我想从我的自定义适配器类刷新 ListFragment 中的数据，但收到错误 NullPointerException。
这是 Adaper 类方法：
b1.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
BasketFragment basketFragment = new BasketFragment();
basketFragment.getBsketList();
}
});
当我在 Fragment 类中调用它时，我得到 java.lang.NullPointerExceptionmDataBase = dbHelper.getWritableDatabase();
获取篮子列表（）：
public void refreshList() {
dbAdaper.setArrayMyData(selectAll());
dbAdaper.notifyDataSetChanged();
}
这是我得到错误的部分：
public ArrayList<BasketData> selectAll() {
Cursor mCursor = null;
dbHelper = new DBHelper(getActivity());
mDataBase = dbHelper.getWritableDatabase();//NullPointerException
mCursor = mDataBase.query("orderTable", null, null, null, null, null, null);
日志猫：
java.lang.NullPointerException
at android.database.sqlite.SQLiteOpenHelper.getDatabaseLocked(SQLiteOpenHelper.java:224)
at android.database.sqlite.SQLiteOpenHelper.getWritableDatabase(SQLiteOpenHelper.java:164)
at com.epon.fragments.BasketFragment.selectAll(BasketFragment.java:100)
at com.epon.fragments.BasketFragment.getBsketList(BasketFragment.java:142)
at com.epon.adapters.DBBasketAdapter$2.onClick(DBBasketAdapter.java:177)
at android.view.View.performClick(View.java:4240)
at android.view.View$PerformClick.run(View.java:17721)
at android.os.Handler.handleCallback(Handler.java:730)
at android.os.Handler.dispatchMessage(Handler.java:92)
at android.os.Looper.loop(Looper.java:137)
at android.app.ActivityThread.main(ActivityThread.java:5103)
at java.lang.reflect.Method.invokeNative(Native Method)
at java.lang.reflect.Method.invoke(Method.java:525)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:737)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:553)
at dalvik.system.NativeStart.main(Native Method)