java - 使用 RecyclerView 并调用 android.support.v7.widget.RecyclerView.setHasFixedSize(boolean) 时应用程序崩溃

Question

我正在使用 Fragments 和 RecyclerView 构建一个应用程序。

我正在关注本教程:THIS TUTORIAL

我正在使用教程的构建消息 fragment 部分来执行此操作。

但我收到此错误:

08-17 10:21:51.674 32646-32646/zca.zcaimobile E/AndroidRuntime: FATAL EXCEPTION: main
    Process: zca.zcaimobile, PID: 32646
    java.lang.RuntimeException: Unable to start activity ComponentInfo{zca.zcaimobile/zca.zcaimobile.activities.MainActivity}: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.support.v7.widget.RecyclerView.setHasFixedSize(boolean)' on a null object reference
        at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2521)
        at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2601)
        at android.app.ActivityThread.access$800(ActivityThread.java:178)
        at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1470)
        at android.os.Handler.dispatchMessage(Handler.java:111)
        at android.os.Looper.loop(Looper.java:194)
        at android.app.ActivityThread.main(ActivityThread.java:5637)
        at java.lang.reflect.Method.invoke(Native Method)
        at java.lang.reflect.Method.invoke(Method.java:372)
        at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:960)
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:755)
     Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.support.v7.widget.RecyclerView.setHasFixedSize(boolean)' on a null object reference
        at zca.zcaimobile.fragments.PaymentFragment.onViewCreated(PaymentFragment.java:43)
        at android.support.v4.app.FragmentManagerImpl.moveToState(FragmentManager.java:1127)
        at android.support.v4.app.FragmentManagerImpl.moveToState(FragmentManager.java:1290)
        at android.support.v4.app.BackStackRecord.run(BackStackRecord.java:801)
        at android.support.v4.app.FragmentManagerImpl.execPendingActions(FragmentManager.java:1677)
        at android.support.v4.app.FragmentController.execPendingActions(FragmentController.java:388)
        at android.support.v4.app.FragmentActivity.onStart(FragmentActivity.java:604)
        at android.support.v7.app.AppCompatActivity.onStart(AppCompatActivity.java:178)
        at android.app.Instrumentation.callActivityOnStart(Instrumentation.java:1244)
        at android.app.Activity.performStart(Activity.java:6116)
        at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2478)
        at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2601) 
        at android.app.ActivityThread.access$800(ActivityThread.java:178) 
        at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1470) 
        at android.os.Handler.dispatchMessage(Handler.java:111) 
        at android.os.Looper.loop(Looper.java:194) 
        at android.app.ActivityThread.main(ActivityThread.java:5637) 
        at java.lang.reflect.Method.invoke(Native Method) 
        at java.lang.reflect.Method.invoke(Method.java:372) 
        at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:960) 
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:755) 

我的PaymentFragment.java

package zca.zcaimobile.fragments;

import android.os.Bundle;
import android.support.annotation.Nullable;
import android.support.v4.app.Fragment;
import android.support.v7.widget.LinearLayoutManager;
import android.support.v7.widget.RecyclerView;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.Toast;

import retrofit2.Call;
import retrofit2.Callback;
import retrofit2.Response;
import retrofit2.Retrofit;
import retrofit2.converter.gson.GsonConverterFactory;
import zca.zcaimobile.R;
import zca.zcaimobile.api.APIService;
import zca.zcaimobile.api.APIUrl;
import zca.zcaimobile.helper.PaymentAdapter;
import zca.zcaimobile.helper.SharedPrefManager;
import zca.zcaimobile.models.Payments;

public class PaymentFragment extends Fragment {

    private RecyclerView recyclerViewMessages;
    private RecyclerView.Adapter adapter;

    @Nullable
    @Override
    public View onCreateView(LayoutInflater inflater, @Nullable ViewGroup container, @Nullable Bundle savedInstanceState) {
        return inflater.inflate(R.layout.fragment_messages, container, false);
    }

    @Override
    public void onViewCreated(View view, @Nullable Bundle savedInstanceState) {
        super.onViewCreated(view, savedInstanceState);
        getActivity().setTitle("Messages");

        recyclerViewMessages = (RecyclerView) view.findViewById(R.id.recyclerViewMessages);
        recyclerViewMessages.setHasFixedSize(true);
        recyclerViewMessages.setLayoutManager(new LinearLayoutManager(getActivity()));


        Retrofit retrofit = new Retrofit.Builder()
                .baseUrl(APIUrl.BASE_URL)
                .addConverterFactory(GsonConverterFactory.create())
                .build();

        APIService service = retrofit.create(APIService.class);

        Call<Payments> call = service.getPayments(SharedPrefManager.getInstance(getActivity()).getUser().getId());

        call.enqueue(new Callback<Payments>() {
            @Override
            public void onResponse(Call<Payments> call, Response<Payments> response) {
                adapter = new PaymentAdapter(response.body().getMessages(), getActivity());
                recyclerViewMessages.setAdapter(adapter);
            }

            @Override
            public void onFailure(Call<Payments> call, Throwable t) {
                Toast.makeText(getActivity(), t.getMessage(), Toast.LENGTH_LONG).show();
            }
        });
    }
}

我的fragment_ payment.xml

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:orientation="vertical"
android:layout_width="match_parent"
android:layout_height="match_parent">

<android.support.v7.widget.RecyclerView
    android:id="@+id/recyclerViewMessages"
    android:layout_width="match_parent"
    android:layout_height="wrap_content">

</android.support.v7.widget.RecyclerView>

我使用该教程的 MessageFragment 部分作为我的 PaymentFragment.java 的引用，因为该部分和我的 paymentfragment 具有相同的功能。

有人可以帮助我吗？我是 Android 编程新手，所以我真的不知道发生了什么。

谢谢。

Answer 1

这是因为您的布局名称 fragment_ payment.xml 而不是 R.layout.fragment_messages。 LayoutInflater在fragment_messages.xml中找不到recyclerview

更改此:

@Nullable
@Override
public View onCreateView(LayoutInflater inflater, @Nullable ViewGroup container, @Nullable Bundle savedInstanceState) {
    return inflater.inflate(R.layout.fragment_payment, container, false);
}