public static final String PREFS_NAME = "MyPrefsFile";
private SharedPreferences settings;
settings = getSharedPreferences(PREFS_NAME, 0);
越來越sharedPreferences時,當我在擴展應用程序,我得到第3行一個空指針,而當我做同樣的活動工作一類使用此代碼。爲什麼是這樣?空指針在應用類
我正在嘗試創建一個單例類來保存幾個變量。只有10個變量不足以使用sqllite左右。
編輯: 在我的第一個電話,我得到一個數據類的單一實例:
boolean active = DataClass.getInstance().getBoolean("active");
完整的數據類:
import android.app.Application;
import android.content.SharedPreferences;
import android.util.Log;
public class DataClass extends Application {
public static final String PREFS_NAME = "MyPrefsFile";
private static DataClass instance = null;
public static DataClass getInstance() {
if(instance == null) {
instance = new DataClass();
}
return instance;
}
private SharedPreferences settings;
public DataClass() {
settings = getSharedPreferences(PREFS_NAME, MODE_PRIVATE); //nullpointer here
Log.e("temp", "DataClass constructor executed");
}
public void setBoolean(boolean trueorfalse, String id) {
SharedPreferences.Editor editor = settings.edit();
editor.putBoolean(id, trueorfalse);
editor.commit();
}
public boolean getBoolean(String id) {
return settings.getBoolean(id, false);
}
}
編輯:添加堆棧跟蹤:
04-15 09:28:25.064: ERROR/AndroidRuntime(16943): FATAL EXCEPTION: main
04-15 09:28:25.064: ERROR/AndroidRuntime(16943): java.lang.RuntimeException: Unable to start activity ComponentInfo{be.test.helloworld/be.test.helloworld.activities.MainActivity}: java.lang.NullPointerException
04-15 09:28:25.064: ERROR/AndroidRuntime(16943): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2781)
04-15 09:28:25.064: ERROR/AndroidRuntime(16943): at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2797)
04-15 09:28:25.064: ERROR/AndroidRuntime(16943): at android.app.ActivityThread.access$2300(ActivityThread.java:135)
04-15 09:28:25.064: ERROR/AndroidRuntime(16943): at android.app.ActivityThread$H.handleMessage(ActivityThread.java:2132)
04-15 09:28:25.064: ERROR/AndroidRuntime(16943): at android.os.Handler.dispatchMessage(Handler.java:99)
04-15 09:28:25.064: ERROR/AndroidRuntime(16943): at android.os.Looper.loop(Looper.java:143)
04-15 09:28:25.064: ERROR/AndroidRuntime(16943): at android.app.ActivityThread.main(ActivityThread.java:4914)
04-15 09:28:25.064: ERROR/AndroidRuntime(16943): at java.lang.reflect.Method.invokeNative(Native Method)
04-15 09:28:25.064: ERROR/AndroidRuntime(16943): at java.lang.reflect.Method.invoke(Method.java:521)
04-15 09:28:25.064: ERROR/AndroidRuntime(16943): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:858)
04-15 09:28:25.064: ERROR/AndroidRuntime(16943): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:616)
04-15 09:28:25.064: ERROR/AndroidRuntime(16943): at dalvik.system.NativeStart.main(Native Method)
04-15 09:28:25.064: ERROR/AndroidRuntime(16943): Caused by: java.lang.NullPointerException
04-15 09:28:25.064: ERROR/AndroidRuntime(16943): at android.content.ContextWrapper.getSharedPreferences(ContextWrapper.java:146)
04-15 09:28:25.064: ERROR/AndroidRuntime(16943): at be.test.helloworld.data.DataClass.<init>(DataClass.java:23)
04-15 09:28:25.064: ERROR/AndroidRuntime(16943): at be.test.helloworld.data.DataClass.getInstance(DataClass.java:14)
04-15 09:28:25.064: ERROR/AndroidRuntime(16943): at be.test.helloworld.activities.MainActivity.onCreate(MainActivity.java:29)
04-15 09:28:25.064: ERROR/AndroidRuntime(16943): at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1065)
04-15 09:28:25.064: ERROR/AndroidRuntime(16943): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2745)
04-15 09:28:25.064: ERROR/AndroidRuntime(16943): ... 11 more
我已將密碼更改爲: \t public void onCreate(){ \t \t super.onCreate(); \t \t settings = getSharedPreferences(PREFS_NAME,MODE_PRIVATE); (「temp」,「DataClass構造函數執行」); \t \t \t } \t/*公共數據類()\t { \t \t設置= getSharedPreferences(PREFS_NAME,MODE_PRIVATE);// nullpointer here \t \t Log.e(「temp」,「DataClass constructor executed」); \t} */ 但getSharedPreferences方法和日誌不會執行 – Vincent 2011-04-15 07:47:03
在'onCreate()'簽名上放置'@ Override'來查看Eclipse是否支付垃圾郵件。調試以查看它是否被調用。 – rajath 2011-04-15 07:50:35
當我在beginpost中使用常規構造函數時,會調用它,但在獲取共享首選項時會給出空指針。當我使用帶有覆蓋符號的oncreate時,它不會被調用.. – Vincent 2011-04-15 07:58:55