[Windows Mobile Software Development] stephj:
Next...........

Let’s work our way down the TODO: list above.

1.) Add reference to “string.h”:

Later on we are going to use a call to towupper() to convert the input into uppercase. It is defined in string.h, so we have to add this to the source file.

At the top of the ISO6346.CPP after the line

#include "ISO6346.h"

Add the line:

#include "string.h"

2.) Create two text boxes and display them......

We will create two windows as text boxes, but we will save their handles as global variables as they are referenced from more than one function. While we are at it we also need a global Boolean variable to prevent the uppercased replacement from causing the runaway reaction mentioned above.

After:

HINSTANCE	g_hInst;	// current instance
HWND	g_hWndMenuBar;	// menu bar handle

Add:

HWND	g_hWndText,g_hWndCheck;
bool	g_Updating;

Now let’s create the text edit boxes. You may already know this, or this may be an eye opener, but all edit controls are actually windows in their own right, albeit that they are child windows of the main form.

In InitInstance() after:

if (!hWnd)
{
return FALSE;
}

add:

g_hWndText= CreateWindow(TEXT("EDIT"),NULL,WS_CHILD | WS_BORDER,40,50,110,20,hWnd,NULL,hInstance,NULL);
g_hWndCheck=CreateWindow(TEXT("EDIT"),NULL,WS_CHILD | WS_BORDER, 160,50,20,20,hWnd,NULL,hInstance,NULL);

This creates the text edit boxes. As yet they won’t be displayed, but we have to tweak them first. We want to disable the checkdigit box, so that the user cannot type anything into it as we will set it with the correct value when a valid container number is entered in the text box. We will disable it by calling the EnableWindow() function.

We also need to set the size of the text edit window to 10 characters. Under MFC and .NET this is a hoot, as it already a property of the edit control object, which has been conveniently wrappered for us, and we can just set that property. Here in the world of Win32, it is not quite so simple. We have to fire an EM_SETLIMITTEXT message at the window, to tell it that that is what we want. While we are at it, let's set the global g_Updating variable to be false, ready for use later, and here is as good a place as any to do it.

After the CreateWindow() lines we have just added, add the next three lines to do the above.

SendMessage(g_hWndText,EM_SETLIMITTEXT,10,0);
EnableWindow(g_hWndCheck,false);
g_Updating=false;

Now the windows exist as we want them, all we have to do is display them. At the bottom of the InitInstance() function after

ShowWindow(hWnd, nCmdShow);

add

ShowWindow(g_hWndText, nCmdShow);
ShowWindow(g_hWndCheck, nCmdShow);

The main window will now look after them and control them as required. Marvellous!

3) Draw an "Enter container number:" text label............

Now we need a label above the two boxes to tell the user to type a valid container number number into the text box. From the resource view of the project, open the String Table folder in ISO6346ppc.rc then open the String Table object. Click in the blank entry at the bottom and change the ID to IDS_ENTER and the Caption to "Enter container number:" Don't worry about the what the value is, if it is not '3', as the IDE will take care of it.

To get it drawn on the form, we will have to add it to the WM_PAINT event of the main window. We'll need a RECT structure to describe where we want the text to go, a buffer to store the string and while we are here let's add the function variables we are going to need later. At the top of the WndProc() function:

After:

int wmId, wmEvent;
PAINTSTRUCT ps;
HDC hdc;

add

TCHAR c,szBuffer[MAX_LOADSTRING];
RECT rt;
int i,j,k;
bool valid;

i,j and k are general variables for calculating the check digit. szBuffer is used to hold the "Enter container number:" string in WM_PAINT, and also for the contents of the edit box when it changes. As these two events will not occur at the same time, we can get away with it having a dual personality. Variable 'c' is used to read the string one character at a time and 'valid' is set to false if the the container number is not in the correct format.

Replace the TODO: line in the WM_PAINT handler

// TODO: Add any drawing code here...

with:

rt.top=20;
rt.bottom=40;
rt.left=40;
rt.right=180;
LoadString(g_hInst,IDS_ENTER,szBuffer,MAX_LOADSTRING);
DrawText(hdc,szBuffer,wcslen(szBuffer),&rt,0);

Now when the form is drawn, the label will appear in the right place.

