How can I launch an activity to be on top of all other activities?

I am trying to create an application that defines two activites. The first activity pretty much runs all of the time. The second activity requires the user to authenticate to use the device.

Most of the time this appli开发者_高级运维cation works fine. However, I am having problems figuring out how to force the second activity to the top of the window stack. The code calls startActivity passing in an intent to start the second activity. The problem is that when another application is running (e.g. a web browser), the second activity is not on top. When the other application exits, the second activity is visible to take input from the user.

Here is the activity definition for the second activity that I want to have always on top when started:

    <activity android:name=".Authenticate"
              android:launchMode="singleTop"
              android:configChanges="orientation|keyboardHidden">
    </activity>

It is my understanding that when start activity is called, it will put the new activity on top. Is there something that I am missing? How can I make the authentication activity come to the top when it is started?

Well AFAIK, you cannot force your Activity to stay on top all the time. If some other process (say Web Browser) creates an Activity after you have created yours, then that processes Activity will have focus and not yours.

whenever a new activity starts it is on top of the stack and if another application is running then it will be on the top of the stack and if you want your activity on top of the stack then you should stop other application being launched....Is there something I am missing then let me know..