扩展Fragment的类的调用方法

Question

I have StartActivity class. It extends from Fragment :

The code for StarActivity.java is shown below:

public class StartActivity extends Fragment {
    public static Context appContext;
    ActionBar actionbar;
    int state = 0;
    /** Called when the activity is first created. */
    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container,
            Bundle savedInstanceState) {
        View rootView = inflater.inflate(R.layout.main, container,
                false);
        return rootView;
    }

    // call draw Tab method
    public void drawTab(){
          //ActionBar
        actionbar = getActivity().getActionBar();
        if(state == 0){
        actionbar.setNavigationMode(ActionBar.NAVIGATION_MODE_TABS);

        ActionBar.Tab PlayerTab = actionbar.newTab().setText("Fragment A");
        ActionBar.Tab StationsTab = actionbar.newTab().setText("Fragment B");

        Fragment PlayerFragment = new AFragment();
        Fragment StationsFragment = new BFragment();

        PlayerTab.setTabListener(new MyTabsListener(PlayerFragment));
        StationsTab.setTabListener(new MyTabsListener(StationsFragment));

        actionbar.addTab(PlayerTab);
        actionbar.addTab(StationsTab);
        state++;
        }
    }

In MainClass.java I declare a variable: Fragment fragment1 = new StartActivity(); How to I can call drawTab method. I try fragment.drawTab but it can't. If I call drawTab in onCreateView in StartActivity.java, it runs OK. but when I don't call drawTab() in onCreateView, error happens:( RUN ERROR:

public View onCreateView(LayoutInflater inflater, ViewGroup container,
            Bundle savedInstanceState) {
        View rootView = inflater.inflate(R.layout.main, container,
                false);
        return rootView;
    }

RUN OK:

 public View onCreateView(LayoutInflater inflater, ViewGroup container,
                Bundle savedInstanceState) {
            View rootView = inflater.inflate(R.layout.main, container,
                    false);
            drawTab();
            return rootView;
        }

MainClass.java

private void selectItem(int position) {
        Toast.makeText(getBaseContext(), Integer.toString(position), 1).show();
        Fragment fragment1 = new StartActivity();
        switch (position) {
        case 5:
            break;
        case 1:
            ((StartActivity) fragment1).drawTab();
            FragmentManager fragmentManager1 = getFragmentManager();
            fragmentManager1.beginTransaction().replace(R.id.content_frame, fragment1).commit();
            break;
        default:
            break;
        }

Answer 1

The problem is when you create an instace of a fragment, it is not attached to the activity yet. So drawing a tab before onAttach method will cause a NPE error.

Try to do something below:

public class StartActivity extends Fragment {
    // TODO: add your other/current fields here
    boolean mDrawTabWhileInitializing = false;
    public StartActivity(boolean drawTabWhileInitializing) {
        mDrawTabWhileInitializing = drawTabWhileInitializing;
    }

    public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
        View rootView = inflater.inflate(R.layout.main, container, false);
        if(mDrawTabWhileInitializing) {
            drawTab();
        }
        return rootView;
    }    

    // TODO: add your other/current methods here
}

Use the boolean flag while initializing your fragment:

private void selectItem(int position) {
    Toast.makeText(getBaseContext(), Integer.toString(position), 1).show();
    Fragment fragment1 = null;
    switch (position) {
        case 1:
            fragment1 = new StartActivity(true);
            FragmentManager fragmentManager1 = getFragmentManager();
            fragmentManager1.beginTransaction().replace(R.id.content_frame, fragment1).commit();
            break;
        default:
            break;
    }
}

Note: Just an advice, the name of a fragment is annoying. Why don't you name it StartFragment?

Answer 2

将其声明为StartActivity Fragment1 = new StartActivity（）;