Check if user type a single character or number in textbox c#

Question

I already can make the login for user, so if user type their username or password wrongly in textbox, the message label that says "Invalid username or password" appear. But, i want to when user type a single character or number in textbox when the message label is appear, the message label will not visible to user (visible = false) as user already type a single character or number in textbox. But the message label didn't disappear when user type a single character or number.

This is the code:

private void CheckTextBox(object sender, EventArgs e) { if (string.IsNullOrEmpty(textBox1.Text) || string.IsNullOrEmpty(textBox2.Text)) { label5.Visible = true; } else { label5.Visible = false; } }

And here is the image:

Below image is when user type wrongly (the username or password), the message label appear:

enter image description here

Below image is when user type a single character or number, but the message label still at there

enter image description here

My question is: How do i set the message label to not show when user type a single character or number in the textbox?

Any help?

Your answer will be great appreciated!

Thank you!

You need to make sure this CheckTextBox method is wired up to the TextChanged event of the checkbox. — Simon Whitehead
– Simon Whitehead, Commented Feb 22, 2014 at 6:33

Sudhakar Tillapudi · Accepted Answer · 2014-02-22 06:47:54Z

Problem : You have not wiredup the CheckTextBox() method for both TextBox1 and TextBox2 TextChanged Event.

Solution : in your Form_Load WireUp the CheckTextBox() method for the Textbox1 and TextBox2 TextChanged Event as below:

 private void Form1_Load(object sender, EventArgs e) { textBox1.TextChanged += new System.EventHandler(this.CheckTextBox); textBox2.TextChanged += new System.EventHandler(this.CheckTextBox); }

Suggestion : i think string.IsNullOrWhiteSpace() is more appropriate as it would also check for Whitespace in addition to null and Empty strings.

Try This:

 private void CheckTextBox(object sender, EventArgs e) { if (string.IsNullOrWhiteSpace(textBox1.Text) || string.IsNullOrWhiteSpace(textBox2.Text)) { label5.Visible = true; } else { label5.Visible = false; } }

Josh Anderson · Accepted Answer · 2014-02-22 06:34:02Z

This line is checking if either textbox has information in it.

if (string.IsNullOrEmpty(textBox1.Text) || string.IsNullOrEmpty(textBox2.Text))

Change the || to && and then the label will only be shown when BOTH textboxes do not have any data.

Raging Bull · Accepted Answer · 2014-02-22 06:34:22Z

If I understand you correctly, try this:

private void CheckTextBox(object sender, EventArgs e) { if (string.IsNullOrEmpty(textBox1.Text) && string.IsNullOrEmpty(textBox2.Text)) { label5.Visible = true; } else { label5.Visible = false; } }

If you change || to && then label5 will be visible only if both textboxes are empty.

Nagaraj S · Accepted Answer · 2014-02-22 06:36:47Z

if (string.IsNullOrEmpty(textBox1.Text) || string.IsNullOrEmpty(textBox2.Text))

Try this..use && instead of ||

private void CheckTextBox(object sender, EventArgs e) { if (string.IsNullOrEmpty(textBox1.Text) && string.IsNullOrEmpty(textBox2.Text)) { label5.Visible = true; } else { label5.Visible = false; } }

Nagaraj S · Accepted Answer · 2014-02-22 06:39:06Z

Check this code, Should be call this OnTextChanged="CheckTextBox" on your textbox

protected void CheckTextBox(object sender, EventArgs e) { if (string.IsNullOrEmpty(textBox1.Text) && string.IsNullOrEmpty(textBox2.Text)) { label5.Visible = true; } else { label5.Visible = false; } }

<asp:TextBox ID="TextBox1" runat="server" OnTextChanged="CheckTextBox"></asp:TextBox>

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