无法从片段获取上下文

Question

I am trying to call a fragment method from an activity but I am getting a null pointer exception when setting the adapter context with getActivity() in that method:

Fragment Method

public void fragmentMethod() {
            String[] names = new String[]{"name1", "name2", "name3"};
            String[] values = new String[]{value1, value2, value3};
            adapter = new MyArrayAdapter(getActivity(), names, values);
            setListAdapter(adapter);
}

Adapter

public class MyArrayAdapter extends ArrayAdapter<String> {

    private final Context context;
    private final String[] names;
    private final String[] values;

    public MyArrayAdapter (Context context, String[] names, String[] values) {
        super(context, R.layout.rowlayout, values);
        this.context = context;
        this.names = names;
        this.values = values;
    }

    @Override
    public View getView(int position, View convertView, ViewGroup parent) {
        ...
    }

}

Call to Fragment Method from Activity

public void activityMethod() {
    FragmentName  test= new FragmentName();
    test.fragmentMethod();
}

I have tried many different things and I'm at a loss here...if I am fundamentally wrong in what I am trying to do, please let me know as I am a novice. Thank you!

Edit: Stack Trace

( Inventory is the Fragment class)

This is after clicking an imageview which calls activityMethod()

06-04 19:55:17.976    1147-1147/company.com.myapp E/AndroidRuntime﹕ FATAL EXCEPTION: main
java.lang.NullPointerException
        at android.widget.ArrayAdapter.init(ArrayAdapter.java:310)
        at android.widget.ArrayAdapter.<init>(ArrayAdapter.java:128)
        at company.com.myapp.MyArrayAdapter.<init>(MyArrayAdapter.java:18)
        at company.com.myapp.Inventory.createList(Inventory.java:105)
        at company.com.myapp.MainActivity.newDay(MainActivity.java:177)
        at company.com.myapp.MainActivity$2.onClick(MainActivity.java:91)
        at android.view.View.performClick(View.java:4240)
        at android.view.View$PerformClick.run(View.java:17721)
        at android.os.Handler.handleCallback(Handler.java:730)
        at android.os.Handler.dispatchMessage(Handler.java:92)
        at android.os.Looper.loop(Looper.java:137)
        at android.app.ActivityThread.main(ActivityThread.java:5103)
        at java.lang.reflect.Method.invokeNative(Native Method)
        at java.lang.reflect.Method.invoke(Method.java:525)
        at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:737)
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:553)
        at dalvik.system.NativeStart.main(Native Method)

Answer 1

if I am fundamentally wrong in what I am trying to do, please let me know as I am a novice

You cannot call getActivity() and get a response until the fragment is attached to an activity. In the case of a dynamic fragment — one you are creating directly via the constructor — this will be sometime after you commit() a FragmentTransaction that will put this fragment in a FragmentManager .

Moreover, there is no point in setting up your adapter until the ListView is ready.

So, simply move your fragmentMethod() code into an onViewCreated() method on your fragment. This will be called at a point in time when both the fragment is attached to the activity and the ListView is ready to receive your adapter.

Answer 2

From the code above, your fragment didn't associate to any activity. So getActivity() call will return null until you attach your fragment to activity.

private void activityMethod() {
    MyFragment fragment = new MyFragment();
    getSupportFragmentManager().beginTransaction()
            .add(fragment, "myfragment").commit();
    fragment.fragmentMethod();
}

Answer 3

在onActivityCreated()或onAttach()内onAttach()