Get soft keyboard's height without ViewTreeObserver

Question

I am currently getting the height of the soft keyboard by using the ViewTreeObserver like:

private final ViewTreeObserver.OnGlobalLayoutListener   mKeyboardLayoutListener = new ViewTreeObserver.OnGlobalLayoutListener() {
    @Override
    public void onGlobalLayout() {
        final int heightDiff = mRootLayout.getRootView().getHeight() - mRootLayout.getHeight();

        if(heightDiff > mStatusBarHeight && mLastHeightDiff != heightDiff){
            mSoftKeyboardHeight = heightDiff;
        }
        mLastHeightDiff = heightDiff;
    }
};

But now I need to get the soft keyboard's height before showing it, as we need another view to have the exact same height than the soft keyboard. How could I do that?

Thanks in advance