处理充当键盘的USB条码扫描器，并在表格上的任何位置使用标头/预告片 [英] Handling USB Barcode Scanner acting as a keyboard, with header/trailers from anywhere on the form

问题描述

在winforms应用程序中，我需要从标准的USB条码扫描器读取输入，该扫描器使iteself像Windows的USB键盘一样显示.这必须在不将焦点放在特定控件上的情况下进行(即，我不能说单击此文本框然后扫描条形码").扫描程序配置为向扫描的每个代码输出标题和结尾.

In a winforms app, I need to read input from a standard USB barcode scanner, one which makes iteself appears as a USB keyboard to windows. This has to work without giving focus to a particular control (ie, I can't say "click on this textbox then scan the barcode"). The scanner is configured to output a header and trailer to every codes it scans.

我宁愿不采用原始"方式，即直接挂接到USB输入或Windows事件(WM_INPUT等).

I'd rather don't go the "raw" way, ie, hooking directly into the USB input or Windows events (WM_INPUT and such).

我当然可以将键击捕获在ProcessCmdKey中，但是随后我似乎无法正确识别页眉/尾部的键(分别为^〜{和}〜^).

I can of course trap the keystrokes in ProcessCmdKey, but then I don't seem to be able to properly identify the keys for the header/trailer (^~{ and }~^ respectively).

您知道如何在托管代码中正确完成此操作吗?

Any idea how this can be done properly in managed code?

推荐答案

这可行，但是有点难看:

This works, but it's kinda ugly:

    [DllImportAttribute("User32.dll")]
    public static extern int ToAscii(int uVirtKey, int uScanCode, byte[] lpbKeyState, byte[] lpChar, int uFlags);

    [DllImportAttribute("User32.dll")]
    public static extern int GetKeyboardState(byte[] pbKeyState);

    public static char GetAsciiCharacter(int uVirtKey, int uScanCode)
    {
        byte[] lpKeyState = new byte[256];
        GetKeyboardState(lpKeyState);
        byte[] lpChar = new byte[2];
        if (ToAscii(uVirtKey, uScanCode, lpKeyState, lpChar, 0) == 1)
            return (char)lpChar[0];
        else
            return new char();
    }

    protected override bool ProcessCmdKey(ref Message msg, Keys keyData)
    {
        if(keyData == Keys.ShiftKey || keyData == Keys.Shift)
            return base.ProcessCmdKey(ref msg, keyData);

        char keyChar = GetAsciiCharacter((int) (keyData & Keys.KeyCode), (((int) msg.LParam) & 0x1000000));

        if(keyChar == '\0')
            return base.ProcessCmdKey(ref msg, keyData);

        _currentSequence.Add(keyChar);

        if (_currentSequence.ToString() == "^~{")
        {
            _handlingInputFromScanner = true;
            _scannerBuffer.Clear();
            return true;
        }

        if (_currentSequence.ToString() == "}~^")
        {
            _handlingInputFromScanner = false;
            OnScannerRead.Invoke(this, new ScannerReadEventArgs { ScannerData = _scannerBuffer.ToString() });
            _scannerBuffer.Clear();
            return true;
        }

        if (keyChar == '}' || keyChar == '{' || keyChar == '~' || keyChar == '^')
        {
            return true;
        }

        if (_handlingInputFromScanner)
        {
            _scannerBuffer.Append(keyChar);
            return true;
        }

        return base.ProcessCmdKey(ref msg, keyData);
    }

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