我试图在共享首选项中保存一个整数值,并在重新启动应用程序时再次加载它.

我在主要活动中创建了一个共享首选项,并尝试在菜单项单击的另一个Menu Listener类中保存整数值. Menu侦听器类位于不同的包中,Menu Listener类扩展了Main Activity.

但是当我尝试这样做时,我得到一个Null指针异常.

我也经历了这个link！但它似乎没有帮助我.

这是我的代码：

主要活动：

    protected SharedPreferences mPrefs;
protected SharedPreferences.Editor mEditor;
protected Context  main_activityclass_context; //EDIT
public static int count=0;

@Override
protected void onCreate(final Bundle savedInstanceState) {

    super.onCreate(savedInstanceState);


     mPrefs = this.getSharedPreferences("THEME", 0);
     mEditor = mPrefs.edit();
    }

菜单监听器类：

    case  mainActivity.MENU_ITEM_THEME_DARK:
    {

        mainActivity.count=1;

        mPrefs =main_activityclass_context.getSharedPreferences("THEME", 0); //EDIT
        mEditor = mPrefs.edit();
        mEditor.putInt("Theme_count", mainActivity.count).commit();


    break;
    }

我在菜单监听器的行上得到一个Null指针异常：

       mPrefs = getSharedPreferences("THEME", 0);
        mEditor = mPrefs.edit();    

我的Logcat：

      08-03 10:54:03.650: E/AndroidRuntime(31258): FATAL EXCEPTION: main
      08-03 10:54:03.650: E/AndroidRuntime(31258): java.lang.NullPointerException
      08-03 10:54:03.650: E/AndroidRuntime(31258):  at               android.content.ContextWrapper.getSharedPreferences(ContextWrapper.java:153)
      08-03 10:54:03.650: E/AndroidRuntime(31258):  at de.exb.ptpt.tablet.menu.TabletMenuListener.onMenuItemClick(TabletMenuListener.java:215)
      08-03 10:54:03.650: E/AndroidRuntime(31258):  at com.android.internal.view.menu.MenuItemImpl.invoke(MenuItemImpl.java:144)
       08-03 10:54:03.650: E/AndroidRuntime(31258):     at com.android.internal.view.menu.MenuBuilder.performItemAction(MenuBuilder.java:874)
       08-03 10:54:03.650: E/AndroidRuntime(31258):     at com.android.internal.view.menu.MenuPopupHelper.onItemClick(MenuPopupHelper.java:156)
       08-03 10:54:03.650: E/AndroidRuntime(31258):     at android.widget.AdapterView.performItemClick(AdapterView.java:292)
       08-03 10:54:03.650: E/AndroidRuntime(31258):     at android.widget.AbsListView.performItemClick(AbsListView.java:1058)
      08-03 10:54:03.650: E/AndroidRuntime(31258):  at android.widget.AbsListView$PerformClick.run(AbsListView.java:2514)
      08-03 10:54:03.650: E/AndroidRuntime(31258):  at android.widget.AbsListView$1.run(AbsListView.java:3168)
      08-03 10:54:03.650: E/AndroidRuntime(31258):  at android.os.Handler.handleCallback(Handler.java:605)
      08-03 10:54:03.650: E/AndroidRuntime(31258):  at android.os.Handler.dispatchMessage(Handler.java:92)
      08-03 10:54:03.650: E/AndroidRuntime(31258):  at android.os.Looper.loop(Looper.java:137)
      08-03 10:54:03.650: E/AndroidRuntime(31258):  at android.app.ActivityThread.main(ActivityThread.java:4424)
      08-03 10:54:03.650: E/AndroidRuntime(31258):  at java.lang.reflect.Method.invokeNative(Native Method)
      08-03 10:54:03.650: E/AndroidRuntime(31258):  at java.lang.reflect.Method.invoke(Method.java:511)
      08-03 10:54:03.650: E/AndroidRuntime(31258):  at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:784)
      08-03 10:54:03.650: E/AndroidRuntime(31258):  at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:551)
      08-03 10:54:03.650: E/AndroidRuntime(31258):  at dalvik.system.NativeStart.main(Native Method)

谁能帮帮我吗？

谢谢.

解决方法:

其中一个好方法是,创建一个帮助类来声明,保存和检索首选项.您可以参考以下代码示例：

public class PreferencesHelper {

private SharedPreferences sharedPreferences;
private Editor editor;

public PreferencesHelper(Context context) {
this.sharedPreferences = getPreferences(MODE_PRIVATE);    
this.editor = sharedPreferences.edit(); }

public String GetPreferences(String key) {
    return sharedPreferences.getString(key, "");
}

public void SavePreferences(String key, String value) {
editor.putString(key, value);    
editor.commit();  
}
}  

在活动的onCreate事件中,您可以创建PreferencesHelper的对象并获取所有已保存的首选项,如：

Prefs = new PreferencesHelper(getApplicationContext());  

Prefs.GetPreferences("YOURARGUMENT");  

并且您可以保存以下偏好：

Prefs.SavePreferences(key, value);  

希望这会帮助你.