Use of android taskaffinity

I am reading about taskaffinity & created a demo app with following Activities :

A
B ===> taskaffinity, com.ando
C
D ===> taskaffinity, com.ando
E

It is written that, Activities with same taskaffinity secretly opens the single instance of another one.

So, I put log in onResume of every activity to see task id. If it creates single instance then why its not executing onResume of B when I open D and vice-versa.

I read developers site and other post but still not got how to use taskaffinity and whats its use, why we should'tn use singleInstance instead ?

Manifest:

 <application
    android:allowBackup="true"
    android:icon="@drawable/ic_launcher"
    android:label="@string/app_name"
    android:theme="@style/AppTheme" >
    <activity
        android:name="com.example.danroid.taskaffinity.A"
        android:label="@string/app_name" >
        <intent-filter>
            <action android:name="android.intent.action.MAIN" />

            <category android:name="android.intent.category.LAUNCHER" />
        </intent-filter>
    </activity>

    <!-- android:taskAffinity="com.ando" -->
    <activity
        android:name="com.example.danroid.taskaffinity.B"
        android:label="@string/app_name"
        android:taskAffinity="@string/task_affinity" >
    </activity>
    <activity
        android:name="com.example.danroid.taskaffinity.C"
        android:label="@string/app_name" >
    </activity>
    <activity
        android:name="com.example.danroid.taskaffinity.D"
        android:label="@string/app_name"
        android:taskAffinity="@string/task_affinity" >
    </activity>
    <activity
        android:name="com.example.danroid.taskaffinity.E"
        android:label="@string/app_name" >
    </activity>
</application>

When you call startActivity() to transition from one Activity to another, if you do not set Intent.FLAG_ACTIVITY_NEW_TASK in the Intent flags, the new Activity will be started in the same task, regardless of the value of taskAffinity.

However, if you set Intent.FLAG_ACTIVITY_NEW_TASK in the Intent flags, the new Activity will still be started in the same task if the new Activity has the same taskAffinity as the taskAffinity of the task (this is determined by the taskAffinity of the root Activity in the task). But, if the new Activity has a different taskAffinity, the new Activity will be started in a new task.

Based on your description, if you don't set Intent.FLAG_ACTIVITY_NEW_TASK when starting a new Activity, then all of your activities will end up in the same task.