使用 Bundle 将列表视图值从片段传递到片段时获取空对象引用

Question

我尝试使用 setOnItemClickListener 将一些数据从 ListView 传递到 Fragment 到另一个 Fragment 使用 bundle，但我得到空对象引用

这是第一个Fragment的ClickListener

HomeMakananMieayamFragment.java

ListViewMenuMieAyam.setOnItemClickListener(new AdapterView.OnItemClickListener() {
            @Override
            public void onItemClick(AdapterView<?> parent, View view, int position, long id ) {
                switch (position) {
                    case 0 :
                        //set getter to be called based on position
                        MieAyam mieAyamGeter1 = (MieAyam)ListViewMenuMieAyam.getItemAtPosition(position);
                        //declare new code
                        String FoodCode1 = "MA1";
                        //get MakananName using getter
                        String FoodName1 = mieAyamGeter1.getmMakananName();
                        //get MakananPrice using getter
                        int FoodPrice1 = mieAyamGeter1.getmMakananHarga();
                        //set the MakananPrice to String to passed to intent
                        String Price1 = String.valueOf(FoodPrice1);
                        //Pass the variables
                        FragmentOrdertoCart fragmentOrdertoCart = new FragmentOrdertoCart();
                        Bundle bundle1 = new Bundle();
                        bundle1.putString("FoodCode", FoodCode1);
                        bundle1.putString("FoodName", FoodName1);
                        bundle1.putString("FoodPrice", Price1);
                        fragmentOrdertoCart.setArguments(bundle1);

                        Fragment FragmentOrdertoCart1 = new FragmentOrdertoCart();
                        // consider using Java coding conventions (upper first char class names!!!)
                        FragmentTransaction transaction1 = getFragmentManager().beginTransaction();
                        // Replace whatever is in the fragment_container view with this fragment,
                        // and add the transaction to the back stack
                        transaction1.replace(R.id.ContainerMieAyam, FragmentOrdertoCart1);
                        transaction1.addToBackStack(null);
                        // Commit the transaction
                        transaction1.commit();
                        break;
                    case 1:
                        MieAyam mieAyamGeter2 = (MieAyam)ListViewMenuMieAyam.getItemAtPosition(position);
                        String FoodCode2 = "MA2";
                        String FoodName2 = mieAyamGeter2.getmMakananName();
                        int FoodPrice2 = mieAyamGeter2.getmMakananHarga();
                        String Price2 = String.valueOf(FoodPrice2);
                        FragmentOrdertoCart fragmentOrdertoCart2 = new FragmentOrdertoCart();
                        Bundle bundle2 = new Bundle();
                        bundle2.putString("FoodCode", FoodCode2);
                        bundle2.putString("FoodName", FoodName2);
                        bundle2.putString("FoodPrice", Price2);
                        fragmentOrdertoCart2.setArguments(bundle2);

                        Fragment FragmentOrdertoCart2 = new FragmentOrdertoCart();
                        // consider using Java coding conventions (upper first char class names!!!)
                        FragmentTransaction transaction2 = getFragmentManager().beginTransaction();

                        // Replace whatever is in the fragment_container view with this fragment,
                        // and add the transaction to the back stack
                        transaction2.replace(R.id.ContainerMieAyam, FragmentOrdertoCart2);
                        transaction2.addToBackStack(null);
                        // Commit the transaction
                        transaction2.commit();
                        break;
                    case 2:
                        MieAyam mieAyamGeter3 = (MieAyam)ListViewMenuMieAyam.getItemAtPosition(position);
                        String FoodCode3 = "MA3";
                        String FoodName3 = mieAyamGeter3.getmMakananName();
                        int FoodPrice3 = mieAyamGeter3.getmMakananHarga();
                        String Price3 = String.valueOf(FoodPrice3);
                        FragmentOrdertoCart fragmentOrdertoCart3 = new FragmentOrdertoCart();
                        Bundle bundle3 = new Bundle();
                        bundle3.putString("FoodCode", FoodCode3);
                        bundle3.putString("FoodName", FoodName3);
                        bundle3.putString("FoodPrice", Price3);
                        fragmentOrdertoCart3.setArguments(bundle3);

                        Fragment FragmentOrdertoCart3 = new FragmentOrdertoCart();
                        // consider using Java coding conventions (upper first char class names!!!)
                        FragmentTransaction transaction3 = getFragmentManager().beginTransaction();
                        // Replace whatever is in the fragment_container view with this fragment,
                        // and add the transaction to the back stack
                        transaction3.replace(R.id.ContainerMieAyam, FragmentOrdertoCart3);
                        transaction3.addToBackStack(null);
                        // Commit the transaction
                        transaction3.commit();
                        break;
                }
            }
        });

这是第二个Fragment FragmentOrdertoCart.java

import android.os.Build;
import android.os.Bundle;

import androidx.annotation.RequiresApi;
import androidx.fragment.app.Fragment;
import androidx.fragment.app.FragmentTransaction;

import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.LinearLayout;
import android.widget.TextView;
import android.widget.Toolbar;

/**
 * A simple {@link Fragment} subclass.
 * Use the {@link FragmentOrdertoCart#newInstance} factory method to
 * create an instance of this fragment.
 */
public class FragmentOrdertoCart extends Fragment {
    TextView TxtvOrdertoCartCode,TxtvOrdertoCartName,TxtvOrdertoCartPrice;
    Toolbar toolbarOrdertoCart;
    LinearLayout ContainerContentOrdertoCart;

    // TODO: Rename parameter arguments, choose names that match
    // the fragment initialization parameters, e.g. ARG_ITEM_NUMBER
    private static final String ARG_PARAM1 = "param1";
    private static final String ARG_PARAM2 = "param2";

