Null pointer exception when loading fragment

Question

I am working on my final project in android-programming course (so I'm still pretty new). I'm building my own media player. I implemented a Drawer that contains the different media types (video, audio, stream etc.) and what I want is to have each clicked item load a fragment that will tackle the task. The first one I'm working on is the audio fragment. It is th esecond on the list but i think it'll e easier than the video. Anyway. when I click on "audio" ( picture link ) I get a null pointer exception. I've been trying to figure it out for a couple of days but now I'm really wasting precious time. What am I doing wrong?

Because there is quite a lot of code involved I'll use snippets (if people prefer I actually paste all the code here, let me know and I'll change it).

MainActivity: http://pastebin.com/zsXuZHkN

FragmentAudio: http://pastebin.com/77XsBbu9

ListAdapterAudio: http://pastebin.com/cfu7azP0

logact log:

09-13 18:31:33.056  11959-11959/com.example.ref_apps.winnerplayer E/AndroidRuntime﹕ FATAL EXCEPTION: main
Process: com.example.ref_apps.winnerplayer, PID: 11959
java.lang.NullPointerException
        at android.support.v4.app.BackStackRecord.doAddOp(BackStackRecord.java:414)
        at android.support.v4.app.BackStackRecord.replace(BackStackRecord.java:449)
        at android.support.v4.app.BackStackRecord.replace(BackStackRecord.java:441)
        at com.example.ref_apps.winnerplayer.MainActivity.selectDrawerItem(MainActivity.java:118)
        at com.example.ref_apps.winnerplayer.MainActivity$1.onItemClick(MainActivity.java:64)
        at android.widget.AdapterView.performItemClick(AdapterView.java:299)
        at android.widget.AbsListView.performItemClick(AbsListView.java:1153)
        at android.widget.AbsListView$PerformClick.run(AbsListView.java:3065)
        at android.widget.AbsListView$3.run(AbsListView.java:4031)
        at android.os.Handler.handleCallback(Handler.java:808)
        at android.os.Handler.dispatchMessage(Handler.java:103)
        at android.os.Looper.loop(Looper.java:193)
        at android.app.ActivityThread.main(ActivityThread.java:5292)
        at java.lang.reflect.Method.invokeNative(Native Method)
        at java.lang.reflect.Method.invoke(Method.java:515)
        at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:825)
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:641)
        at dalvik.system.NativeStart.main(Native Method)

there are other files, obviously, but I don't think that they are the culprits. I'll add file by request.

Thanks!!

Answer 1

Try after adding addToBackstack(null) in fragment replace.

(or)

Check backStack count and you should clear all the count before replace another fragment.

Answer 2

In your Activity you are importing android.support.v4.app.Fragment and your Fragment is android.app.Fragment . That's why your cast fails after calling newInstance() and your fragment is null. The same goes with your ListFragment .

You also need to implement newInstance() in your fragment.

public static Fragment newInstance() 
{
    FragmentAudio myFragment = new FragmentAudio();
    return myFragment;
}