4.) Intercept the EN_CHANGE message from the main edit box..........

There is no easy way to do the next bit step-by-step, so we will just do it, I'll explain later.........

Replace the standard code for the response to the WM_COMMAND message:

case WM_COMMAND:
wmId = LOWORD(wParam);
wmEvent = HIWORD(wParam);
// Parse the menu selections:
switch (wmId)
{
case IDM_HELP_ABOUT:
DialogBox(g_hInst, (LPCTSTR)IDD_ABOUTBOX, hWnd, About);
break;
case IDM_OK:
SendMessage (hWnd, WM_CLOSE, 0, 0);
break;
default:
return DefWindowProc(hWnd, message, wParam, lParam);
}
break;

with this:

case WM_COMMAND:
wmId = LOWORD(wParam);
wmEvent = HIWORD(wParam);
// Parse the menu selections:
switch (wmId)
{
case IDM_HELP_ABOUT:
DialogBox(g_hInst, (LPCTSTR)IDD_ABOUTBOX, hWnd, (DLGPROC)About);
break;
case IDOK:
SendMessage (hWnd, WM_CLOSE, 0, 0);
break;
}

switch (wmEvent)
{
case EN_CHANGE:
if(g_hWndText == (HWND) lParam && !g_Updating)
{
GetWindowText(g_hWndText, szBuffer,MAX_LOADSTRING);
if(wcslen(szBuffer)==10)
{
k=0;
valid=true;
for(i=0; i<10; i++)
{
c=szBuffer[i]=towupper(szBuffer[i]);
if((i<4 && (c<'A' || c>'Z')) || (i>3 && (c<'0' || c>'9')))
valid = false;
j=int(c);
if (j > 64 && j < 91)
k += ((j - 55) + (j - 56) / 10) << i;
else
k += (j - 48) << i;
}

if(valid)
{
// Calculate final check digit
k = ((k % 11) % 10);
// Do not process the following update
g_Updating = true;
SetWindowText(g_hWndText,szBuffer);
g_Updating = false;
// Set check window to correct value
szBuffer[0]='0'+k;
szBuffer[1]='\0';
SetWindowText(g_hWndCheck,szBuffer);
// Position cursor at end of edit field.
SendMessage(g_hWndText,EM_SETSEL,10,10);
}
else
SetWindowText(g_hWndCheck,TEXT(""));
}
else
SetWindowText(g_hWndCheck,TEXT(""));
}
break;
default:
return DefWindowProc(hWnd, message, wParam, lParam);
}
break;

When the text edit box contents are changed, a EN_CHANGE message arrives at the parent window. It appears as a WM_COMMAND message with the wmEvent parameter containing the EN_CHANGE identifier, together with the handle of the window that generated the message. That is why the second 'switch' code exists to trap the EN_CHANGE event message.

If the EN_CHANGE message came from the Text edit window, not the Checksum window, then get the text within it. If the length is 10 characters long, then process the string. The variable k is used as a running total for the checksum. If after processing all 10 characters, the string is still valid, it is converted modulo 11 and then modulo 10 into the final checksum number. The checksum edit box is then updated with this value. The contents of the Edit box are replaced with its uppercase value. In doing so, we will cause another EN_CHANGE message to be sent to the parent window, which would cause this function to be executed again, and so on and so forth, causing an infinite shower of messages. To prevent this, we set the global variable g_Updating to true before making the change, and then setting it to false immediately afterwards. The test in the first line of the EN_CHANGE processing code, does not execute at all if g_Updating is true, thereby preventing this problem.

Build the final program, and test it in the emulator. Switch the build to 'Release' and the target to Windows Mobile Device, and run the executable on your device.

The complete ISO6346.cpp file is included in the attached zip file.

Here endeth the lesson...........

As a continuation, we will build the whole thing again from scratch, but next time using the Microsoft Foundation Class, MFC.

Watch this space..................