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how to use TextBox_Textchanged event with Regex for RequiredField Control

the textbox is associated with two RequiredFiled validators
also this textbox has TextChanged event.
I would like to allow first execute RequiredFiled validators then execute Textchanged event.
protected void TextBox1_TextChanged(object sender, EventArgs e)
{
if (!System.Text.RegularExpressions.Regex.IsMatch(TextBox1.Text,Regular_Expression))
{
Label2.Text = "from textChanged.";
}
}
if (!System.Text.RegularExpressions.Regex.IsMatch(TextBox1.Text,Regular_Expression))
here how to use regular expression with (requiedfiled, regularExpression controls)?
Can someone help me how to use RequiredFiled controls with text-box?
Actually, this script is for first validate required filed controls then execute textbox_Textchanged event. because the movement when the filled value in textbox, textbox change event is firing, so OOB(out of the box) control is not executing properly. to execute textbox required filed OOB control if the value is valid then textbox_TextChanged event should execute. just googled and find the
Regex.IsMatch(textbox,RegularExepression) but don't know how to use Regular
Expressions.

How to check whether text input is finished

I'm developing a simple WPF application where I want to use the text changed method for a specific text field. the thing is I implemented the method but, the method gets fired in very short period, like even after i enter one character. I want to check whether the text change is completed in order to go with the methods written in the text changed method.
private void searchBox_TextChanged(object sender, TextChangedEventArgs e)
{
if (...) // how to check whether the typing is finished?
{
// code goes here
}
}

I think you'll need the LostFocus event for this. As #SLaks comment says, you can't predict whether the user will press another key. Alternatively, you could databind the control - depending on what you're actually trying to do that may make more sense.

Instead of TextChanged, try monitoring the LostFocus event, which will fire when the user has left the textbox, either through pressing Enter/Tab or clicking somewhere else on the form.

Agree with LostFocus
UIElement.LostFocus Event
Question does not ask about binding but something to consider.
In binding the equivalent is UpdateSourceTrigger="LostFocus"
Binding.UpdateSourceTrigger Property
With binding you can get into more advanced validation UI effects.
How to: Implement Binding Validation

What validation events are raised for the TextBox control?

Is there any event that fire when the value of the textbox change from a peace of code and when the textbox is validated or lost the focus and the event don't fire on the key press,because I have a lot of calculation and It's not possible to do it on every key press

Use TextChanged for text changed.
Use LostFocus for when textbox looses focus.
Use Validating or Validated for validation.
Here is the order in which events are called for TextBox:
// Reference : http://msdn.microsoft.com/en-us/library/system.windows.forms.control.validated.aspx
1) Enter
2) GotFocus
3) Leave
4) Validating
5) Validated
6) LostFocus
This should help you decide where you want to put your code.

There's no event that will fulfill your requirement of being raised when the textbox's value is changed programmatically through code, but not when text is typed into it by the user. The TextChanged event is going to be raised either way (this is fairly intuitive—the text value is changing, and the computer doesn't know or care what is responsible for changing it). As the documentation for this event indicates:
User input or setting the Text property to a new value raises the TextChanged event.
If you need to run custom validation logic when you add text to your textbox in code, you will need to invoke whatever method contains the validation logic yourself. Extract it into a separate method, which you call from the Validating/Validated event handler and from all of the places in your code where you set the textbox's Text property.
As a supplement to the other answers that have already been posted, I strongly recommend using either the Validating (if you want to be able to cancel the validation) or Validated events to handle the textbox losing focus, rather than the somewhat more obviously named LostFocus event.

You can use the LostFocus or Validated events.

Use a member variable.
private bool _changeByCode;
public void DoSomeChanges()
{
_changeByCode = true;
textbox1.Text = "Hello";
_changeByCode = false;
}
public void Textbox1_Change(object source, EventArgs e)
{
if (_changeByCode)
return;
//do your validation here.
}

Equivalent of WinForms TextBox.Validating event in WPF

In WinForms I could handle the Validated event to do something after the user changed text in a TextBox. Unlike TextChanged, Validated didn't fire for every character change; it only fired when the user was done.
Is there anything in WPF I can use to get the same result, an event raised only after the user is done changing the text?

LostFocus will fire when the user moves from your textbox onto any other control.

It seems that there is no native solution.
The LostFocus event is a good idea. But when the user click on Enter, he wants the TextBox to validate the change.
So here is my suggestion : use the LostFocus event and the KeyDown event when the key is Enter.
private void TextBox_LostFocus(object sender, RoutedEventArgs e)
{
// code to lauch after validation
}
private void TextBox_KeyDown(object sender, KeyEventArgs e)
{
if (e.Key == Key.Enter)
{
// call the LostFocus event to validate the TextBox
((TextBox)sender).RaiseEvent(new RoutedEventArgs(TextBox.LostFocusEvent));
}
}

LostFocus is not equivalent to Validate. It creates lots of problem when you have multiple text boxes on one screen and every text box has some logic written in Validate. In validate event you can control focus easily but not in LostFocus so easily.

You can also try Binding.ValidationRules
Documented at : http://msdn.microsoft.com/en-us/library/system.windows.data.binding.validationrules.aspx
Here is the article to get started:
How to implement binding validations :
http://msdn.microsoft.com/en-us/library/ms753962.aspx

How to determine if a textbox in a windows form has focus

Let's say I have internet explorer embedded in a windows form and I then navigate to a random page on the web. How can I determine when a textbox (or any other control that can accept text input for that matter) becomes the item in focus? Basically, every time the mouse is clicked I can check to see if the item in focus is a textbox or some other control for text input and then act appropriately.
Thanks in advance,
Bob

You still haven't explained the roll of the WebBrowser but the problem seems to be tracking the Input Focus. I don't know of a Form level event but you can hook an eventhandler to the Enter or GotFocus event of all relevant Controls.
// in Form_Load
foreach (var control in this.Controls) control.Enter += OnEnterControl;
private void OnEnterControl(object sender, EventArgs e)
{
focusControl = (sender as Control);
}

I believe what you want to do is sink the HTMLTextContainerEvents2 dispinterface and respond to onFocus (and potentially onBlur).
You're right that you'll have to do the interop via pinvoke yourself. I assume you can get IHTMLElement pointers to all of the objects you want to track (by using getElementsByTagName or some such thing). Once you have that,
Query the IHTMLElemnt for IConnectionPointContainer.
Call IConnectionPointContainer::FindConnectionPoint(DIID_DHTMLTextContainerEvents2)
Call IConnectionPoint::Advise() on the IConnectionPoint obtained in step 2.
And of course you need to implement IDispatch::Invoke() which will be your callback.
Handle DISPID_HTMLELEMENTEVENTS2_ONFOCUS, etc.