DanielGreen wrote:
I don't totally understand "swallowing" but I'm sure I can figure it out, I've messed with it before but haven't really looked into it.
Hi Daniel,
"swallowing" an event means that the event will not be passed to the control, and the control will behave like the event didn't happen. To swallow an event, the callback function should return 1 instead of 0. Here is a list of all events that can be swallowed (you can find this list in the CVI help, look for "Swallowing Events"):
EVENT_COMBO_BOX_INSERT
EVENT_COLLAPSE
EVENT_COMMIT
EVENT_DRAG
EVENT_DROP
EVENT_END_TASK
EVENT_EXPAND
EVENT_HSCROLL (Swallowable for tabs only.)
EVENT_KEYPRESS
EVENT_LEFT_CLICK
EVENT_LEFT_DOUBLE_CLICK
EVENT_MARK_STATE_CHANGE
EVENT_MOUSE_WHEEL_SCROLL
EVENT_RIGHT_CLICK
EVENT_RIGHT_DOUBLE_CLICK
EVENT_SELECTION_CHANGE (Swallowable for trees only.)
EVENT_SORT
Short example: suppose you created a string control on a panel, and you want the user only to enter alphanumeric characters in this control. All you need to do is catch the keypress event and swallow it if the key that is pressed is not alphanumeric. If this event is swallowed, the keypress will not be passed to the string control, and the string will remain unchanged.
int CVICALLBACK StringCallback (int panel, int control, int event, void *callbackData, int eventData1, int eventData2) {
int key; // The ASCII part of the pressed key.
switch (event){
case EVENT_KEYPRESS:
// Get the pressed key character.
key = GetKeyPressEventCharacter (eventData2);
// If a character is pressed, and it's not alpanumeric, swallow the event.
if (key && !isalnum (key))
return 1;
break;
}
}
Message Edited by Wim S on
04-02-2008 01:44 PM
