SharedPreferences Android中的空指针异常

时间：2012-08-10 09:08:47

标签： android nullpointerexception sharedpreferences

这是我的SharedPreference类：

public class MySharedPrefs {
private static final String APP_SHARED_PREFS = "com.astroved.Horawatch";
private SharedPreferences appSharedPrefs;
private Editor prefsEditor;

public MySharedPrefs(Context context)
{
    this.appSharedPrefs = context.getSharedPreferences(APP_SHARED_PREFS, Activity.MODE_PRIVATE);
    this.prefsEditor = appSharedPrefs.edit();
}

public String getPrefsValue(String value) {
    return appSharedPrefs.getString(value, "");
}

public void savePrefsValue(String key , String Value) {
    prefsEditor.putString(key, Value);
    prefsEditor.commit();
}

public Boolean checkKey(String Key)
{
    if(appSharedPrefs.contains(Key))
        return true;    
    else
        return false;
}

}

MyFunctionClass：

public class Functions_class extends Activity{


AstroVedTime tz,lat,lon;
TimeZone tz1;
protected MySharedPrefs appPrefs;

public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);{
        appPrefs = new MySharedPrefs(Functions_class.this);
    }
    }

public void user_informations(int myear,int mMonth, int mDay){

    int year = myear,month = mMonth+1,day = mDay;
    Moment mn = new Moment(year,month,day,user_device_time());
    //appPrefs = new MySharedPrefs(Functions_class.this);

    if(appPrefs.checkKey("City_name1")){
        TimeZone.setDefault(TimeZone.getTimeZone(appPrefs.getPrefsValue("selected_time_zone")));
        Log.v("LOG_TAG"+"here the error is : ", appPrefs.getPrefsValue("selected_lat")+"");
        Log.v("LOG_TAG", appPrefs.getPrefsValue("selected_longi")+"");
        tz1 = TimeZone.getDefault();
        lat = new AstroVedTime(Double.parseDouble(appPrefs.getPrefsValue("selected_lat")));// Latitude
        lon = new AstroVedTime(Double.parseDouble(appPrefs.getPrefsValue("selected_longi")));// Longitude
    }

这是我的logcat：

 08-10 14:07:14.947: E/AndroidRuntime(475): FATAL EXCEPTION: Thread-13
08-10 14:07:14.947: E/AndroidRuntime(475): java.lang.NullPointerException
08-10 14:07:14.947: E/AndroidRuntime(475):  at com.astroved.horawatch.Functions_class.user_informations(Functions_class.java:46)
08-10 14:07:14.947: E/AndroidRuntime(475):  at com.astroved.horawatch.HoraWatchActivity$13$1.run(HoraWatchActivity.java:1106)
08-10 14:07:16.628: E/WindowManager(475): Activity com.astroved.horawatch.HoraWatchActivity has leaked window com.android.internal.policy.impl.PhoneWindow$DecorView@407f1950 that was originally added here
08-10 14:07:16.628: E/WindowManager(475): android.view.WindowLeaked: Activity com.astroved.horawatch.HoraWatchActivity has leaked window com.android.internal.policy.impl.PhoneWindow$DecorView@407f1950 that was originally added here
08-10 14:07:16.628: E/WindowManager(475):   at android.view.ViewRoot.<init>(ViewRoot.java:258)
08-10 14:07:16.628: E/WindowManager(475):   at android.view.WindowManagerImpl.addView(WindowManagerImpl.java:148)
08-10 14:07:16.628: E/WindowManager(475):   at android.view.WindowManagerImpl.addView(WindowManagerImpl.java:91)
08-10 14:07:16.628: E/WindowManager(475):   at android.view.Window$LocalWindowManager.addView(Window.java:424)
08-10 14:07:16.628: E/WindowManager(475):   at android.app.Dialog.show(Dialog.java:241)
08-10 14:07:16.628: E/WindowManager(475):   at com.astroved.horawatch.HoraWatchActivity$13.onClick(HoraWatchActivity.java:1103)
08-10 14:07:16.628: E/WindowManager(475):   at android.view.View.performClick(View.java:2485)
08-10 14:07:16.628: E/WindowManager(475):   at android.view.View$PerformClick.run(View.java:9080)
08-10 14:07:16.628: E/WindowManager(475):   at android.os.Handler.handleCallback(Handler.java:587)
08-10 14:07:16.628: E/WindowManager(475):   at android.os.Handler.dispatchMessage(Handler.java:92)
08-10 14:07:16.628: E/WindowManager(475):   at android.os.Looper.loop(Looper.java:123)
08-10 14:07:16.628: E/WindowManager(475):   at android.app.ActivityThread.main(ActivityThread.java:3683)
08-10 14:07:16.628: E/WindowManager(475):   at java.lang.reflect.Method.invokeNative(Native Method)
08-10 14:07:16.628: E/WindowManager(475):   at java.lang.reflect.Method.invoke(Method.java:507)
08-10 14:07:16.628: E/WindowManager(475):   at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:839)
08-10 14:07:16.628: E/WindowManager(475):   at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:597)
08-10 14:07:16.628: E/WindowManager(475):   at dalvik.system.NativeStart.main(Native Method)

