c# - ASP.net 中文本框的占位符

Question

需要一个占位符来显示文本框的文本，当我在文本框中单击或输入文本时该文本消失

using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;
using System.Web.UI;
using System.Web.UI.WebControls;
using System.Data.SqlClient;
 using System.Data;



 public partial class SIGNUPaspx : System.Web.UI.Page
{

protected void Page_Load(object sender, EventArgs e)
{

}

protected void Button1_Click(object sender, EventArgs e)
{
    SqlConnection con = new SqlConnection(@"Data            Source=.\SQLEXPRESS;AttachDbFilename=C:\Users\Admin\Documents\Visual Studio  2010\WebSites\my website\App_Data\GYMDatabase.mdf;Integrated Security=True;User Instance=True");
    con.Open();
    SqlCommand cmd = new SqlCommand();
    cmd.CommandText = "select * from Client_Data Where C_Email='" + TextBox6.Text + "'";
    cmd.Connection = con;
    SqlDataReader rd = cmd.ExecuteReader();
    rd.Read();
    if (rd.HasRows)
    {
        Label1.Text = "Email Already Exist";
    }
    else
    {
        SqlConnection con1 = new SqlConnection(@"Data Source=.\SQLEXPRESS;AttachDbFilename=C:\Users\Admin\Documents\Visual Studio 2010\WebSites\my website\App_Data\GYMDatabase.mdf;Integrated Security=True;User Instance=True");
        con1.Open();
        String str = "INSERT INTO Client_Data(C_FName,C_LName,C_Address,C_Gender,C_Email,C_Password,C_MobileNo,C_RegistrationCode) VALUES ('" + TextBox1.Text + "','" + TextBox2.Text + "','" + TextBox8.Text + "','" + RadioButtonList1.Text + "','" + TextBox6.Text + "','" + TextBox4.Text + "','" + TextBox7.Text + "','" + TextBox5.Text + "')";
        SqlCommand cm = new SqlCommand(str, con1);
        String str1 = "INSERT INTO PaymentTable(C_Email) VALUES ('" +         TextBox6.Text + "')";
        SqlCommand cmp = new SqlCommand(str1, con1);
        cm.ExecuteNonQuery();
        cmp.ExecuteNonQuery();
        con.Close();
        Label1.Visible = true;
        Response.AddHeader("REFRESH", "3;URL=LOGIN.aspx");
    }
    rd.Close();
    con.Close();

}
private void TextBox1_Enter(object sender, EventArgs e)
{
    if (TextBox1.Text == "First Name")
    {
        TextBox1.Text = "";
    }
}
private void TextBox1_Leave(object sender, EventArgs e)
{

        if (TextBox1.Text == "")
        {
            TextBox1.Text = "First Name";
            TextBox1.ForeColor = System.Drawing.Color.LightGray;
        }
    }

}

Answer 1

您不需要在 C# 中执行所有这些操作。只需在 TextBox 中添加占位符属性

<asp:TextBox ID="UserName" runat="server" CssClass="form-control" placeholder="Username or Email" Width="350"></asp:TextBox>