The Focus method returns true if the control successfully received input focus. The control can have the input focus while not displaying any visual cues of having the focus. This behavior is primarily observed by the nonselectable controls listed below, or any controls derived from them.
A control can be selected and receive input focus if all the following are true: the Selectable value of ControlStyles is set to true, it is contained in another control, and all its parent controls are both visible and enabled.
The Windows Forms controls in the following list are not selectable. Controls derived from these controls are also not selectable.
LinkLabel (when there is no link present in the control)
Focus is a low-level method intended primarily for custom control authors. Instead, application programmers should use the Select method or the ActiveControl property for child controls, or the Activate method for forms.
Windows 8.1, Windows Server 2012 R2, Windows 8, Windows Server 2012, Windows 7, Windows Vista SP2, Windows Server 2008 (Server Core Role not supported), Windows Server 2008 R2 (Server Core Role supported with SP1 or later; Itanium not supported)