Введение в Xamarin.Forms для разработчиков Android (часть 5)

Результат:

Переходя на вторую страницу:

И третья страница:

Обратите внимание, что мы должны импортировать изображения в папку Resource> drawable  в проекте Android:

Навигация между страницами

In theory, to move from one page to another, an application will push a new page onto the navigation stack, where it will become the active page, and to return back to the previous page, the application will pop the current page from the navigation stack. We can pass data from a page to another page during navigation.

In practice, the navigation includes the following operators:

• Creating a root page, which is the first page is added to a navigation stack by using the NavigationPage object, in the App.xaml.cs file.
• Navigating to the next page by pushing this page to the navigation stack. We can use methods such as the PushAsync or the PushModalAsync on the Navigation property of the current page.
• By default, we can use the Back button on the device to naviage back to previous page but we can program by using the PopAsync or the PopModalAsync on the Navigation property to pop the active page from the navigation stack.
• Passing data when navigating through a page constructor or a BindingContext.

In our NavigApp application, suppose the NagvigApp application has the MainPage.xaml as follows:

<?xml version="1.0" encoding="utf-8" ?>
<ContentPage xmlns="http://xamarin.com/schemas/2014/forms"
             xmlns:x="http://schemas.microsoft.com/winfx/2009/xaml"
             xmlns:local="clr-namespace:NavigApp"
             x:Class="NavigApp.MainPage"
             Title="Main Page">
    <StackLayout>
    <Label Text="I am Main Page" HorizontalOptions="Center"
VerticalOptions="Center"/>
        <Button Text="Next Page" HorizontalOptions="Center" VerticalOptions="Center"
Clicked="nextPage"/>
    </StackLayout>
</ContentPage>

namespace NavigApp
{
       public partial class MainPage : ContentPage
    {
       public  MainPage()
       {
             InitializeComponent();                            
        }
        private void nextPage(object sender, EventArgs e)
        {
        }
    }
}

namespace NavigApp
{
       public partial class App : Application
       {
              public App ()
              {
                     InitializeComponent();
                     //MainPage = new NavigApp.MainPage();
                     MainPage = new NavigationPage(new MainPage());
              }
...
}

<?xml version="1.0" encoding="utf-8" ?>
<ContentPage xmlns="http://xamarin.com/schemas/2014/forms"
             xmlns:x="http://schemas.microsoft.com/winfx/2009/xaml"
             x:Class="NavigApp.SecondPage"
             Title="Second Page">
    <ContentPage.Content>
        <StackLayout>
            <Label Text="Welcome to second page!"
                VerticalOptions="CenterAndExpand"
                HorizontalOptions="CenterAndExpand" />
            <Button Text="Previous Page"
                VerticalOptions="CenterAndExpand"
                HorizontalOptions="CenterAndExpand"
                    Clicked="prevPage"/>
        </StackLayout>
    </ContentPage.Content>
</ContentPage>

namespace NavigApp
{
       [XamlCompilation(XamlCompilationOptions.Compile)]
       public partial class SecondPage : ContentPage
       {
              public SecondPage ()
              {
                     InitializeComponent ();
              }
              private void prevPage(object sender, EventArgs e)
              {
              }
       }
}

async private void nextPage(object sender, EventArgs e)
     {
         await Navigation.PushAsync(new SecondPage());
     }

async private void prevPage(object sender, EventArgs e)
   {
            await Navigation.PopAsync();
   }

public App ()
{
    InitializeComponent();
MainPage = new NavigationPage(new MainPage("Minh"));
}

<ContentPage ...>
    <StackLayout>
        <Label x:Name="name" Text="I am " HorizontalOptions="Center" 
               VerticalOptions="Center"/>
        <Button .../>
    </StackLayout>
</ContentPage>

public  MainPage(string name)
       {
            InitializeComponent();
            var lbName = this.FindByName<Label>("name");
            lbName.Text += name;    
        }