小贝子编程

我在一个布局中创建了两个回收器视图，我有nullPointerException



当我尝试在android studio中实现两个回收器视图时。我得到了像NullPointerException这样的误差。我为这两个视图创建了两个适配器和助手class，并在java中调用了它们的函数。

import android.content.Intent;
import android.os.Bundle;
import android.view.WindowManager;
import androidx.appcompat.app.AppCompatActivity;
import androidx.recyclerview.widget.LinearLayoutManager;
import androidx.recyclerview.widget.RecyclerView;
import com.example.college.HelperClasses.CollegeAdapter.CollegeAdapter;
import com.example.college.HelperClasses.CollegeAdapter.CollegeHelperClass;
import com.example.college.HelperClasses.HomeAdapter.DeptAdapter;
import com.example.college.HelperClasses.HomeAdapter.DeptHelperClass;
import com.example.college.R;
import java.util.ArrayList;
public class UserDashboard extends AppCompatActivity implements DeptAdapter.onDeptListener {
RecyclerView deptRecycler,collegeRecycler;
RecyclerView.Adapter adapter,adapter_clg;
ArrayList<DeptHelperClass> deptLocations = new ArrayList<>();
ArrayList<CollegeHelperClass> collegeLocations = new ArrayList<>();
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
getWindow().setFlags(WindowManager.LayoutParams.FLAG_FULLSCREEN,WindowManager.LayoutParams.FLAG_FULLSCREEN);
setContentView(R.layout.activity_user_dashboard);
deptRecycler =(RecyclerView) findViewById(R.id.dept_recycler);
collegeRecycler =(RecyclerView) findViewById(R.id.clg_recycler);
deptRecycler();
collegeRecycler();

}
private void collegeRecycler() {
collegeRecycler.setHasFixedSize(true);
collegeRecycler.setLayoutManager(new LinearLayoutManager(this,LinearLayoutManager.HORIZONTAL,false));

collegeLocations.add(new CollegeHelperClass(R.drawable.anti_ragging,"AntiRagging","Anti Ragging Committee helps to stop ragging activities in our College"));
collegeLocations.add(new CollegeHelperClass(R.drawable.anti_ragging,"AntiRagging","Anti Ragging Committee helps to stop ragging activities in our College"));
collegeLocations.add(new CollegeHelperClass(R.drawable.anti_ragging,"AntiRagging","Anti Ragging Committee helps to stop ragging activities in our College"));
adapter_clg  = new CollegeAdapter(collegeLocations);
collegeRecycler.setAdapter(adapter_clg);
}
private void deptRecycler() {
deptRecycler.setHasFixedSize(true);
deptRecycler.setLayoutManager(new LinearLayoutManager(this,LinearLayoutManager.HORIZONTAL,false));
deptLocations.add(new DeptHelperClass(R.drawable.cse,"Computer Science & Engineering","Dazzling CSE"));
deptLocations.add(new DeptHelperClass(R.drawable.auto,"Automobile Engineering","Amazing Auto"));
deptLocations.add(new DeptHelperClass(R.drawable.mechanic,"Mechanical Engineering","Royal Mech"));
deptLocations.add(new DeptHelperClass(R.drawable.biotech,"Bio-Technology","Beautiful Bio"));
deptLocations.add(new DeptHelperClass(R.drawable.civil,"Civil Engineering","Clever Civil"));
deptLocations.add(new DeptHelperClass(R.drawable.electrical,"Electrical and Electronics Engineering","#Psych EEE"));
deptLocations.add(new DeptHelperClass(R.drawable.chemistry,"Chemistry","Toxic chemistry"));
deptLocations.add(new DeptHelperClass(R.drawable.computer_app,"Computer Applications","Playful Applications"));
deptLocations.add(new DeptHelperClass(R.drawable.ece,"ECE","Dominating ECE"));
deptLocations.add(new DeptHelperClass(R.drawable.english,"English","Educative English"));
deptLocations.add(new DeptHelperClass(R.drawable.it_dept,"Information Technology","Informative IT"));
deptLocations.add(new DeptHelperClass(R.drawable.management,"Management Studies","Magical Management"));
deptLocations.add(new DeptHelperClass(R.drawable.maths,"Mathematics","Scary Mathematics"));
deptLocations.add(new DeptHelperClass(R.drawable.petro,"Petrochemical Technology","Purposeful Petro"));
deptLocations.add(new DeptHelperClass(R.drawable.pharma,"Pharma","Fundamental Pharma"));
deptLocations.add(new DeptHelperClass(R.drawable.physics,"Physics","Mesmerising Physics"));
deptLocations.add(new DeptHelperClass(R.drawable.physical_edu,"Physical Education","Sweaty PE"));
adapter = new DeptAdapter(deptLocations, this);
deptRecycler.setAdapter(adapter);
}
@Override
public void onDeptClick(int position) {
deptLocations.get(position);
if(position==0){
Intent intent = new Intent(this,comp_science.class);
intent.putExtra("CSE","Called");
startActivity(intent);
}
else if(position==1){
Intent intent = new Intent(this,auto_engg.class);
intent.putExtra("Automobile","Called");
startActivity(intent);
}
}
}

