How to display remaining textbox characters in a label in C#?

问题

I'm not sure if I have the last bit right? I changed the max length of the textbox to 140. I can't seem to use TextLength. Help please?! I have this so far:

protected void textBox_TextChanged(object sender, EventArgs e)
{
    characterCountLabel.Text = textBox.MaxLength - textBox.TextLength;
}

回答1:

characterCountLabel.Text is in string format. So you might want to convert it before you set its value like this:

protected void textBox_TextChanged(object sender, EventArgs e)
{
    characterCountLabel.Text = (textBox.MaxLength - textBox.Text.Length).ToString();
}

I think you are trying to display the remaining characters the user can input to your text box? I suggest that you can set the limit as constant like this:

protected void textBox_TextChanged(object sender, EventArgs e)
    {
        characterCountLabel.Text = (140 - textBox.Text.Length).ToString(); // in here 140 is your limit
    }

If you are using ASP.NET in C#. Don't limit yourself from using javascript like in this link

回答2:

I think this will be a better answer...

Header code:

<script language="javascript" type="text/javascript">
    function getCountDown() 
    {
        //Get the Textbox control
        var textField = document.getElementById("<%#TextBox1.ClientID %>");
        //Do the math of chars left and pass the value to the label
        document.getElementById('<%#Label1.ClientID %>').innerHTML = textField.maxLength - textField.value.length;
        return false;
    }        
</script>

ASP code:

<asp:TextBox ID="TextBox1" runat="server" MaxLength="729" Height="80px" 
                Width="591px" onkeyup="getCountDown();" ClientIDMode="Static"></asp:TextBox>

<asp:Label ID="Label1" runat="server" Text="" ClientIDMode="Static"></asp:Label>

It is important to set the TextBox and Label control's property as ClientIDMode="Static" otherwise the control name will not be found on the javascript.

CS code:

protected void Page_Load(object sender, EventArgs e)
{
    Page.Header.DataBind();
}

That's it for a SingleLine TextBox.

Now for a MultiLine TextBox you need to add this on your Page_Load() so the maxLength takes the TextBox1.MaxLength value.:

this.TextBox1.Attributes.Add("maxLength", TextBox1.MaxLength.ToString());

Also the MaxLength property of the TextBox doesn't work when is on Multiline mode so you need to add on your javascript getCountDown() function the following lines:

// Check if user is entering more than the limit of characters
if (textField.value.length >= textField.maxLength) {
    // Cut extra text
    document.getElementById("<%#TextBox1.ClientID %>").innerHTML = textField.value.substring(0, textField.maxLength);
}

add them right after the var textField = document.getElementById("<%#TextBox1.ClientID %>"); line. This is to prevent the user from entering more characters than the MaxLength value.

Pablo

来源：https://stackoverflow.com/questions/16908006/how-to-display-remaining-textbox-characters-in-a-label-in-c

标签

textbox

character