Develop Reference

Disable button when the selected value in comboBox changed

I have a button and a comboBox. The comboBox has 2 value, 'yes and no' I want to disable the button if the selected value is no while i want to enabled if the value selected is yes what would I do, I dont know where will I put the code and also my code seems wrong.
if (ComboBoxCustType.SelectedIndex = 0)
{
Button1.Enabled = false;
}
else
Button1.Enabled = true;

Since you didn't specify WinForms or WPF, this is for WinForms.
You have to create an event on the ComboBox.SelectedIndexChanged and inside the event handler, you write your code to handle the selecteditem text.
public Form1()
{
comboBox1.SelectedIndexChanged += ComboBox1_SelectedIndexChanged;
InitializeComponent();
CheckSelction();
}
private void ComboBox1_SelectedIndexChanged(object sender, EventArgs e)
{
CheckSelction();
}
void CheckSelction()
{
if (comboBox1.SelectedItem != null)
{
var item = comboBox1.SelectedItem.ToString();
button1.Enabled = item == "yes";
}
else
button1.Enabled = false;
}

Simple login screen with user name and password

I'm trying to create a simple login screen, which has 2 textboxes and 1 button. When strings i've insterted in the first textbox (username) and the second textbox (password) matches the strings i've defined before, the buttons Enabled propertie should become True and when clicked, it should open another form, here's the code i've written so far:
public partial class LogInScreen : Form
{
public LogInScreen()
{
InitializeComponent();
string lietotajvards = "user";
string parole = "user";
if (textBox1.Text == lietotajvards && textBox2.Text == parole)
{
button1.Enabled = true;
}
else
{
button1.Enabled = true;
}
}
private void button1_Click(object sender, EventArgs e)
{
Form1 f1 = new Form1();
this.Hide();
f1.Show();
}
}
The thing is that with my code it doesn't work as expected and the button is enabled all the time. Where's the problem?

Your code will only execute once when the form is initialized, you have to make use of a textchanged event on textbox1 and textbox2, thereafter you can use the code you wrote to check if the button needs to be enabled. In the else you must disable the button.
Text changed event handlers:
void textBox1_TextChanged(object sender, EventArgs e)
{
handleLoginButton();
}
void textBox2_TextChanged(object sender, EventArgs e)
{
handleLoginButton();
}
Enable/disable button:
private void handleLoginButton(){
string lietotajvards = "user";
string parole = "user";
if (textBox1.Text == lietotajvards && textBox2.Text == parole)
{
button1.Enabled = true;
}
else
{
button1.Enabled = false;
}
}

The constructor only runs once for the form, you need to handle the text changed events for the input controls and then re-evaluate your condition again.
Also it should go without saying (although it is being said here) that this is a terrible way to handle logging in to an application.

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

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

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;
}
}

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.

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.

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;
}
}

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>

Making picturebox appear when combobox element is selected

I'm trying to make pictures appear, when the element in combobox is selected.
private void Form4_Load(object sender, EventArgs e)
{
if (comboBox1.SelectedIndex == 0)
{
pictureBox1.Visible = true;
pictureBox2.Visible = true;
pictureBox3.Visible = true;
pictureBox4.Visible = true;
}
}
I tried to do it this way, but that doesn't work. Where I’ve made the mistake?

The naming of your method makes me think you're doing that inside the form loading event.
Use the SelectedIndexChanged event of the combobox instead.

Why Doesn't Regex give a chance to input data?

I have a event which doesn't give a any opportunity to input data in TextBox. When I'm trying to input data in Textbox, then Textbox doesn't give to do it:
private void Login_textbox_KeyPress(object sender, KeyPressEventArgs e)
{
if (!System.Text.RegularExpressions.Regex.IsMatch(textbox1.Text, #"^[a-zA-Z]+$"))
e.Handled = true;
}
I just want to input data in TextBox which isn't digit or any symbols.

Try using the following code
private void textBox1_KeyPress(object sender, KeyPressEventArgs e)
{
if (!System.Text.RegularExpressions.Regex.IsMatch(e.KeyChar.ToString() , #"^[a-zA-Z]+$"))
e.Handled = true;
}
Thanks!

It seems you are using c#.
Then steps you need to follow :
1) Set causesValidation property of your textbox to true
2) Set event listeners for causes validation
myTextBox1.Validating +=
new System.ComponentModel.CancelEventHandler(myTextBox1_Validating);
myTextBox1.Validated +=
new System.EventHandler(myTextBox1_Validated);
3) Implement these event hadler functions
private void myTextBox1_Validating(object sender,System.ComponentModel.CancelEventArgs e)
{
if(!CheckIfTextBoxNumeric(myTextBox1))
{
myLabel.Text = "Has to be numeric";
e.Cancel = true;
}
}
private void myTextBox1_Validated(object sender,System.EventArgs e)
{
myLabel.Text = "Validated first control";
}
If you instead want to use maskedTextBox refer http://msdn.microsoft.com/en-us/library/ms234064(v=vs.80).aspx