    // TODO: Rename and change types of parameters
    private String mParam1;
    private String mParam2;

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

    /**
     * Use this factory method to create a new instance of
     * this fragment using the provided parameters.
     *
     * @param param1 Parameter 1.
     * @param param2 Parameter 2.
     * @return A new instance of fragment FragmentOrdertoCart.
     */
    // TODO: Rename and change types and number of parameters
    public static FragmentOrdertoCart newInstance(String param1, String param2) {
        FragmentOrdertoCart fragment = new FragmentOrdertoCart();
        Bundle args = new Bundle();
        args.putString(ARG_PARAM1, param1);
        args.putString(ARG_PARAM2, param2);
        fragment.setArguments(args);
        return fragment;
    }

    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        if (getArguments() != null) {
            mParam1 = getArguments().getString(ARG_PARAM1);
            mParam2 = getArguments().getString(ARG_PARAM2);
        }
    }

    @RequiresApi(api = Build.VERSION_CODES.LOLLIPOP)
    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container,
                             Bundle savedInstanceState) {
        View viewRoot = inflater.inflate(R.layout.fragment_orderto_cart, container, false);

        TxtvOrdertoCartCode = viewRoot.findViewById(R.id.TxtvOrdertoCartCode);
        TxtvOrdertoCartName = viewRoot.findViewById(R.id.TxtvOrdertoCartName);
        TxtvOrdertoCartPrice = viewRoot.findViewById(R.id.TxtvOrdertoCartPrice);
        ContainerContentOrdertoCart = viewRoot.findViewById(R.id.ContainerContentOrdertoCart);

        Bundle bundle = this.getArguments();
        assert bundle != null;
        String Code = bundle.getString("FoodCode");
        String Name = bundle.getString("FoodName");
        String Price = bundle.getString("FoodPrice");

        TxtvOrdertoCartCode.setText(Code);
        TxtvOrdertoCartName.setText(Name);
        TxtvOrdertoCartPrice.setText(Price);

        toolbarOrdertoCart = viewRoot.findViewById(R.id.ToolbarOrdertoCart);
        toolbarOrdertoCart.setNavigationIcon(R.drawable.arrowbackicon);
        toolbarOrdertoCart.setNavigationOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                ContainerContentOrdertoCart.setVisibility(View.GONE);
                // Create new fragment and transaction
                Fragment FragmentMieAyam = new HomeMakananMieayamFragment();
                // consider using Java coding conventions (upper first char class names!!!)
                FragmentTransaction transaction = getFragmentManager().beginTransaction();
                // Replace whatever is in the fragment_container view with this fragment,
                // and add the transaction to the back stack
                transaction.replace(R.id.COntainerOrdertoCart, FragmentMieAyam);
                transaction.addToBackStack(null);
                // Commit the transaction
                transaction.commit();
            }
        });
        // Inflate the layout for this fragment
        return viewRoot;
    }
}

错误日志

    Process: com.example.pesanpalgading20, PID: 28032
    java.lang.NullPointerException: Attempt to invoke virtual method 'java.lang.String android.os.BaseBundle.getString(java.lang.String)' on a null object reference
        at com.example.pesanpalgading20.FragmentOrdertoCart.onCreateView(FragmentOrdertoCart.java:79)
        at androidx.fragment.app.Fragment.performCreateView(Fragment.java:2600)
        at androidx.fragment.app.FragmentManagerImpl.moveToState(FragmentManagerImpl.java:881)
        at androidx.fragment.app.FragmentManagerImpl.moveFragmentToExpectedState(FragmentManagerImpl.java:1238)
        at androidx.fragment.app.FragmentManagerImpl.moveToState(FragmentManagerImpl.java:1303)
        at androidx.fragment.app.BackStackRecord.executeOps(BackStackRecord.java:439)
        at androidx.fragment.app.FragmentManagerImpl.executeOps(FragmentManagerImpl.java:2079)
        at androidx.fragment.app.FragmentManagerImpl.executeOpsTogether(FragmentManagerImpl.java:1869)
        at androidx.fragment.app.FragmentManagerImpl.removeRedundantOperationsAndExecute(FragmentManagerImpl.java:1824)
        at androidx.fragment.app.FragmentManagerImpl.execPendingActions(FragmentManagerImpl.java:1727)
        at androidx.fragment.app.FragmentManagerImpl$2.run(FragmentManagerImpl.java:150)
        at android.os.Handler.handleCallback(Handler.java:751)
        at android.os.Handler.dispatchMessage(Handler.java:95)
        at android.os.Looper.loop(Looper.java:154)
        at android.app.ActivityThread.main(ActivityThread.java:6119)
        at java.lang.reflect.Method.invoke(Native Method)
        at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:886)
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:776)

Answer 1

看来你练错了。

1. 在每种情况下，您只需要一个 Fragment 实例，现在您正在初始化两个。
2. 另外，您犯了一个错误，即在与第二个片段进行交易时将捆绑包传递给第一个片段。在每种情况下。

在每个 ccase 中尝试以下代码：

Bundle bundle1 = new Bundle();
bundle1.putString("FoodCode", FoodCode1);
bundle1.putString("FoodName", FoodName1);
bundle1.putString("FoodPrice", Price1);
   

Fragment fragmentOrdertoCart1 = new FragmentOrdertoCart();
fragmentOrdertoCart1.setArguments(bundle1);                    
FragmentTransaction transaction1 = getFragmentManager().beginTransaction();
transaction1.replace(R.id.ContainerMieAyam, fragmentOrdertoCart1);
transaction1.addToBackStack(null);
transaction1.commit();