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Current Focus

All PegThing based classes support the idea of gaining and losing focus. If a PegThing

has current focus, it means all key input is sent to that object. The user typically changes

the input focus by pressing the pen on an object. When an object gets the input focus it

gets a PM_CURRENT message and its PSF_CURRENT status is set. All its parents up

the tree also become current. You can detect if an object is a member of the input focus

branch of the presentation tree at any time by testing the PSF_CURRENT system status

flag:

if (StatusIs(PSF_CURRENT))

{

// this object is in the branch of the

// display tree that has input focus.

}

Just because an object is a member of the input focus tree does not mean the object is the

end leaf of the input focus branch. You can obtain a pointer to the final input object by

calling the PegPresentationManager::GetCurrentThing() function. This function will

return a pointer to the actual default input object, or NULL if no object has been selected

to receive input events.

Setting Focus

You can override the user’s input selection and manually command

PegPresentationManager to move the input focus at any time by calling:

void MoveFocusTree(PegThing *pThing);

When focus is moved from one PegThing to another, PM_NONCURRENT messages are

sent to objects that are no longer members of the input focus branch, and PM_CURRENT

messages are sent to objects that are members of the new input focus branch. The effect

is that non-directed input messages will be sent to the newly designated input object.

When children are added to the presentation list, the newest child is always placed at the

beginning of an object’s children list. By default, the first child in a parent’s list is the

child that has focus. This means that last child added to a PegThing will always have

default focus (Add() always adds a child to the front of the sibling list). Since this may

not be the desired result, there are three functions that explicitly assign or test which child

has default focus:

virtual BOOL HasDefaultFocus(void);

virtual PegThing* GetDefaultFocus(void);

virtual void SetDefaultFocus(PegThing* pThing);

HasDefaultFocus() tests if an object has default focus. GetDefaultFocus() returns the

PegThing that has default focus. SetDefaultFocus() assigns a PegThing default focus.

Casio ClassPad 300 Programming Guide

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