我不知道为什么java.lang.NullPointerException在将适配器设置为autocomplete. 正是这个语句产生了这个异常:
textView.setAdapter(adapter);
我在布局文件夹中有两个布局。
         AlertDialog.Builder helpBuilder = new AlertDialog.Builder(this);
     helpBuilder.setTitle("Search Location");
     LayoutInflater inflater = getLayoutInflater();
     View PopupLayout = inflater.inflate(R.layout.custom_autocomplete, null);
     helpBuilder.setView(PopupLayout);
     AlertDialog helpDialog = helpBuilder.create();
     helpDialog.show();
     textView = (AutoCompleteTextView)findViewById(R.id.locationAutoCompleteTv);
     adapter = new ArrayAdapter<String>(this,R.layout.item_list);
     adapter.setNotifyOnChange(true);
     textView.setAdapter(adapter);