getSupportActionBar() The method getSupportActionBar() is undefined for the type TaskActivity. Why?

Your class needs to extend from ActionBarActivity, rather than a plain Activity in order to use the getSupport*() methods.

Update [2015/04/23]: With the release of Android Support Library 22.1, you should now extend AppCompatActivity. Also, you no longer have to extend ActionBarActivity or AppCompatActivity, as you can now incorporate an AppCompatDelegate instance in any activity.

Here is another solution you could have used. It is working in my app.

      @Override
      public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        android.support.v7.app.ActionBar actionBar =getSupportActionBar();
        actionBar.setDisplayHomeAsUpEnabled(true);            
        setContentView(R.layout.activity_main)

Then you can get rid of that import for the one line ActionBar use.

If you are already extending from ActionBarActivity and you are trying to get the action bar from a fragment:

ActionBar mActionBar = (ActionBarActivity)getActivity()).getSupportActionBar();