Text Changed Event Not Firing

Question

I got 2 Dropdown list, 1 Radio button and 1 Textbox along with a Button. I am trying to Disable Button when Dropdowns,Radio Buttons are not selected alon with Empty Textbox. I am able to Disable the button for Dropdown and Radio Button and displaying the message as "Invalid Selection" and for this I have written code on Selected Index Change Event and even in Button Click Event and its working fine. But I am not able to Disable the Button when the Textbox is Empty. Want this Button to be Enabled only when I type something in Textbox and when i try to Click the Button When Textbox is Empty i need a message to be displayed saying "Please Enter a Comment". I have tried Text Changed Event for TextBox too but it is not firing. And Please anybody let me know how to put all these together in Button Click event using Flags.

Note: There are 2 Error messages to be displayed upon Button Click. This should come in loop with Flags being assigned.

So far I have tried this,

Button Click Code:

protected void BtnSave_Click(object sender, EventArgs e)
    {
        if (DrpForYear.SelectedItem.Text == "Please Select" || DrpForMonth.SelectedItem.Text == "Please Select" || RadView.SelectedItem.Text == "")
        {
            LblErr.Text = "Invalid Selection!!!";
            LblErr.Visible = true;
            BtnSave.Enabled = false;
            BtnSave.BackColor = Color.Gray;
            BtnSave.ForeColor = Color.Red;
        }

        else
            {
                DTO objc = new DTO();

                int Flag = 0;

                LblLogdInUsername.Text = Session["Username"].ToString();
                objc.LogdInUsername = LblLogdInUsername.Text;

                objc.DateTime = DateTime.Now;

                objc.Comments = Server.HtmlEncode(this.TxtComments.Text);

                objc.Company = LblCompany.Text;

                LblName.Text = Session["Name"].ToString();
                objc.Name = LblName.Text;

                objc.Year = DrpForYear.SelectedItem.Text;

                objc.Month = DrpForMonth.SelectedItem.Text;

                objc.ViewPreference = RadView.SelectedItem.Text;


                int X = obj.InsertButtonComment(objc);

                if (X >= 0)
                {
                    Flag = 1;
                }

                else
                {
                    Flag = 0;
                }

                if (Flag == 1)
                {
                    LblSuccess.Visible = true;
                    LblSuccess.Text = "Comment Saved";
                    LblErr.Visible = false;
                    BtnSave.Enabled = true;
                }
                else
                {
                    LblErr.Visible = true;
                    LblErr.Text = "Failed To Save Comment!!!";
                    LblSuccess.Visible = false;
                }

                objc.LogdInUsername = Convert.ToString(Session["LogdInUsername"]);
                DataSet GrdVC = obj.GetButtonComment(objc);
                DataView GrdViewC = new DataView();
                GrdViewC.Table = GrdVC.Tables[0];
                gvData.DataSource = GrdViewC;
                gvData.DataBind();

                TxtComments.Text = "";
                DrpForYear.ClearSelection();
                DrpForMonth.ClearSelection();
                RadView.Text = "";
         }
    }

DDL Selected Index Codes:

    protected void DrpForYear_SelectedIndexChanged(object sender, EventArgs e)
    {
        if (DrpForYear.SelectedItem.Text == "Please Select")
        {
            LblErr.Text = "Invalid Selection!!!";
            LblErr.Visible = true;
            BtnSave.Enabled = false;
            BtnSave.BackColor = Color.Gray;
            BtnSave.ForeColor = Color.Red;
        }

        else
        {
            BtnSave.Enabled = true;
            BtnSave.BackColor = ColorTranslator.FromHtml("#666666");
            BtnSave.ForeColor = Color.White;
        }
    }

    protected void DrpForMonth_SelectedIndexChanged(object sender, EventArgs e)
    {
        if (DrpForMonth.SelectedItem.Text == "Please Select")
        {
            LblErr.Text = "Invalid Selection!!!";
            LblErr.Visible = true;
            BtnSave.Enabled = false;
            BtnSave.BackColor = Color.LightGray;
            BtnSave.ForeColor = Color.Red;
        }

        else
        {
            BtnSave.Enabled = true;
            BtnSave.BackColor = ColorTranslator.FromHtml("#666666");
            BtnSave.ForeColor = Color.White;
        }
    }

