WPF

Public interface ViewModel
{
        Visibility ControlHideShow { get; set; }
}
    
public class MainPageViewModel : ViewModelBase, IMainPageViewModel
{
    
        private Visibility _controlHideShow = Visibility.Visible;
        public Visibility ControlHideShow
        {
            get => _controlHideShow;
            set{ _controlHideShow = value;  OnPropertyChanged(nameof(ControlHideShow)); }
        }
}

<controls:WaitTicker_Control
                        x:Name="WaitCursor"
                        Width="60" Height="30"
                        Grid.Row="4" Grid.Column="1" 
                        HorizontalAlignment="Center" 
                        VerticalAlignment="Center"
                        Margin="100 0 0 0"
                
                        ControlBackground1="#FFA5CD3C"
                        ControlBackground2="#FF208D2F" 
                        ControlBackground3="#FF206A8D" 
                
                        ControlCornerRadius1="2" 
                        ControlCornerRadius2="2"
                        ControlCornerRadius3="2"           
                
                        PulseHeight1="25" PulseHeight2="25" PulseHeight3="25"
                        PulseWidth1="5" PulseWidth2="5" PulseWidth3="5"
                        PulseMaxValue="50" PulseMinValue="5"
                        PulseSpeedValue="0.0001"
                        PulseIncrementValue="1" 
                        PulseCurrentValue1="1" PulseCurrentValue2="25" PulseCurrentValue3="50"
                        ControlHideShow="{Binding ControlHideShow}"/>

<UserControl x:Class="DES.CATIAV6.ClearanceContactAndClashManager.UI.Controls.WaitTicker_Control"
                 xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
                 xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
                 xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006" 
                 xmlns:d="http://schemas.microsoft.com/expression/blend/2008" 
                 xmlns:local="clr-namespace:DES.CATIAV6.ClearanceContactAndClashManager.UI.Controls"
                 mc:Ignorable="d" 
                 DataContext="{Binding RelativeSource={RelativeSource Self}}" 
                 Background="Transparent" 
                 Height="70" Width="60"
                 Name="WaitTickerControl">
        <Grid Name="WaitTickerMainGrid" Visibility="{Binding Path=ControlHideShow,ElementName=WaitTickerControl, FallbackValue=Hidden}">

        </Grid>
    
    </UserControl>

    public partial class WaitTicker_Control : UserControl, INotifyPropertyChanged
        {
            public event PropertyChangedEventHandler? PropertyChanged;
    
            protected void OnPropertyChanged([CallerMemberName] string? propertyName = null)
            {
                PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(propertyName));
            }

    
            public Visibility ControlHideShow
            {
                get { return (Visibility)GetValue(ControlHideShowProperty); }
                set { SetValue(ControlHideShowProperty, value); }
            }
            public static readonly DependencyProperty ControlHideShowProperty =
                DependencyProperty.Register("ControlHideShow", typeof(Visibility), typeof(WaitTicker_Control),
                   new PropertyMetadata(Visibility.Hidden));

          

public EquipmentIdentity()
        {
            InitializeComponent();
            EquipmentIdentityViewModel eivm = new EquipmentIdentityViewModel();
            DataContext = eivm;
            dataPager.OnDemandLoading += dataPager_OnDemandLoading;
        }

private void dataPager_OnDemandLoading(object sender, Syncfusion.UI.Xaml.Controls.DataPager.OnDemandLoadingEventArgs args)
        {
            //some codes here
        }

Quote:

System.NullReferenceException: 'Object reference not set to an instance of an object.'

<Style TargetType="{x:Type local:MyControl}">

    <Setter Property="Template">

        <Setter.Value>

            <ControlTemplate TargetType="{x:Type local:MyControl}">

                <Border Background="{TemplateBinding Background}"
                    BorderBrush="{TemplateBinding BorderBrush}"
                    BorderThickness="{TemplateBinding BorderThickness}">

                    <TreeView ItemsSource="{Binding TreeDataItems, RelativeSource={RelativeSource TemplatedParent}}">

                        <TreeView.Resources>
                            <HierarchicalDataTemplate DataType="{x:Type local:TreeItem}" ItemsSource="{Binding Children}">
                                <TextBlock Text="{Binding Path=Caption}" />
                            </HierarchicalDataTemplate>
                        </TreeView.Resources>