我的Logcat说

java.lang.NullPointerException: Attempt to invoke virtual method 'void androidx.recyclerview.widget.RecyclerView.setHasFixedSize(boolean)' on a null object reference
at com.example.college.User.UserDashboard.collegeRecycler(UserDashboard.java:42) 02-28 13:37:50.367 25630-25630/com.example.college E/AndroidRuntime: FATAL EXCEPTION: main
Process: com.example.college, PID: 25630
java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.college/com.example.college.User.UserDashboard}: java.lang.NullPointerException: Attempt to invoke virtual method 'void androidx.recyclerview.widget.RecyclerView.setHasFixedSize(boolean)' on a null object reference
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2684)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2750)
at android.app.ActivityThread.access$1100(ActivityThread.java:186)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1606)
at android.os.Handler.dispatchMessage(Handler.java:111)
at android.os.Looper.loop(Looper.java:238)
at android.app.ActivityThread.main(ActivityThread.java:6006)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:937)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:798)
Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'void androidx.recyclerview.widget.RecyclerView.setHasFixedSize(boolean)' on a null object reference
at com.example.college.User.UserDashboard.collegeRecycler(UserDashboard.java:42)
at com.example.college.User.UserDashboard.onCreate(UserDashboard.java:35)
at android.app.Activity.performCreate(Activity.java:6466)
at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1113)
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2637)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2750) 
at android.app.ActivityThread.access$1100(ActivityThread.java:186) 
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1606) 
at android.os.Handler.dispatchMessage(Handler.java:111) 
at android.os.Looper.loop(Looper.java:238) 
at android.app.ActivityThread.main(ActivityThread.java:6006) 
at java.lang.reflect.Method.invoke(Native Method) 
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:937) 
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:798) ```

我的布局文件是

<?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:layout_width="match_parent"
android:layout_height="match_parent"
android:layout_margin="10dp"
android:background="@color/white"
android:orientation="vertical"
tools:context=".User.UserDashboard">
<RelativeLayout
android:layout_width="match_parent"
android:layout_height="wrap_content">

<ImageView
android:id="@+id/textView"
android:layout_width="40dp"
android:layout_height="40dp"
android:layout_centerVertical="true"
android:contentDescription="@string/menu_bar"
android:src="@drawable/menu_icon_userdash_black" />
</RelativeLayout>
<ScrollView
android:layout_width="match_parent"
android:layout_height="match_parent"
android:scrollbars="none"
>
<LinearLayout
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:orientation="vertical">

<RelativeLayout
android:layout_width="match_parent"
android:layout_height="wrap_content">
<TextView
android:id="@+id/userdash_title"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_centerHorizontal="true"
android:fontFamily="@font/josefin_regular"
android:text="@string/logo_name"
android:textSize="24sp"
android:textStyle="bold"
/>
<RelativeLayout
android:layout_width="match_parent"
android:layout_height="40dp"
android:layout_below="@id/userdash_title"
android:layout_marginLeft="40dp"
android:layout_marginTop="20dp"
android:layout_marginRight="40dp"
android:layout_marginBottom="20dp"
android:background="@color/white"
android:elevation="8dp">
<TextView
android:id="@+id/search_string"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_centerVertical="true"
android:layout_marginStart="15dp"
android:text="@string/search_string" />
<ImageView
android:id="@+id/search_bar"
android:layout_width="30dp"
android:layout_height="30dp"
android:layout_alignParentEnd="true"
android:layout_centerVertical="true"
android:layout_marginRight="15dp"
android:contentDescription="@string/search_bar_userdash"
android:src="@drawable/search_userdash_black" />

