Windows Forms

Re: Simple Invoice Capture: To databind or not to databind?

10-Nov-07 21:09

I have a small invoicing application in MS Access that I have started converting to SQL Server 2005 and WinForms. This is a very small application, and I should have full functionality in two or three days, with all bells and whistles by the end of next weekend.
I'm in two minds whether to sweat it out and implement databinding, or just do what I know best and code all my own data access, using DataTable objects as 'proxies' for detail grids etc. All I know about data binding is the problems I've had previously when changing column names etc. Visual Studio 2005 seems to remember things you want forgotten in very secret places. Unsure | :~

However, this is a great opportunity for me to overcome my lack of experience and learn to deal with the problems I have encountered before. What is the general opinion on this? At least I now have internet at home, so my friend Google will be looking over my shoulder when I attempt a data bound application.

BTW, I am also moving forward in learning NHibernate, but I feel the overhead of learning something at that level, outside of the intrinsic .NET tools, is a little too much for a project of this size.

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Rajasekharan Vengalil12-Nov-07 19:46

Rajasekharan Vengalil

12-Nov-07 19:46

Mostly, databinding is a good idea. As Charles Petzold[^] puts it in his WPF book[^], there are less moving parts in your program that way. Lesser code means lesser stuff that can go wrong! But yeah, VS is notorious for doing some pretty crazy things when using the designer to implement databinding. I mostly stay away from the designer for stuff like this, except when I am trying to quickly prototype something.

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Checking for a Key Sequence

Brady Kelly10-Nov-07 3:51

10-Nov-07 3:51

I'm trying to monitor keypresses for a sequence that indicates the characters following the sequence belong in my BarCode control, so when the sequence is detected, that Control receives focus. How do I maintain a fixed length buffer of key presses, compared to the following code. My buffer should only be as long as the sequence I'm looking for, but I don't know how to shift the incoming key presses through the buffer.

private readonly string SCAN_START_SEQ = new string(new char[] { (char)2 });
private StringBuilder keyBuffer = new StringBuilder();

private void ScannerInputForm_KeyPress(object sender, KeyPressEventArgs e)
{
    keyBuffer.Append(e.KeyChar);
    string buff = keyBuffer.ToString();
    if (buff.EndsWith(SCAN_START_SEQ))
    {
        keyBuffer.Remove(0, keyBuffer.Length);
        e.Handled = true;
        textBarCode.Focus();
    }
}

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Trollslayer10-Nov-07 5:28

Trollslayer

10-Nov-07 5:28

The lazy way is to have an edit box, set the maximum text length and use an event handler for when the limit is reached then readt the text.
This has the GUI advantage that the user can see the barcode is scanned, that's how I've done it in the past.

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Brady Kelly10-Nov-07 5:36

10-Nov-07 5:36

I need to detect the sequence before the barcode textbox is filled. My buffer starts empty, and lets say I defined my scanner to send '02x03x' before the main barcode. When I receive the first char, I add it to the buffer and check if the buffer ends with '02x03x'. It doesn't yet, so I keep it. When I receive the next char, the 03x, I do the same, but the compare passes this time. I then empty the buffer, and move focus to the barcode texbox. But now, until the next '02x03x', my buffer is going to get quite full if the user types a lot and scans little. I don't want the user seeing anything of this buffer.

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Trollslayer10-Nov-07 5:55

Trollslayer

10-Nov-07 5:55

This sounds like it's more about the architecture of the application than the scanner.
If you check for keys received by the application then you can detect the 02x03x sequence there and clear the buffer, move the focus etc.
This could be done using accelerators for example.

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Brady Kelly10-Nov-07 6:04

10-Nov-07 6:04

You're right, it is about the application, not the scanner. That's why I moved it here. Wink | ;)

I'm a little concerned about the potential size of the buffer before a 02x03x is detected, so when I get home I'm going to look into a either a circular buffer, or a background thread to clear the buffer during states where a scan should not occur.

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Trollslayer10-Nov-07 6:28

Trollslayer

10-Nov-07 6:28

Sorry, I don't see why you need a buffer at all.
Step 1: start sequence received as a pair of accelerators
Step 2: set focus to edit box
Step 3: use EN_MAXLEN event to detect when the bar code has been scanned (no terminator needed)
Step 4: read edit box and get the barcode

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Brady Kelly10-Nov-07 19:48

10-Nov-07 19:48

Elaine, I want to be able to define any sequence of characters as my signal for scanner input, where using accelerators would limit my options there. I also want to cater for EAN-8 as well as 13, so the TAB terminator is perfect, as it will raise the Leave event of my barcode edit box when any code, of any length, is read.

My next challenge is a nice to have, which is a global keyboard hook that ignores all key inputs between my scan signal and terminator. You get some really funny effects scanning when other Windows applications have focus. Windows pop in and out etc.

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Luc Pattyn10-Nov-07 14:24

Luc Pattyn

10-Nov-07 14:24

Hi Brady,

if you want to recognize a specific string (SEQ) the only thing you need
is a buffer of length SEQ.Length; since you need the string value for every
character you append, it is not useful to have a StringBuilder.

Hence use a string (say buf, initialized at "") and do:

buf=buf+e.KeyChar;
if (buf.Length>SEQ.Length) buf=buf.SubString(buf.Length-SEQ.Length, SEQ.Length);
if (buf.Equals(SEQ)) ...

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Brady Kelly10-Nov-07 19:53

10-Nov-07 19:53

Luc, it's easier to say,

if (buf.EndsWith(SEQ)) ...

I was doing that before, but I worried about the size of buf just using a string. If the user doing data capture without scanning, bu could get pretty big, and unless there is some internalisation magic I don't understand, every key press will create a new string . I use a StringBuilder so that I can remove the first character before appending the last. It seems to have acceptable performance.

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Luc Pattyn11-Nov-07 3:34

Luc Pattyn

11-Nov-07 3:34

Hi Brady,

Brady Kelly wrote:
every key press will create a new string

So does your statement string buff = keyBuffer.ToString();

Brady Kelly wrote:
I worried about the size of buf just using a string

My statement if (buf.Length>SEQ.Length) buf=buf.SubString(buf.Length-SEQ.Length, SEQ.Length);
limits the string length at all times (to 2 chars in case SEQ=x02x03).

If you don't want to do all the buffer stuff, there is one (slightly more complex)
alternative using a state machine, which basically remembers how many characters of SEQ
have been matched so far. So in one implementation it would use an int state;
and basically do:

if (e.KeyChar==SEQ[state]) state++; else state=0;
if (state==SEQ.Length) {
    state=0;
    ... we got a match
}

the above code however is incorrect as soon as SEQ contains repeating characters though;
if you must cope with the general case it becomes much more complex...

Smile | :)

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Brady Kelly11-Nov-07 3:39

Mater / Detail Datagridview

11-Nov-07 3:39

Ooh, I really didn't read your first reply properly. Blush | :O

Thanks, I'll look into the state machine a bit later in the project, when I create a base form for all forms that use a scanner.

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Mr. Candyman7-Nov-07 8:41

Mr. Candyman

7-Nov-07 8:41

Anyone can point me to some Windows Form Free DataGrid-like control that can support Master / Detail View (a hirarchical sub-rows view, that is), if there is any? I've been searching google but couldn't find anything free :P.
Thanks.

led mike7-Nov-07 8:46

led mike

7-Nov-07 8:46

Mr. Candyman wrote:
I've been searching google

Interesting[^]

Mr. Candyman7-Nov-07 9:40

Mr. Candyman

7-Nov-07 9:40

Thank you, but I was looking for a control to use in a Windows Application, and all I can see is for web app.

led mike7-Nov-07 10:41

led mike

7-Nov-07 10:41

Mr. Candyman wrote:
but I was looking for a control to use in a Windows Application

Interesting[^]