trouble about setting value of slider in wpf?

trouble about setting value of slider in wpf?

I have a slider in wpf and want the user , set the min and max value of it.
in xaml code :
<Slider x:Name="slider1" Width="34" Minimum="{Binding Path=Minval}"
Value="10" Height="105" Margin="5,5,5,5" Maximum="{Binding
Path=Maxcamdistance}"/>
<TextBox Height="23" HorizontalAlignment="Left" Margin="5,5,5,5"
Name="minvaltxt" VerticalAlignment="Top" Width="120" />
<TextBox Height="23" HorizontalAlignment="Left" Margin="5,5,5,5"
Name="maxvaltxt" VerticalAlignment="Top" Width="120" />
<Button Content="Apply" Name="btn" Height="23"
HorizontalAlignment="Left" Margin="5,5,5,5" VerticalAlignment="Top"
Width="24" Click="btn_Click" />
in code behind :
private double maxval = 80;
public double Maxval
{
get { return maxval; }
set { value = maxval; }
}
private double minval = 5;
public double Minval
{
get { return minval; }
set { value = minval; }
}
private void btn_Click(object sender, RoutedEventArgs e)
{
minval= double.Parse(minvaltxt.Text);
maxval= double.Parse(maxvaltxt.Text);
slider1.Minimum = Minval
slider1.Maximum = Maxval;
}
but it does not update the min and max value of silder ! what is the
problem ? thanks for any help.
sorry for copy-paste mistake. the question now edited. thanks.