</RelativeLayout>

</RelativeLayout>
<LinearLayout
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_gravity="center_horizontal"
android:orientation="horizontal">
<LinearLayout
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_margin="5dp"
android:orientation="vertical">
<RelativeLayout
android:layout_width="60dp"
android:layout_height="60dp"
android:background="@drawable/card_one_userdash"
android:elevation="8dp">
<ImageView
android:layout_width="30dp"
android:layout_height="30dp"
android:layout_centerInParent="true"
android:src="@drawable/cse" />
</RelativeLayout>
<TextView
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:fontFamily="@font/josefin_regular"
android:gravity="center_horizontal"
android:text="@string/CSE"
android:textAlignment="center"
android:textSize="11sp"
android:textStyle="bold" />

</LinearLayout>
<LinearLayout
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_margin="5dp"
android:orientation="vertical">
<RelativeLayout
android:layout_width="60dp"
android:layout_height="60dp"
android:background="@drawable/card_two_userdash"
android:elevation="8dp">
<ImageView
android:layout_width="30dp"
android:layout_height="30dp"
android:layout_centerInParent="true"
android:src="@drawable/auto" />
</RelativeLayout>
<TextView
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:fontFamily="@font/josefin_regular"
android:gravity="center_horizontal"
android:text="@string/automob"
android:textAlignment="center"
android:textSize="11sp"
android:textStyle="bold" />

</LinearLayout>
<LinearLayout
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_margin="5dp"
android:orientation="vertical">
<RelativeLayout
android:layout_width="60dp"
android:layout_height="60dp"
android:background="@drawable/card_three_userdash"
android:elevation="8dp">
<ImageView
android:layout_width="30dp"
android:layout_height="30dp"
android:layout_centerInParent="true"
android:src="@drawable/mechanic" />
</RelativeLayout>
<TextView
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:fontFamily="@font/josefin_regular"
android:gravity="center_horizontal"
android:text="@string/mechanical"
android:textAlignment="center"
android:textSize="11sp"
android:textStyle="bold" />

</LinearLayout>
<LinearLayout
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_margin="5dp"
android:orientation="vertical">
<RelativeLayout
android:layout_width="60dp"
android:layout_height="60dp"
android:background="@drawable/card_four_userdash"
android:elevation="8dp">
<ImageView
android:layout_width="30dp"
android:layout_height="30dp"
android:layout_centerInParent="true"
android:src="@drawable/electrical" />
</RelativeLayout>
<TextView
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:fontFamily="@font/josefin_regular"
android:gravity="center_horizontal"
android:text="@string/EEE"
android:textAlignment="center"
android:textSize="11sp"
android:textStyle="bold" />

</LinearLayout>

</LinearLayout>
<RelativeLayout
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:layout_marginLeft="10dp"
android:layout_marginTop="20dp"
android:background="@color/white">
<LinearLayout
android:id="@+id/featured_background"
android:layout_width="120dp"
android:layout_height="280dp"
android:layout_margin="10dp"
android:background="@color/ColorPrimaryDark"
android:orientation="vertical">
<TextView
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_marginStart="10dp"
android:layout_marginTop="50dp"
android:fontFamily="@font/josefin_regular"
android:text="@string/featured_locations"
android:textAllCaps="true"
android:textColor="@color/white"
android:textSize="14sp"
android:textStyle="bold" />
<TextView
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_margin="10dp"
android:fontFamily="@font/josefin_regular"
android:text="Featured List of All Departments"
android:textColor="@color/colorPrimary"
android:textSize="12sp" />

</LinearLayout>
<androidx.recyclerview.widget.RecyclerView
android:id="@+id/dept_recycler"
android:layout_width="match_parent"
android:layout_height="280dp"
android:layout_marginTop="10dp"
android:layout_toEndOf="@id/featured_background"
android:background="@color/card_two_userdash" />

</RelativeLayout>
<LinearLayout
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:layout_marginTop="30dp"
android:orientation="vertical"
android:padding="20dp">
<RelativeLayout
android:layout_width="match_parent"
android:layout_height="wrap_content">
<TextView
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:fontFamily="@font/josefin_regular"
android:text="@string/most_viewed_locations"
android:textAllCaps="true"
android:textColor="@color/black"
android:textSize="20sp" />
<TextView
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_alignParentRight="true"
android:layout_centerVertical="true"
android:text="@string/view_all" />

