Android 应用程序 - 错误崩溃 - ListView SetAdapter

Question

My app is crashing and it only crashes when I add the line "listView.setAdapter(adapter);"the app is just 2 fragments connected to 1 main activity I am learning how to communicate. I will include all the code, the top fragment is a list view, and the bottom is just a textview, objective is to click/press an item in the listview and the text should change. Also looks like some of the methods were depreciated since these notes so I have tried to work around it moving from OnActivityCreated to OnCreate in the fragment classes, and added a FragmentContainer instead of a Fragment in the xml.

Code: fragment_text.xml

<?xml version="1.0" encoding="utf-8"?>
<FrameLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:id="@+id/TextFragment_layout1"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    tools:context=".TextFragment">


    <TextView
        android:id="@+id/textView1"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:padding="16dp"
        android:text="@string/text_box" />

</FrameLayout>


package com.example.tourguide;

import android.content.res.Resources;
import android.net.Uri;
import android.os.Bundle;

import androidx.fragment.app.Fragment;

import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.ArrayAdapter;
import android.widget.ListView;
import android.widget.TextView;

/**
 * A simple {@link Fragment} subclass.
 * Use the {@link TextFragment#newInstance} factory method to
 * create an instance of this fragment.
 */
public class TextFragment extends Fragment
{
    private TextView textView;


    // 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 TextFragment() {
        // 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 TextFragment.
     */
    // TODO: Rename and change types and number of parameters
    public static TextFragment newInstance(String param1, String param2) {
        TextFragment fragment = new TextFragment();
        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);
        }
        textView = (TextView)getActivity().findViewById(R.id.textView1);
    }

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

        public interface OnFragmentInteractionListener
    {
        public void onFragmentInteraction(Uri uri);
    }
}


fragment_list.xml

<?xml version="1.0" encoding="utf-8"?>
<FrameLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:id="@+id/ListFragment_layout1"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    tools:context=".ListFragment">

    <ListView
        android:id="@+id/listView1"
        android:layout_width="match_parent"
        android:layout_height="match_parent" />

</FrameLayout>

package com.example.tourguide;

import android.content.res.Resources;
import android.net.Uri;
import android.os.Bundle;

import androidx.fragment.app.Fragment;

import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.ArrayAdapter;
import android.widget.AdapterView;

import android.widget.ListView;

/**
 * A simple {@link Fragment} subclass.
 * Use the {@link ListFragment#newInstance} factory method to
 * create an instance of this fragment.
 */
public class ListFragment extends Fragment implements AdapterView.OnItemClickListener
{
    private ListView listView;
    private String[] array;



    // 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 ListFragment() {
        // 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 ListFragment.
     */
    // TODO: Rename and change types and number of parameters
    public static ListFragment newInstance(String param1, String param2) {
        ListFragment fragment = new ListFragment();
        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);
        }
        listView = (ListView)getActivity().findViewById(R.id.listView1);
        //Resources res = getResources();
        array = getResources().getStringArray(R.array.string_array_cities);
        ArrayAdapter<String> adapter = new ArrayAdapter<String>(getActivity(), android.R.layout.simple_list_item_1, array);
        listView.setAdapter(adapter);

    }

    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container,
                             Bundle savedInstanceState)
    {
        // Inflate the layout for this fragment
        return inflater.inflate(R.layout.fragment_list, container, false);

    }



    public interface OnFragmentInteractionListener
    {
        public void onFragmentInteraction(Uri uri);
    }

    @Override
    public void onItemClick(AdapterView<?> adapterView, View view, int position, long l)
    {

    }
}

activity_main.xml

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    android:id="@+id/LinearLayout_1"
    android:orientation="vertical"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    tools:context=".MainActivity">

    <androidx.fragment.app.FragmentContainerView
        android:id="@+id/fragmentContainerView1"
        android:name="com.example.tourguide.ListFragment"
        android:layout_width="wrap_content"
        android:layout_height="357dp"
        tools:layout="@layout/fragment_list" />

    <androidx.fragment.app.FragmentContainerView
        android:id="@+id/fragmentContainerView2"
        android:name="com.example.tourguide.TextFragment"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        tools:layout="@layout/fragment_text" />
</LinearLayout>

package com.example.tourguide;

import androidx.appcompat.app.AppCompatActivity;
import android.app.Fragment;
import android.app.FragmentManager;
import android.net.Uri;
import android.os.Bundle;

public class MainActivity extends AppCompatActivity implements TextFragment.OnFragmentInteractionListener, ListFragment.OnFragmentInteractionListener
{

    @Override
    protected void onCreate(Bundle savedInstanceState)
    {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
    }


    @Override
    public void onFragmentInteraction(Uri uri)
    {

    }

}

strings.xml

<resources>
    <string name="app_name">Tour Guide</string>
    <string name="hello_blank_fragment">Hello blank fragment</string>
    <string name="text_box">default</string>
    <string-array name="string_array_cities">
        <item>Richmond</item>
        <item>Vancouver</item>
        <item>Toronto</item>
        <item>New West</item>
        <item>Montreal</item>
        <item>Aldergrove</item>
    </string-array>


