如何解决Android中的静态片段要求？

Question

I recently figured out that lines of code similar to button.setText("Hello World"); in the onCreate() method will throw a nullPointerException if you assigned the button as so:

 Button button=(Button)findViewById(R.id.myLayout); 

This is because of the fact that the fragment the button came from wasn't inflated before the button was assigned, thus making the button null. So I learned that I need to put the code in the onCreateView() method in the fragment extension class. But, in the app I am currently making, I am implementing this code in the onCreate():

 SharedPreferences activitiesFile = getApplicationContext().getSharedPreferences("Activities", 0);
    Set<String> keylist = activitiesFile.getAll().keySet();
    for (String s : keylist) {
        String active = activitiesFile.getString(s, "");
        Button activeName=new Button(this);
        activeName.setText(active);
        activeName.setLayoutParams(new LayoutParams(LayoutParams.MATCH_PARENT, 
                LayoutParams.WRAP_CONTENT));
        LinearLayout layout=(LinearLayout) findViewById(R.id.ActivityList);
        activeName.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                FillInInfo(v);
            }
        });
        layout.addView(activeName);

    }

Everything is this code block works completely fine, except for the layout.addView(activeName); because of the nullPointerException I mentioned before. So, I decided to put this code block into the onCreateView() to fix the problem, but putting this code in the fragment class creates a couple of syntax errors saying "can not make a static reference to a non-staic method". I tried taking away the static from the fragment class, and in the end, it went from one problem to the next. So, my question is how should I implement this code block when it works in neither onCreate() nor onCreateView(). (Keep in mind that this whole code block needs to stay together)

Fragment Class:

 public static class PlaceholderFragment extends Fragment {
    /**
     * The fragment argument representing the section number for this
     * fragment.
     */
    private static final String ARG_SECTION_NUMBER = "section_number";

    /**
     * Returns a new instance of this fragment for the given section number.
     */
    public static PlaceholderFragment newInstance(int sectionNumber) {
        PlaceholderFragment fragment = new PlaceholderFragment();
        Bundle args = new Bundle();
        args.putInt(ARG_SECTION_NUMBER, sectionNumber);
        fragment.setArguments(args);
        return fragment;
    }

    public PlaceholderFragment() {
    }

    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container,
            Bundle savedInstanceState) {
        View rootView = inflater.inflate(R.layout.fragment_manage_day,
                container, false);


        TextView textView = (TextView) rootView
                .findViewById(R.id.section_label);
        textView.setText(Integer.toString(getArguments().getInt(
                ARG_SECTION_NUMBER)));
        return rootView;
    }

    @Override
    public void onAttach(Activity activity) {
        super.onAttach(activity);
        ((ManageDay) activity).onSectionAttached(getArguments().getInt(
                ARG_SECTION_NUMBER));
    }
}

The whole class code:

 public class ManageDay extends ActionBarActivity implements

    NavigationDrawerFragment.NavigationDrawerCallbacks {

/**
 * Fragment managing the behaviors, interactions and presentation of the
 * navigation drawer.
 */
private NavigationDrawerFragment mNavigationDrawerFragment;

/**
 * Used to store the last screen title. For use in
 * {@link #restoreActionBar()}.
 */
private CharSequence mTitle;

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_manage_day);

    Intent intent=getIntent();

    SharedPreferences activitiesFile = getApplicationContext().getSharedPreferences("Activities", 0);
    Set<String> keylist = activitiesFile.getAll().keySet();
    for (String s : keylist) {
        String active = activitiesFile.getString(s, "");
        Button activeName=new Button(this);
        activeName.setText(active);
        activeName.setLayoutParams(new LayoutParams(LayoutParams.MATCH_PARENT, 
                LayoutParams.WRAP_CONTENT));
        LinearLayout layout=(LinearLayout) findViewById(R.id.ActivityList);
        activeName.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                FillInInfo(v);
            }
        });
        layout.addView(activeName);

    }


    mNavigationDrawerFragment = (NavigationDrawerFragment) getSupportFragmentManager()
            .findFragmentById(R.id.navigation_drawer);
    mTitle = getTitle();

    // Set up the drawer.
    mNavigationDrawerFragment.setUp(R.id.navigation_drawer,
            (DrawerLayout) findViewById(R.id.drawer_layout));
}

