It’d be cool to have an Activity to be shown like a Dialog, with the previous activity still in the background.

It turns out that this can easily be done, making use of the android:theme attribute in your activity tag in the AndroidManifest.xml file.

<activity
 android:name=".YourActivityName"
 android:theme="@style/CustomDialog" >
 </activity>

where CustomDialog is a style that we declare in styles.xml (which should go into the res/values folder). Put the following inside the styles.xml.

<?xml version="1.0" encoding="utf-8"?>
<resources>

<style name="CustomDialog" parent="@android:style/Theme.Dialog">
 <item name="android:windowBackground">@color/transparent</item>
 <item name="android:windowIsFloating">true</item>
 <item name="android:windowNoTitle">true</item>
 </style>

</resources>

Start your activity, as you normally would, using startActivity(Intent intent).