Xamarin forms how to keep label text value after navigation - xaml

Question

On my Main Page, I will set my label text (#lblStartDateTime) to current time stamp when user click on a button. It will navigate to Second Page, and once I click "done" button, it will go back to Main Page.
When I navigate back to Main Page from Second Page, my label text disappeared. Does anyone know how to keep the label text value after navigation?
Main Page
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using Xamarin.Forms;
using Xamarin.Forms.Xaml;
namespace Test
{
[XamlCompilation(XamlCompilationOptions.Compile)]
public partial class MainPage: ContentPage
{
public string previouspagevalue;
public MainPage()
{
InitializeComponent();
}
protected override void OnAppearing()
{
base.OnAppearing();
lblEndDT.Text = previouspagevalue;
}
private void btnOffline_Clicked(object sender, EventArgs e)
{
Navigation.PushAsync(new SecondPage());
string currentDT = DateTime.Now.ToString();
lblStartDT.Text = currentDT;
}
}
}
Second Page
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using Xamarin.Forms;
using Xamarin.Forms.Xaml;
namespace Test
{
[XamlCompilation(XamlCompilationOptions.Compile)]
public partial class SecondPage: ContentPage
{
public SecondPage()
{
InitializeComponent();
}
protected void btnDone_Clicked(object sender, EventArgs e)
{
MainPage mainpage = new MainPage();
string edt = DateTime.Now.ToString();
lblEndDateTime.Text = edt;
mainpage.previouspagevalue = lblEndDateTime.Text;
Navigation.PushAsync(mainpage);
}
}
}

Answer 1

In you btnDone_Clicked event , you should use Navigation.PopAsync to go back to MainPage, Navigation.PushAsync(mainpage); means to go to a new MainPage not the previous Page.
protected void btnDone_Clicked(object sender, EventArgs e)
{
Navigation.PopAsync();
}
Please read document to learn about how NavigationPage works.
Update, you can pass the value you need to the SecondPage when you push to SecondPage:
Codes in MainPage:
public partial class MainPage : ContentPage
{
public string previouspagevalue;
public MainPage()
{
InitializeComponent();
previouspagevalue = "I'm previouspagevalue";
}
protected override void OnAppearing()
{
base.OnAppearing();
//if you set the lblEndDT.Text = "someValue"; in the secondPage, there is no need to update it here
lblEndDT.Text = previouspagevalue;
}
private void btnOffline_Clicked(object sender, EventArgs e)
{
//Pass the parametere you need when you go to SecondPage
Navigation.PushAsync(new SecondPage(this, lblEndDT));
string currentDT = DateTime.Now.ToString();
lblStartDT.Text = currentDT;
}
}
SecondPage:
public partial class SecondPage : ContentPage
{
Label MainPagelblEndDT;
MainPage mainPage;
public SecondPage()
{
InitializeComponent();
}
public SecondPage(MainPage mainP,Label lblEndDT)
{
InitializeComponent();
//Get the lblEndDT reference here
MainPagelblEndDT = lblEndDT;
//Get the MainPage reference here
mainPage = mainP;
}
private void Button_Clicked(object sender, EventArgs e)
{
string edt = DateTime.Now.ToString();
//Use it
MainPagelblEndDT.Text = edt;
mainPage.previouspagevalue = MainPagelblEndDT.Text;
Navigation.PopAsync();
}
}
I uploaded a sample project here and you can check it. Feel free to ask me any question if you have.

Answer 2

I would suggest you wrap your pages in a navigation stack, use a NavigationPage and navigate to next page then when you pop back it will maintain your state.
In your App.xaml.cs
MainPage = new NavigationPage(new YourFirstPage);
Then push a page into the navigation and when you want to go back just do a
Navigation.PopAsync();
Goodluck
Feel free to get back if you have queries