                        <i:Interaction.Triggers>
                            <i:EventTrigger EventName="TreeViewItem.Expanded">
                                <i:InvokeCommandAction Command="{Binding TreeItemExpandedCommand, RelativeSource={RelativeSource TemplatedParent}}"
                                                    CommandParameter="{Binding}">

                                </i:InvokeCommandAction>
                            </i:EventTrigger>
                        </i:Interaction.Triggers>

                    </TreeView>
                </Border>

            </ControlTemplate>

        </Setter.Value>

    </Setter>

</Style>

private ICommand _TreeItemExpandedCommand;
public ICommand TreeItemExpandedCommand
{
    get
    {
        if (_TreeItemExpandedCommand == null)
            _TreeItemExpandedCommand = new RelayCommand<object>(p => TreeItemExpandedExecuted(p));
        return _TreeItemExpandedCommand;
    }
}

private void TreeItemExpandedExecuted(object args)
{
}

<TreeView TreeViewItem.Expanded="TreeViewItem_Expanded">
    ...
</TreeView/>

and

 private void TreeViewItem_Expanded(object sender, RoutedEventArgs e)
    {
        TreeViewItem tvi = e.OriginalSource as TreeViewItem;
        if (tvi != null)
        {
          // Do something
        }
    }

<Style x:Key="dataGridCurrencyCellStyle" 
        BasedOn="{StaticResource dataGridCellStyle}"
        TargetType="{x:Type DataGridCell}">

    <Setter Property="Width" Value="75"/>
    <Setter Property="TextBlock.TextAlignment" Value="Left"/>
    <Setter Property="TextBlock.Text" Value="{Binding StringFormat=C}"/>
    <Setter Property="IsEnabled" Value="{Binding DataContext.AreFieldsEnabled, ElementName=budgetControl}"/>

</Style>

<Style x:Key="dataGridCurrencyCellStyle" 
        BasedOn="{StaticResource dataGridCellStyle}"
        TargetType="{x:Type DataGridCell}">

    <Setter Property="Width" Value="75"/>
    <Setter Property="TextBlock.TextAlignment" Value="Left"/>
    <Setter Property="TextBlock.Text" Value="{Binding StringFormat=C}"/>
    <Setter Property="IsEnabled" Value="False"/>

    <Style.Triggers>
        <MultiTrigger>
            <MultiTrigger.Conditions>
                <Condition Property="AreFieldsEnabled" Value="True" />
                <Condition Property="IsCellEnabled " Value="True" />
            </MultiTrigger.Conditions>
            <MultiTrigger.Setters>
                <Setter Property="IsEditing" Value="True" />
            </MultiTrigger.Setters>
        </MultiTrigger>
    </Style.Triggers>

</Style>

foreach (string item in columnNames)
{
    // Create binding
    Binding binding = new Binding(item);
    string styleName = "";

    // Get binding mode and style name
    if (item == "Type")
    {
        binding.Mode = BindingMode.OneTime;
        styleName = "budgetGridCellStyle";
    }
    else
    {
        binding.Mode = BindingMode.TwoWay;
        binding.UpdateSourceTrigger = UpdateSourceTrigger.PropertyChanged;
        styleName = "dataGridCurrencyCellStyle";
    }

    // Get the style
    var style = Application.Current.FindResource(styleName) as Style;

    // Bind the column
    var col = new DataGridTextColumn()
    {
        Header = item,
        Binding = binding,
        Visibility = Visibility.Visible,
        CellStyle = style
    };

    DataGridColumns.Add(col);
}

<Style x:Key="dataGridCurrencyCellStyle" 
        BasedOn="{StaticResource dataGridCellStyle}"
        TargetType="{x:Type DataGridCell}">

    <Setter Property="Width" Value="75"/>
    <Setter Property="TextBlock.TextAlignment" Value="Right"/>
    <Setter Property="TextBlock.Text" Value="{Binding StringFormat={}{0:0.##}}"/>
    <Setter Property="IsEnabled" Value="{Binding DataContext.AreFieldsEnabled, ElementName=budgetControl}"/>

</Style>