Xamarin Prism cannot navigate with parameters - xamarin

Question

for my app i create my own buttons using a frame and adding a tapgesture to it. here i use the navigation of prism to go to a specific page with a parameter. however. the viewmodel i'm going to does not trigger the Navigated to method. here is some code.
during debugging it seems that the adding of the parameters is no problem. however the constructor for the viewmodel is called instead.
button
public class FolderButton : Frame
{
public FolderButton(Folder folder, INavigationService navigationService)
{
var navParams = new NavigationParameters();
navParams.Add("folder", folder);
GestureRecognizers.Add(new TapGestureRecognizer()
{
Command = new Command(async () => { await navigationService.NavigateAsync("FolderInventory", navParams); }),
});
BackgroundColor = Color.CornflowerBlue;
var thickness = new Thickness();
thickness.Bottom = 10;
thickness.Left = 10;
thickness.Right = 10;
thickness.Top = 10;
Margin = thickness;
CornerRadius = 5;
var completeStack = new StackLayout();
var imgStack = new StackLayout();
imgStack.Padding = thickness;
imgStack.Children.Add(new Image { Source = "folder.png" });
completeStack.Children.Add(imgStack);
var lblStack = new StackLayout();
lblStack.Padding = thickness;
lblStack.Children.Add(new Label
{
Text = folder.Name,
HorizontalTextAlignment = TextAlignment.Center,
VerticalTextAlignment = TextAlignment.Start
});
completeStack.Children.Add(lblStack);
Content = completeStack;
}
}
called viewmodel
public class FolderInventoryViewModel : BindableBase, INavigatedAware
{
public Folder Folder => _folder;
private readonly INavigationService _navigationService;
private Folder _folder;
private readonly ISQLiteService _sqlService;
private List<Frame> _buttons;
public List<Frame> Buttons
{
get => _buttons;
set => _buttons = value;
}
public FolderInventoryViewModel(Folder folder, INavigationService navigationService, ISQLiteService sqlService)
{
_folder = folder;
_sqlService = sqlService;
_navigationService = navigationService;
GetItemsForFolder();
}
private void GetItemsForFolder()
{
var itemList = _sqlService.GetAllFolderItems(Folder.Name);
foreach (var item in itemList)
{
var itemButton = new ItemButton(_navigationService, item);
_buttons.Add(itemButton);
}
}
public void OnNavigatedFrom(NavigationParameters parameters)
{
if (parameters["folder"] is Folder folder)
{
_folder = folder;
}
}
public void OnNavigatedTo(NavigationParameters parameters)
{
if (parameters["folder"] is Folder folder)
{
_folder = folder;
}
}
}

Answer 1

This is not the essence of using the framework. To properly use the Prism with its NavigationParameters you first properly maintain the MVVM idea behind it.
E.g.
<Button Command="{Binding testCommand}" text="TestButton"/>
Your ViewModel (Pardon about this, you need to inject NavigationService to your ViewModel's constructor)
private DelegateCommand _testCommand;
public DelegateCommand testCommand =>
_testCommand?? (_testCommand= new DelegateCommand(ExecuteTest));
private void ExecuteTest()
{
NavigationParameters navigationParameters = new NavigationParameters();
navigationParameters.Add("yourParameterId", value);
NavigationService.NavigateAsync("YourPage", navigationParameters);
}
And then onto your next page
Inherit INavigationAware to your NextPage : YourNextPage: BaseViewModel, INavigationAware
INavigationAware has 3 methods NavigatingTo, NavigatedTo, NavigatedFrom
Inside OnNavigatedTo you can call the parameters you have passed
public void OnNavigatedTo(NavigationParameters parameters)
{
//You can check if parameters has value before passing it inside
if(parameters.ContainsKey("YourParameterId")
{
yourItem = (dataType)parameters[YourParameterId];
}
}
Also note: The constructor will always be called first before the Navigating methods