I Was Done Validation In Wcf And Refer Into Wpf. Now I Want Show Error Msg Bind With Text Box. How To Do This

namespace userregistration
{    
    public class Service1 : IService1
    {
        XmlDocument xdoc;
        XmlNode root;
        XmlNode xn;
        public string ufname;
        public string ulname;
        public string uemail;
        public string upass;
        public string uconfpass;
        public string uadd;
        public bool firstnameinput(string fnametext)
         {
            if (fnametext == "")
             {
                   return true;
             }
             else
               {
                   return false;
               }

         }
    }
  }

void validation()
  {
      fnametext = textboxFirstName.Text;
      lnametext = textboxlastname.Text;
      emailtext = textboxEmail.Text;
      passtext = password.Password;
      confpasstext = confpass.Password;
      addtext = addtexbox.Text;
      ServiceReference1.Service1Client input = new ServiceReference1.Service1Client();
      if (input.firstnameinput(fnametext))
      {
           textboxFirstName.ToolTip= "Enter Your First Name";
          // the tooltip message bind with text box........how to do this
      }
      else if (input.lastnameinput(lnametext))
      {
          MessageBox.Show("Enter Your Last Name");
      }
    
  }

<pre lang="HTML">

<Window x:Class="Registration_Form1.MainWindow"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        Title="MainWindow" Height="350" Width="525">
    <Grid Margin="22,0,25,15" removed="#FFC3A1AC" Height="283" VerticalAlignment="Bottom">
        <Button Content="SUBMIT" Margin="62,240,318,20" x:Name="Submitbtn" Foreground="#FFEC4AA9" Click="Submitbtn_Click"/>
        <Label Content="Regestration Form"  Margin="153,10,172,244" Foreground="#FFEC4AA9" FontWeight="Bold" FontStyle="Italic" FontSize="14" />
        <Label Content="First Name:"  Margin="37,56,326,204" Foreground="#FFEC4AA9" />
        <Label Content="Last Name:"  Margin="37,88,326,172" Foreground="#FFEC4AA9"  />
        <Label Content="Email ID:"  Margin="37,116,326,144" Foreground="#FFEC4AA9"  />
        <Label Content="Password:"  Margin="37,144,326,116" Foreground="#FFEC4AA9" />
        <Label Content="Confirm Password:"  Margin="37,172,326,88" Foreground="#FFEC4AA9" />
        <Label Content="Address:"  Margin="37,205,326,55" Foreground="#FFEC4AA9" />
        <TextBox  Margin="155,56,70,204" x:Name="textboxFirstName" Foreground="#FFEC4AA9"/>
        <TextBox  Margin="155,87,70,173" x:Name="textboxlastname" Foreground="#FFEC4AA9" />
        <TextBox  Margin="155,116,70,144" x:Name="textboxEmail" RenderTransformOrigin="0.323,-2.08" Foreground="#FFEC4AA9" />
        <PasswordBox  Margin="155,144,70,116" x:Name="password" Foreground="#FFEC4AA9" />
        <!--For password-->
        <PasswordBox  Margin="155,172,70,88" x:Name="confpass" Foreground="#FFEC4AA9" />
        <TextBox Margin="155,205,70,55" x:Name="addtexbox" Foreground="#FFEC4AA9" />
        <Button Content="RESET"  Margin="182,240,192,20" x:Name="resetbtn" Foreground="#FFEC4AA9" Click="resetbtn_Click"/>
        <Button Content="CANCEL"  Margin="308,240,50,20" x:Name="cancelbtn" Foreground="#FFEC4AA9" Click="cancelbtn_Click" />
        <TextBlock Name="message" Margin="62,115,50,135" FontWeight="Bold" FontStyle="Italic" FontSize="18"/>
    </Grid>
</Window>