Java 在Android的onCreate（）中从SQLite数据库填充ListView

我创建了活动“A”和“B”。我在活动“A”中插入了一些数据，我想在活动“A”中单击按钮时显示活动“B”中listview中的所有数据。但是，当我运行应用程序时，它会崩溃并出现错误和nullpointerException。请帮助我。提前感谢

这是我的数据库方法代码

public Cursor employeeName(){
            ArrayList<Employee> EmployeeNameList = new ArrayList<Employee>();
            String selectQuery = "SELECT * FROM " + EMPLOYEE_DETAILS_TABLE;
            SQLiteDatabase db = this.getWritableDatabase();
            Cursor cursor = db.rawQuery(selectQuery, null);
            if(cursor.moveToFirst())
            {
                do{

                    Employee empName = new Employee();
                    empName.setName(cursor.getString(1));
                    empName.setDepartment(cursor.getString(2));
                    empName.setDesignation(cursor.getString(3));


                    EmployeeNameList.add(empName);
                } while(cursor.moveToNext());
            }
            return cursor;
        }




        public List<String> getAllEmployeeName() {
            List<String> labels = new ArrayList<String>();

               // Select All Query
               String selectQuery = "SELECT  * FROM " + EMPLOYEE_DETAILS_TABLE;

               SQLiteDatabase db = this.getReadableDatabase();
               Cursor cursor = db.rawQuery(selectQuery, null);
               if (cursor.moveToFirst()) {
                   do {
                    labels.add(cursor.getString(1));
                   } while (cursor.moveToNext());
               }

              cursor.close();
               db.close();
            return labels;


        }

这是我的日志

06-27 15:25:51.498: E/AndroidRuntime(12033): FATAL EXCEPTION: main
06-27 15:25:51.498: E/AndroidRuntime(12033): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.employee_review/com.employee_review.Employee_List}: java.lang.NullPointerException
06-27 15:25:51.498: E/AndroidRuntime(12033):    at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1647)
06-27 15:25:51.498: E/AndroidRuntime(12033):    at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:1663)
06-27 15:25:51.498: E/AndroidRuntime(12033):    at android.app.ActivityThread.access$1500(ActivityThread.java:117)
06-27 15:25:51.498: E/AndroidRuntime(12033):    at android.app.ActivityThread$H.handleMessage(ActivityThread.java:931)
06-27 15:25:51.498: E/AndroidRuntime(12033):    at android.os.Handler.dispatchMessage(Handler.java:99)
06-27 15:25:51.498: E/AndroidRuntime(12033):    at android.os.Looper.loop(Looper.java:123)
06-27 15:25:51.498: E/AndroidRuntime(12033):    at android.app.ActivityThread.main(ActivityThread.java:3683)
06-27 15:25:51.498: E/AndroidRuntime(12033):    at java.lang.reflect.Method.invokeNative(Native Method)
06-27 15:25:51.498: E/AndroidRuntime(12033):    at java.lang.reflect.Method.invoke(Method.java:507)
06-27 15:25:51.498: E/AndroidRuntime(12033):    at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:839)
06-27 15:25:51.498: E/AndroidRuntime(12033):    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:597)
06-27 15:25:51.498: E/AndroidRuntime(12033):    at dalvik.system.NativeStart.main(Native Method)
06-27 15:25:51.498: E/AndroidRuntime(12033): Caused by: java.lang.NullPointerException
06-27 15:25:51.498: E/AndroidRuntime(12033):    at android.database.sqlite.SQLiteOpenHelper.getWritableDatabase(SQLiteOpenHelper.java:118)
06-27 15:25:51.498: E/AndroidRuntime(12033):    at com.employee_review.DatabaseHelper.employeeName(DatabaseHelper.java:129)
06-27 15:25:51.498: E/AndroidRuntime(12033):    at com.employee_review.Employee_List.populateListView(Employee_List.java:35)
06-27 15:25:51.498: E/AndroidRuntime(12033):    at com.employee_review.Employee_List.onCreate(Employee_List.java:28)
06-27 15:25:51.498: E/AndroidRuntime(12033):    at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1047)
06-27 15:25:51.498: E/AndroidRuntime(12033):    at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1611)
06-27 15:25:51.498: E/AndroidRuntime(12033):    ... 11 more

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此处传递给数据库帮助器构造函数的

上下文

未初始化：

DatabaseHelper databaseHelper = new DatabaseHelper(context);

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将

上下文

替换为例如

此

请发布堆栈跟踪并标记错误发生的行@OpiatefuchsCursor=（cursor）databaseHelper.employeeName（）；为什么不从sqlite显示我的listview呢？请帮助我。

DatabaseHelper databaseHelper = new DatabaseHelper(context);