How do I access a slider value from content page in ObservableObject view model

Question

I have a slider on my Content Page and I want to access the value of it from an ObservableCollection (used in the content page) to check the time value I need to compare with. Below is the function I am using in the Observable Collection but the reference to the slider does not work...

 public void OnTimedEvent(object? source, System.Timers.ElapsedEventArgs e)
{
    
    var VM = App.Current?.Resources["AppViewModel"] as AppViewModel;

    if (VM != null && CurrentTimeOn.Seconds > VM.sliderValue)
    {
        Labcolor = Color.FromRgb(255, 0, 0);
        OnPropertyChanged(nameof(Labcolor));
    }
}

Below is the XAML for the Content page....

<?xml version="1.0" encoding="utf-8" ?>
<ContentPage
    x:Class="MauiSubHub.PressAndReleaseButtonPage"
    xmlns="http://schemas.microsoft.com/dotnet/2021/maui"
    xmlns:x="http://schemas.microsoft.com/winfx/2009/xaml"
    xmlns:local="clr-namespace:MauiSubHub"
    Title="SubHub"
    IconImageSource="appicon.png"
         xmlns:viewmodel="clr-namespace:MauiSubHub"
    x:DataType="local:AppViewModel"
    xmlns:toolkit="http://schemas.microsoft.com/dotnet/2022/maui/toolkit"
    xmlns:system="clr-namespace:System;assembly=netstandard">


    <Grid RowDefinitions="Auto,Auto,Auto,*">


        <Entry Placeholder="Enter player name" Text="{Binding NewName, Mode=TwoWay}" Grid.Row="1" MinimumWidthRequest="400" HorizontalOptions="Start"/>

        <Button 
            x:Name="btnAddPlayer"
            Grid.Row="2"
            BackgroundColor="Orange"
            HorizontalOptions="Start"
            LineBreakMode="WordWrap"
            Pressed="AddPlayer"
            Text="Add Player"
            VerticalOptions="End" />

        
        <Grid Grid.Row="3" RowDefinitions="Auto,*">
            <Slider x:Name="slider"
                Maximum="90" 
                    HorizontalOptions="Start"
                WidthRequest="400"/>
            <Label x:Name="displayLabel"
                Padding="20"
               Text="{Binding x:DataType='Slider',
                              Source={x:Reference slider},
                              Path=Value,
                              StringFormat='Alert when {0:F0} minutes on'}"
               HorizontalOptions="Start"
               VerticalOptions="End" />

            <CollectionView
                x:Name="MyCollectionViews"
                Grid.Row="1"
                ItemsSource="{Binding UserItems}"
                SelectedItem="{Binding SelectedListItem, Mode=TwoWay}"
                SelectionMode="Single"
                SelectionChanged="OnSelectionVIewChanged"
                >

                <VisualStateManager.VisualStateGroups>
                    <VisualStateGroup Name="CommonStates">
                        <VisualState Name="Normal"></VisualState>
                        <VisualState Name="Selected">
                            <VisualState.Setters>
                                <Setter Property="BackgroundColor" Value="Blue"></Setter>
                            </VisualState.Setters>
                        </VisualState>
                    </VisualStateGroup>
                </VisualStateManager.VisualStateGroups>

                <CollectionView.ItemTemplate>
                    <DataTemplate x:DataType="local:UserItem">
                        <Grid Padding="10"  BackgroundColor="White" ColumnDefinitions="Auto,200">
                            <BoxView Grid.Row="0" Grid.Column="0"
                                Color="LightSkyBlue" />
                            <BoxView Grid.Row="0" Grid.Column="1"
                                 Color="LightSkyBlue" />
                            <BoxView Grid.Row="1" Grid.Column="0"
                                Color="LightSkyBlue" />
                            <BoxView Grid.Row="1" Grid.Column="1"
                                Color="LightSkyBlue" />
                        
                            <Label x:Name="label1" Grid.Column="0" HorizontalOptions="Start" >
                                <Label.FormattedText>
                                    <FormattedString >
                                        <Span FontAttributes="Bold" Text="{Binding Name}" />
                                        <Span Text="{x:Static system:Environment.NewLine}"/>
                                        <Span Text="{Binding PositionOn,StringFormat='Total Time On: {0:mm\\mss\\s}'}" />
                                        <Span Text="{x:Static system:Environment.NewLine}"/>
                                        <Span Text="{Binding PositionOff,StringFormat='Total Time Off: {0:mm\\mss\\s}'}" />
                                        <Span Text="{x:Static system:Environment.NewLine}"/>
                                        <Span Text="{Binding CurrentTimeOn,StringFormat='Current Time On: {0:mm\\mss\\s}'}" BackgroundColor="{Binding Labcolor, Mode=TwoWay}" />
                                        
                                    </FormattedString>
                                </Label.FormattedText>
                                <Label.GestureRecognizers>
                                    <SwipeGestureRecognizer  Command="{Binding Source={x:Reference MyCollectionViews}, Path=BindingContext.DeleteCommand}" CommandParameter="{Binding .}"       
                                           />
                                    <TapGestureRecognizer  Command="{Binding Source={RelativeSource AncestorType={x:Type ContentPage}}, Path=BindingContext.DeleteCommand}"  CommandParameter="{Binding .}"     
                                    />
                                </Label.GestureRecognizers>
                            </Label>

                            <Button x:Name="btnStartStop" Grid.Column="1" BackgroundColor="Red" HorizontalOptions="End"  MinimumWidthRequest="100"
                                TextColor="White"  
                                Text="Off">
                                <Button.GestureRecognizers>
                                    <TapGestureRecognizer Command="{Binding StartStopCommandCommand}" CommandParameter="{x:Reference btnStartStop}"   />
                                </Button.GestureRecognizers>                                
                            </Button> 
                            
                        </Grid>
                    </DataTemplate>
                </CollectionView.ItemTemplate>
            </CollectionView>
        </Grid>
    </Grid>
</ContentPage>

Well, seems you know Binding but you use it by rolling a dice. Even the way you get the ViewModel of the page is very uncommon. — Sir Rufo
– Sir Rufo, Commented Jun 1 at 5:55
if OnTimedEvent is a handler in your code behind, you should be able to reference the slider by name — Jason
– Jason, Commented Jun 1 at 15:22
The OnTimedEvent is in the view model as I need to check the value against each of my items in the collection. How do I reference a slider in the main page in the viewmodel? — Aeneas
– Aeneas, Commented Jun 1 at 20:01

halfer · Accepted Answer · 2025-09-28 13:07:06Z

1

You could use the Value property to do this

<Slider
Value = "{Binding SliderValue}"
....
>

And then in your ViewModel:

[ObservableProperty]
public partial double SliderValue { get; set; }

And then in your ViewModel, configure the DragCompletedCommand of the slider.

edited Sep 28 at 13:07

halfer

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answered Jun 1 at 19:56

FreakyAli

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2 Comments

Stephen Quan Jun 2 at 21:50

You should switch to the partial property syntax, e.g. public partial double SliderValue { get; set; } = 0.0;. See devblogs.microsoft.com/dotnet/…🎉

FreakyAli Jun 2 at 22:36

@StephenQuan Hey man, thank,s I will definitely check that :)

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