Wie beheben Sie NullPointerException in v4.DrawerLayout?

Ich versuche, eine Navigationsschublade zu implementieren, aber aus bestimmten Gründen bekomme ich diese Nullzeiger Ausnahme.Wie beheben Sie NullPointerException in v4.DrawerLayout?

Ich habe viel Zeit darauf verbracht, aber vergeblich. Dies ist ein Teil meines Codes. Ich kann nicht verstehen, warum es Nullzeigerausnahme zurückgibt.

Muss ich irgendeine Bibliothek importieren?

Vielen Dank im Voraus.

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); 
    }

Dies ist der logcat Ausgang

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)

Quelle

2015-07-19 varunkr