Page 65 - DCAP408_WEB_PROGRAMMING

Unit 4: Windows Controls

Notes

Notes As you can observe, this is a quite simple task. If the listbox has the LBS_SORT style,
the new item will be added in alphabetical order, or else it will just be added to the end of
the list.
This message returns the index of the new item either manner and we can utilize this to perform
other tasks on the item, like relating some data with it. Generally this will be things like a
pointer to a struct including more information, or maybe an ID that you will use to identify the
item, it’s up to you.
SendDlgItemMessage(hwnd, IDC_LIST, LB_SETITEMDATA, (WPARAM)index,
(LPARAM)nTimes);

4.6.2 Getting Data from the ListBox

Now that we recognize the selection has changed, or at the request of the user, we require to
obtain the selection from the listbox and do something functional with it.

Example: In this example I’ve used a multi-selection list box, so obtaining the list of
chosen items is a little trickier. If it were a single selection listbox, than you could just send
LB_GETCURSEL to retrieve the item index.

First we require to obtain the number of selected items, so that we can assign a buffer to save the
indexes in.
HWND hList = GetDlgItem(hwnd, IDC_LIST);
int count = SendMessage(hList, LB_GETSELCOUNT, 0, 0);
Then we allocate a buffer based on the number of items, and send LB_GETSELITEMS to fill in the
array.
int *buf = GlobalAlloc(GPTR, sizeof(int) * count);
SendMessage(hList, LB_GETSELITEMS, (WPARAM)count, (LPARAM)buf);

// ... Do stuff with indexes

GlobalFree(buf);
In this example, buf[0] is the first index, and so on up to buf[count - 1].
One of the things you would likely want to do with this list of indexes, is recover the data
connected with each item, and perform some processing with it. This is just as uncomplicated as
setting the data was originally, we just send another message.
int data = SendMessage(hList, LB_GETITEMDATA, (WPARAM)index, 0);
If the data was some other type of value (anything that is 32-bits) you could just cast to the
suitable type.

Example: For example if you accumulated HBITMAPs instead of ints...
HBITMAP hData = (HBITMAP)SendMessage(hList, LB_GETITEMDATA, (WPARAM)index, 0);

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