Spinner mCategory = (Spinner)findViewById(R.id.mCategory);
   mCategory.setOnItemSelectedListener(this);
       
   ArrayList<String> categories = new ArrayList<>();
categories.add("A");
categories.add("B");
categories.add("C");
categories.add("D");
	
ArrayAdapter<String> categoryAdapter = new ArrayAdapter<String>(this, android.R.layout.simple_spinner_item, categories);
mCategory.setAdapter(categoryAdapter);