Android: how can i tell if the soft keyboard is showing or not?

As far as I know, you can't.

However, you can monitor size changes of your layout, and since keyboard showing up is the main cause for the resizes, you might be able to assume that the keyboard is shown or not.

Here's a sample code for monitoring the size-changes of a layout. Just use this layout as the parent of your original layout, and use its listener. If the height has decreased, you can assume the keyboard is shown, and if it was increased, you can assume it got closed.

public class LayoutSizeChangedSensorFrameLayout extends FrameLayout {
    public enum SizeChange {
        HEIGHT_INCREASED, HEIGHT_DECREASED, WIDTH_INCREASED, WIDTH_DECREASED
    }

    public interface OnLayoutSizeChangedListener {
        void onSizeChanged(EnumSet<SizeChange> direction);
    }

    private OnLayoutSizeChangedListener mLayoutSizeChangeListener;

    public LayoutSizeChangedSensorFrameLayout(final Context context) {
        super(context);
    }

    public LayoutSizeChangedSensorFrameLayout(final Context context, final AttributeSet attributeSet) {
        super(context, attributeSet);
    }

    public LayoutSizeChangedSensorFrameLayout(final Context context, final AttributeSet attrs, final int defStyle) {
        super(context, attrs, defStyle);
    }

  @Override
  protected void onSizeChanged(final int w, final int h, final int oldw, final int oldh) {
      super.onSizeChanged(w, h, oldw, oldh);
      if (mLayoutSizeChangeListener != null) {
          final EnumSet<SizeChange> result = EnumSet.noneOf(SizeChange.class);
          if (oldh > h)
              result.add(SizeChange.HEIGHT_DECREASED);
          else if (oldh < h)
              result.add(SizeChange.HEIGHT_INCREASED);
          if (oldw > w)
              result.add(SizeChange.WIDTH_DECREASED);
          else if (oldw < w)
              result.add(SizeChange.WIDTH_INCREASED);
          if (!result.isEmpty())
              mLayoutSizeChangeListener.onSizeChanged(result);
      }
  }

    public void setOnLayoutSizeChangedListener(final OnLayoutSizeChangedListener layoutSizeChangeListener) {
        this.mLayoutSizeChangeListener = layoutSizeChangeListener;
    }

    public OnLayoutSizeChangedListener getOnLayoutSizeChangeListener() {
        return mLayoutSizeChangeListener;
    }
}

Determining if the keyboard is showing is not possible apparently.

You might want to disable it alltogether with the windowSoftInputMode xml tag in your manifest: http://developer.android.com/reference/android/R.attr.html#windowSoftInputMode. Or you can have a look on how to remove focus to hide the keyboard: Hide soft keyboard on activity without any keyboard operations.

Neither will exactly solve your problem. I remember reading a blogpost strongly advising not to use tabs at the bottom, rather than the top of the screen, for UI clarity reasons. I recommend you to follow up on that.