Exception de pointeur nul utilisant l'intention

Question

Je reçois une exception de pointeur null essayant de démarrer une nouvelle activité lorsque l'utilisateur choisit un environnement local différent. Il semble se produire dans la ligne d'intention comme marqué. (! Je suis un noob si des explications simples s'il vous plaît) Merci

public void changeLocale(String locale){ 
    try{ 
    String l=locale; 
    if(l.equals("uk")){ 
     this.isUk=true; 
     Log.i(Log_tag,"isUk is true"); 
     //Toast.makeText(this, "UK region selected in Prefs", Toast.LENGTH_SHORT).show(); 
     Intent intent = new Intent(Prefs.this, UK.class);//<---ERROR IS OCCURING HERE 
     startActivity(intent); 
    }else if(l.equals("eu")){ 
     this.isEu=true; 
     Toast.makeText(this, "EU region selected", Toast.LENGTH_SHORT).show(); 
     Intent intent = new Intent(Prefs.this, EU.class); 
     startActivity(intent); 
    }else if(l.equals("us")){ 
     this.isUs=true; 
     Toast.makeText(this, "Us region selected", Toast.LENGTH_SHORT).show(); 
     Intent intent = new Intent(Prefs.this, US.class); 
     startActivity(intent); 
    }else if (l.equals("")){ 
     Log.i(Log_tag,"no locale passed in"); 
     finish(); 
    } 
    }catch (NullPointerException e){ 
     Log.i(Log_tag, "Null Pointer Error in changeLocale()"+e); 
     finish(); 
    } 
} 

Mon logcat dit ceci:

05-25 11:55:57.851: WARN/KeyCharacterMap(898): No keyboard for id 0 
05-25 11:55:57.861: WARN/KeyCharacterMap(898): Using default keymap: /system/usr/keychars/qwerty.kcm.bin 

05-25 11:56:01.522: INFO/(898): UK selected in UsFM 
05-25 11:56:01.543: INFO/(898): editRegion() started 
05-25 11:56:01.642: INFO/(898): isUk is true 
05-25 11:56:01.642: INFO/(898): Null Pointer Error in changeLocale()java.lang.NullPointerException 

05-25 11:56:01.953: INFO/NotificationService(69): enqueueToast pkg=com.silifeform.android callback=android.app.ITransientNotification$Stub$Proxy@4380ba08 duration=0 
05-25 11:56:01.995: INFO/ActivityManager(69): Starting activity: Intent { cmp=com.silifeform.android/.Us } 

05-25 11:56:02.182: WARN/InputManagerService(69): Starting input on non-focused client com.android.internal.view.IInputMethodClient$Stub$Proxy@438d8b88 (uid=10024 pid=898) 

La classe entière ressemble à ceci:

package com.silifeform.android; 
import android.app.Activity; 
import android.content.Context; 
import android.content.Intent; 
import android.content.SharedPreferences; 
import android.os.Bundle; 
import android.util.Log; 
import android.widget.Toast; 

public class Prefs extends Activity { 
    public static final String PREFS_NAME="LocalePrefs"; 
    private String region; 
    public boolean isUk; 
    public boolean isUs; 
    public boolean isEu; 
    private String Log_tag; 

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

     //restore prefs 
     SharedPreferences settings= getSharedPreferences(PREFS_NAME,0); 
     String myRegion = settings.getString(region,"us"); 

     this.region=myRegion; 
     changeLocale(getRegion(this)); 
    } 


    @Override 
    protected void onResume() { 
     super.onResume(); 
     changeLocale(getRegion(this)); 
    } 

    public void editRegion(Context cxt, String sregion) { 
     setRegion(sregion); 
     Log.i(Log_tag,"editRegion() started"); 
     SharedPreferences settings = cxt.getSharedPreferences(PREFS_NAME,0); 
     SharedPreferences.Editor ed = settings.edit(); 
     ed.clear(); 
     ed.putString(this.region,sregion); 
     ed.commit(); 
     changeLocale(sregion); 
    } 

    public String getRegion(Context cxt){ 
      SharedPreferences settings= cxt.getSharedPreferences(PREFS_NAME,0); 
      String myRegion = settings.getString(this.region,"us"); 
      return myRegion; 
     } 

    public void setRegion(String region) { 
     this.region = region; 
    } 


    public void changeLocale(String locale){ 
     try{ 
     String l=locale; 
     if(l.equals("uk")){ 
      this.isUk=true; 
      Log.i(Log_tag,"isUk is true"); 
      Log.i(Log_tag,l); 
      //Toast.makeText(this, "UK region selected in Prefs", Toast.LENGTH_SHORT).show(); 
      Intent intent = new Intent(Prefs.this, UkFuelMoney.class); 
      startActivity(intent); 
     }else if(l.equals("eu")){ 
      this.isEu=true; 
      Toast.makeText(this, "EU region selected", Toast.LENGTH_SHORT).show(); 
      Intent intent = new Intent(Prefs.this, EuFuelMoney.class); 
      startActivity(intent); 
     }else if(l.equals("us")){ 
      this.isUs=true; 
      Toast.makeText(this, "Us region D selected", Toast.LENGTH_SHORT).show(); 
      Intent intent = new Intent(Prefs.this, UsFuelMoney.class); 
      startActivity(intent); 
     }else if (l.equals("")){ 
      Log.i(Log_tag,"no locale passed in"); 
      finish(); 
     } 
     }catch (NullPointerException e){ 
      Log.i(Log_tag, "Null Pointer Error in changeLocale()"+e); 
      finish(); 
     } 
    } 

