Creating an Access Bar

You first need to decide what you want your access bar to do and what it should look like. I decided that mine should look a bit like the taskbar and that it should contain buttons that let the user change the bar's position (right, left, top, or bottom). To create the access bar itself, I used CreateWindowEx and the extended style WS_EX_TOOLWINDOW:

// Create the access bar.

g_hWndAppBar = CreateWindowEx (WS_EX_TOOLWINDOW,

"AppBarClass", "AppBar",

WS_POPUP | WS_THICKFRAME | WS_CLIPCHILDREN,

0, 0, DEF_APPBAR_WIDTH, DEF_APPBAR_HEIGHT,

NULL, NULL, hInstance, NULL);



// Now create the button children.

g_hwndBtn1 = CreateWindow (

"BUTTON", // create a button

"&Right", // window title

BS_PUSHBUTTON | BS_CENTER | WS_VISIBLE | WS_CHILD,

0, 0, 0, 0,

g_hWndAppBar, // parent window

(HMENU)IDM_RIGHT, // ID

hInstance, // instance

NULL); 



g_hwndBtn2 = CreateWindow (

"BUTTON", // create a button

"&Left", // window title

BS_PUSHBUTTON | BS_CENTER | WS_VISIBLE | WS_CHILD,

0, 0, 0, 0,

g_hWndAppBar, // parent window

(HMENU)IDM_LEFT, // ID

hInstance, // instance

NULL);



g_hwndBtn3 = CreateWindow (

"BUTTON", // create a button

"&Top", // window title

BS_PUSHBUTTON | BS_CENTER | WS_VISIBLE | WS_CHILD, 

0, 0, 0, 0,

g_hWndAppBar, // parent window

(HMENU)IDM_TOP, // ID

hInstance, // instance

NULL); 



g_hwndBtn4 = CreateWindow (

"BUTTON", // create a button

"&Bottom", // window title

BS_PUSHBUTTON | BS_CENTER | WS_VISIBLE | WS_CHILD,

0, 0, 0, 0,

g_hWndAppBar, // parent window

(HMENU)IDM_BOTTOM, // ID

hInstance, // instance

NULL);

Of course, it's not enough to just create the windows and wish upon a star for an access bar—you need to register it with the system. SHELLFUN does this when the user chooses to add the access bar. As I did for the taskbar notification, I filled out a structure, APPBARDATA, and used a special function, SHAppBarMessage, to register the access bar:

case IDM_ADD:

if (! g_fRegistered)

{

// Fill out the structure needed to register the new access bar.

g_appBar.hWnd = g_hWndAppBar;

g_appBar.cbSize = sizeof (APPBARDATA);



// Identifier for notifications

g_appBar.uCallbackMessage = APPBAR_CALLBACK;



// Register the access bar.

if (! SHAppBarMessage (ABM_NEW, &g_appBar)) 

break;



// Set the default size and position of the access bar.

AppBarPosChanged (ABE_TOP, &g_appBar);



ShowWindow (g_hWndAppBar, SW_SHOW);



// Set the registered flag to TRUE.

g_fRegistered = TRUE; 

}

break;

The access bar initially appears anchored to the top of the desktop, as shown in Figure 11-7. Clicking one of the buttons on the bar will change its position.

Figure 11-7.

The access bar in SHELLFUN.

To remove the access bar, you use the same SHAppBarMessage function, specifying the ABM_REMOVE message as the first parameter. In SHELLFUN, I don't actually destroy the window; I hide it in case the user chooses to add it again later. When the application closes, however, I do destroy the window in my cleanup code:

case IDM_REMOVE:

if (g_fRegistered)

{

// Unregister the access bar.

SHAppBarMessage (ABM_REMOVE, &g_appBar);

ShowWindow (g_hWndAppBar, SW_HIDE);

g_fRegistered = FALSE;

}

break;

Because an access bar is a window in its own right, it has its own window procedure, in which events such as activation, creation, and destruction (and lots of other words ending in -tion) happen. This is also where the callback message specified in the ABM_NEW message is sent. Here is the window procedure for SHELLFUN's access bar:

LRESULT CALLBACK AppBarWndProc (HWND hwnd, UINT msg,
WPARAM wparam, 

LPARAM lparam)

{

static HWND hwndBtn1, hwndBtn2, hwndBtn3, hwndBtn4;



switch (msg)

{

case WM_CREATE:

g_fRegistered = FALSE;

break;



case WM_DESTROY:

DestroyWindow (hwndBtn1);

DestroyWindow (hwndBtn2);

DestroyWindow (hwndBtn3);

DestroyWindow (hwndBtn4);

break;



case WM_WINDOWPOSCHANGED:

case WM_ACTIVATE:

{

APPBARDATA abd;

abd.cbSize = sizeof (APPBARDATA);

abd.hWnd = hwnd;

abd.lParam = (LONG)NULL;

SHAppBarMessage (ABM_ACTIVATE, &abd);

break;

}



case WM_COMMAND:

if (HIWORD (wparam) == BN_CLICKED)

AppBarClicked (LOWORD (wparam), (APPBARDATA *)&g_appBar);

break;



case APPBAR_CALLBACK:

AppBarCallback (hwnd, msg, wparam, lparam);

return 0;



default:

return DefWindowProc (hwnd, msg, wparam, lparam);

}

}