Passing data between view in xamarin forms using mvvm

Question

I\'m trying to navigate between pages and bind data at same time.

This is what I have tried :

public ICommand GetIdeasCommand
{
    get
    {
              


        

Answer 1

Your problem is obvious, you are passing the data to the ContentPage but you do nothing with it. Generally speaking passing a parameter from one ViewModel to another ViewModel is a very simple problem.

Here is an illustration without XAML:

public class MyFirstPage : ContentPage
{
  public MyFirstPage()
  {
    this.BindingContext = new MyFirstPageViewModel();
  }
}

public class MyFirstPageViewModel : INotifyPorpertyChanged
{
  public ICommand<List<string>> DownloadDataCmd { get; }

  public MyFirstPageViewModel()
  {
    DownloadDataCmd = new Command<List<string>>(async () => {
        var data = await dataService.DownloadData();
        await navService.PushAsync(new MySecondPage(data));
    });
  }
}

public class MySecondPage : ContentPage
{
  public MySecondPage(List<string> downloadedData)
  {
    this.BindingContext = new MySecondPageViewModel(downloadedData);
  }
}

public class MySecondPageViewModel : INotifyPropertyChanged
{
  public List<string> Data { get; }
  public MySecondPageViewModel(List<string> downloadedData)
  {
     // Do whatever is needed with the data
     Data = downloadedData;
  }
}

Now, looking at this solution there are few questions:
1. Why not to download the data directly on the second page?
2. Why not to store the data in cache or db if you need it across the app?

Answer 2

Your understanding of BindingContext is lacking. Usually you bind a ViewModel to a BindingContext. What you're doing here

this.BindingContext = new IdeasSinglePage(ideas); //the app breaks here

doesn't make sense.

You are passing as context the page you want to load ? Just delete this line completely. Since in your recent comments you said you didn't want a ViewModel to begin with, what you will do in your CodeBehind is:

public partial class IdeasSinglePage : ContentPage
{
  public IdeasSinglePage(List<Models.Ideas> ideas)
  {
    InitializeComponent();
    listViewName.ItemsSource = ideas;
  }
}

And in your xml you give your listView a Name. You need this Name for referencing the list on code behind.

Hope it helps