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Create a login form with enable/disable button

I learned how to have a textbox and when the value is empty the button is disabled and when I enter a value in the textbox the button is enabled.
Now I want to have a login form that contains one textbox (for username) and another textbox (for password), so here I learned how to code.
But how should I write the code so that when the condition (both text boxes are empty) the button is disabled and when the condition is (both text boxes have values) the button is enabled.

Try this:
private void txtUserName_TextChanged(object sender, EventArgs e)
{
CheckFields();
}
private void txtPassword_TextChanged(object sender, EventArgs e)
{
CheckFields();
}
private void CheckFields()
{
btnLogin.Enabled = txtPassword.Text.Length == 0 || txtUserName.Text.Length == 0 ? false : true;
}
I assume that your username textbox is named, txtUserName, and your password textbox is named, txtPassword. Also the login button is named, btnLogin. I recommend setting the btnLogin enabled property to false when the form first loads. You can set that in the form's Load event:
private void Form1_Load(object sender, EventArgs e)
{
btnLogin.Enabled = false;
}

I think it would be better if you implement this logic on the client side (javascript), it is unnecessary to go to the server again and again for every text change.
you should add onclick function on username and password textboxes and implement the logic to check whether both have values then enable the button else disable it.

You should add the TextChanged event for both boxes and have it be something like this:
private void CheckTextboxes(object sender, EventArgs e)
{
if (string.IsNullOrWhiteSpace(txtUsername.Text) || string.IsNullOrWhiteSpace(txtPassword.Text))
{
button.Enabled = false;
return;
}
button.Enabled = true;
}
private void txtUsername_TextChanged(object sender, EventArgs e)
{
CheckTextboxes();
}
private void txtPassword_TextChanged(object sender, EventArgs e)
{
CheckTextboxes();
}
That way you ensure that if the user enters values on the textboxes in either order the button only enables if both have actual text written on them.

Setting myButton.Enabled = true causes radiobutton's CheckedChanged handler to fire

I have absolutely no programmatic links or properties set such that my CheckedChanged fires as a result of anything except checking the radio button.
However, when I click a different, unrelated button, the button's click handler fires (this is expected). In this click handler, the button disables itself (it re-enables on a different button's click), which then triggers myRadioButton_CheckedChanged handle for an unrelated radiobutton fires.
The call stack that I'm seeing is essentially
myRadioButton_CheckedChanged (...)
myButton_Click(...)
Main(...)
The line in myButton_Click that is triggering the myRadioButton_CheckedChanged is apparently
myButton.Enabled = false;
The related code is:
private void radioButton1_CheckedChanged(object sender, EventArgs e)
{
// L-R
if (radioButton1.Checked == true)
{
orientation_left = 3;
pictureBox2.Invalidate();
Debug.Print("left {0}", orientation_left);
}
}
private void select1_Click(object sender, EventArgs e)
{
Debug.Print("select1click");
if (select1Down == false)
{
// ... stuff
select1.Enabled = false; // Causing the CheckedChanged to fire
select2.Enabled = false;
select1Down = true;
}
}

Ok, got it.
Check the TabOrder on your Button and RadioButton.
Seems that when you disable the Button, the focus is shifted to the next control, which is probably your RadioButton, causing it to become checked.
On my test From, all I had to do was to make sure that the RadioButton's TabOrder was not right after the Button.
Cheers
EDIT:
This seems to be a known problem as I just found this MSDN thread: http://social.msdn.microsoft.com/Forums/windows/en-US/77fbec3b-1f63-42e1-a200-19b261b63794/the-radiobutton-clicked-event-is-fired-without-the-radio-button-beeing-clicked-?forum=winforms

Okay, it's kinda hacky but it works without changing anything to the tab order:
private void select1_Click(object sender, EventArgs e)
{
if (!select1Down)
{
// ... stuff
SendKeys.SendWait("{Tab}");
select1.Enabled = false;
select2.Enabled = false;
select1Down = true;
}
}

Validate a textbox in a windows form

Windows form application(.Net 3.5) I have a textbox and a button on the form.
I want to disable the button once the textbox is empty.
I don't want to use this method. Because the button is still enabled.
Thanks.

