android - ¿Cómo rectificar NullPointerException en v4.DrawerLayout?

navigation-drawer android-actionbaractivity

Question

Estoy tratando de implementar un cajón de navegación, pero por alguna razón estoy recibiendo esta excepción de puntero nulo .

He pasado mucho tiempo en ello, pero fue en vano. Esto es parte de mi código. No puedo entender por qué está devolviendo la excepción del puntero nulo.

¿Debo importar alguna biblioteca más o menos?

Gracias por adelantado.

package com.motobeans.productions.aloha;

import android.app.FragmentManager;
import android.os.Bundle;
import android.support.v4.widget.DrawerLayout;
import android.support.v7.app.ActionBarActivity;
import android.support.v7.app.ActionBarDrawerToggle;
import android.view.LayoutInflater;
import android.view.Menu;
import android.view.MenuItem;
import android.view.View;
import android.view.ViewGroup;
import android.widget.AdapterView;
import android.widget.ArrayAdapter;
import java.util.Locale;
import android.app.Fragment;

import android.support.v7.widget.Toolbar;
import android.widget.ImageView;
import android.widget.ListView;

public class Activity_test extends ActionBarActivity {
private String[] mPlanetTitles;
    private DrawerLayout mDrawerLayout;
    private ListView mDrawerList;
    private ActionBarDrawerToggle mDrawerToggle;
    private CharSequence mTitle;
    private CharSequence mDrawerTitle;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);

        setContentView(R.layout.activity_test);
        Toolbar toolbar = (Toolbar) findViewById(R.id.tool_bar);
        setSupportActionBar(toolbar);

        mPlanetTitles = getResources().getStringArray(R.array.planets_array);
        mDrawerLayout = (DrawerLayout) findViewById(R.id.drawer_layout);
        mDrawerList = (ListView) findViewById(R.id.left_drawer);

        mTitle = mDrawerTitle = getTitle();

        // Set the adapter for the list view
        mDrawerList.setAdapter(new ArrayAdapter<String>(this,
                R.layout.drawer_list_item, mPlanetTitles));
        // Set the list''s click listener
        mDrawerList.setOnItemClickListener(new DrawerItemClickListener());


        mDrawerToggle = new ActionBarDrawerToggle(this, mDrawerLayout, toolbar,
                 R.string.drawer_open, R.string.drawer_close) {

            /** Called when a drawer has settled in a completely closed state. */
            public void onDrawerClosed(View view) {
                super.onDrawerClosed(view);
                getActionBar().setTitle(mTitle);
                invalidateOptionsMenu(); // creates call to onPrepareOptionsMenu()
            }

            /** Called when a drawer has settled in a completely open state. */
            public void onDrawerOpened(View drawerView) {
                super.onDrawerOpened(drawerView);
                getActionBar().setTitle(mDrawerTitle);
                invalidateOptionsMenu(); // creates call to onPrepareOptionsMenu()
            }
        };

        // Set the drawer toggle as the DrawerListener
        mDrawerLayout.setDrawerListener(mDrawerToggle);

    }

    @Override
    public boolean onPrepareOptionsMenu(Menu menu) {
        // If the nav drawer is open, hide action items related to the content view
        boolean drawerOpen = mDrawerLayout.isDrawerOpen(mDrawerList);
        menu.findItem(R.id.action_websearch).setVisible(!drawerOpen);
        return super.onPrepareOptionsMenu(menu);
    }

Esta es la salida de logcat

Process: com.motobeans.productions.aloha, PID: 1330
    java.lang.RuntimeException: Unable to start activity ComponentInfo{com.motobeans.productions.aloha/com.motobeans.productions.aloha.Activity_test}: java.lang.NullPointerException: Attempt to invoke virtual method ''void android.support.v4.widget.DrawerLayout.setDrawerListener(android.support.v4.widget.DrawerLayout$DrawerListener)'' on a null object reference
            at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2325)
            at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2387)
            at android.app.ActivityThread.access$800(ActivityThread.java:151)
            at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1303)
            at android.os.Handler.dispatchMessage(Handler.java:102)
            at android.os.Looper.loop(Looper.java:135)
            at android.app.ActivityThread.main(ActivityThread.java:5254)
            at java.lang.reflect.Method.invoke(Native Method)
            at java.lang.reflect.Method.invoke(Method.java:372)
            at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:903)
            at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:698)
     Caused by: java.lang.NullPointerException: Attempt to invoke virtual method ''void android.support.v4.widget.DrawerLayout.setDrawerListener(android.support.v4.widget.DrawerLayout$DrawerListener)'' on a null object reference
            at com.motobeans.productions.aloha.Activity_test.onCreate(Activity_test.java:74)
            at android.app.Activity.performCreate(Activity.java:5990)
            at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1106)
            at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2278)
            at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2387)
            at android.app.ActivityThread.access$800(ActivityThread.java:151)
            at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1303)
            at android.os.Handler.dispatchMessage(Handler.java:102)
            at android.os.Looper.loop(Looper.java:135)
            at android.app.ActivityThread.main(ActivityThread.java:5254)
            at java.lang.reflect.Method.invoke(Native Method)
            at java.lang.reflect.Method.invoke(Method.java:372)
            at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:903)
            at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:698)

Answer 1

Parece que mDrawerLayout es nulo cuando se llama a .setDrawerListener() .

Asegúrese de estar utilizando la misma identificación para el cajón de navegación en findViewById(R.id.drawer_layout) y en el archivo de diseño.

Answer 2

Se informó un problema similar en google en https://code.google.com/p/android/issues/detail?id=202478

DrawerLayout.removeDrawerListener () se invoca sin un conjunto DrawerLayout.DrawerListener

Pero después del lanzamiento de Android Support Library, revisión 23.2.1 (marzo de 2016) Este problema ha sido resuelto.

actualice Support Library to Android Support Library to 23.2.1 o a una versión más actualizada.

Answer 3

use getSupportActionBar() lugar de getActionBar()