Shift Keys on Android

Shift Keys on Android

When you press the CAPS button, a little green dot appears. At this point, you might be wondering: why?

Source code

Diving into the Keyboard.java source code, we find the following:

@Override
public void onCreateInputView() {

public static final int KEYCODE_SHIFT = -1;

...

public boolean setShifted(boolean shiftState) {
    for (Key shiftKey : mShiftKeys) {
        if (shiftKey != null) {
            shiftKey.on = shiftState;
        }  
    }  
    if (mShifted != shiftState) {
        mShifted = shiftState;
        return true;
    }  
    return false;
}
...

if (key.codes[0] == KEYCODE_SHIFT) {
    // Find available shift key slot and put this shift key in it
    for (int i = 0; i < mShiftKeys.length; i++) {
        if (mShiftKeys[i] == null) {
            mShiftKeys[i] = key;  
            mShiftKeyIndices[i] = mKeys.size()-1;
            break;
        }
    }
    mModifierKeys.add(key);
} else if (key.codes[0] == KEYCODE_ALT) {
    mModifierKeys.add(key);
}
...
public int[] getCurrentDrawableState() {
    int[] states = KEY_STATE_NORMAL;
    if (on) {
        if (pressed) {
            states = KEY_STATE_PRESSED_ON;
        } else {
            states = KEY_STATE_NORMAL_ON;
        }      
    } else {
        if (sticky) {
            if (pressed) {
                states = KEY_STATE_PRESSED_OFF;
            } else {
                states = KEY_STATE_NORMAL_OFF;
            }
        } else {
            if (pressed) {
                states = KEY_STATE_PRESSED;
            }      
        }      
    }
    return states;
}

}

So if the first keyCode is equal to KEYCODE_SHIFT, i.e. -1, then it gets turned on and rendered differently. When we look up these constants, we find that "on" corresponds to android.R.attr.state_checked.

That's all I know and understand at this point.