In the event handler for TextChanged, simply determine if the text box contains any data. If it does, enable it. Otherwise, disable it. Add your event handler and then implement something like the following,
private void textBox1_TextChanged(object sender, EventArgs e)
{
button1.Enabled = !(textBox1.Text == String.Empty);
}

Handle the on text change event
check and see what textbox.text is like this
if(string.IsNullOrEmpty(textbox1.text))
{
Button1.enabled = false;
}

if you want to disable the textbox, then using textChanged:
if (textbox.Text == ""){
button.Enabled = false;
}
Hope it helps

Make button1.Enabled = false;
and add EventHandler to textbox1.TextChanged = new System.EventHandler(SearchBoxTextChanged);
private void textbox1_TextChanged(object sender, EventArgs e)
{
button1.Enabled = (textBox1.Text.Trim() != string.Empty);
}

Problem controlling input on treeViewNode LabelEdit

I am trying to control user input when he/she wants to edit a treeNode. I don't want him to be able to write numbers (or even better not write a number at given index of the text but thats a bonus)
What I did was make a boolean on the mainWindow that determines if the user is editing the treeNode or not like this:
void Tree_AfterLabelEdit(object sender, System.Windows.Forms.NodeLabelEditEventArgs e) {
isEditing = false;
}
void Tree_BeforeLabelEdit(object sender, System.Windows.Forms.NodeLabelEditEventArgs e) {
isEditing = true;
}
private void Tree_KeyDown(object sender, KeyEventArgs e) {
control input. (e.Handled = true when keyDown is a number.)
}
This is what I tried but the event keydown is only called when I am NOT editing a treenode. So it falls out of purpose. (I use keydown already to handle arrow key events but I want to do both.)
Tried with keypress aswell to no avail.

The TreeView does not have any mechanism to control the LabelEdit part. Even if you can handle the KeyDown part of the Label to prevent numbers, you would still have to inspect the contents on the AfterLabelEdit because the user can "paste" numbers into the field as well. It's best to just control it during the AfterLabelEdit event:
private void treeView1_AfterLabelEdit(object sender, NodeLabelEditEventArgs e)
{
foreach (char c in e.Label)
{
if (char.IsNumber(c))
e.CancelEdit = true;
}
}

Tabpage control leave

I have a tab control and 3 tabpages in it. ( C#)
if i am in tab 2, and edit a text box value
and then click tab 3, i need to validate what was enetered in the text box.
if correct i should allow to to switch to tab 3 else should remain in tab 2 it self
how do i achieve this?
iam curently handling the "leave" event of the tabpage2,
i validate the text box value there and if found invalid
i set as tabcontrol.Selectedtab = tabpage2; this does
the validation but switches to new tab! how could i restrict the navigation.
I am a novice to C#, so may be i am handling a wrong event!
Here is the relevant code:
private void tabpage2_Leave(object sender, EventArgs e)
{
if (Validatetabpage2() == -1)
{
this.tabcontrol.SelectedTab =this.tabpage2;
}
}

While the other approaches may work, the Validating event is designed specifically for this.
Here's how it works. When the SelectedIndex of the tab control changes, set the focus to the newly selected page and as well as CausesValidation = true. This ensures the Validating event will called if the user tries to leave the tab in any way.
Then do your normal validation in a page specific Validating event and cancel if required.
You need to make sure to set the initial selected tab page in the Form Shown event (Form_Load will not work) and also wire up the tab page specific validating events.
Here's an example:
private void Form_Shown(object sender, System.EventArgs e)
{
// Focus on the first tab page
tabControl1.TabPages[0].Focus();
tabControl1.TabPages[0].CausesValidation = true;
tabControl1.TabPages[0].Validating += new CancelEventHandler(Page1_Validating);
tabControl1.TabPages[1].Validating += new CancelEventHandler(Page2_Validating);
}
void Page1_Validating(object sender, CancelEventArgs e)
{
if (textBox1.Text == "")
{
e.Cancel = true;
}
}
void Page2_Validating(object sender, CancelEventArgs e)
{
if (checkBox1.Checked == false)
{
e.Cancel = true;
}
}
private void tabControl1_SelectedIndexChanged(object sender, System.EventArgs e)
{
// Whenever the current tab page changes
tabControl1.TabPages[tabControl1.SelectedIndex].Focus();
tabControl1.TabPages[tabControl1.SelectedIndex].CausesValidation = true;
}

You can use the TabControl Selecting event to cancel switching pages. Setting e.Cancel to true in the event stops the tabcontrol from selecting a different tab.
private bool _cancelLeaving = false;
private void tabpage2_Leave(object sender, EventArgs e)
{
_cancelLeaving = Validatetabpage2() == -1;
}
private void tabcontrol_Selecting(object sender, TabControlCancelEventArgs e)
{
e.Cancel = _cancelLeaving;
_cancelLeaving = false;
}