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.

Originally posted 2014-01-05 09:58:23.