Android changing tableLayout from code doesn't work

Question

I got a strange problem with replacing a table row from code.

My XML code looks like this:

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
     android:orientation="vertical"
     android:layout_width="fill_parent"
     android:layout_height="fill_parent"
>

<TableLayout 
 xmlns:android="http://schemas.android.com/apk/res/android"
 android:id="@+id/columnheadings"
 android:layout_height="wrap_content" 
 android:layout_width="fill_parent"/>        

<ListView
    android:id="@+id/android:list"
    android:layout_width="fill_parent"
    android:layout_height="fill_parent"
    android:dividerHeight="2px"
    />
    ...     
</LinearLayout>

When the activity is created, I can successfully insert a TableRow to the TableLayout "columnheadings":

 table = (TableLayout)findViewById(R.id.columnheadings);
 table.removeAllViews();
 TableRow tr = new TableRow(this);
 TextView tv = new TextView(activity);
 tv.setText("asdf");
 tr.addView(tv);
 table.addView(tr);
 table.postInvalidate();

The contents (and width) of the table columns are dynamically calculated.

Now I want to also redraw the TableLayout, when there are updates within the Adapter of the ListView. For this purpose, I'm creating the adapter with a reference to the activity.

From within the adapter I can successfully change e.g. the text of a column.

What I try to do (without success):

 TableLayout tableLayout = (TableLayout)activity.findViewById(android.app.R.id.columnheadings);         

 tableLayout.removeAllViews();
 TableRow row=new TableRow(activity);
 TextView tv = new TextView(activity);
 tv.setText("test");

 row.addView(tv);
 tableLayout.addView(row);

 tableLayout.postInvalidate();

Unfortunately, the only thing that happens is a removal of the current table row. The new row isn't added to the tableLayout from the adapter.

Any suggestions ?