如何重写后退按钮的操作

Question

In Page-A, I write a command to direct to Page-B using

App.Current.MainPage.Navigation.PushAsync(new B_Page())

The original behavior of the back button's action(on the left-top of the page) is to go back to the last page(Page-A). -->Action_A

And now, I want to rewrite the behavior to change page to a new page(called Page-C) by pressing the back button. -->Action_B

using Xamarin.Forms.Application.Current.MainPage = new NavigationPage(new C_Page());

But I want to keep both of these behaviors, because I will use each of them in different scenarios.

How to retain both behaviors and how to make me specify which action I want to use?

Let me use Action_A in scenario A and use Action_B in scenario B.

Thanks for the kind reply.

Answer 1

You can Manage Above Scenario with this Override Method

`

    protected override bool OnBackButtonPressed()
    {
        //here you can manage your Navigation.

        return base.OnBackButtonPressed();
    }

`

Answer 2

We could re-write the Navigation View of the ContentPage.And re-write the back button as you want.

Create a BaseContentPage

using System;


using Xamarin.Forms;
using Xamarin.Forms.Xaml;

namespace xxx
{
    [XamlCompilation(XamlCompilationOptions.Compile)]
    public partial class BaseContentPage: ContentPage
    {

        public event EventHandler BackButtonAction;

        public BaseContentPage()
        {
            InitializeComponent();

            NavigationPage.SetHasBackButton(this, false);

            TitleLab.Text = Title;

        }

        private void Button_Clicked(object sender, EventArgs e)
        {
            this.BackButtonAction(sender,e);
        }
    }
}

<?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="xxx.BaseContentPage">


    <NavigationPage.TitleView>

        <Grid>

            <Grid.ColumnDefinitions>

                <ColumnDefinition Width="0.2*" />
                <ColumnDefinition Width="0.6*" />
                <ColumnDefinition Width="0.2*" />
                                              
            </Grid.ColumnDefinitions>

            
            <!--you could set the icon or image here as back button-->
            <Button BackgroundColor="Transparent" TextColor="White" Grid.Column="0" Text="Back" Clicked="Button_Clicked"  />

            <Label x:Name="TitleLab"  Grid.Column="1" TextColor="White" FontSize="18" HorizontalTextAlignment="Center" VerticalTextAlignment="Center" />

        </Grid>


    </NavigationPage.TitleView>

    
</ContentPage>

And you just need to create the subclass of the BaseContentPage

using System;


using Xamarin.Forms;
using Xamarin.Forms.Xaml;

namespace App11
{
    [XamlCompilation(XamlCompilationOptions.Compile)]
    public partial class PageA : Page1
    {
        public PageA()
        {
            InitializeComponent();

            this.BackButtonAction += PageA_BackButtonAction;

        }

        private void PageA_BackButtonAction(object sender, EventArgs e)
        {
           //do something you want 
        }
    }
}

<?xml version="1.0" encoding="utf-8" ?>
<local:Page1  xmlns:local="clr-namespace:App11" xmlns="http://xamarin.com/schemas/2014/forms"
             xmlns:x="http://schemas.microsoft.com/winfx/2009/xaml"
             x:Class="App11.PageA">
    <ContentPage.Content>
        <StackLayout>
            <Label Text="Welcome to Xamarin.Forms!"
                VerticalOptions="CenterAndExpand" 
                HorizontalOptions="CenterAndExpand" />
        </StackLayout>
    </ContentPage.Content>
</local:Page1>

You could handle different navigation logic in different scenario as you want.