java我在一个布局中创建了两个回收器视图,我有nullPointerException
当我尝试在安卓 studio中实现两个回收器视图时。我得到了类似NullPointerException
的错误。我为这两个视图创建了两个适配器和助手class
,并用java调用了它们的函数
import 安卓.content.Intent;
import 安卓.os.Bundle;
import 安卓.view.WindowManager;
import 安卓x.appcompat.app.AppCompatActivity;
import 安卓x.recyclerview.widget.LinearLayoutManager;
import 安卓x.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 安卓x.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 安卓x.recyclerview.widget.RecyclerView.setHasFixedSize(boolean)' on a null object reference
at 安卓.app.ActivityThread.performLaunchActivity(ActivityThread.java:2684)
at 安卓.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2750)
at 安卓.app.ActivityThread.access$1100(ActivityThread.java:186)
at 安卓.app.ActivityThread$H.handleMessage(ActivityThread.java:1606)
at 安卓.os.Handler.dispatchMessage(Handler.java:111)
at 安卓.os.Looper.loop(Looper.java:238)
at 安卓.app.ActivityThread.main(ActivityThread.java:6006)
at java.lang.reflect.Method.invoke(Native Method)
at com.安卓.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:937)
at com.安卓.internal.os.ZygoteInit.main(ZygoteInit.java:798)
Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'void 安卓x.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 安卓.app.Activity.performCreate(Activity.java:6466)
at 安卓.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1113)
at 安卓.app.ActivityThread.performLaunchActivity(ActivityThread.java:2637)
at 安卓.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2750)
at 安卓.app.ActivityThread.access$1100(ActivityThread.java:186)
at 安卓.app.ActivityThread$H.handleMessage(ActivityThread.java:1606)
at 安卓.os.Handler.dispatchMessage(Handler.java:111)
at 安卓.os.Looper.loop(Looper.java:238)
at 安卓.app.ActivityThread.main(ActivityThread.java:6006)
at java.lang.reflect.Method.invoke(Native Method)
at com.安卓.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:937)
at com.安卓.internal.os.ZygoteInit.main(ZygoteInit.java:798) ```
我的布局文件是
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:安卓="http://schemas.安卓.com/apk/res/安卓"
xmlns:app="http://schemas.安卓.com/apk/res-auto"
xmlns:tools="http://schemas.安卓.com/tools"
安卓:layout_width="match_parent"
安卓:layout_height="match_parent"
安卓:layout_margin="10dp"
安卓:background="@color/white"
安卓:orientation="vertical"
tools:context=".User.UserDashboard">
<RelativeLayout
安卓:layout_width="match_parent"
安卓:layout_height="wrap_content">
<ImageView
安卓:id="@+id/textView"
安卓:layout_width="40dp"
安卓:layout_height="40dp"
安卓:layout_centerVertical="true"
安卓:contentDescription="@string/menu_bar"
安卓:src="@drawable/menu_icon_userdash_black" />
</RelativeLayout>
<ScrollView
安卓:layout_width="match_parent"
安卓:layout_height="match_parent"
安卓:scrollbars="none"
>
<LinearLayout
安卓:layout_width="match_parent"
安卓:layout_height="wrap_content"
安卓:orientation="vertical">
<RelativeLayout
安卓:layout_width="match_parent"
安卓:layout_height="wrap_content">
<TextView
安卓:id="@+id/userdash_title"
安卓:layout_width="wrap_content"
安卓:layout_height="wrap_content"
安卓:layout_centerHorizontal="true"
安卓:fontFamily="@font/josefin_regular"
安卓:text="@string/logo_name"
安卓:textSize="24sp"
安卓:textStyle="bold"
/>
<RelativeLayout
安卓:layout_width="match_parent"
安卓:layout_height="40dp"
安卓:layout_below="@id/userdash_title"
安卓:layout_marginLeft="40dp"
安卓:layout_marginTop="20dp"
安卓:layout_marginRight="40dp"
安卓:layout_marginBottom="20dp"
安卓:background="@color/white"
安卓:elevation="8dp">
<TextView
安卓:id="@+id/search_string"
安卓:layout_width="wrap_content"
安卓:layout_height="wrap_content"
安卓:layout_centerVertical="true"
安卓:layout_marginStart="15dp"
安卓:text="@string/search_string" />
<ImageView
安卓:id="@+id/search_bar"
安卓:layout_width="30dp"
安卓:layout_height="30dp"
安卓:layout_alignParentEnd="true"
安卓:layout_centerVertical="true"
安卓:layout_marginRight="15dp"
安卓:contentDescription="@string/search_bar_userdash"
安卓:src="@drawable/search_userdash_black" />
</RelativeLayout>
</RelativeLayout>
<LinearLayout
安卓:layout_width="wrap_content"
安卓:layout_height="wrap_content"
安卓:layout_gravity="center_horizontal"
安卓:orientation="horizontal">
<LinearLayout
安卓:layout_width="wrap_content"
安卓:layout_height="wrap_content"
安卓:layout_margin="5dp"
安卓:orientation="vertical">
<RelativeLayout
安卓:layout_width="60dp"
安卓:layout_height="60dp"
安卓:background="@drawable/card_one_userdash"
安卓:elevation="8dp">
<ImageView
安卓:layout_width="30dp"
安卓:layout_height="30dp"
安卓:layout_centerInParent="true"
安卓:src="@drawable/cse" />
</RelativeLayout>
<TextView
安卓:layout_width="match_parent"
安卓:layout_height="wrap_content"
安卓:fontFamily="@font/josefin_regular"
安卓:gravity="center_horizontal"
安卓:text="@string/CSE"
安卓:textAlignment="center"
安卓:textSize="11sp"
安卓:textStyle="bold" />
</LinearLayout>
<LinearLayout
安卓:layout_width="wrap_content"
安卓:layout_height="wrap_content"
安卓:layout_margin="5dp"
安卓:orientation="vertical">
<RelativeLayout
安卓:layout_width="60dp"
安卓:layout_height="60dp"
安卓:background="@drawable/card_two_userdash"
安卓:elevation="8dp">
<ImageView
安卓:layout_width="30dp"
安卓:layout_height="30dp"
安卓:layout_centerInParent="true"
安卓:src="@drawable/auto" />
</RelativeLayout>
<TextView
安卓:layout_width="match_parent"
安卓:layout_height="wrap_content"
安卓:fontFamily="@font/josefin_regular"
安卓:gravity="center_horizontal"
安卓:text="@string/automob"
安卓:textAlignment="center"
安卓:textSize="11sp"
安卓:textStyle="bold" />
</LinearLayout>
<LinearLayout
安卓:layout_width="wrap_content"
安卓:layout_height="wrap_content"
安卓:layout_margin="5dp"
安卓:orientation="vertical">
<RelativeLayout
安卓:layout_width="60dp"
安卓:layout_height="60dp"
安卓:background="@drawable/card_three_userdash"
安卓:elevation="8dp">
<ImageView
安卓:layout_width="30dp"
安卓:layout_height="30dp"
安卓:layout_centerInParent="true"
安卓:src="@drawable/mechanic" />
</RelativeLayout>
<TextView
安卓:layout_width="match_parent"
安卓:layout_height="wrap_content"
安卓:fontFamily="@font/josefin_regular"
安卓:gravity="center_horizontal"
安卓:text="@string/mechanical"
安卓:textAlignment="center"
安卓:textSize="11sp"
安卓:textStyle="bold" />
</LinearLayout>
<LinearLayout
安卓:layout_width="wrap_content"
安卓:layout_height="wrap_content"
安卓:layout_margin="5dp"
安卓:orientation="vertical">
<RelativeLayout
安卓:layout_width="60dp"
安卓:layout_height="60dp"
安卓:background="@drawable/card_four_userdash"
安卓:elevation="8dp">
<ImageView
