Android: why is my linearlayout crashing when switching at runtime?-Collection of common programming errors

when user presses a button i would like to switch to the ‘details’ layout which is like this:

and this is how i am trying to switch it:

 switch(item.getItemId())
                {
                case ID_DETAILS:
                    // show new layout to for details                   
                    LinearLayout detailsLayout = (LinearLayout) findViewById(R.id.layoutDetails);
                    LayoutInflater detailsvi = (LayoutInflater) getSystemService(Context.LAYOUT_INFLATER_SERVICE);
                    View detailsv = detailsvi.inflate(R.layout.activity_details, null);

// IT CRASHES ON THIS LINE
                    detailsLayout.addView(detailsv,new LinearLayout.LayoutParams(detailsLayout.getLayoutParams().width, detailsLayout.getLayoutParams().height));

                            return true;
}

It gives a null pointer exception error!!!

08-09 17:23:47.146: E/AndroidRuntime(1572): FATAL EXCEPTION: main
08-09 17:23:47.146: E/AndroidRuntime(1572): java.lang.NullPointerException

1. Here is how you solve this:

   1) put a breakpoint on the crashline and run in debug mode. You can immediately see if detailsLayout is null or not. If not do step 2 Also check if detailsv is null.

   2) details Object o1 = etailsLayout.getLayoutParams(); // check if this is null.

   It has to be one or the other.

   Update: Since its detailsLayout is in fact null. It must be that either

   1) setContentView was not called prior to requsting detailsLayout, or 2) setContentView was set to a layout that did not define detailsLayout, or 3) setContentView was called correctly but detailsLayout is not correctly id in that layout file.

   It must be one of these three.