Java 如何将活动作为意图传递？

我试图在按下微调器按钮后看到一个

ActionBarActivity

打开的视图

我的微调器上有两个项目，第二个运行正常，但当我尝试访问

分类

项目时，应用程序在

抽屉实用性

类中抛出一个

NullPointerException

。我不知道问题出在哪里。我拥有的另一个

ActionBarActivity

扩展类运行良好。 我是Android/Java开发新手

旋转器碎片

import inmostla.ligatangamanga.pruebaintegrar.navigationdrawer.NavigationDrawerActivity;
import android.content.Intent;
import android.os.Bundle;
import android.support.v4.app.Fragment;
import android.support.v7.app.ActionBarActivity;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.AdapterView;
import android.widget.Spinner;
import android.widget.AdapterView.OnItemSelectedListener;

public class SpinnerFragment extends Fragment {

private static Spinner spinner;
private int selected;
private View mView;

static void setSpinnerContent( View view ){
    spinner = (Spinner) view.findViewById(R.id.spinner1);

    return ;
}

public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
    View view = inflater.inflate(R.layout.fragment_spinner, container, false);
 // Now use the above view to populate the spinner.
    setSpinnerContent( view );

    /**
     * Maneja las acciones seleccionadas del Spinner
     */
    spinner.setOnItemSelectedListener(new OnItemSelectedListener() {
        @Override
        public void onItemSelected(AdapterView<?> arg0, View arg1, int arg2, long arg3) {


            selected = spinner.getSelectedItemPosition();
            switch(selected){
            case 1:
                Intent categorias = new Intent(  );

                categorias.setClass( getActivity() , NavigationDrawerActivity.class );
                startActivity(categorias);
                break;
            case 2:

                Intent convenios = new Intent();
                convenios.setClass(getActivity(), ConveniosFragment.class);
                startActivity(convenios);

                break;
            }

        }

        @Override
        public void onNothingSelected(AdapterView<?> arg0) {
        }

    });

return view;
}

 }

---

可能是因为

getActivity（）

返回null。尝试重写

onAttach（）

并将

Activity

引用作为类中的字段。当您需要对上下文或活动的引用时，请使用此引用而不是

getActivity（）

package inmostla.ligatangamanga.pruebaintegrar.navigationdrawer;

import inmostla.ligatangamanga.pruebaintegrar.navigationdrawer.NavigationDrawerFragment;
import inmostla.ligatangamanga.pruebaintegrar.R;

import android.app.Activity;
import android.support.v7.app.ActionBarActivity;
import android.support.v7.app.ActionBar;
import android.support.v4.app.Fragment;
import android.support.v4.app.FragmentManager;
import android.support.v4.widget.DrawerLayout;
import android.os.Bundle;
import android.view.LayoutInflater;
import android.view.Menu;
import android.view.MenuItem;
import android.view.View;
import android.view.ViewGroup;

public class NavigationDrawerActivity 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.navigation_drawer);

    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));
}...