AutoCompleteTextView NullPointer Exception

I have searched a long time and cannot find a solution to my problem. I am trying to create a Dialog with an AutoCompleteTextView. I followed the tutorial on the Android developer website, and it worked great. I have been successful using layouts on Dialogs before, so I thought this would be just as easy. I created a layout for my Dialog and I made sure that the AutoCompleteTextView has an ID. Here's where the interesting stuff happens...

 dialog.setContentView(R.layout.auto_layout);       
 AutoCompleteTextView auto_tv = (AutoCompleteTextView)findViewById(R.id.role_ac);

Here is the layout as well.

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout
  xmlns:android="http://schemas.android.com/apk/res/android"
  android:layout_width="wrap_content"
  android:layout_height="wrap_content">
  <TextView android:layout_width="wrap_content"
        android:layout_height="wrap_content" android:text="Role" />
    <AutoCompleteTextView android:id="@+id/role_ac" android:layout_width="280dip" android:layout_height="wrap_content"/>
    <Button android:layout_height="wrap_content"
        android:layout_width="fill_parent" android:text="Done"
        android:id="@+id/auto_doneButton" />
</LinearLayout>

For some reason, auto_tv is null even though it does exist in the layout auto_layout. The only way I have been able to get an AutoCompleteTextView in a Dialog is by building the layo开发者_如何学Pythonut programmatically. Why is the AutoCompletTextView null when I try to use it? Did I forget something in my layout or am I not constructing the object correctly? Any help on this would be greatly appreciated. Thanks.

You're mixing two different contexts in your calls to setContentView and findViewById. In the first statement you're setting the content view of the object dialog. In the second statement you're looking for an view in the parent activity. You want to make both calls using the dialog object. The correct syntax should be:

dialog.setContentView(R.layout.auto_layout);       
AutoCompleteTextView auto_tv = (AutoCompleteTextView) dialog.findViewById(R.id.role_ac);

Ok. Just figured it out. Looked at too much code to catch my mistake. Here's the solution.

 dialog.setContentView(R.layout.auto_layout);       
 AutoCompleteTextView auto_tv = (AutoCompleteTextView)dialog.findViewById(R.id.role_ac);

I needed to specify to use the Dialog's layout and not the main application's layout that was implied by not using dialog.findViewByID.