
            NSLog(@"The internet is working via WWAN.");
            self.internetActive = YES;

            break;

        }
    }

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

            {
            case NotReachable:
        {
            NSLog(@"A gateway to the host server is down.");
            self.hostActive = NO;

            break;

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

            break;

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

        break;

    }
}
}

- (void)dealloc {
[super dealloc];

    [[NSNotificationCenter defaultCenter] removeObserver:self];

}

@end

该应用程序运行良好，没有任何错误或警告，但在没有互联网连接时不会显示警报。有谁知道这是为什么？

您实际上并没有在任何地方显示警报。为此，您将执行类似于以下操作的操作：

UIAlertView *errorView = [[UIAlertView alloc] initWithTitle:@"Internet Unavailable" message:@"MESSAGE ABOUT INTERNET UNAVAILABLE HERE." delegate:nil cancelButtonTitle:@"Dismiss" otherButtonTitles:nil];
[errorView show];
[errorView release];

另外，需要注意的是，初始化后 viewDidLoad 可以在视图控制器上调用任意次数。最好在指定的初始值设定项中声明任何通知观察者。