5.3 KiB
ALT Sequence and Control Focus
If a focusable control is put on a window, by setting the Alt property to a value, for example "X", then it could get focused by pressing ALT followed by X (not ALT+X).
The Alt property could accept a sequence of characters, not just one. Characters in such a sequence needs to be entered to activate this control.
If ESC is pressed, it goes back to the previous container.
If BACKSPACE is pressed, it cancels the last character in the sequence.
When ALT is pressed, all valid ALT sequences will be printed on the window. All labels rendering these sequences will get changed
Example
The operation is done by pressing the following keys: - ALT: Enter the ALT sequence mode. - P: There are two controls with the Alt property set to "P". It filters them out and wait for a number key. - 0: The dropdown button is activated, a sub menu is opened. - ESC: Close the sub menu and go back to the previous container, which is the window. - P: Filter again. - BACKSPACE: Cancel the last character "P" in the sequence, showing all available items. - P: Filter again. - 1: The paste button is activated, a piece of text get pasted to the editor. The ALT sequence mode is exited because an item is finally chosen. - ALT: Enter the ALT sequence mode. - D: Give the focus to the editor control. - CTRL+A: Select all text. - DELETE: Delete the selection.
Behavior after being Focused
There are three kinds of behaviors when a control is focused by a ALT sequence. If a control is focused by TAB, it could behaves differently. - empty list item Just being focused Controls with complex keyboard behaviors like editors or list controls, will just get focused and do nothing else. - empty list item Execute a Command Controls with simple executable behaviors like buttons, will do what it does when clicked, after being focused by an ALT sequence. - empty list item Just being focused Controls that are not executable but contains executable items, like menu items with a sub menu, will render all executable items after being focused by an ALT sequence. A menu item with a sub menu does nothing when it is clicked. But if it is activated by an ALT sequence, the sub menu will be opened and wait for more keys.
Create your own Behavior
If a new control class is created, there are multiple ways to customize the behavior about how a control should react to an ALT sequence:
Using IGuiAltAction
IGuiAltAction is a protected base class of all controls. If a new control is created, methods could be overriden.
Properly assigning an ALT sequence to the Alt property of a control could also make these methods behave as expected easily. IsAltEnabled returns true if the control is visible and enabled. IsAltAvailable returns true if the control is focusable and the Alt property is not empty.
When the window is in the ALT sequence mode, a label rendering the sequence for this control will be put in the composition from GetAltComposition.
If both IsAltEnabled and IsAltAvailable returns true, then the result of GetAlt(), which is also the value from the Alt property by default, becomes one of an candidate. OnActiveAlt will be called when this control is selected by a ALT sequence.
Using IGuiAltActionContainer
IGuiAltActionContainer is a service object . A service object could be attached to a control by calling AddService or overriding QueryService.
If an IGuiAltActionContainer instance is attached to a control, then all methods in IGuiAltAction are ignored. Instead, multiple IGuiAltAction object returned from this interface will be used.
You could now assign multiple ALT sequence to a control, with each sequence binded to a different behavior.
All IGuiAltAction returned from IGuiAltActionContainer must be enabled and available.
Using IGuiAltActionHost
An IGuiAltActionHost instance could be attached to a control by calling SetActivatingAltHost or overriding GetActivatingAltHost.
When a control is selected by a ALT sequence, if IGuiAltActionHost is attached to this control, then the ALT sequence mode will not exit. Instead, this IGuiAltActionHost is treated as a nested container, and GacUI calls CollectAltActions to collect all valid IGuiAltAction, renders all ALT and wait for keyboard input.
All top level controls like a window or a menu are attached by an IGuiAltActionHost by default. If a sub menu is created on a menu item, IGuiAltActionHost is attached to this control. So when it is activated, it opens the sub menu and continue to wait for more keys, instead of executing this menu item.
GuiAltActionHostBase is the default implementation of IGuiAltActionHost. If it is attached to a control, all child controls with valid IGuiAltAction are not visible from the container, instead they are available when the parent control is selected by an ALT sequence. GuiAltActionHostBase::SetAltControl must be called to initialize this class, it tells this implementation where to search for child controls to collect IGuiAltAction.