安卓:layout_width="30dp"
安卓:layout_height="30dp"
安卓:layout_centerInParent="true"
安卓:src="@drawable/electrical" />
</RelativeLayout>
<TextView
安卓:layout_width="match_parent"
安卓:layout_height="wrap_content"
安卓:fontFamily="@font/josefin_regular"
安卓:gravity="center_horizontal"
安卓:text="@string/EEE"
安卓:textAlignment="center"
安卓:textSize="11sp"
安卓:textStyle="bold" />
</LinearLayout>
</LinearLayout>
<RelativeLayout
安卓:layout_width="match_parent"
安卓:layout_height="wrap_content"
安卓:layout_marginLeft="10dp"
安卓:layout_marginTop="20dp"
安卓:background="@color/white">
<LinearLayout
安卓:id="@+id/featured_background"
安卓:layout_width="120dp"
安卓:layout_height="280dp"
安卓:layout_margin="10dp"
安卓:background="@color/ColorPrimaryDark"
安卓:orientation="vertical">
<TextView
安卓:layout_width="wrap_content"
安卓:layout_height="wrap_content"
安卓:layout_marginStart="10dp"
安卓:layout_marginTop="50dp"
安卓:fontFamily="@font/josefin_regular"
安卓:text="@string/featured_locations"
安卓:textAllCaps="true"
安卓:textColor="@color/white"
安卓:textSize="14sp"
安卓:textStyle="bold" />
<TextView
安卓:layout_width="wrap_content"
安卓:layout_height="wrap_content"
安卓:layout_margin="10dp"
安卓:fontFamily="@font/josefin_regular"
安卓:text="Featured List of All Departments"
安卓:textColor="@color/colorPrimary"
安卓:textSize="12sp" />
</LinearLayout>
<安卓x.recyclerview.widget.RecyclerView
安卓:id="@+id/dept_recycler"
安卓:layout_width="match_parent"
安卓:layout_height="280dp"
安卓:layout_marginTop="10dp"
安卓:layout_toEndOf="@id/featured_background"
安卓:background="@color/card_two_userdash" />
</RelativeLayout>
<LinearLayout
安卓:layout_width="match_parent"
安卓:layout_height="wrap_content"
安卓:layout_marginTop="30dp"
安卓:orientation="vertical"
安卓:padding="20dp">
<RelativeLayout
安卓:layout_width="match_parent"
安卓:layout_height="wrap_content">
<TextView
安卓:layout_width="wrap_content"
安卓:layout_height="wrap_content"
安卓:fontFamily="@font/josefin_regular"
安卓:text="@string/most_viewed_locations"
安卓:textAllCaps="true"
安卓:textColor="@color/black"
安卓:textSize="20sp" />
<TextView
安卓:layout_width="wrap_content"
安卓:layout_height="wrap_content"
安卓:layout_alignParentRight="true"
安卓:layout_centerVertical="true"
安卓:text="@string/view_all" />
</RelativeLayout>
<安卓x.recyclerview.widget.RecyclerView
安卓:id="@+id/clg_recycler"
安卓:layout_width="match_parent"
安卓:layout_height="100dp" />
</LinearLayout>
<LinearLayout
安卓:layout_width="match_parent"
安卓:layout_height="wrap_content"
安卓:layout_marginTop="30dp"
安卓:orientation="vertical"
安卓:padding="20dp">
<RelativeLayout
安卓:layout_width="match_parent"
安卓:layout_height="wrap_content">
<TextView
安卓:layout_width="wrap_content"
安卓:layout_height="wrap_content"
安卓:fontFamily="@font/josefin_regular"
安卓:text="@string/categories"
安卓:textAllCaps="true"
安卓:textColor="@color/black"
安卓:textSize="20sp" />
<TextView
安卓:layout_width="wrap_content"
安卓:layout_height="wrap_content"
安卓:layout_alignParentRight="true"
安卓:layout_centerVertical="true"
安卓:text="@string/view_all" />
</RelativeLayout>
<安卓x.recyclerview.widget.RecyclerView
安卓:layout_width="match_parent"
安卓:layout_height="100dp" />
</LinearLayout>
</LinearLayout>
</ScrollView>
</LinearLayout>
# 1 楼答案