关于android：自定义ArrayAdapter的getView中的Nullpointerexception

Nullpointerexception in getView of custom ArrayAdapter

我的应用程序中的自定义ArrayAdapter中出现了Nullpointerexception。我不知道为什么在这里提出Nullpointer。我无法重现这个例外。异常没有出现很长时间，我没有代码更改，所以这使它更奇怪。
代码是：

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private class MyAdapter< T > extends ArrayAdapter<String> {

private Map<String, String> selectedDevices;

public MyAdapter(Context context, int textViewResourceId) {
super(context, textViewResourceId);
BluetoothDbAdapter dbHelper = new BluetoothDbAdapter(context);
dbHelper.open();
selectedDevices = dbHelper.fetchAllDevicesAsMap();
dbHelper.close();
}

@Override
public View getView(int position, View convertView, ViewGroup parent) {
View view = super.getView(position, convertView, parent);
CheckedTextView item = (CheckedTextView) view;
CharSequence text = item.getText();
if (selectedDevices.values().contains(text)) {
item.setChecked(true);
}
return item;
}

}

在第一行的getView方法中引发了异常。我调试了我的应用程序并使用null参数调用了super.getView，但没有引发Nullpointerexception，所以它看起来super已经为null，但是怎么会这样？ StackTrace是：

java.lang.NullPointerException
at android.widget.ArrayAdapter.createViewFromResource(ArrayAdapter.java:355)
at android.widget.ArrayAdapter.getView(ArrayAdapter.java:323)
at de.hartig.abt.activity.BluetoothDeviceList$MyAdapter.getView(BluetoothDeviceList.java:140)
at android.widget.AbsListView.obtainView(AbsListView.java:1408)
at android.widget.ListView.makeAndAddView(ListView.java:1727)
at android.widget.ListView.fillDown(ListView.java:652)
at android.widget.ListView.fillFromTop(ListView.java:709)
at android.widget.ListView.layoutChildren(ListView.java:1580)
at android.widget.AbsListView.onLayout(AbsListView.java:1240)
at android.view.View.layout(View.java:7057)
at android.widget.FrameLayout.onLayout(FrameLayout.java:333)
at android.view.View.layout(View.java:7057)
at android.widget.LinearLayout.setChildFrame(LinearLayout.java:1249)
at android.widget.LinearLayout.layoutVertical(LinearLayout.java:1125)
at android.widget.LinearLayout.onLayout(LinearLayout.java:1042)
at android.view.View.layout(View.java:7057)
at android.widget.FrameLayout.onLayout(FrameLayout.java:333)
at android.view.View.layout(View.java:7057)
at android.view.ViewRoot.performTraversals(ViewRoot.java:1045)
at android.view.ViewRoot.handleMessage(ViewRoot.java:1727)
at android.os.Handler.dispatchMessage(Handler.java:99)
at android.os.Looper.loop(Looper.java:123)
at android.app.ActivityThread.main(ActivityThread.java:4680)
at java.lang.reflect.Method.invokeNative(Native Method)
at java.lang.reflect.Method.invoke(Method.java:521)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:858)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:616)
at dalvik.system.NativeStart.main(Native Method)

有没有人知道我怎么能解决这个问题？感谢帮助！！！