Using MFC in C++ Part 4: Controls, DDX and DDV - The list box control

(Page 6 of 9 )

The list box control is used to display a number of options in a selectable, scrollable list format. You can allow the user to select one/more options inside of the list. The syntax for a list box control is shown below:

LISTBOX [Control Id], [X Pos], [Y Pos], [Width], [Height], [Style Options]

A sample declaration for a list box control is shown below:

LISTBOX IDLB_NAMES, 10, 105, 100, 100, WS_VISIBLE | WS_CHILD | WS_TABSTOP | LBS_NOTIFY

We have already talked about the first five options for this control: They are the same as those for the EDITTEXT control. Notice though, that we have added the LBS_NOTIFY macro to the list boxes’ style. This tells windows to send us notification messages whenever the list is changed, clicked on, etc.

Simply creating a list box control isn’t enough, because it starts out empty. We can use the AddString method to add options to the list, like this:

CListBox* pList = (CListBox*)GetDlgItem(IDLB_NAMES);



pList->AddString("John");

pList->AddString("Fred");

pList->AddString("Mark");

In our example above, we retrieve a pointer-to-CListBox reference to the list box. The CListBox class is used to communicate with a LISTBOX control. Next, we simply use the AddString method of the CListBox class to add three new options to our list. In this case, we are adding three names, as shown below:



As mentioned earlier, the support material included with this article contains a complete application demonstrating each of the controls we are discussing. In the included application, when you click on the “Add Names” button, three names are added to our list box control.

To retrieve the value of the selected option, we use the GetText function. The GetText function takes two parameters: The index of the list item to retrieve the value from (list box indexes start from zero), and a reference to a CString variable, which windows will store the value of the option in. To retrieve a name from our example list (as pictured above), we would use the following code:

CListBox* pList = (CListBox*)GetDlgItem(IDLB_NAMES);

CString name;



if(pList->GetCurSel() >=0)

{

pList->GetText(pList->GetCurSel(), name);

MessageBox(name);

}

else

MessageBox("Please select a name first!");

We use the GetCurSel function to return the index of the currently selected item. If the index is equal to –1, then no option is selected, and we kindly inform the user to select an option. On the other hand, if the user has selected an option, we use the GetText function and save its value to the CString name variable.

As with most of the controls discussed so far, there are several other functions that you can use to manipulate list boxes, and you should explore these further on your own.

Next: The group box control >>
 

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