Question

首先显示 MainPage ，然后点击按钮并调用 SecondPage 。 Everthing看起来很好，但是当我点击后退按钮时（显示器的方向应该是纵向的，但是我会得到一些奇怪的行为，比如纵向和横向（水平）视图。

Page1 （右侧垂直方向） - ＆gt; Page2 （右侧水平方向） - ＆gt;（后退按钮操作） - ＆gt; Page1 （错误的垂直方向）。

   when firstly showing                         when click back button

的MainPage：

public partial class MainPage : ContentPage
    {
        public MainPage()
        {
            InitializeComponent();
        }

        async void OnTapGestureRecognizerTapped(object sender, EventArgs args)
        {
            var fullScreenVideoPage = new SecondPage();
            NavigationPage.SetHasNavigationBar(fullScreenVideoPage, false);
            await Navigation.PushAsync(fullScreenVideoPage);
        }
        protected override void OnAppearing()
        {
            base.OnAppearing();
            MessagingCenter.Send(this, "preventLandScape");
        }
    }

XAML （MainPage）：

<ContentPage xmlns="http://xamarin.com/schemas/2014/forms"
             xmlns:x="http://schemas.microsoft.com/winfx/2009/xaml"
             xmlns:local="clr-namespace:App1"
             x:Class="App1.MainPage"
             BackgroundColor="Black">
      <StackLayout x:Name="stackLayout" Orientation="Horizontal">
            <Image Source="icon.png"               
                   WidthRequest="150"
                   HeightRequest="150"
                   HorizontalOptions ="CenterAndExpand"
                   VerticalOptions="CenterAndExpand">
                <Image.GestureRecognizers>
                    <TapGestureRecognizer
                        Tapped="OnTapGestureRecognizerTapped"  />
                </Image.GestureRecognizers>
            </Image>     
            </StackLayout>
</ContentPage>

SecondPage：

public partial class SecondPage : ContentPage
    {
        public SecondPage()
        {
            InitializeComponent();
        }

        protected override void OnAppearing()
        {
            base.OnAppearing();
            MessagingCenter.Send(this, "showLandscapeOrientation");
        }

        protected override void OnDisappearing()
        {
            base.OnDisappearing();
            MessagingCenter.Send(this, "showPortraitOrientation");
        }

        async void OnTapGestureRecognizerTapped(object sender, EventArgs args)
        {
            await Navigation.PushAsync(new NavigationPage(new MainPage()));
        }
    }

MainActivity：

[Activity(Label = "App1", Icon = "@drawable/icon", Theme = "@style/MainTheme", MainLauncher = true, ConfigurationChanges = ConfigChanges.ScreenSize | ConfigChanges.Orientation, ScreenOrientation = ScreenOrientation.Portrait)]
    public class MainActivity : global::Xamarin.Forms.Platform.Android.FormsAppCompatActivity
    {
        protected override void OnCreate(Bundle bundle)
        {

            TabLayoutResource = Resource.Layout.Tabbar;
            ToolbarResource = Resource.Layout.Toolbar;
            base.OnCreate(bundle);
            global::Xamarin.Forms.Forms.Init(this, bundle);

            LoadApplication(new App());
            //allowing the device to change the screen orientation based on the rotation
            MessagingCenter.Subscribe<SecondPage>(this, "showLandscapeOrientation", sender =>
            {
                RequestedOrientation = ScreenOrientation.Landscape;
            });

            //during page close setting back to portrait
            MessagingCenter.Subscribe<SecondPage>(this, "preventLandScape", sender =>
            {
                RequestedOrientation = ScreenOrientation.Portrait;
            });

            MessagingCenter.Subscribe<MainPage>(this, "showPortraitOrientation", sender =>
            {
                RequestedOrientation = ScreenOrientation.Portrait;
            });
        }
    }

Answer 1

问题是您为showPortraitOrientation订阅了MainPage，但是您从preventLandScape致电MainPage。

因此，您可以修改OnAppearing() MainPage中的代码，如下所示：

protected override void OnAppearing()
{
    base.OnAppearing();
    MessagingCenter.Send(this, "showPortraitOrientation");
}

其他问题是，在从横向屏幕切换回纵向屏幕时，您可能需要重新绘制布局。对于Android平台，您可以使用以下代码：

protected override void OnAppearing()
{
    base.OnAppearing();
    MessagingCenter.Send(this, "showPortraitOrientation");

    //force redraw
    this.InvalidateMeasure();
}

protected override void InvalidateMeasure()
{
    Task.Delay(200).Wait();
    base.InvalidateMeasure();
}

从具有水平方向的一页返回到具有垂直方向的另一页的问题

1 个答案: