Java 具有多个片段的两个活动之间的空对象引用

错误是： 空对象引用上的“void android.widget.TableRow.setVisibility（int）”无效

android studio和java非常新，已经使用它几周了。基本上，问题是我有多个活动，每个活动都有多个片段。其中一个名为Calculator的有三个片段，在fragemntCalc2中，我有很多表行，我想通过一个不同的activities片段（特别是一个名为profile的片段和它的第二个片段）的下拉列表使它们不可见

public class Fragment2 extends Fragment {

Context context;
Spinner CourseNameSpinner1;
Spinner QualificationSpinner1;
Spinner ExamboardSpinner1;
Spinner spinner_switch;

public static Fragment2 newInstance()
{
    Fragment2 fragment = new Fragment2();
    return fragment;
}

public Fragment2() {}

@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
    View rootView = inflater.inflate(R.layout.fragment_profile2, container, false);
    context = container.getContext();


    CourseNameSpinner1 = (Spinner) rootView.findViewById(R.id.CourseNameSpinner1);
    QualificationSpinner1 = (Spinner) rootView.findViewById(R.id.QualificationSpinner1);
    ExamboardSpinner1 = (Spinner) rootView.findViewById(R.id.ExamboardSpinner1);
    spinner_switch = (Spinner) rootView.findViewById(R.id.spinner_switch);

    //Course Dropdown
    Spinner spinner2 = (Spinner) rootView.findViewById(R.id.CourseNameSpinner1);
    ArrayAdapter<CharSequence> adapter2 = ArrayAdapter.createFromResource(context, R.array.Course_Array, android.R.layout.simple_spinner_item);
    adapter2.setDropDownViewResource(android.R.layout.simple_spinner_dropdown_item); // Specify the layout to use when the list of choices appears
    spinner2.setAdapter(adapter2); // Apply the adapter to the spinner

    //Qualification Dropdown
    Spinner spinner3 = (Spinner) rootView.findViewById(R.id.QualificationSpinner1);
    ArrayAdapter<CharSequence> adapter3 = ArrayAdapter.createFromResource(context, R.array.Qualification_Array, android.R.layout.simple_spinner_item);
    adapter3.setDropDownViewResource(android.R.layout.simple_spinner_dropdown_item); // Specify the layout to use when the list of choices appears
    spinner3.setAdapter(adapter3); // Apply the adapter to the spinner

    //ExamBoard Dropdown
    Spinner spinner4 = (Spinner) rootView.findViewById(R.id.ExamboardSpinner1);
    ArrayAdapter<CharSequence> adapter4 = ArrayAdapter.createFromResource(context, R.array.Exam_Array, android.R.layout.simple_spinner_item);
    adapter4.setDropDownViewResource(android.R.layout.simple_spinner_dropdown_item); // Specify the layout to use when the list of choices appears
    spinner4.setAdapter(adapter4); // Apply the adapter to the spinner

    Spinner spinner23 = (Spinner) rootView.findViewById(R.id.spinner_switch);
    ArrayAdapter<CharSequence> adapter23 = ArrayAdapter.createFromResource(context, R.array.Switch_Array, android.R.layout.simple_spinner_item);
    adapter23.setDropDownViewResource(android.R.layout.simple_spinner_dropdown_item); // Specify the layout to use when the list of choices appears
    spinner23.setAdapter(adapter23); // Apply the adapter to the spinner

    //ArrayAdapter<CharSequence> adapter2 = ArrayAdapter.createFromResource(context, R.array.Course_Array, android.R.layout.simple_spinner_item);
    //Where context is, originally it was a this.
    //Changed as the spinner isn't declared in main activity
    //this is fragment java, therefore it needs context to declare the spinner

    SharedPreferences sharedPref = context.getSharedPreferences("Units", context.MODE_PRIVATE);
    int spinnerValue = sharedPref.getInt("UserCourseChoiceSpinner1", -1);
    int spinnerValue2 = sharedPref.getInt("UserCourseChoiceSpinner2",-1);
    int spinnerValue3 = sharedPref.getInt("UserCourseChoiceSpinner3",-1);
    if(spinnerValue != -1)

    CourseNameSpinner1.setSelection(spinnerValue);
    QualificationSpinner1.setSelection(spinnerValue2);
    ExamboardSpinner1.setSelection(spinnerValue3);


    Button button = (Button) rootView.findViewById(R.id.button_savecourse);
    button.setOnClickListener(new View.OnClickListener()
    {
        @Override
        public void onClick(View v)
        {
            int userChoice = CourseNameSpinner1.getSelectedItemPosition();
            int userChoice2 = QualificationSpinner1.getSelectedItemPosition();
            int userChoice3 = ExamboardSpinner1.getSelectedItemPosition();

            SharedPreferences sharedPref = context.getSharedPreferences("Units", Context.MODE_PRIVATE);
            SharedPreferences.Editor prefEditor = sharedPref.edit();

            prefEditor.putInt("UserCourseChoiceSpinner1",userChoice);
            prefEditor.putInt("UserCourseChoiceSpinner2",userChoice2);
            prefEditor.putInt("UserCourseChoiceSpinner3",userChoice3);

            prefEditor.commit();

            Toast.makeText(context, "Data was saved successfully", Toast.LENGTH_LONG).show();
        }
    });

    Spinner spinner_switch = (Spinner)rootView.findViewById(R.id.spinner_switch);
    spinner_switch.setOnItemSelectedListener(new AdapterView.OnItemSelectedListener()
    {
        @Override
        public void onItemSelected(AdapterView<?> parent, View view, int position, long id)
        {
            TableRow tableRow;
            if (position != 1)
            {
                tableRow = (TableRow) getActivity().findViewById(R.id.table13);
                tableRow.setVisibility(View.GONE);
                tableRow = (TableRow) getActivity().findViewById(R.id.table14);
                tableRow.setVisibility(View.GONE);
                tableRow = (TableRow) getActivity().findViewById(R.id.table15);
                tableRow.setVisibility(View.GONE);
                tableRow = (TableRow) getActivity().findViewById(R.id.table16);
                tableRow.setVisibility(View.GONE);
                tableRow = (TableRow) getActivity().findViewById(R.id.table17);
                tableRow.setVisibility(View.GONE);
                tableRow = (TableRow) getActivity().findViewById(R.id.table18);
                tableRow.setVisibility(View.GONE);

                tableRow = (TableRow) getActivity().findViewById(R.id.tablegrade13);
                tableRow.setVisibility(View.GONE);
                tableRow = (TableRow) getActivity().findViewById(R.id.tablegrade14);
                tableRow.setVisibility(View.GONE);
                tableRow = (TableRow) getActivity().findViewById(R.id.tablegrade15);
                tableRow.setVisibility(View.GONE);
                tableRow = (TableRow) getActivity().findViewById(R.id.tablegrade16);
                tableRow.setVisibility(View.GONE);
                tableRow = (TableRow) getActivity().findViewById(R.id.tablegrade17);
                tableRow.setVisibility(View.GONE);
                tableRow = (TableRow) getActivity().findViewById(R.id.tablegrade18);
                tableRow.setVisibility(View.GONE);

            }
            else
            {
                tableRow = (TableRow) getActivity().findViewById(R.id.table13);
                tableRow.setVisibility(View.VISIBLE);
                tableRow = (TableRow) getActivity().findViewById(R.id.table14);
                tableRow.setVisibility(View.VISIBLE);
                tableRow = (TableRow) getActivity().findViewById(R.id.table15);
                tableRow.setVisibility(View.VISIBLE);
                tableRow = (TableRow) getActivity().findViewById(R.id.table16);
                tableRow.setVisibility(View.VISIBLE);
                tableRow = (TableRow) getActivity().findViewById(R.id.table17);
                tableRow.setVisibility(View.VISIBLE);
                tableRow = (TableRow) getActivity().findViewById(R.id.table18);
                tableRow.setVisibility(View.VISIBLE);

                tableRow = (TableRow) getActivity().findViewById(R.id.tablegrade13);
                tableRow.setVisibility(View.VISIBLE);
                tableRow = (TableRow) getActivity().findViewById(R.id.tablegrade14);
                tableRow.setVisibility(View.VISIBLE);
                tableRow = (TableRow) getActivity().findViewById(R.id.tablegrade15);
                tableRow.setVisibility(View.VISIBLE);
                tableRow = (TableRow) getActivity().findViewById(R.id.tablegrade16);
                tableRow.setVisibility(View.VISIBLE);
                tableRow = (TableRow) getActivity().findViewById(R.id.tablegrade17);
                tableRow.setVisibility(View.VISIBLE);
                tableRow = (TableRow) getActivity().findViewById(R.id.tablegrade18);
                tableRow.setVisibility(View.VISIBLE);
            }
        }
        @Override
        public void onNothingSelected(AdapterView<?> parent)
        {

        }
    });
    return rootView;
}

所以我想剩下的都不行了。同样作为信息，这些表位于完全不同的活动片段上，因此，我应该如何设置它，以便即使我声明了上下文，片段也可以找到tablerows。

如下更改

tableRow = (TableRow) rootView.findViewById(R.id.table13);
            tableRow.setVisibility(View.GONE);

并声明

rootView

global，然后对所有TableRow使用单独的变量

tableRow = (TableRow) rootView.findViewById(R.id.table13);
            tableRow.setVisibility(View.GONE);

---

并声明

rootView

global，您为所有TableRow使用单独的变量

我已将表行更改为显示rootView，但我不理解第二部分，也不确定如何将变量设置为全局变量。如果您在oncreateview中找到控件，则不必设置为全局变量，否则设置为全局控件您所说的控件是什么意思？这里的控件表示您的TableRow，所以我有在创建时将tablerow变量放入，但my tablerow.setvisibility表示它们必须声明为最终变量。rootView也会导致fragment_profile2，但是表在fragment_calc2中，这些是完全不同的活动，还是这样吗？我已经将表行更改为显示rootView，但是我不理解第二部分，也不确定如何将变量设置为全局。如果在oncreateview中找到控件，则不必设置为全局。否则，将其设置为全局。控件是什么意思？这里的控件表示您的tablerow，因此我将tablerow变量设置为on创建但my tablerow.setvisibility表示它们必须声明为最终。rootView也会导致fragment_profile2，但是表在fragment_calc2中，这些是完全不同的活动，对吗？