ios - AlertViewController - 其 View 不在窗口层次结构中问题

Question

在下面的代码中，我试图仅在发生特定事件时调用方法 handleEvent。为此，我发布了事件发生的通知(未在下面的代码中显示)，以便观察者和 handleEvent 观察到通知(如下面的代码中所示)。

我想要一个警报 viewController 弹出并获取文本输入，以便我可以接收它。
但我收到以下错误:

Warning: Attempt to present <UIAlertController: 0x7f9d1347ed90> on <MSMDemoFirstViewController: 0x7f9d1347e920> whose view is not in the window hierarchy!

尽管我使用的是单例，但我无法理解，但我无法正确获取 alertViewController。任何帮助都会很有用。

   #import "MSMDemoFirstViewController.h"
#import "CAMDOReporter.h"
static MSMDemoFirstViewController * instance = nil;
@interface MSMDemoFirstViewController ()

@end

@implementation MSMDemoFirstViewController

+ (MSMDemoFirstViewController *)sharedInstance {
    // Singleton implementation
    static dispatch_once_t onceToken;
    dispatch_once(&onceToken, ^{
        if (instance == nil) {
            instance = [[MSMDemoFirstViewController alloc] init];
        }
    });
    return instance;
}

+(void)load{
[[NSNotificationCenter defaultCenter] addObserver:[MSMDemoFirstViewController sharedInstance] selector:@selector(handleEvent:) name:EVENT_OCCURRED object:nil];
}


+(void) initialize{

}
- (void) viewDidAppear:(BOOL)animated {
    [super viewDidAppear:animated];
    //[[CAMDOReporter sharedInstance] startApplicationTransaction:@"DemoEventApplicationTransaction"];
   // [self showAlert];
}

-(void)showAlert{
    NSLog(@"2ew");
    NSString *title = NSLocalizedString(@"A Short Title Is Best", nil);
    NSString *message = NSLocalizedString(@"A message should be a short, complete sentence.", nil);
    NSString *cancelButtonTitle = NSLocalizedString(@"Cancel", nil);
    NSString *otherButtonTitle = NSLocalizedString(@"OK", nil);

    UIAlertController *alertController = [UIAlertController alertControllerWithTitle:title message:message preferredStyle:UIAlertControllerStyleAlert];

    [alertController addTextFieldWithConfigurationHandler:^(UITextField *textField) {
        // If you need to customize the text field, you can do so here.
    }];

    // Create the action.
    UIAlertAction *cancelAction = [UIAlertAction actionWithTitle:cancelButtonTitle style:UIAlertActionStyleCancel handler:^(UIAlertAction *action) {
        NSLog(@"The simple alert's cancel action occured.");
    }];

    UIAlertAction *otherAction = [UIAlertAction actionWithTitle:otherButtonTitle style:UIAlertActionStyleDefault handler:^(UIAlertAction *action) {
        NSLog(@"The \"Text Entry\" alert's other action occured.");
    }];
    // Add the action.
    [alertController addAction:cancelAction];
    [alertController addAction:otherAction];
    [self presentViewController:alertController animated:YES completion:nil];
}

-(void)handleEvent:(NSNotification *)note{
    NSLog(@"Handle Crash Event");
    NSDictionary *crashData  = [note userInfo];
    if(crashData !=nil){
        //Implement any UI Logic to get any response from the user. e.g. AlertView, TextFields.
        //Once the feedback is received convert it into NSString and send the data.
        // Show a text entry alert with two custom buttons.
        [[MSMDemoFirstViewController sharedInstance] showAlert];
        NSString *feedback=[[NSUserDefaults standardUserDefaults] objectForKey:@"crashDetails"];
        [[CAMDOReporter sharedInstance] setCustomerFeedback:feedback];
    }
}

- (void)didReceiveMemoryWarning
{
    [super didReceiveMemoryWarning];
    // Dispose of any resources that can be recreated.
}

@end

现在我得到的输出是:

2015-01-21 20:17:45.762 CAMAADemo[18891:1558312] Handle Crash Event
2015-01-21 20:17:45:762 CAMAADemo[18891:1807] Posting Notification about crash
2015-01-21 20:17:45.762 CAMAADemo[18891:1558312] 2ew
2015-01-21 20:17:45.778 CAMAADemo[18891:1558312] Warning: Attempt to present <UIAlertController: 0x7ff5d2273580> on <MSMDemoFirstViewController: 0x7ff5d2204be0> whose view is not in the window hierarchy!

这意味着调用将使用 showAlert 方法，但是尽管我得到了同样的错误。

即使下面的代码也无济于事。

-(void)viewDidLoad{
    [super viewDidLoad];
    [[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(handleCrashEvent:) name:CAMAA_CRASH_OCCURRED object:nil];
}
-(void)showAlert{
    NSLog(@"2ew");
    NSString *title = NSLocalizedString(@"A Short Title Is Best", nil);
    NSString *message = NSLocalizedString(@"A message should be a short, complete sentence.", nil);
    NSString *cancelButtonTitle = NSLocalizedString(@"Cancel", nil);
    NSString *otherButtonTitle = NSLocalizedString(@"OK", nil);

    UIAlertController *alertController = [UIAlertController alertControllerWithTitle:title message:message preferredStyle:UIAlertControllerStyleAlert];

    [alertController addTextFieldWithConfigurationHandler:^(UITextField *textField) {
        // If you need to customize the text field, you can do so here.
    }];

    // Create the action.
    UIAlertAction *cancelAction = [UIAlertAction actionWithTitle:cancelButtonTitle style:UIAlertActionStyleCancel handler:^(UIAlertAction *action) {
        NSLog(@"The simple alert's cancel action occured.");
    }];

    UIAlertAction *otherAction = [UIAlertAction actionWithTitle:otherButtonTitle style:UIAlertActionStyleDefault handler:^(UIAlertAction *action) {
        NSLog(@"The \"Text Entry\" alert's other action occured.");
    }];
    // Add the action.
    [alertController addAction:cancelAction];
    [alertController addAction:otherAction];
    [self presentViewController:alertController animated:YES completion:nil];
}

-(void)handleCrashEvent:(NSNotification *)note{
    NSLog(@"Handle Crash Event");
    NSDictionary *crashData  = [note userInfo];
    if(crashData !=nil){
        //Implement any UI Logic to get any response from the user. e.g. AlertView, TextFields.
        //Once the feedback is received convert it into NSString and send the data.
        // Show a text entry alert with two custom buttons.
        [self showAlert];
        NSString *feedback=[[NSUserDefaults standardUserDefaults] objectForKey:@"crashDetails"];
        [[CAMDOReporter sharedInstance] setCustomerFeedback:feedback];
    }
}

Answer 1

您的代码的问题是您创建了一个全新的 View Controller 并显示来自新 Controller 的警报。但是该 Controller 尚未显示，因此出现错误消息。

修复此代码的正确方法是显示来自实际呈现的 View Controller 的警报。

为此，将实际的 View Controller 实例注册为通知处理程序，而不是在 load 中注册类。方法。

进行以下更改:

消除 load方法。

将电话移至 [[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(handleEvent:) name:EVENT_OCCURRED object:nil];到viewDidLoad方法。

更改handleEvent:成为一个实例方法。

更改[[[self alloc]init] showAlert];至[self showAlert]; .

添加 dealloc方法并注销通知观察者。