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Lesson -8:Common Controls

8.2- The Up-Down Control

An up-down control, which is little more than a couple of arrows that the user clicks to increase or decrease the control’s setting. Typically, an edit control next to the up-down control, called a buddy edit control or just a buddy control, displays the value to the user.

In the Common application, you can change the setting of the up-down control by clicking either of its arrows. When you do, the value in the attached edit box changes, indicating the up-down control’s current setting. After the control has the focus, you can also change its value by pressing your keyboard’s Up and Down arrow keys.

Creating the Up-Down Control

Add another call to CCommonView::OnCreate(), this time calling it CreateUpDownCtrl(). Add the member function and the code in Listing 8.3. Also add resource symbols for IDC_BUDDYEDIT and IDC_UPDOWN.

Listing 8.3 CommonView.cpp—CCommonView::CreateUpDownCtrl()

void CCommonView::CreateUpDownCtrl()

{

m_buddyEdit.Create(WS_CHILD | WS_VISIBLE | WS_BORDER,

CRect(50, 120, 110, 160), this, IDC_BUDDYEDIT);

m_upDown.Create(WS_CHILD | WS_VISIBLE | WS_BORDER |

UDS_ALIGNRIGHT | UDS_SETBUDDYINT | UDS_ARROWKEYS,

CRect(0, 0, 0, 0), this, IDC_UPDOWN);

m_upDown.SetBuddy(&m_buddyEdit);

m_upDown.SetRange(1, 100);

m_upDown.SetPos(50);

}

The program creates the up-down control by first creating the associated buddy control to which the up-down control communicates its current value. In most cases, including this one, the buddy control is an edit box, created by calling the CEdit class’s Create() member function. This function’s four arguments are the control’s style flags, the control’s size, a pointer to the control’s parent window, and the control’s ID. If you recall the control declarations, m_buddyEdit is an object of the CEdit class.

Now that the program has created the buddy control, it can create the up-down control in much the same way, by calling the object’s Create() member function. As you can probably guess by now, this function’s four arguments are the control’s style flags, the control’s size, a pointer to the control’s parent window, and the control’s ID. As with most controls, the style constants include the same constants that you use for creating any type of window. The CSpinButtonCtrl class, of which m_upDown is an object, however, defines special styles to be used with up-down controls. Table 8.1 lists these special styles.

Table 8.1 Up-Down Control Styles

Styles Description

UDS_ALIGNLEFT
Places the up-down control on the left edge of the buddy control

UDS_ALIGNRIGHT
Places the up-down control on the right edge of the buddy control

UDS_ARROWKEYS
Enables the user to change the control’s values by using the keyboard’s Up and Down arrow keys

UDS_AUTOBUDDY
Makes the previous window the buddy control

UDS_HORZ Creates a horizontal up-down control

UDS_NOTHOUSANDS
Eliminates separators between each set of three digits

UDS_SETBUDDYINT
Displays the control’s value in the buddy control

UDS_WRAP Causes the control’s value to wrap around to its minimum when the maximum is reached, and vice versa

This Unit’s sample application establishes the up-down control with calls to SetBuddy(), SetRange(), and SetPos(). Thanks to the UDS_SETBUDDYINT flag passed to Create() and the call to the control’s SetBuddy() member function, Common doesn’t need to do anything else for the control’s value to appear on the screen. The control automatically handles its buddy. Try building and testing now.

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