@Override
public void onNavigationDrawerItemSelected(int position) {
    // update the main content by replacing fragments
    FragmentManager fragmentManager = getSupportFragmentManager();
    fragmentManager
            .beginTransaction()
            .replace(R.id.container,
                    PlaceholderFragment.newInstance(position + 1)).commit();
}

public void onSectionAttached(int number) {
    switch (number) {
    case 1:
        mTitle = getString(R.string.title_section1);
        break;
    case 2:
        mTitle = getString(R.string.title_section2);
        break;
    case 3:
        mTitle = getString(R.string.title_section3);
        break;
    }
}

public void restoreActionBar() {
    ActionBar actionBar = getSupportActionBar();
    actionBar.setNavigationMode(ActionBar.NAVIGATION_MODE_STANDARD);
    actionBar.setDisplayShowTitleEnabled(true);
    actionBar.setTitle(mTitle);
}

@Override
public boolean onCreateOptionsMenu(Menu menu) {
    if (!mNavigationDrawerFragment.isDrawerOpen()) {
        // Only show items in the action bar relevant to this screen
        // if the drawer is not showing. Otherwise, let the drawer
        // decide what to show in the action bar.
        getMenuInflater().inflate(R.menu.manage_day, menu);
        restoreActionBar();
        return true;
    }
    return super.onCreateOptionsMenu(menu);
}

@Override
public boolean onOptionsItemSelected(MenuItem item) {
    // Handle action bar item clicks here. The action bar will
    // automatically handle clicks on the Home/Up button, so long
    // as you specify a parent activity in AndroidManifest.xml.
    int id = item.getItemId();
    if (id == R.id.action_settings) {
        return true;
    }
    return super.onOptionsItemSelected(item);
}

/**
 * A placeholder fragment containing a simple view.
 */
public static class PlaceholderFragment extends Fragment {
    /**
     * The fragment argument representing the section number for this
     * fragment.
     */
    private static final String ARG_SECTION_NUMBER = "section_number";

    /**
     * Returns a new instance of this fragment for the given section number.
     */
    public static PlaceholderFragment newInstance(int sectionNumber) {
        PlaceholderFragment fragment = new PlaceholderFragment();
        Bundle args = new Bundle();
        args.putInt(ARG_SECTION_NUMBER, sectionNumber);
        fragment.setArguments(args);
        return fragment;
    }

    public PlaceholderFragment() {
    }

    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container,
            Bundle savedInstanceState) {
        View rootView = inflater.inflate(R.layout.fragment_manage_day,
                container, false);


        TextView textView = (TextView) rootView
                .findViewById(R.id.section_label);
        textView.setText(Integer.toString(getArguments().getInt(
                ARG_SECTION_NUMBER)));
        return rootView;
    }

    @Override
    public void onAttach(Activity activity) {
        super.onAttach(activity);
        ((ManageDay) activity).onSectionAttached(getArguments().getInt(
                ARG_SECTION_NUMBER));
    }
}


public void CreateActivity(View view){

    EditText editText = (EditText) findViewById(R.id.edit_message);
    String activity = editText.getText().toString();
    Button button=new Button(this);
    button.setText(activity);
    LinearLayout layout=(LinearLayout) findViewById(R.id.ActivityList);
    button.setLayoutParams(new LayoutParams(LayoutParams.MATCH_PARENT, LayoutParams.WRAP_CONTENT));
    button.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View v) {
            FillInInfo(v);
        }
    });
    layout.addView(button);
    editText.setText("");

    SharedPreferences activitiesFile = getApplicationContext().getSharedPreferences("Activities", 0);   
    SharedPreferences.Editor editor = activitiesFile.edit();
    editor.putString(activity, activity);
    editor.apply();
}

public void FillInInfo(View view){
    Intent intent=new Intent(this,ActivityInfo.class);
    Button button=(Button)view;
    String buttonName=button.getText().toString();
    intent.putExtra("Name",buttonName);
    startActivity(intent);

}

Answer 1

The view (in your case "ActivityList") doesn't get inflated untill after onCreateView() is called.

So in onCreate(), it is null.

You'll have to put this code block in onCreateView() or onViewCreated() (onViewCreated is called right after the view is correctly inflated).

To combat the static problem you're having, you'll have to tell us exactly WHERE you're having this problem in your code.