c# - username and email validation works but when I hit in submit button, it still proceeds -

i have these codes username , email validation if existing in database or not. far able make them work(validations appear) however, though example username exists , clicked on submit, still pushes through? missing here?

protected void txtuser_textchanged(object sender, eventargs e)     {         if (!string.isnullorempty(txtuser.text))         {             sqlconnection conn = new sqlconnection(configurationmanager.connectionstrings["registrationconnectionstring"].connectionstring);             conn.open();             sqlcommand cmd = new sqlcommand("select * userdata username=@username", conn);             cmd.parameters.addwithvalue("@username", txtuser.text);             sqldatareader dr = cmd.executereader();             if (dr.hasrows)             {                 lblusercheck.text = "username exists";                 lblusercheck.forecolor = system.drawing.color.red;                 imgstatus.visible = true;                 imgstatus.imageurl = "images1/work/notavailable.png";             }             else             {                 lblusercheck.text = "username available!";                 lblusercheck.forecolor = system.drawing.color.limegreen;                 imgstatus.visible = true;                 imgstatus.imageurl = "images1/work/available.png";             }             conn.close();           }     }      protected void txtemail_textchanged(object sender, eventargs e)     {         if (!string.isnullorempty(txtemail.text))         {             sqlconnection conn = new sqlconnection(configurationmanager.connectionstrings["registrationconnectionstring"].connectionstring);             conn.open();             sqlcommand cmd = new sqlcommand("select * userdata email=@email", conn);             cmd.parameters.addwithvalue("@email", txtemail.text);             sqldatareader dr = cmd.executereader();             if (dr.hasrows)             {                 lblemailcheck.text = "email used";                 lblemailcheck.forecolor = system.drawing.color.red;                 imageemail.visible = true;                 imageemail.imageurl = "images1/work/notavailable.png";             }             else             {                 lblemailcheck.text = "email approved";                 lblemailcheck.forecolor = system.drawing.color.limegreen;                 imageemail.visible = true;                 imageemail.imageurl = "images1/work/available.png";             }             conn.close();         } 

and here submit button code:

protected void btn_registration_click(object sender, eventargs e)     {         try         {             sqlconnection conn = new sqlconnection(configurationmanager.connectionstrings["registrationconnectionstring"].connectionstring);             conn.open();             string insertquery = "insert userdata(username,firstname,lastname,email,password,customertype,deliveryaddress,zip,contactnumber)values(@username,@firstname,@lastname,@email,@password,@customertype,@deliveryaddress,@zip,@contactnumber)";             sqlcommand scm = new sqlcommand(insertquery, conn);             scm.parameters.addwithvalue("@username", txtuser.text);             scm.parameters.addwithvalue("@firstname", txtfn.text);             scm.parameters.addwithvalue("@lastname", txtln.text);             scm.parameters.addwithvalue("@email", txtemail.text);             scm.parameters.addwithvalue("@password", businesslayer.shoppingcart.createshahash(txtpw.text));             scm.parameters.addwithvalue("@customertype", radiobuttonlist1.selecteditem.tostring());             scm.parameters.addwithvalue("@deliveryaddress", txtaddress.text);             scm.parameters.addwithvalue("@zip", txtzip.text);             scm.parameters.addwithvalue("@contactnumber", txtcontact.text);              scm.executenonquery();             session["contact"] = txtcontact.text;             session["email"] = txtemail.text;             session["deliveryaddress"] = txtaddress.text;             label_register_success.text = ("registration successful!");             //response.redirect("home.aspx");             conn.close();         }         catch (exception ex)         {             response.write("error:" + ex.tostring());         }     }