Textbox Changed Event Code:

    protected void TxtComments_TextChanged(object sender, EventArgs e)
    {
        if (TxtComments.Text == "")
        {
            LblErr.Text = "Please Enter a Comment!!!";
            LblErr.Visible = true;
            BtnSave.Enabled = false;
            BtnSave.BackColor = Color.LightGray;
            BtnSave.ForeColor = Color.Red;
        }

        else if (TxtComments.Text != "")
        {
            BtnSave.Enabled = true;
            BtnSave.BackColor = ColorTranslator.FromHtml("#666666");
            BtnSave.ForeColor = Color.White;
        }
    }   

aspx code:

<asp:TextBox ID="TxtComments" runat="server" BorderColor="#666666" BorderWidth="1px" 
 Font-Names="Calibri" Font-Size="Small" ForeColor="#034599" Height="106px" TextMode="MultiLine" Width="617px" ontextchanged="TxtComments_TextChanged">

Answer 1

1. You need to set AutoPostBack property of the TextBox to True .

2. while comparing the input String with EmptyString , you need to Trim the input so that whitespaces would be removed.

or

you can use String.IsNullOrWhiteSpace() to check for null , empty and whitespaces . Try This:

Design Code

<asp:TextBox ID="TxtComments" runat="server" OnTextChanged="TxtComments_TextChanged"   
AutoPostBack="True"></asp:TextBox>

Code Behind: using Trim() function

   protected void TxtComments_TextChanged(object sender, EventArgs e)
    {
        if (TxtComments.Text.Trim().Equals(""))
        {
            LblErr.Text = "Please Enter a Comment!!!";
            LblErr.Visible = true;
            BtnSave.Enabled = false;
            BtnSave.BackColor = Color.LightGray;
            BtnSave.ForeColor = Color.Red;
        }    
        else
        {
            BtnSave.Enabled = true;
            BtnSave.BackColor = ColorTranslator.FromHtml("#666666");
            BtnSave.ForeColor = Color.White;
        }
    }     

or using String.IsNullOrWhiteSpace() function

 protected void TxtComments_TextChanged(object sender, EventArgs e)
    {
        if (String.IsNullOrWhiteSpace(TxtComments.Text))
        {
            LblErr.Text = "Please Enter a Comment!!!";
            LblErr.Visible = true;
            BtnSave.Enabled = false;
            BtnSave.BackColor = Color.LightGray;
            BtnSave.ForeColor = Color.Red;
        }    
        else
        {
            BtnSave.Enabled = true;
            BtnSave.BackColor = ColorTranslator.FromHtml("#666666");
            BtnSave.ForeColor = Color.White;
        }
    }     

Solution 2: display TextBox error message as first error

protected void BtnSave_Click(object sender, EventArgs e)
{
   if (TxtComments.Text.Trim().Equals(""))
    {
        LblErr.Text = "Please Enter a Comment!!!";
        LblErr.Visible = true;
        BtnSave.Enabled = false;
        BtnSave.BackColor = Color.LightGray;
        BtnSave.ForeColor = Color.Red;
    }    
   else if (DrpForYear.SelectedItem.Text == "Please Select" || DrpForMonth.SelectedItem.Text == "Please Select" || RadView.SelectedItem.Text == "")
    {
        LblErr.Text = "Invalid Selection!!!";
        LblErr.Visible = true;
        BtnSave.Enabled = false;
        BtnSave.BackColor = Color.Gray;
        BtnSave.ForeColor = Color.Red;
    }

    else
    {
          /*your code*/
    }
  }

Answer 2

You need to set

TxtComments.AutoPostBack= true

in Code behind

Or

AutoPostBack="True" in TextBox Design Page

Like this

<asp:TextBox ID="TxtComments" runat="server" AutoPostBack="True"></asp:TextBox>   

Answer 3

将自动回传设置为true

<asp:TextBox ID="TxtComments" runat="server" BorderColor="#666666" BorderWidth="1px" Font-Names="Calibri" Font-Size="Small" ForeColor="#034599" Height="106px" TextMode="MultiLine" Width="617px" ontextchanged="TxtComments_TextChanged" AutoPostBack="true">