使用Bundle在Fragment间传值时触发NullPointerException问题求助

问题现象 #

出现空指针异常：

java.lang.NullPointerException: Attempt to invoke virtual method 'java.lang.String android.os.Bundle.getString(java.lang.String)' on a null object reference

相关代码 #

signupFragment 代码 #

public class signupFragment extends Fragment {

    private AutoCompleteTextView autoCompleteTextView;
    private EditText name,address,phone,alt_phone;
    private CountryCodePicker ccp;
    private ImageView user_dp;
    private Button signup_btn;
    private NavController navController;
    private Uri imageUri;

    public signupFragment() {
        // Required empty public constructor
    }


    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container,
                             Bundle savedInstanceState) {
        // Inflate the layout for this fragment
        View layoutSignup= inflater.inflate(R.layout.fragment_signup, container, false);
        ((AppCompatActivity)getActivity()).getSupportActionBar().hide();
        return layoutSignup;
    }

    @Override
    public void onViewCreated(@NonNull View view, @Nullable Bundle savedInstanceState) {
        super.onViewCreated(view, savedInstanceState);


        autoCompleteTextView = view.findViewById(R.id.auto_signup);
        name = view.findViewById(R.id.name_signup);
        address = view.findViewById(R.id.address_signup);
        phone = view.findViewById(R.id.phone_signup);
        alt_phone = view.findViewById(R.id.alt_phone_signup);
        ccp = view.findViewById(R.id.ccp_signup);
        user_dp = view.findViewById(R.id.img_signup);
        signup_btn = view.findViewById(R.id.btn_signup);

        navController = Navigation.findNavController(view);

        ccp.registerCarrierNumberEditText(phone);

        ArrayAdapter<CharSequence> adapter = ArrayAdapter.createFromResource(getContext(), R.array.user_type, R.layout.dropdown_register);
        autoCompleteTextView.setAdapter(adapter);

        signup_btn.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {

                Bundle bundle = new Bundle();
                bundle.putString("name",name.getText().toString());
                bundle.putString("phone",ccp.getFullNumberWithPlus().replace(" ",""));
                bundle.putString("user_type",autoCompleteTextView.getText().toString());
                bundle.putString("alt_phone",alt_phone.getText().toString());
                bundle.putString("address",address.getText().toString());
                bundle.putString("dp_url",user_dp.getResources().toString());

                otpFragment OtpFragment = new otpFragment();
                OtpFragment.setArguments(bundle);

               getFragmentManager().beginTransaction().replace(R.id.fragmentContainerView2,OtpFragment).commit();


                navController.navigate(R.id.action_signupFragment_to_otpFragment);
            }
        });

        user_dp.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {

                setimage();
            }
        });

    }

    // This is to select the image from the mobile
    private void setimage() {

        Intent intent = new Intent();
        intent.setType("image/*");
        intent.setAction(Intent.ACTION_GET_CONTENT);
        startActivityForResult(intent,100);
    }

    // This is to set the image and to check if we got an image or not
    @Override
    public void onActivityResult(int requestCode, int resultCode, @Nullable Intent data) {
        super.onActivityResult(requestCode, resultCode, data);

        if(requestCode==100 && data!=null && data.getData()!=null){

            imageUri = data.getData();
            user_dp.setImageURI(imageUri);

        }
    }

}

otpFragment 代码 #

public class otpFragment extends Fragment {

    private Button verify_otp_btn;
    private EditText edt_otp;
    private TextView resend_otp;
    private FirebaseAuth mAuth;
    private String dp_url="";
    private String name="";
    private String phoneNumber="";
    private String otpid="";
    private String user_type="";
    private String user_id="";
    private String alt_phone="";
    private String address="";
    private NavController navController;



    // firebase declaration
    private FirebaseFirestore firestore;


    public otpFragment() {
        // Required empty public constructor
    }


    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container,
                             Bundle savedInstanceState) {
        // Inflate the layout for this fragment
        View layoutOtp= inflater.inflate(R.layout.fragment_otp, container, false);
        ((AppCompatActivity)getActivity()).getSupportActionBar().hide();
        return layoutOtp;
    }

    @Override
    public void onViewCreated(@NonNull View view, @Nullable Bundle savedInstanceState) {
        super.onViewCreated(view, savedInstanceState);

        verify_otp_btn= view.findViewById(R.id.verify_otp_btn);
        edt_otp= view.findViewById(R.id.code_otp);
        resend_otp=view.findViewById(R.id.resend_otp);

        navController= Navigation.findNavController(view);
    
        Bundle result;
        result = this.getArguments();


        name = result.getString("name");
            phoneNumber = result.getString("phone");
            user_type = result.getString("user_type");
            alt_phone = result.getString("alt_phone");
            address = result.getString("address");
            dp_url = result.getString("dp_url");


        Log.d("phone no",phoneNumber+" this is ");
        Log.d("phone no",name+" this is ");
        Log.d("phone no",user_type+" this is ");
        Log.d("phone no",alt_phone+" this is ");
        Log.d("phone no",address+" this is ");
        Log.d("phone no",dp_url+" this is ");


        verify_otp();

}

问题根源 #

你同时使用了Fragment事务和Navigation组件来跳转Fragment：

1. 你创建了带Bundle的otpFragment实例并通过事务提交，但随后又调用了navController.navigate()，这会创建一个全新的otpFragment实例（不带Bundle），覆盖之前的实例
2. 最终显示的是Navigation创建的无Bundle实例，导致getArguments()返回null，调用getString()时触发空指针异常

另外还有两个次要问题：

• 图片Uri获取错误：user_dp.getResources().toString()无法获取选中的图片Uri，应该使用onActivityResult中赋值的imageUri
• otpFragment中未做Bundle空判断，即使传值正常也可能因异常情况导致崩溃

解决方案 #

1. 移除冗余的Fragment事务代码，改用Navigation传递Bundle #

修改signupFragment中点击事件的代码，删除Fragment事务相关代码，将Bundle作为参数传给navController.navigate()：

signup_btn.setOnClickListener(new View.OnClickListener() {
    @Override
    public void onClick(View v) {
        Bundle bundle = new Bundle();
        bundle.putString("name", name.getText().toString());
        bundle.putString("phone", ccp.getFullNumberWithPlus().replace(" ", ""));
        bundle.putString("user_type", autoCompleteTextView.getText().toString());
        bundle.putString("alt_phone", alt_phone.getText().toString());
        bundle.putString("address", address.getText().toString());
        // 修正图片Uri获取逻辑
        bundle.putString("dp_url", imageUri != null ? imageUri.toString() : "");

        // 移除以下三行冗余代码
        // otpFragment OtpFragment = new otpFragment();
        // OtpFragment.setArguments(bundle);
        // getFragmentManager().beginTransaction().replace(R.id.fragmentContainerView2,OtpFragment).commit();

        // 使用Navigation传递Bundle跳转
        navController.navigate(R.id.action_signupFragment_to_otpFragment, bundle);
    }
});

2. 增加Bundle空指针防护 #

在otpFragment中先判断Bundle是否为null，避免空指针异常：

Bundle result = getArguments();
if (result != null) {
    name = result.getString("name", "");
    phoneNumber = result.getString("phone", "");
    user_type = result.getString("user_type", "");
    alt_phone = result.getString("alt_phone", "");
    address = result.getString("address", "");
    dp_url = result.getString("dp_url", "");
}

3. 验证图片Uri传递正确性 #

确保imageUri在onActivityResult中正确赋值，并且传递时做非空判断，避免传递无效字符串。

内容的提问来源于stack exchange，提问作者zuni