java.lang.NullPointerException, 'void android.widget.ListView.setAdapter(android.widget.ListAda-CodePudding

2022-09-03 17:02:35.870 14558-14558/com.example.myapplication_study E/AndroidRuntime: FATAL EXCEPTION: main Process: com.example.myapplication_study, PID: 14558 java.lang.NullPointerException: Attempt to invoke virtual method 'void android.widget.ListView.setAdapter(android.widget.ListAdapter)' on a null object reference at com.example.myapplication_study.ManagerUserman.onCreateView(ManagerUserman.java:40) at androidx.fragment.app.Fragment.performCreateView(Fragment.java:2995) at androidx.fragment.app.FragmentStateManager.createView(FragmentStateManager.java:523) at androidx.fragment.app.FragmentStateManager.moveToExpectedState(FragmentStateManager.java:261) at androidx.fragment.app.FragmentManager.executeOpsTogether(FragmentManager.java:1840) at androidx.fragment.app.FragmentManager.removeRedundantOperationsAndExecute(FragmentManager.java:1758) at androidx.fragment.app.FragmentManager.execPendingActions(FragmentManager.java:1701) at androidx.fragment.app.FragmentManager$4.run(FragmentManager.java:488) at android.os.Handler.handleCallback(Handler.java:938) at android.os.Handler.dispatchMessage(Handler.java:99) at android.os.Looper.loop(Looper.java:223) at android.app.ActivityThread.main(ActivityThread.java:7656) at java.lang.reflect.Method.invoke(Native Method) at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:592) at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:947)

If you get this error, the app won't run don't you know what's the problem? my code is here please help me tt

ManagerUserman.class

import android.content.Intent;
import android.os.Bundle;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.ListView;

import androidx.annotation.NonNull;
import androidx.annotation.Nullable;
import androidx.fragment.app.Fragment;

import java.util.ArrayList;
import java.util.List;


public class ManagerUserman extends Fragment {
    private View view;

    private ListView listView;
    private ManagerUsermanListAdapter managerUsermanListAdapter;
    private List<ManagerUsermanList> usermanList;

    @Nullable
    @Override
    public View onCreateView(@NonNull LayoutInflater inflater, @Nullable ViewGroup container, @Nullable Bundle savedInstanceState) {
        view = inflater.inflate(R.layout.activity_manageruserman_list, container, false);
        Intent intent = getActivity().getIntent();


        listView = getActivity().findViewById(R.id.listView);
        usermanList = new ArrayList<ManagerUsermanList>();

        usermanList.add(new ManagerUsermanList("name", "ID", "Password"));
        managerUsermanListAdapter = new ManagerUsermanListAdapter(getActivity().getApplicationContext(), usermanList);
        listView.setAdapter(managerUsermanListAdapter);
        return view;
    }
}

ManagerUsermanListAdapter.class

public class ManagerUsermanListAdapter extends BaseAdapter {
    private Context context;
    private List<ManagerUsermanList> usermanList;

    public ManagerUsermanListAdapter(Context context, List<ManagerUsermanList> usermanList) {
        this.context = context;
        this.usermanList = usermanList;
    }

    @Override
    public int getCount() {
        return usermanList.size();
    }

    @Override
    public Object getItem(int i) {
        return usermanList.get(i);
    }

    @Override
    public long getItemId(int i) {
        return i;
    }

    @Override
    public View getView(int i, View convertView, ViewGroup parent) {
       View v = View.inflate(context, R.layout.activity_manageruserman_list, null);

       TextView userName = (TextView) v.findViewById(R.id.userName);
       TextView userID = (TextView) v.findViewById(R.id.userID);
       TextView userPassword = (TextView) v.findViewById(R.id.userPassword);

       userName.setText(usermanList.get(i).getName());
       userID.setText(usermanList.get(i).getUser_id());
       userPassword.setText(usermanList.get(i).getUser_pass());

       v.setTag(usermanList.get(i).getUser_id());
        return v;
    }
}

ManagerUsermanList.class

public class ManagerUsermanList {

    String name;
    String user_id;
    String user_pass;

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public String getUser_id() {
        return user_id;
    }

    public void setUser_id(String user_id) {
        this.user_id = user_id;
    }

    public String getUser_pass() {
        return user_pass;
    }

    public void setUser_pass(String user_pass) {
        this.user_pass = user_pass;
    }


    public ManagerUsermanList(String name, String user_id, String user_pass) {
        this.name = name;
        this.user_id = user_id;
        this.user_pass = user_pass;
    }
}

mangeruserman.xml

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:orientation="vertical"
    tools:context=".ManagerUserman">

        <ListView
            android:id="@ id/listView"
            android:layout_width="match_parent"
            android:layout_height="match_parent"
            android:layout_marginTop="10dp"
            android:layout_marginRight="15dp"
            android:layout_marginLeft="15dp"
            android:dividerHeight="10dp"/>
</LinearLayout>

mangeruserman_list.xml

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    xmlns:app="http://schemas.android.com/apk/res-auto">

    <ScrollView
        android:layout_width="match_parent"
        android:layout_height="match_parent">

        <LinearLayout
            android:layout_width="match_parent"
            android:layout_height="match_parent"
            android:orientation="vertical">

            <ScrollView
                android:layout_width="wrap_content"
                android:layout_height="wrap_content">

            </ScrollView>

            <TextView
                android:id="@ id/userName"
                android:layout_width="wrap_content"
                android:layout_height="wrap_content"
                android:text="name"
                android:textColor="#000"
                android:textSize="20dp" />

            <TextView
                android:id="@ id/userID"
                android:layout_width="wrap_content"
                android:layout_height="wrap_content"
                android:text="id"
                android:textColor="#000"
                android:textSize="15dp" />

            <TextView
                android:id="@ id/userPassword"
                android:layout_width="wrap_content"
                android:layout_height="wrap_content"
                android:text="pass"
                android:textColor="#000"
                android:textSize="15dp" />

            <LinearLayout
                android:layout_width="match_parent"
                android:layout_height="38dp"
                android:orientation="horizontal">

                <Button
                    android:id="@ id/manager_user_delete_btn"
                    android:layout_width="100dp"
                    android:layout_height="wrap_content"
                    android:layout_weight="1"
                    android:text="del" />
            </LinearLayout>
        </LinearLayout>
    </ScrollView>
</LinearLayout>

CodePudding user response：

first: The layout file is wrong in your fragment. should right is like "mangeruserman" but yours "activity_manageruserman_list".

second: You don't need to use "getActivity().findViewById()", should use "view.findViewById()".

sorry, my English is not well, hope help for you.