    @Override 
    protected void onStop() { 
     super.onStop(); 
     SharedPreferences settings = getPreferences(0); 
     SharedPreferences.Editor ed = settings.edit(); 
     ed.putString(region,region); 
     ed.commit(); 

    } 
} 

Merci Keno. La trace de la pile ressemble à ceci:

05-25 12:10:44.162: WARN/System.err(961): java.lang.NullPointerException 
05-25 12:10:44.172: WARN/System.err(961):  at android.content.ContextWrapper.getPackageName(ContextWrapper.java:120) 
05-25 12:10:44.182: WARN/System.err(961):  at android.content.ComponentName.<init>(ComponentName.java:75) 
05-25 12:10:44.182: WARN/System.err(961):  at android.content.Intent.<init>(Intent.java:2302) 
05-25 12:10:44.182: WARN/System.err(961):  at com.silifeform.android.Prefs.changeLocale(Prefs.java:68) 
05-25 12:10:44.192: WARN/System.err(961):  at com.silifeform.android.Prefs.editRegion(Prefs.java:46) 
05-25 12:10:44.192: WARN/System.err(961):  at com.silifeform.android.Us.onOptionsItemSelected(Us.java:347) 
05-25 12:10:44.192: WARN/System.err(961):  at android.app.Activity.onMenuItemSelected(Activity.java:2096) 
05-25 12:10:44.202: WARN/System.err(961):  at com.android.internal.policy.impl.PhoneWindow.onMenuItemSelected(PhoneWindow.java:825) 
05-25 12:10:44.202: WARN/System.err(961):  at com.android.internal.view.menu.MenuItemImpl.invoke(MenuItemImpl.java:139) 
05-25 12:10:44.202: WARN/System.err(961):  at com.android.internal.view.menu.MenuBuilder.performItemAction(MenuBuilder.java:813) 
05-25 12:10:44.202: WARN/System.err(961):  at com.android.internal.view.menu.MenuDialogHelper.onClick(MenuDialogHelper.java:120) 
05-25 12:10:44.212: WARN/System.err(961):  at com.android.internal.app.AlertController$AlertParams$3.onItemClick(AlertController.java:884) 
05-25 12:10:44.212: WARN/System.err(961):  at android.widget.AdapterView.performItemClick(AdapterView.java:284) 
05-25 12:10:44.212: WARN/System.err(961):  at android.widget.ListView.performItemClick(ListView.java:3246) 
05-25 12:10:44.222: WARN/System.err(961):  at android.widget.AbsListView$PerformClick.run(AbsListView.java:1635) 
05-25 12:10:44.222: WARN/System.err(961):  at android.os.Handler.handleCallback(Handler.java:587) 
05-25 12:10:44.222: WARN/System.err(961):  at android.os.Handler.dispatchMessage(Handler.java:92) 
05-25 12:10:44.232: WARN/System.err(961):  at android.os.Looper.loop(Looper.java:123) 
05-25 12:10:44.232: WARN/System.err(961):  at android.app.ActivityThread.main(ActivityThread.java:4203) 
05-25 12:10:44.242: WARN/System.err(961):  at java.lang.reflect.Method.invokeNative(Native Method) 
05-25 12:10:44.242: WARN/System.err(961):  at java.lang.reflect.Method.invoke(Method.java:521) 
05-25 12:10:44.242: WARN/System.err(961):  at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:791) 
05-25 12:10:44.252: WARN/System.err(961):  at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:549) 
05-25 12:10:44.252: WARN/System.err(961):  at dalvik.system.NativeStart.main(Native Method) 
05-25 12:10:44.252: INFO/(961): Null Pointer Error in changeLocale()java.lang.NullPointerException 

Answer 1

Votre Prefs activité n'est pas peuplée que vous avez probablement instancié vous-même dans com.silifeform.android.Us.onOptionsItemSelected() (je suppose que la mise en œuvre est encore semblable à celui que vous avez posté here). Comme je l'ai déjà souligné en réponse à la question référée, si la classe Prefs n'est pas instanciée (et gérée) par Android, vous ne pouvez pas supposer qu'elle fonctionne correctement (en particulier toutes les méthodes de Context) car elle n'est pas correctement lancée. Encore une fois la même stratégie s'applique, utilisez un objet Context séparé que vous passez à changeLocale pour résoudre ce problème.