Null PointerException in spinner in android

I am working in Android. I want to design a spinner of song categories.

This is my code:

public Spinner spinner_category_forSong;

String[] arr_Category={"Select","sad","dj","rock"};

ArrayAdapter<String> adapter = new ArrayAdapter<String>(
    this,android.R.layout.simple_spinner_item,arr_Category);

spinner_category_forSong = (Spinner)findViewById(R.id.Spinner_category_forUpload);    
spinner_ca开发者_运维百科tegory_forSong.setPrompt("Music Category :");
spinner_category_forSong.setAdapter(adapter);

But whenever I run my project, a null pointer exception is created in spinner_category_forSong.setPrompt("Music Category :"); and spinner_category_forSong.setAdapter(adapter);.

Please tell me what mistake I have made in this code.

---

From your exception it seems that findViewById(R.id.Spinner_category_forUpload) returns null. My guess is that you didn't call setContentView() prior to your method calls.

From the code sample your class structure is not clear. Are some lines inside onCreate()?

---

try after setting adapter spinner_category_forSong.setAdapter(adapter); before spinner_category_forSong.setPrompt("Music Category :");