java - 为什么我的包是空对象引用？

Question

我正在构建一个应用程序，用户在其中创建一个 listView，然后用户可以单击其中一个 listView，然后会弹出一个对话框，让用户编辑他们单击的 listView。这是我的 EditCityFragment，一旦用户单击 listView，就会调用这个片段。我也在使用数组列表来存储我的数据，我已经想出了如何添加一个城市。

 static AddCityFragment newInstance(City city){
        AddCityFragment fragment = new AddCityFragment();
        Bundle args = new Bundle();
        args.putSerializable("city", city);
        fragment.setArguments(args);
        return fragment;
    }

    @NonNull
    @Override
    public Dialog onCreateDialog(@Nullable Bundle savedInstanceState){
        View view = LayoutInflater.from(getActivity()).inflate(R.layout.add_city_fragment_layout, null);
        AddCityFragment.newInstance(savedInstanceState);
        cityName = view.findViewById(R.id.city_name_editText);
        provinceName = view.findViewById(R.id.province_editText);

        city = (City) getArguments().getSerializable("city");
        String s = city.getCityName();
        String p = city.getProvinceName();
        cityName.setText(s);
        provinceName.setText(p);

        AlertDialog.Builder builder = new AlertDialog.Builder(getContext());
        return builder
                .setView(view)
                .setTitle("Edit City")
                .setNegativeButton("Cancel", null)
                .setPositiveButton("Ok", new DialogInterface.OnClickListener() {
                    @Override
                    public void onClick(DialogInterface dialogInterface, int i) {

                        String city = cityName.getText().toString();
                        String province = provinceName.getText().toString();
                        listener.onOkPressed(new City(city, province));

                    }}).create();
    }


}

这是错误

E/AndroidRuntime: FATAL EXCEPTION: main
    Process: com.example.simpleparadox.listycity, PID: 13929
    java.lang.NullPointerException: Attempt to invoke virtual method 'java.io.Serializable android.os.Bundle.getSerializable(java.lang.String)' on a null object reference
        at com.example.simpleparadox.listycity.EditCityFragment.onCreateDialog(EditCityFragment.java:57)
        at androidx.fragment.app.DialogFragment.onGetLayoutInflater(DialogFragment.java:330)
        at androidx.fragment.app.Fragment.performGetLayoutInflater(Fragment.java:1308)
        at androidx.fragment.app.FragmentManagerImpl.moveToState(FragmentManager.java:1460)
        at androidx.fragment.app.FragmentManagerImpl.moveFragmentToExpectedState(FragmentManager.java:1784)
        at androidx.fragment.app.FragmentManagerImpl.moveToState(FragmentManager.java:1852)
        at androidx.fragment.app.BackStackRecord.executeOps(BackStackRecord.java:802)
        at androidx.fragment.app.FragmentManagerImpl.executeOps(FragmentManager.java:2625)
        at androidx.fragment.app.FragmentManagerImpl.executeOpsTogether(FragmentManager.java:2411)
        at androidx.fragment.app.FragmentManagerImpl.removeRedundantOperationsAndExecute(FragmentManager.java:2366)
        at androidx.fragment.app.FragmentManagerImpl.execPendingActions(FragmentManager.java:2273)
        at androidx.fragment.app.FragmentManagerImpl$1.run(FragmentManager.java:733)
        at android.os.Handler.handleCallback(Handler.java:883)
        at android.os.Handler.dispatchMessage(Handler.java:100)
        at android.os.Looper.loop(Looper.java:214)
        at android.app.ActivityThread.main(ActivityThread.java:7356)
        at java.lang.reflect.Method.invoke(Native Method)
        at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:492)
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:930)

标签： javaandroid