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Textbox leave event unless tab changes

Using c# winforms vs2008
I'm using a TabControl on a form. Each tab has a different set of input fields. Some of those fields has to be completed. Such as Username. Multiple users will use the same PC, so a the username must remain static. I have a leave event on the require fields which triggers when the textbox loses focus to check if a value was added. In the case of Username, a popup would then presents possible values. That works pretty awesome to ensure accuracy and speed. To problem comes in when the user clicks on another tab, the textbox leave event triggers. How can I prevent the leave_event code from running if the focus changes to a control not on the current Tab?
I have tried different event handlers, but the leave event seem to occur first. I tried textbox validating event handler, but also no success. I tried adding a If-statement in front of the code to check the tab number, or tabcontrol state - no joy - as before anything else changes, the leave event fires.
The only remaining thing I can think of is to loop through all the controls on the tab to check if they have focus, but that just feels messy.
Any other suggestions?

I have found a partial solution. Using a Mouse_Enter and _Leave event on the tab, I set a flag to determine whether the mouse was clicked in the form or outside. If the flag is set to false, the leave event dont run. This will not solve short cut key presses though. But that I can handle later.

WinForms Button Click event and similar events depend on focus

I have the next situation:
there is a client app with a Form
the Form contains a few TabControl's
there are different controls on TabPage's of TabControl's
when the user clicks on any control, I need to activate the TabPage that is a parent of a control. For that I use a TabPage Enter event
when the TabPage gets activated, I need to make request to the server app, and I put focus to a hidden TextBox to disable UI
The problem is, when I click on a Button on another TabPage, in TabPage.Enter event handler I take focus to my hidden TextBox, and it seems like Button click event doesn't have enough time to be processed. When I put timer and handle TabPage.Enter event after 100 ms, the Button click event seems to be fired well. Same thing happens to all the controls: CheckBox doesn't get checked, RadioButton too. I wouldn't like to use timer, as that is not a stable solution.
Any ideas how could I make TabPage to process all mouse events before I take focus to hidden TextBox? I tried to use Application.DoEvents(), but that didn't help.

You are using a wrong event for a wrong control for what you are trying to do.
Enter event for TabPage is going to be fired when that page becomes an active control of the current form which might not happen under certain conditions. Instead, you need to use Selecting or Selected event of TabControl, depending on whether you want to cancel switching to a different tab or not (see TabControlCancelEventArgs parameter of Selecting event). In your case, Selecting event would be more appropriate since it won't allow switching to a selected tab until event is complete (unless you're doing an asynchronous request to the server). Additionally, you may no longer need to use the hidden TextBox.
UPDATE
Regarding comments to OP, when you have 2 (or more) TabControls on a form and you want to get notified when you press a button in any tab of a different TabControl, you can use Enter event for TabControl. Use a global variable to store which TabControl was activated in the Enter event and then send server request for a currently active tab of that activate TabControl.
If this doesn't work for your scenario, then you need to carefully examine your workflow and see if it can be improved in relation to what you want to accomplish.

C#: click (where applicable) versus validating event

I am recently working on windows forms with visual C# and I have a bunch of radio buttons grouped together.
I needed to call some methods if the radio button is clicked and also do some validation.
So I have two methods,
public void doSomeStuff()
public bool valRadioButton1()
I can call doSomeStuff() in the click event and the latter in the validating event of the radiobutton but I could also just call both in either the click event or the validating event.
My question is that are there any advantages and disadvantages as to what event I would use to call these? Or is there any particular way is more efficient. Right now it seems that both events would do the exact same thing so why use one or another or both.

Radio buttons are kind of strange in combination with the conventional validation. The validating event seems to be designed to allow you to validate a value once when the user is done entering a value instead of every time the value changes as the user is entering it. This makes sense for a textbox where you want to look at the completed text instead of after each character that the user types. But it's a little more obscure for radio buttons. In fact I think you should generally avoid the validating event of radio buttons and instead use the validating event of the container (radio buttons should always be in an embedded container). This allows a keyboard user to select/move through different options to arrive at the one they want without repeated validations as they move through the options. Then when they move focus out of the group box (or whatever container you used), you can validate the whole option group at once. This behavior is more consistent, then, with that of other controls' validation. In fact I see very little purpose to using the validating event on individual radio buttons. The only reason I see is if you want to cancel the user's new selection without causing extra click events. But be aware that when no radio button is selected and the user first clicks on one, no validating event will occur! No radio button lost focus and validating events only occur when a control loses focus. So this is why I think you should just avoid the validating event on radio buttons and just use the validating event of the container or the click event of a radio button.
Also, I think if you want to be nice to keyboard users, you should keep the validation logic separate from the click logic and use the events appropriately. Things like enabling controls based on which option is selected would belong in the click event of a radio button, but error and warning messages about the currently selected option should go in the validating event of the container.
Edit: You asked specifically about when one event occurs and not the other. I would add this information in response to that:
Validate will be called without calling click if the code is what causes the selected radio button to change, assuming focus then passes to the radio button (or container, if you are using the container's validate event).
Click will be called without (or should I say before) calling validate if no radio button was selected and the user then clicks on one (validate only occurs when the control loses focus). Validate will eventually occur for the clicked option, though.
Click will be called without (or should I say before) calling validate if your validate handler is not linked to the specific option that was previously selected or its container. It will be called for the option that is now selected (and the container) when this option (or the container) loses focus, though.
Click could be called without validate being called if your code that looks at the value doesn't require the selected option to lose focus before looking at it.

The validation event exist for when a controls value has changes, this is decoupled from how the controls value was changed. Was it changed because a datasource was refreshed, was it changed by an end user, was it changed on a timer? Doesn't matter!
I would use the validating event to evaluate if something is valid. Even if you know that there is "no way ever that it could happen any other way".

in WinForms can control focus change "automatically"? if yes, can I somehow distinguish this from user triggered focus change?

I am not fully sure about this, but I seem to be observing cases where focus shifts automatically from one control to another, even after I explicitly programmatically set the focus to control that I want to have focused. Maybe it has to do with the control in question being a panel, and it seems that WinForms is happier to have a textbox focused than a panel.
Well, first of all, can somebody provide expert insight on this matter? And also, if it is indeed possible for the focus to change without explicit order from me (whether user action or programmatic) is it possible to programmatically distinguish the resulting Leave and Enter events? That is, I would like to programmatically counteract Leave/Enter events not caused by myself, but I still want to allow the user to change focus normally as part of work with the GUI.

Yes, that can happen. It is probably a ContainerControl that's messing up your focus, Form is derived from it. A ContainerControl goes hunting for a control to focus when it gets an activation event. It likes nested child controls, it will definitely skip your Panel if it has any controls.
The logic involved in WF to handle focus is very complicated, most of all due to validation. You'd be best off by staying out of trouble and avoid ever giving a Panel the focus. It isn't designed to be a focusable control, it has no way to indicate focus to the user. This is enforced by it having the ControlStyles.Selectable style turned off and the TabStop property set to false so the user can never focus it by tabbing or clicking.
The Enter event won't help, the Panel gets Enter both when it gets the focus or when one of its child controls get the focus. Either by the user tabbing or when you use the Focus() method. You'd have to wait until all focus events are done firing, something you can do with Control.BeginInvoke() or a Timer.
Well, I'm sure that doesn't help much but your problem description is fuzzy. Best way to proceed is to post a sample project that exhibits this behavior to a file sharing service or, as indicated, avoid ever trying to give a parent control the focus.

One thing to keep in mind is many winforms controls cannot be focused at all - winforms provides a CanFocus property to indicate this. Panels have CanFocus set to false, so there is no way to focus directly on a panel without using a derived class that sets that property to true.

Can't seem to get Timepicker to work (C# / WPF)

I'm sure I'm missing something very easy here. Pretty much any internet search for a Timepicker for C#/WPF points to this webpage: http://jobijoy.blogspot.com/2007/10/time-picker-user-control.html and as such I figured it would work correctly. However, when I copy/paste this into a user control and run it, the control shows up as it should, but when I click on the digits and press Up or Down, nothing happens. Even in debug mode with a break point on the switch case for the KeyDown event, nothing happens. It's not registering the KeyDown event. It's supposed to focus on the grid that contains the TextBlock, so I tried changing the KeyDown to the TextBlock, but to no avail. I cannot seem to get this to work! :( I'm using Visual Studio 2008.

There is an official Microsoft DateTimePicker control included in the WPF Toolkit. This will be part of the framework in .NET 4.0

I think you're the control is not getting focused, for some reason. I tried it, too, and the event wouldn't fire for me, either. This post might offer some insight. Manually setting focus to the user control in the Loaded event didn't work for me, though.
The only thing that did work for me was doing all of the following:
changing the TextBlock to a TextBox and moving the event there (focus is pretty evident with a TextBox)
changing the cast in the event to FrameworkElement (which is where the Name property comes from) instead of Grid
changing the case to the TextBox's name (instead of the grid's name)
changing the event to a PreviewKeyDown (to get the cursor keys to register)
Of course, this only got the event to fire and register properly, the values don't seem to show up (even before I changed the code), but it handles the specific issue of the event not firing.

There's a DatePicker and a TimePicker in silverlight 4
If you want you can create your own control with those or simply use each one separated.