</resources>

Exception: E/AndroidRuntime: FATAL EXCEPTION: main Process: com.example.tourguide, PID: 32432 java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.tourguide/com.example.tourguide.MainActivity}: android.view.InflateException: Binary XML file line #11: Binary XML file line #11: Error inflating class androidx.fragment.app.FragmentContainerView at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:3121) at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:3264) at android.app.servertransaction.LaunchActivityItem.execute(LaunchActivityItem.java:78) at android. app.servertransaction.TransactionExecutor.executeCallbacks(TransactionExecutor.java:108) at android.app.servertransaction.TransactionExecutor.execute(TransactionExecutor.java:68) at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1955) at android.os.Handler.dispatchMessage(Handler.java:106) at android.os.Looper.loop(Looper.java:214) at android.app.ActivityThread.main(ActivityThread.java:7078) at java.lang.reflect.Method.invoke(Native Method) at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:494) at Z4D236D9A2D102C5FE 6AD1C50DA4BEC50Z.android.internal.os.ZygoteInit.main(ZygoteInit.java:964) Caused by: android.view.InflateException: Binary XML file line #11: Binary XML file line #11: Error inflating class androidx.fragment.app.FragmentContainerView Caused by: android.view.InflateException: Binary XML file line #11: Error inflating class androidx.fragment.app.FragmentContainerView Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.widget.ListView.setAdapter(android.widget.ListAdapter)' on a null object reference at com.example.tourguide.ListFragment.onCreate(List Fragment.java:72) at androidx.fragment.app.Fragment.performCreate(Fragment.java:2949) at androidx.fragment.app.FragmentStateManager.create(FragmentStateManager.java:475) at androidx.fragment.app.FragmentStateManager.moveToExpectedState(FragmentStateManager.java:278) at androidx.fragment.app.FragmentManager.executeOpsTogether(FragmentManager.java:2189) at androidx.fragment.app.FragmentManager.removeRedundantOperationsAndExecute(FragmentManager.java:2106) at androidx.fragment.app.FragmentManager.execSingleAction(FragmentManager.java:1971) at androidx.fragment.app.BackStackRecord.commitNowAllowingStateLoss(BackStackRecord.java:311) at androidx.fragment.app.FragmentContainerView.(FragmentContainerView.java:180) at androidx.f ragment.app.FragmentLayoutInflaterFactory.onCreateView(FragmentLayoutInflaterFactory.java:52) at androidx.fragment.app.FragmentController.onCreateView(FragmentController.java:135) at androidx.fragment.app.FragmentActivity.dispatchFragmentsOnCreateView(FragmentActivity.java:319) at androidx.fragment.app.FragmentActivity.onCreateView(FragmentActivity.java:298) at android.view.LayoutInflater.createViewFromTag(LayoutInflater.java:819) at android.view.LayoutInflater.createViewFromTag(LayoutInflater.java:769) at android.view.LayoutInflater.rInflate(LayoutInflater.java:902) at android.view.LayoutInflater.rInflateChildren(LayoutInflater.java:863) at ZC 31B32364CE19CA8FCD150A417ECCE58Z.view.LayoutInflater.inflate(LayoutInflater.java:554) at android.view.LayoutInflater.inflate(LayoutInflater.java:461) at android.view.LayoutInflater.inflate(LayoutInflater.java:383) at androidx.appcompat.app.AppCompatDelegateImpl.setContentView(AppCompatDelegateImpl.java:706) at androidx.appcompat.app.AppCompatActivity.setContentView(AppCompatActivity.java:195) at com.example.tourguide.MainActivity.onCreate(MainActivity.java:16) at android.app.Activity.performCreate(Activity.java:7327) at android.app.Activity.performCreate(Activity.java:7318) at android.ap p.Instrumentation.callActivityOnCreate(Instrumentation.java:1275) at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:3101) at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:3264) E/AndroidRuntime: at android.app.servertransaction.LaunchActivityItem.execute(LaunchActivityItem.java:78) at android.app.servertransaction.TransactionExecutor.executeCallbacks(TransactionExecutor.java:108) at android.app.servertransaction.TransactionExecutor.execute(TransactionExecutor.java:68) at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1955) at android.o s.Handler.dispatchMessage(Handler.java:106) at android.os.Looper.loop(Looper.java:214) at android.app.ActivityThread.main(ActivityThread.java:7078) at java.lang.reflect.Method.invoke(Native Method) at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:494) at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:964)

Answer 1

Everything seems okay only a few lines of code need to be changed.

Inside you need to remove textView initialization from onCreate(...){} method to onCreateView(....) like as follows:

@Override
public void onCreate(....){
 .......
 .....
 textView = (TextView)getActivity().findViewById(R.id.textView1); //remove this line of code.
}

@Override
public View onCreateView(......){
 View view = inflater.inflate(R.layout.fragment_text, container, false);
 textView = view.findViewById(R.id.textView1); //you need to initialize textview here.
 return view;
}

And, Inside you need to remove all code of initialization from onCreate(..){} to onCreateView(...){} like as follows:

@Override
public void onCreate(...){
 .......
 ....
 ...
 //remove all this code to another method.
 /*listView = (ListView)getActivity().findViewById(R.id.listView1);
 //Resources res = getResources();
 array = getResources().getStringArray(R.array.string_array_cities);
 ArrayAdapter<String> adapter = new ArrayAdapter<String>(getActivity(), android.R.layout.simple_list_item_1, array);
 listView.setAdapter(adapter);*/
}

@Override
 public View onCreateView(.....){
  View view = inflater.inflate(R.layout.fragment_list, container, false);
  listView = view.findViewById(R.id.listView1);
  array = getResources().getStringArray(R.array.string_array_cities);
  ArrayAdapter<String> adapter = new ArrayAdapter<String>(getActivity(), android.R.layout.simple_list_item_1, array);
  listView.setAdapter(adapter);
  return view;
 }