ToAscii/ToUnicode in a keyboard hook destroys dead keys

问题

It seems that if you call ToAscii() or ToUnicode() while in a global WH_KEYBOARD_LL hook, and a dead-key is pressed, it will be 'destroyed'.

For example, say you've configured your input language in Windows as Spanish, and you want to type an accented letter á in a program. Normally, you'd press the single-quote key (the dead key), then the letter "a", and then on the screen an accented á would be displayed, as expected.

But this doesn't work if you call ToAscii() or ToUnicode() in a low-level keyboard hook function. It seems that the dead key is destroyed, and so no accented letter á shows up on screen. Removing a call to the above functions resolves the issue... but unfortunately, I need to be able to call those functions.

I Googled for a while, and while a lot of people seemed to have this issue, no good solution was provided.

Any help would be much appreciated!

EDIT: I'm calling ToAscii() to convert the virtual-key code and scan code received in my LowLevelKeyboardProc hook function into the resulting character that will be displayed on screen for the user.

I tried MapVirtualKey(kbHookData->vkCode, 2), but this isn't as "complete" a function as ToAscii(); for example, if you press Shift + 2, you'll get '2', not '@' (or whatever Shift + 2 will produce for the user's keyboard layout/language).

ToAscii() is perfect... until a dead-key is pressed.

EDIT2: Here's the hook function, with irrelevant info removed:

LRESULT CALLBACK keyboard_LL_hook_func(int code, WPARAM wParam, LPARAM lParam) {

    LPKBDLLHOOKSTRUCT kbHookData = (LPKBDLLHOOKSTRUCT)lParam;
    BYTE keyboard_state[256];

    if (code < 0) {
        return CallNextHookEx(keyHook, code, wParam, lParam);
    }

    WORD wCharacter = 0;

    GetKeyboardState(&keyboard_state);
    int ta = ToAscii((UINT)kbHookData->vkCode, kbHookData->scanCode,
                     keyboard_state, &wCharacter, 0);

    /* If ta == -1, a dead-key was pressed. The dead-key will be "destroyed"
     * and you'll no longer be able to create any accented characters. Remove
     * the call to ToAscii() above, and you can then create accented characters. */

    return CallNextHookEx(keyHook, code, wParam, lParam);
}

回答1:

stop using ToAscii() and use ToUncode()
remember that ToUnicode may return you nothing on dead keys - this is why they are called dead keys.
Any key will have a scancode or a virtual key code but not necessary a character.

You shouldn't combine the buttons with characters - assuming that any key/button has a text representation (Unicode) is wrong.

So:

for input text use the characters reported by Windows
for checking button pressed (ex. games) use scancodes or virtual keys (probably virtual keys are better).
for keyboard shortcuts use virtual key codes.

回答2:

Call 'ToAscii' function twice for a correct processing of dead-key, like in:

int ta = ToAscii((UINT)kbHookData->vkCode, kbHookData->scanCode,
                 keyboard_state, &wCharacter, 0);
int ta = ToAscii((UINT)kbHookData->vkCode, kbHookData->scanCode,
                 keyboard_state, &wCharacter, 0);
If (ta == -1)
 ...

回答3:

Calling the ToAscii or ToUnicode twice is the answer. I found this and converted it for Delphi, and it works!

cnt:=ToUnicode(VirtualKey, KeyStroke, KeyState, chars, 2, 0);
cnt:=ToUnicode(VirtualKey, KeyStroke, KeyState, chars, 2, 0); //yes call it twice

回答4:

Quite an old thread. Unfortunately it didn't contain the answer I was looking for and none of the answers seemed to work properly. I finally solved the problem by checking the MSB of the MapVirtualKey function, before calling ToUnicode / ToAscii. Seems to be working like a charm:

if(!(MapVirtualKey(kbHookData->vkCode, MAPVK_VK_TO_CHAR)>>(sizeof(UINT)*8-1) & 1)) {
    ToAscii((UINT)kbHookData->vkCode, kbHookData->scanCode,
        keyboard_state, &wCharacter, 0);
}

Quoting MSDN on the return value of MapVirtualKey, if MAPVK_VK_TO_CHAR is used:

[...] Dead keys (diacritics) are indicated by setting the top bit of the return value. [...]

回答5:

I encountered this issue while creating a key logger in C# and none of the above answers worked for me.

After a deep blog searching, I stumbled across this keyboard listener which handles dead keys perfectly.

回答6:

I copy the vkCode in a queue and do the conversion from another thread

@HOOKPROC
def keyHookKFunc(code,wParam,lParam):
    global gkeyQueue
    gkeyQueue.append((code,wParam,kbd.vkCode))
    return windll.user32.CallNextHookEx(0,code,wParam,lParam)

This has the advantage of not delaying key processing by the os

来源：https://stackoverflow.com/questions/1964614/toascii-tounicode-in-a-keyboard-hook-destroys-dead-keys

标签

windows

unicode

diacritics

keyboard-hook