Ios 警告：调用通知时尝试显示模式

我正在使用以下命令调用viewDidAppear上的presentModal方法：

当picker出现时，它给了我设备和模拟器上的警告

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警告：在演示过程中，尝试在UINavigationController:0x90ad610上演示PickerModalViewController:0x10ec7280

警告告诉你，出了什么问题。 要避免此警告，您可以使用UINavigationController的委托属性并实现

-voidnavigationController:UINavigationController*navigationController didShowViewController:UIViewController*viewController 动画：BOOLanimated

[[NSNotificationCenter defaultCenter] addObserver:self         
                                             selector:@selector(presentModal)         
                                                 name:@"xxxxxxx"         
                                               object:nil];

-(void)presentModal 
{
    PickerModalViewController *pickerModalViewController = [Appdelegate.window.rootViewController.storyboard instantiateViewControllerWithIdentifier:@"PickerModalViewController"];

    pickerType = 2;
    pickerModalViewController.choices = self.localArray;
    pickerModalViewController.buttonTag = pickerType;

    pickerModalViewController.delegate = self;
    self.pickerPresenter = self;

    if (self.pickerPresenter) {
        [self.pickerPresenter presentViewController:pickerModalViewController animated:YES completion:nil];
    }
}