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Changing focus from on textbox to another, when tabpages is changed in C#?

I have several tabs in a form. Each tab has one textbox. When I enter tabpage1 I have managed to set the focus on the textBox1. When I press a button in tabpage1 I jump to a random tab in the controller. What I want now is to have the focus set on textBox in the active tabpage. I have tried using tabpage_Enter event, but it does not seem to work. My code look like this :
private void tabPage2_Enter(object sender, EventArgs e)
{
textBox2.Select();
}
Any suggestions?

I think you need to use SelectedIndexChanged event of TabControl instead of _Enter, using Enter event, focus will change to textBox2 every time the cursor enter the tabPage control.

You can use the Focus() method set the focus on a textbox. I would probably set on the tabPage_Enter event.
private void tabPage_Enter(object sender, EventArgs e){
{
var tab = sender as tabPage;
if(!tab.Focused) tab.focus();
}

Change the default selected item to none

I have a WindowsForm that contains a lot of UserControl.
Each UserControl has a PictureBox, a few TextBox and a Button.
As soon as my program loads, my first TextBox is Highlighted in blue and I don't want that.
In fact I don't want anything to be selected at all.(Buttons, TextBox etc..)
I've looked into the properties but I can't find exactly how to totally remove this 'Feature'.
All my TextBox are ReadOnly but can become Write/Read while the program is running.
Any Idea how i could do this ?
Thanks in advance.
Update
Changing the TabStop properties to false did part of the job since it doesn't allow selection with tab at all. But I don't want to block the user from using tab to navigate between boxes I just don't want any selection when I run the program. Is there another way ?
Thanks for your time again.

On form Load set Focus to any label or any other control which is not tab stop on the form
private void Form1_Load(object sender, EventArgs e)
{
this.ActiveControl = label1;
}
How to remove the focus from a TextBox in WinForms?

You need to set TabFocus to false for textboxes etc
//textBox1.TabFocus = false;
textBox1.TabStop = false;

comboBoxName.SelectedIndex = -1;

How to make a Ctrl+Tab when pressed works like Tab when pressed in a MultiLine TextBox?

I have a TextBox and set the MiltiLine property to true and AcceptsTab property to false.
When the TextBox has focus and i press Tab it works fine and the next control get the focus, but when i press Ctrl+Tab it works as if AcceptsTab property is set to true and makes a tab character into the TextBox.
The reason i press Ctrl+Tab.. when switching between forms in my MDI application.
Now how to make a Ctrl+Tab when pressed works like Tab when pressed in a MultiLine TextBox?

Well, if you want to suppress Ctrl+Tab press event in textbox, you may hanlde TextBox.KeyDown event with code like this:
private void textBox1_KeyDown(object sender, KeyEventArgs e)
{
if (e.Control && e.KeyCode == Keys.Tab)
{
e.Handled = true;
}
}
This code will suppress Tab behaviour in TextBox. But I don't know if it keeps child forms switching behaviour. Possibly you will have to implement it programmatically. In my simple MDI application with one MDIContainer form and two child forms showed this behaviour doesn't appear by default.

Validating Data In A WinForm

I have created a dialog box in my WinForms application. This has many text boxes and ok/cancel buttons. When the user clicks ok, I only want the dialog box to close if all entries are valid. I can see how to do this with the "Validating" events for each control separately. That is fine. But these only seem to fire when a control loses focus. However, empty text boxes in my dialog are also invalid input which means the user may never have focused on that control. I would prefer to just validate all controls on clicking OK.
I can't work out how to do this though. Overriding the onclick of the OK button doesn't seem to have an option for stopping the window from closing. The Form IsClosing event does by setting Cancel = true. But this doesn't seem to be able to distinguish between whether the OK or Cancel button is clicked. Obviously if the cancel button is clicked I don't care about validation and want to allow the form to close regardless.
What is the best approach for doing this?]
Update:
I already had CausesValidation set to true on both my form and ok button but my validation event does not get fired when I click the ok button. I mention this as it was suggested as a solution below.

Please select the form > Set the property CausesValidation to true
Select OK button and again set property CausesValidation to true
and then it will take care of all the validations.
Important points:
1) You must mention e.Cancel=true in all the validating eventhandlers
2) If your buttons are in panels then you must set panels (or any parent control's) CausesValidation property to true
Edit:
3) Validate fires just before loss of focus. While pressing Enter will
cause the default button to Click, it doesn't move the focus to that
button, hence no validation event will be fired if you have set forms AcceptButton Property to OK button

First make sure to cancel the validation when any of the textboxes have validation errors. For example:
private void nameTextBox_Validating(object sender, CancelEventArgs e) {
if (nameTextBox.Text.Length == 0)
{
e.Cancel = true;
return;
}
}
Now add the following code to the beginning of the ok button action:
if (!ValidateChildren())
return;
This will trigger the validation event for all controls on the form,

You can also use this simple code. just introducing a simple Boolean variable named hasError can do the job.
public partial class Form1 : Form
{
private bool hasError;
public Form1()
{
InitializeComponent();
}
private void OkBtn_Click(object sender, EventArgs e)
{
errorProvider1.Clear(); hasError=false;
if (ValidateTxt.Text.Length == 0)
{
errorProvider1.SetError(ValidateTxt, "must have a value");
hasError=true;
}
if (!hasError)
{
//Do what you want to do and close your application
Close();
}
}
private void CancelBtn_Click(object sender, EventArgs e)
{
Close();
}
}

CF - Set Focus to a specific control

I have a Form that has a panel with some textBoxes and checkBox that is outside the panel.
Every time the Form is loaded the checkBox has focus.
I have put en event handler when form loads and tried to set focus on first textbox instead having it on the checkbox.
this.Activated += new EventHandler(form_Activated);
in the method i try to set the focus on the first textbox in the panel
private void form_Activated(object sender, EventArgs e)
{
if (this.parametersPanel.Controls.Count > 0)
{
this.parametersPanel.Focus();
(this.parametersPanel.Controls[0]).Focus();
}
}
This does not work, can some1 help me pls?

try setting the focus directly on the textbox instead of using panel's controls index.

In desing mode, select your control and set it's tabindex to 0

Option 1:
Put this in the form's load event:
this.ActiveControl = myTextBox;
Option 2:
Put this in the form's load event:
this.Show();
myTextBox.Focus();
Focus() will not work until the TextBox is visible.

Instead of Activated try Shown

Yoc can use the solution provided by Ahmet. Since you want the text box to have the focus...setting the tab index to zero will do that.
Also you can use the textbox'e focus method to set the focus, in the form's load event....