>Net Maui - Passing object between pages

Question

>Net Maui - Passing object between pages

John Rutherford 41

I'm having trouble getting my DetailsPage to show the Observation obs object passed from my ResultsPage. I have a TapGestureRecognizer_Tapped method in the code behind the ResultsPage

private async void TapGestureRecognizer_Tapped(object sender, TappedEventArgs e)
{
    if (((VisualElement)sender).BindingContext is not Observation obs)
        return;
    var navigationParameter = new ShellNavigationQueryParameters
    {
        {"Observation", obs }
    };
    await Shell.Current.GoToAsync(nameof(DetailsPage), navigationParameter);
}

and on my DetailsPage ViewModel the following initialization code

using CommunityToolkit.Mvvm.ComponentModel;
using CommunityToolkit.Mvvm.Input;
using SunObs.Models;
using SunObs.Services;
namespace SunObs.ViewModel
{
    [QueryProperty(nameof(Observation), "Observation")]
    public partial class DetailsViewModel : BaseViewModel
    {
        [ObservableProperty]
        Observation obs;
        [ObservableProperty]
        [NotifyCanExecuteChangedFor(nameof(UpdateObservationAsyncCommand))]
        private bool calcDone;
        public IAsyncRelayCommand ComputeObsAsyncCommand { get; }
        public IAsyncRelayCommand UpdateObservationAsyncCommand { get; }
        readonly ObservationService _observationService;
        public DetailsViewModel(ObservationService observationService)
        {
            Title = "Edit Observation";
            _observationService = observationService;
            CalcDone = false;
            ComputeObsAsyncCommand = new AsyncRelayCommand(ComputeObsAsync);
            UpdateObservationAsyncCommand = new AsyncRelayCommand(UpdateObservationAsync);
        }

The details ContentPage has the following

<?xml version="1.0" encoding="utf-8" ?>
<ContentPage xmlns="http://schemas.microsoft.com/dotnet/2021/maui"
            xmlns:x="http://schemas.microsoft.com/winfx/2009/xaml"
            x:Class="SunObs.Views.DetailsPage"
            xmlns:converters="clr-namespace:SunObs.Converters"
            xmlns:toolkit="http://schemas.microsoft.com/dotnet/2022/maui/toolkit"
            xmlns:local="clr-namespace:SunObs.Models"
            xmlns:model="clr-namespace:SunObs.Models"
            xmlns:viewmodel="clr-namespace:SunObs.ViewModel"
            x:DataType="viewmodel:DetailsViewModel"
            Title="{Binding Obs.Id, StringFormat='Edit Observation : {0}'}">
    <ContentPage.Resources>
        <converters:AngleConverter x:Key="AngConv"/>
    </ContentPage.Resources>
    <Shell.BackButtonBehavior>
        <BackButtonBehavior IsEnabled="False"/>
    </Shell.BackButtonBehavior>
    <VerticalStackLayout BackgroundColor="Transparent" Spacing="10" Margin="10,10,10,0">
        <Grid RowDefinitions="Auto, Auto, Auto, Auto, Auto, Auto, Auto, Auto, Auto, Auto, Auto, Auto, Auto, Auto, Auto, Auto, Auto, Auto"
          ColumnDefinitions="Auto,*" RowSpacing="5" ColumnSpacing="5" Margin="8">
            
            <Border Grid.Row="2" Grid.Column="0" Style="{StaticResource borderinput}">
                <Label Style="{StaticResource lbl}" Text="Observation Date"/>
            </Border>
            <DatePicker Grid.Row="2" Grid.Column="1"
                        x:Name="DPicker" Date="{Binding Obs.ObsDate}"
                        VerticalOptions="Center" 
                        DatePicker.Format="dd-MMM-yyyy"/>
            
            <Border Grid.Row="3" Grid.Column="0" Style="{StaticResource borderinput}">
                <Label Style="{StaticResource lbl}" Text="Watch Time"/>
            </Border>
            <Entry Placeholder="00:00:00" PlaceholderColor="Blue"
                    x:Name="WT" Text="{Binding Obs.WT}"
                    VerticalOptions="Center"
                    Grid.Row="3" Grid.Column="1">
                <Entry.Behaviors>
                    <toolkit:SelectAllTextBehavior />
                </Entry.Behaviors>
            </Entry>

to bind the Observation object obs along with all the other properties needed.

However, when the page displays, all the properties are set to zero. I've watched many videos and read the documentation. Can you please show me how to pass the object correctly.

TIA

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Answer accepted by question author

1 additional answer

Your answer

Answer 1

Hello,

I know you've already solved the issue, but I wanted to provide some information that might be helpful for others facing similar problems

Shell navigation in .NET MAUI serializes all parameters as URI strings for the underlying navigation system. When complex objects (non-primitive types) are passed via ShellNavigationQueryParameters, the framework attempts to convert them to string representations, which often results in:

Loss of object data
Default property values (nulls, zeros)
Silent failures without error messages

Recommended Solution

Use a shared static service or singleton to store the object before navigation. Here's how:

1. Create a static data service

public static class NavigationDataStore
{
    public static Observation CurrentObservation { get; set; }
}

2. Set the object before navigating

private async void TapGestureRecognizer_Tapped(object sender, TappedEventArgs e)
{
    if (((VisualElement)sender).BindingContext is not Observation obs)
        return;
 
    NavigationDataStore.CurrentObservation = obs;
    await Shell.Current.GoToAsync(nameof(DetailsPage));
}

3. Retrieve the object in the DetailsViewModel

public DetailsViewModel(ObservationService observationService)
{
    Title = "Edit Observation";
    _observationService = observationService;
    Obs = NavigationDataStore.CurrentObservation;
    CalcDone = false;
    ComputeObsAsyncCommand = new AsyncRelayCommand(ComputeObsAsync);
    UpdateObservationAsyncCommand = new AsyncRelayCommand(UpdateObservationAsync);
}

Alternative

If you need to persist data across sessions or support deep linking, consider serializing the object to JSON and passing it as a string, then deserializing it on the target page. However, this only works if the object is serializable and the data size is small.

I hope this helps clarify the issue.

References:

.NET MAUI Shell navigation - Pass data

Michael Le (WICLOUD CORPORATION) 11,235 Reputation points Microsoft External Staff Moderator

2025-08-12T03:07:30.08+00:00

Hello, I hope my answer were able to clarify the problem. Let me know if you need further assistance.
John Rutherford 41 Reputation points

2026-04-12T05:45:38.86+00:00

Thanks for the tip. I like the clever and neat way that it works. Sorry it took so long to get back to you.
Michael Le (WICLOUD CORPORATION) 11,235 Reputation points Microsoft External Staff Moderator

2026-04-13T02:23:54.8+00:00

Thanks for your feedback. Feel free to reach out anytime if you have any questions.

Answer 2

John Rutherford 41

Solved it myself.

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