android custom dialog background

Question

I need to show a custom dialog in my Android application. Standard AlertDialog design is unacceptable. Android docs say:

Tip: If you want a custom dialog, you can instead display an Activity as a dialog instead of using the Dialog APIs. Simply create an activity and set its theme to Theme.Holo.Dialog in the manifest element:

That's it. The activity now displays in a dialog window instead of fullscreen.

Sounded promising. I did it, but transparency does not work! Background is always grey:

Here is a desc in the manifest:

<activity
    android:name=".MyDialogActivity"
    android:screenOrientation="portrait"
    android:theme="@android:style/Theme.Holo.Dialog.NoActionBar" >
</activity>

Here is a root of my activity:

<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:background="#00000000"
    android:layout_width="400dp"
    android:layout_height="wrap_content" >

    // Content ... //

</RelativeLayout>

I tried also android:background="@null" - effect was the same. If I use android:background="#ff0000" then it's red (as it should be). But how do I make it transparent?

Update

I ended up with

<style name="MyThemeDialogCustom" parent="android:Theme.Holo.Dialog.NoActionBar" >
    <item name="android:windowBackground">@color/transparent</item>
    <item name="android:colorBackgroundCacheHint">@null</item>
</style>

Answer 1

make theme like this

<style name="ThemeDialogCustom">
<item name="android:windowFrame">@null</item>
<item name="android:windowIsFloating">true</item>
<item name="android:windowContentOverlay">@null</item>
<item name="android:windowAnimationStyle">@android:style/Animation.Dialog</item>
<item name="android:windowBackground">@color/transparent</item>
<item name="android:colorBackgroundCacheHint">@null</item>
</style>