我收到了上述错误。我在调用SharedPreference值时犯了一些错误。我无法理解。以前我收到此错误

at android.content.contextwrapper.getsharedpreferences contextwrapper.java 146

我通过调用SharedPreferences中的OnCreate清除了上述错误。如何清除上面显示的Logcat错误。我错在哪里？

我在另一个活动的onclick期间调用MyFunctionClass中的方法。如下所示

HoraWatchActivity：

public Functions_class func_cls = new Functions_class();
 private OnClickListener show_panchang_page = new OnClickListener(){

    public void onClick(View v) { 

        pbarDialog = new ProgressDialog( HoraWatchActivity.this );
        pbarDialog.setProgressStyle(ProgressDialog.STYLE_SPINNER);
        pbarDialog.setMessage("Loading Panchang...");
        pbarDialog.show();
               Thread t = new Thread(){
                   public void run(){
                       func_cls.user_informations(mYear, mMonth, mDay); 
                       Message myMessage=new Message();
                       Bundle resBundle = new Bundle();
                       resBundle.putString("status", "SUCCESS"); 
                       myMessage.obj=resBundle;
                       handler.sendMessage(myMessage);
                   }
               };
              t.start();
    }
};

更快的回复将帮助我很多。谢谢。

3 个答案:

答案 0 :(得分：2)

好的发现了问题。问题在于appPrefs user_informations中的此变量Function class。那时它是空的。

你正在做的是，你已经在onCreate（）中启动了appPrefs，但当你做这样的事情时，public Functions_class func_cls = new Functions_class();你的onCreate没有被调用，这意味着它直接进入方法并向你返回null 。您必须对现有代码进行一些修改。

试试这个，

1）首先将您的当前活动上下文传递给您的方法，

2）在方法appPrefs = new MySharedPrefs(context);

中取消注释此行 
public void user_informations(int myear,int mMonth, int mDay,Context context){

    int year = myear,month = mMonth+1,day = mDay;
    Moment mn = new Moment(year,month,day,user_device_time());
    appPrefs = new MySharedPrefs(context);

    if(appPrefs.checkKey("City_name1")){
        TimeZone.setDefault(TimeZone.getTimeZone(appPrefs.getPrefsValue("selected_time_zone")));
        Log.v("LOG_TAG"+"here the error is : ", appPrefs.getPrefsValue("selected_lat")+"");
        Log.v("LOG_TAG", appPrefs.getPrefsValue("selected_longi")+"");
        tz1 = TimeZone.getDefault();
        lat = new AstroVedTime(Double.parseDouble(appPrefs.getPrefsValue("selected_lat")));// Latitude
        lon = new AstroVedTime(Double.parseDouble(appPrefs.getPrefsValue("selected_longi")));// Longitude
    }

答案 1 :(得分：1)

您手动实例化活动类Functions_class。如果您开始活动，框架将处理此问题。即使不将functions_class用作活动，也必须手动调用functions_class的oncreate。这就是初始化appPrefs的地方。 user_informations函数中的appPrefs为null。初始化它。

答案 2 :(得分：1)

我认为你的方法是错误的，因为你正在调用一个Activity（iefunc_cls.user_informations（mYear，mMonth，mDay）;）的方法，这个方法不是来自可见的Activity（HoraWatchActivity.this）..并且该函数除了从共享偏好中获取价值之外什么都不做数据检索应在NonActivity类中完成.appPrefs为null未初始化。

相关问题
最新问题