Passing data between pages C# WPF

Question

I am trying to pass a simple string between pages but I don't know how to.

I created a test app where I click a button, the the value of "a" will pass on the next page (Page1.xaml.cs)

    private void button1_Click(object sender, RoutedEventArgs e)
    {
        string a = "hello";

        Page2 p2 = new Page2();
        NavigationService.Navigate(p2, a);
    }

Now, I want to extract the data from Page1 (Page2.xaml.cs)

    private void NavigationService_LoadCompleted(object sender, NavigationEventArgs e)
    {
        string str = (string)e.ExtraData;
    }

And then subscribing in the constructor (Page2.xaml.cs)

    public Page2()
    {
        InitializeComponent();
        NavigationService.LoadCompleted += NavigationService_LoadCompleted;
    }

However when I ran the program I get an error. Can someone point out what am I missing?

Answer 1

Without a good Minimal, Complete, and Verifiable code example, it's impossible to know for sure everything that would be needed to address your question. However, if all you're asking is how to allow data to pass from one page to the next when navigating, it seems to me that the NavigationService.Navigate(object, object) overload would be useful for you.

The second parameter is the data you want to pass. The target page can handle the NavigationService.LoadCompleted event (or any other appropriate one you prefer), where the object value that was passed to the Navigate() method can be retrieved via the NavigationEventArgs.ExtraData property.

For example, in your first page:

private void button_Click(object sender, RoutedEventArgs e)
{
    Page2 p2 = new Page2();
    NavigationService.Navigate(p2, v.str);
}

then in your second page:

private void NavigationService_LoadCompleted(object sender, NavigationEventArgs e)
{
    string str = (string)e.ExtraData;

    // do whatever with str, like assign to a view model field, etc.
}

Of course, you'll subscribe the event handler, e.g. in your page's constructor or in XAML. For example:

public partial class Page2 : Page
{
    public Page2()
    {
        InitializeComponent();

        NavigationService.LoadCompleted += NavigationService_LoadCompleted;
    }

    private void button_Click(object sender, RoutedEventArgs e)
    {
        NavigationService.GoBack();
    }

    private void NavigationService_LoadCompleted(object sender, NavigationEventArgs e)
    {
        string str = (string)e.ExtraData;

        // do whatever with str, like assign to a view model field, etc.
    }
}

Answer 2

Instead of setting the textbox DataContext, set the entire page’s datacontext to some class ie the ViewModel for page1. Implement the interface INotifyPropertyChanged and ensure that in the set of the string property, the NotifyPropertyChanged(“ElementName”) is raised.

Now create a new view with a corresponding view model like this which should also implement the interface INotifyPropertyChanged. Create a textbox and bind it to a string property like in first page. Ensure TwoWay binding for both properties to ensure both target and source is updated while data is changed.

Create the instance of both viewModels in MainWindow. When user navigates to 2nd user control, set

Page2ViewModel.TextBoxString = Page1ViewModel.TextBoxString;

Like this do vice versa while navigating from Page2 to Page1.

Page1ViewModel.TextBoxString = Page2ViewModel.TextBoxString;

This way, both the textboxes will be updated during navigation. This is just an overall idea. You need to learn more about MVVM and WPF from some tutorials. Search in google.

Answer 3

Here is my example, maybe it helps someone

in Page1.cs

examsStr = result.Content.ReadAsStringAsync().Result;
List<Exam> exams = JsonConvert.DeserializeObject<List<Exam>>(examsStr);
for (int i = 0; i < exams.Count; i++)
{
    btnExam.Click += BtnExam_OptionsShow;
    btnExam.DataContext = exams[i];
}
private void BtnExam_OptionsShow(object sender, EventArgs e)
{
        ExamRead examPage = new ExamRead();
        examPage.DataContext = ((sender as Button).DataContext as Exam);
        this.NavigationService.Navigate(examPage);
}

in Page2.cs

this.Loaded += ExamRead_Loaded;

private void ExamRead_Loaded(object sender, RoutedEventArgs e)
{

     examObj = (exam.DataContext as Exam);
     (exam.Children[2] as Label).Content = examObj.ExamName + " - Exam Options";
}

Page2 has attribute Name="exam" and examObj is global variable in that Page2 class