Progress Bar Control

A progress bar is a window that an application can use to indicate the progress of a lengthy operation. It consists of a rectangle that is gradually filled with the system highlight color as an operation progresses. The following illustration shows a progress bar positioned along the bottom of a window.

• Using Progress Bars
• Progress Bar Control Updates in Internet Explorer

Using Progress Bars

You create a progress bar by using the CreateWindowEx function, specifying the PROGRESS_CLASS window class. This window class is registered when the common control dynamic-link library (DLL) is loaded. To ensure that this DLL is loaded, use the InitCommonControls function first.

Range and Current Position

A progress bar's range represents the entire duration of the operation, and the current position represents the progress that the application has made toward completing the operation. The window procedure uses the range and the current position to determine the percentage of the progress bar to fill with the highlight color. Because the range and current position values are expressed as unsigned integers, the highest possible range or current position value is 65,535.

The minimum value in the range can be from 0 to 65,535. Likewise, the maximum value can be from 0 to 65,535. If you do not set the range values, the system sets the minimum value to 0 and the maximum value to 100. You can adjust the range to convenient integers by using the PBM_SETRANGE message.

A progress bar provides several messages that you can use to set the current position. The PBM_SETPOS message sets the position to a given value. The PBM_DELTAPOS message advances the position by adding a specified value to the current position.

The PBM_SETSTEP message allows you to specify a step increment for a progress bar. Subsequently, whenever you send the PBM_STEPIT message to the progress bar, the current position advances by the specified increment. By default, the step increment is set to 10.

Default Progress Bar Message Processing

This section describes the messages handled by the window procedure for the PROGRESS_CLASS class.

Progress Bar Example

The following example shows how to use a progress bar to indicate the progress of a lengthy file-parsing operation. The example creates a progress bar and positions it along the bottom of the parent window's client area. The height of the progress bar is based on the height of the arrow bitmap used in a scroll bar. The range is based on the size of the file divided by 2048, which is the size of each "chunk" of data read from the file. The example also sets an increment and advances the current position of the progress bar by the increment after parsing each chunk.

Example

// ParseALargeFile - parses a large file and uses a
// progress bar to indicate the progress of the
// parsing operation. 
// Returns TRUE if successful, or FALSE otherwise. 
// hwndParent - parent window of the progress bar. 
// lpszFileName - name of the file to parse. 
// 
// Global variable 
//     g_hinst - instance handle 

extern HINSTANCE g_hinst; 

BOOL ParseALargeFile(HWND hwndParent, LPSTR lpszFileName) 
{ 
    RECT rcClient;  // Client area of parent window 
    int cyVScroll;  // Height of scroll bar arrow 
    HWND hwndPB;    // Handle of progress bar 
    HANDLE hFile;   // Handle of file 
    DWORD cb;       // Size of file and count of
                    // bytes read 
    LPCH pch;       // Address of data read from
                    // file 
    LPCH pchTmp;    // Temporary pointer 

 

    // Ensure that the common control DLL is loaded
    // and create a progress bar along the bottom of
    // the client area of the parent window. 
    // Base the height of the progress bar on the
    // height of a scroll bar arrow. 
    InitCommonControls(); 
    GetClientRect(hwndParent, &rcClient); 
    cyVScroll = GetSystemMetrics(SM_CYVSCROLL); 
    hwndPB = CreateWindowEx(0, PROGRESS_CLASS,
	         (LPSTR) NULL, WS_CHILD | WS_VISIBLE,
             rcClient.left, rcClient.bottom
             cyVScroll, rcClient.right, cyVScroll, 
             hwndParent, (HMENU) 0, g_hinst, NULL); 

   // Open the file for reading, and retrieve the
   // size of the file. 

    hFile = CreateFile(lpszFileName, GENERIC_READ,
            FILE_SHARE_READ, (LPSECURITY_ATTRIBUTES)
            NULL, OPEN_EXISTING,
            FILE_ATTRIBUTE_NORMAL, (HANDLE) NULL); 

    if (hFile == (HANDLE) INVALID_HANDLE_VALUE) 
        return FALSE; 

    cb = GetFileSize(hFile, (LPDWORD) NULL); 

    // Set the range and increment of the progress
    // bar. 

    SendMessage(hwndPB, PBM_SETRANGE, 0,
                MAKELPARAM(0, cb / 2048)); 
    SendMessage(hwndPB, PBM_SETSTEP, (WPARAM) 1, 0); 

    // Parse the file. 
    pch = (LPCH) LocalAlloc(LPTR, sizeof(char) *
	       2048); 
    pchTmp = pch; 
    do { 
        ReadFile(hFile, pchTmp, sizeof(char) * 2048,
		         &cb, 
            (LPOVERLAPPED) NULL);
		// TODO: Write an error handler to check that all the
        // requested data was read. 
        . 
        . 
        // Include here any code that parses the
        // file. 
        . 
       // Advance the current position of the
       // progress bar by the increment. 
       SendMessage(hwndPB, PBM_STEPIT, 0, 0); 
      } while (cb); 

   CloseHandle((HANDLE) hFile); 
   DestroyWindow(hwndPB);
    
    return TRUE; 
} 
 

Progress Bar Control Updates in Internet Explorer

Progress bar controls in Microsoft Internet Explorer support the following new features.