Android : My PopupWindow's background is transparent
<p>I created a PopupWindow like this :</p>

<pre><code>PopupWindow popupWindow = new PopupWindow(LayoutInflater.from(this).inflate(R.layout.main_popup_navigation, null, false), ViewGroup.LayoutParams.WRAP_CONTENT, ViewGroup.LayoutParams.WRAP_CONTENT);
popupWindow.setWidth((int) this.getResources().getDimension(R.dimen.navigation_popup_width));
popupWindow.showAsDropDown(toolbar);
</code></pre>

<p>It works fine, except that it doesn't have any background. The popup's background is totally transparent.</p>

<p>How can I set a background (window + shadow) similar to a PopupMenu or a Spinner of the ThemeOverlay.AppCompat.Light theme? Thank You.</p>