How to write WPF DataTrigger within Border Style and how to Find Element in Setter?

Question

I need a WPF DataTrigger for the Mouse Hover functionality of a Border. The Border Contains a Button, initially its Visibility is Collapsed. The Button should be Visible only on Mouse Hover otherwise Collapsed.

<Border Width="100" Height="30" HorizontalAlignment="Center" VerticalAlignment="Top" Background="#FFF2FFC6" Margin="0,20,0,0">
    <Button x:Name="btn" Content="iApp" HorizontalAlignment="Center" VerticalAlignment="Center" Width="75" Visibility="Collapsed" />
    <Border.Style>
        <Style TargetType="Border">
            <Style.Triggers>
                <DataTrigger Binding="{Binding RelativeSource={RelativeSource Self}, Path=IsMouseOver}" Value="True">
                    <Setter TargetName="btn" Property="Visibility" Value="Visible"></Setter>
                </DataTrigger>
            </Style.Triggers>
        </Style>
    </Border.Style>
</Border>

Note: I need only DataTrigger. Don't suggest Event Trigger.

Here I Can't able to find the TargetName, it produces the Build Error "Error 1 The name "btn" is not recognized"

Answer 1

1. TragetName cannot be used in Style.Triggers. It should be used in ControlTemplete.Triggers.
2. You can write code like this(Not test).

Add the namespace in you xaml

     xmlns:converter="clr-namespace:yours coverter's namespace"

Add the converter in your resources

     <UserControl.Resources>
           <converter:BooleanToVisibilityConverter x:Key="BooleanToVisibilityConverter" />
     </UserControl.Resources>

This is your border:

     <Border x:Name="m_Border" Margin="0,20,0,0">
     <Button x:Name="btn" Content="iApp"  Visibility="{Binding  IsMouseOver,ElementName=m_Border,Converter="{StaticResource BooleanToVisibilityConverter},ConverterParameter=Normal}"}" />
    </Border> 

3. Using this converter

     public enum BooleanToVisibilityConverterType
     {
           /// <summary>
           /// Normal
           /// </summary>
           Normal = 1,
   
           /// <summary>
           /// Reverse
           /// </summary>
           Reverse = 2
      }
   
     public class BooleanToVisibilityConverter : IValueConverter
     {
           public object Convert(object value, Type targetType, object parameter, CultureInfo culture)
           {
                var targertValue = false;
   
            if (value == null)
            {
                throw new Exception("BooleanToVisibilityConverter - Convert Error");
            }
            else if (!Boolean.TryParse(value.ToString(), out targertValue))
            {
                throw new Exception("BooleanToVisibilityConverter - Convert Error");
            }
            else
            {
                var parameterValue = BooleanToVisibilityConverterType.Normal;
   
                if (parameter != null)
                {
                    Enum.TryParse<BooleanToVisibilityConverterType>(parameter.ToString(), out parameterValue);
                }
   
                if (parameterValue == BooleanToVisibilityConverterType.Reverse)
                {
               return targertValue ? Visibility.Collapsed : Visibility.Visible;
                }
                else
                {
                    return targertValue ? Visibility.Visible : Visibility.Collapsed;                    
                }
            }
        }
   
   public object ConvertBack(object value, Type targetType, object parameter, CultureInfo culture)
   {
       var targetValue = Visibility.Collapsed;
   
       if (value == null)
       {
           throw new Exception("BooleanToVisibilityConverter - ConvertBack Error");
       }
       else if (!Enum.TryParse<Visibility>(value.ToString(), out targetValue))
       {
           throw new Exception("BooleanToVisibilityConverter - ConvertBack Error");
       }
       else
       {
           var parameterValue = BooleanToVisibilityConverterType.Normal;
   
           if (parameter != null)
           {
               Enum.TryParse<BooleanToVisibilityConverterType>(parameter.ToString(), out parameterValue);
           }
   
           if (parameterValue == BooleanToVisibilityConverterType.Reverse)
           {
               return targetValue == Visibility.Visible ? false : true;
           }
           else
           {
               return targetValue == Visibility.Visible ? true : false;
           }
       }
   }