</RelativeLayout>
<androidx.recyclerview.widget.RecyclerView
android:id="@+id/clg_recycler"
android:layout_width="match_parent"
android:layout_height="100dp" />
</LinearLayout>
<LinearLayout
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:layout_marginTop="30dp"
android:orientation="vertical"
android:padding="20dp">
<RelativeLayout
android:layout_width="match_parent"
android:layout_height="wrap_content">
<TextView
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:fontFamily="@font/josefin_regular"
android:text="@string/categories"
android:textAllCaps="true"
android:textColor="@color/black"
android:textSize="20sp" />
<TextView
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_alignParentRight="true"
android:layout_centerVertical="true"
android:text="@string/view_all" />

</RelativeLayout>
<androidx.recyclerview.widget.RecyclerView
android:layout_width="match_parent"
android:layout_height="100dp" />
</LinearLayout>
</LinearLayout>

</ScrollView>

</LinearLayout>

private void collegeRecycler() {
if(collegeRecycler!=null)//add this line 
{
collegeRecycler.setLayoutManager(new LinearLayoutManager(this,LinearLayoutManager.HORIZONTAL,false));
collegeRecycler.setHasFixedSize(true);
collegeLocations.add(new CollegeHelperClass(R.drawable.anti_ragging,"AntiRagging","Anti Ragging Committee helps to stop ragging activities in our College"));
collegeLocations.add(new CollegeHelperClass(R.drawable.anti_ragging,"AntiRagging","Anti Ragging Committee helps to stop ragging activities in our College"));
collegeLocations.add(new CollegeHelperClass(R.drawable.anti_ragging,"AntiRagging","Anti Ragging Committee helps to stop ragging activities in our College"));
adapter_clg  = new CollegeAdapter(collegeLocations);
collegeRecycler.setAdapter(adapter_clg);
}
}
private void deptRecycler() {
if(deptRecycler!=null)//add this line
{
deptRecycler.setLayoutManager(new LinearLayoutManager(this,LinearLayoutManager.HORIZONTAL,false));
deptRecycler.setHasFixedSize(true);
deptLocations.add(new DeptHelperClass(R.drawable.cse,"Computer Science & Engineering","Dazzling CSE"));
deptLocations.add(new DeptHelperClass(R.drawable.auto,"Automobile Engineering","Amazing Auto"));
deptLocations.add(new DeptHelperClass(R.drawable.mechanic,"Mechanical Engineering","Royal Mech"));
deptLocations.add(new DeptHelperClass(R.drawable.biotech,"Bio-Technology","Beautiful Bio"));
deptLocations.add(new DeptHelperClass(R.drawable.civil,"Civil Engineering","Clever Civil"));
deptLocations.add(new DeptHelperClass(R.drawable.electrical,"Electrical and Electronics Engineering","#Psych EEE"));
deptLocations.add(new DeptHelperClass(R.drawable.chemistry,"Chemistry","Toxic chemistry"));
deptLocations.add(new DeptHelperClass(R.drawable.computer_app,"Computer Applications","Playful Applications"));
deptLocations.add(new DeptHelperClass(R.drawable.ece,"ECE","Dominating ECE"));
deptLocations.add(new DeptHelperClass(R.drawable.english,"English","Educative English"));
deptLocations.add(new DeptHelperClass(R.drawable.it_dept,"Information Technology","Informative IT"));
deptLocations.add(new DeptHelperClass(R.drawable.management,"Management Studies","Magical Management"));
deptLocations.add(new DeptHelperClass(R.drawable.maths,"Mathematics","Scary Mathematics"));
deptLocations.add(new DeptHelperClass(R.drawable.petro,"Petrochemical Technology","Purposeful Petro"));
deptLocations.add(new DeptHelperClass(R.drawable.pharma,"Pharma","Fundamental Pharma"));
deptLocations.add(new DeptHelperClass(R.drawable.physics,"Physics","Mesmerising Physics"));
deptLocations.add(new DeptHelperClass(R.drawable.physical_edu,"Physical Education","Sweaty PE"));
adapter = new DeptAdapter(deptLocations, this);
deptRecycler.setAdapter(adapter);
}

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