Question

我已就此问题做了大量研究，但我无法解决此错误。在Internet上，人们建议使用findFragmentBy ID或Tag，但这两者都会导致空指针异常。这是我写的代码：

这是托管此更新按钮的主要片段。按照预期，此按钮打开一个对话框以选择日期或时间，然后激发另一个允许用户编辑日期或时间的对话框。我在这里设置setTargetFragment。

 updateInfo= (Button) v.findViewById(R.id.update_info);
        ...// Code to display date on button(unnecessary code)
        updateInfo.setText(currentData+" "+currentDataTime);
        updateInfo.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                FragmentManager fm=getActivity().getSupportFragmentManager();
                Date date=crime.getDate();
                UpdateSelector updateSelector=UpdateSelector.newInstance(date);
                updateSelector.setTargetFragment(CrimeFragment.this,getRequest_code_updateSelector);
                updateSelector.show(fm,Update_Selector);
            }
        });

以下是updateSelector类的代码

public Dialog onCreateDialog(Bundle savedInstanceState)
    {
        AlertDialog.Builder builder=new AlertDialog.Builder(getActivity());
        ... //unnecessary code
        builder.setPositiveButton(android.R.string.ok, new DialogInterface.OnClickListener() {
            @Override
            public void onClick(DialogInterface dialog, int which) {
                if (selected == 0) {
                    FragmentManager fm = getActivity().getSupportFragmentManager();
                    DatePickerFragment datePicker = DatePickerFragment.newInstance(date);
                    datePicker.show(fm, datepickertag);
                }
                if (selected == 1) {
                    FragmentManager fm = getActivity().getSupportFragmentManager();
                    TimePickerFragment timePicker = TimePickerFragment.newInstance(date);
                    timePicker.show(fm, timepickertag);

                }
            }
        });
        return builder.create();
   }

        public void sendResult(int resultCode)
    {

        if(getTargetFragment== null)
           return;
        Intent intent=new Intent();
        date= (Date) getArguments().getSerializable(tag);
        intent.putExtra(tag, date);
        getTargetFragment().onActivityResult(getTargetRequestCode(), resultCode, intent);

    }
//New Instance method to create instance

我设计了datePickerFragment和TimePickerFragment，打开第二个对话框（Spinner进行编辑）。因此，我正在使用它们将结果发送到CrimeFragment。

public class DatePickerFragment extends DialogFragment {
    public final static String Extra_Date="date";
    private Date date;
    UpdateSelector update;
    @Override
    public Dialog onCreateDialog(Bundle savedInstanceState)
    {
     //Setup of dialog elements and get date (Unnecessary code)
        return new AlertDialog.Builder(getActivity()).setView(view).setTitle(R.string.date_picker).setPositiveButton(android.R.string.ok, new DialogInterface.OnClickListener() {
            @Override
            public void onClick(DialogInterface dialog, int which) {
                update.sendResult(Activity.RESULT_OK);
            }
        }).create();
    }

现在，update.sendResult（Activity.OK）将结果发送到此方法

public void sendResult(int resultCode)
    {

        if(getTargetFragment== null)
           return;
        Intent intent=new Intent();
        date= (Date) getArguments().getSerializable(tag);
        intent.putExtra(tag, date);
        getTargetFragment().onActivityResult(getTargetRequestCode(), resultCode, intent);

    }

其中fragment是null。请详细解释。感谢

Get Target Fragment（）返回null

0 个答案: