Question

我正在尝试使用Dependency Service在xamarin.forms项目中的android和iOS中显示吐司消息。在iOS中，项目消息显示在MainPage或NavigationPage上。但是当我使用PushModalAsync浏览按钮单击的第二页时，不会显示消息。

我如何浏览页面

public LoginPage()
{
Device.BeginInvokeOnMainThread(() =>
                {
                    CustomToast.LongMessage("Hiiiiii");  // Message shown
                });

 Navigation.PushModalAsync(new RegisterPage());   //Doesn't show
//var reg = new RegisterPage();
//Application.Current.MainPage = reg;  // toast shown here
}

iOS中alertController的代码：

        const double SHORT_DELAY = 2.0;

        NSTimer alertDelay;
        UIAlertController alert;

        public void LongAlert(string message)
        {
            ShowAlert(message, LONG_DELAY);
        }
        public void ShortAlert(string message)
        {
            ShowAlert(message, SHORT_DELAY);
        }

        void ShowAlert(string message, double seconds)
        {
            try
            {
                if (alert == null && alertDelay == null)
                {
                    alertDelay = NSTimer.CreateScheduledTimer(seconds, (obj) =>
                    {
                        Device.BeginInvokeOnMainThread(() =>
                        {
                            DismissMessage();
                        });
                    });

                    Device.BeginInvokeOnMainThread(() =>
                    {
                        try
                        {
                            alert = UIAlertController.Create("", message, UIAlertControllerStyle.ActionSheet);
                            UIApplication.SharedApplication.KeyWindow.RootViewController.PresentViewController(alert, true, null);
                        }
                        catch (Exception ex)
                        {
                            var Error = ex.Message;
                        }                        
                    });
                }
            }
            catch (Exception ex)
            {
                TraceLog("Message iOS ShowAlert : " + ex.Message);
            }
        }

        void DismissMessage()
        {
            if (alert != null)
            {
                alert.DismissViewController(true, null);
                alert = null;
            }
            if (alertDelay != null)
            {
                alertDelay.Dispose();
                alertDelay = null;
            }
        }

然后我从注册页面构造函数中调用它

Device.BeginInvokeOnMainThread(() =>
                {
                    CustomToast.LongMessage("Hiiiiii");
                });

它不会随处可见，但也不会显示。任何人都可以请一些建议吗？

Answer 1

这是因为RegisterPage是您的LoginPage上显示的页面，UIApplication.SharedApplication.KeyWindow.RootViewController此代码无法为RegisterPage检索正确的视图控制器。它只是在上一页显示了一个操作表，但是您的应用已到达新页面，然后可以在屏幕上显示此 Toast 。首先，您必须在窗口中找到首页：

UIViewController topViewControllerWithRootViewController(UIViewController rootViewController)
{
    if (rootViewController is UITabBarController)
    {
        UITabBarController tabBarController = (UITabBarController)rootViewController;
        return topViewControllerWithRootViewController(tabBarController.SelectedViewController);
    }
    else if (rootViewController is UINavigationController)
    {
        UINavigationController navigationController = (UINavigationController)rootViewController;
        return topViewControllerWithRootViewController(navigationController.VisibleViewController);
    }
    else if (rootViewController.PresentedViewController != null)
    {
        UIViewController presentedViewController = rootViewController.PresentedViewController;
        return topViewControllerWithRootViewController(presentedViewController);
    }
    return rootViewController;
}

第二，调整您的演示代码，例如：

Device.BeginInvokeOnMainThread(() =>
{
    try
    {
        alert = UIAlertController.Create("", messages, UIAlertControllerStyle.ActionSheet);
        topViewControllerWithRootViewController(UIApplication.SharedApplication.KeyWindow.RootViewController).PresentViewController(alert, true, null);
    }
    catch (Exception ex)
    {
        var Error = ex.Message;
    }
});

最后，您可以使用Navigation.PushModalAsync(new RegisterPage());

使用PushModalAsync显示页面时无法显示alertcontroller

1 个答案: