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size of recycler view item changes when user scrolls down and up

I am working on a chat functionality to implement in my app. The purpose is that when a message comes from another user, the message item will align parent's start and when the user sends a message, it will align to the end. The send button on upper left corner simulates the other user sending a message. The problem is that when items recycles, some of them mathes the width of parent layout. I do not really understand why this happens and how to fix it. Thanks in advance...
package com.example.messageapp;
import androidx.appcompat.app.AppCompatActivity;
import androidx.recyclerview.widget.LinearLayoutManager;
import androidx.recyclerview.widget.RecyclerView;
import android.app.Activity;
import android.content.Context;
import android.database.Observable;
import android.os.Bundle;
import android.view.View;
import android.view.inputmethod.InputMethodManager;
import android.widget.Button;
import android.widget.EditText;
import java.util.ArrayList;
import java.util.List;
public class MainActivity extends AppCompatActivity {
Button sendBtn;
Button otherSendBtn;
EditText editText;
RecyclerView recyclerView;
MessagesAdapter adapter;
List<ChatMessage> messageList;
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
messageList=new ArrayList<>();
sendBtn=findViewById(R.id.sendBtn);
otherSendBtn=findViewById(R.id.otherSendBtn);
editText=findViewById(R.id.editText);
recyclerView=findViewById(R.id.recyclerView);
adapter=new MessagesAdapter(this,messageList);
recyclerView.setAdapter(adapter);
recyclerView.setLayoutManager(new LinearLayoutManager(this));
recyclerView.setHasFixedSize(true);
for(int i=0; i<4; i++){
if(i%2==0){
messageList.add(new ChatMessage("from him","self"));
}else{
messageList.add(new ChatMessage("from me","other"));
}
adapter.notifyItemInserted(messageList.size()-1);
}
otherSendBtn.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View view) {
messageList.add(new ChatMessage("random","other"));
adapter.notifyItemInserted(messageList.size()-1);
}
});
sendBtn.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View view) {
String txt=editText.getText().toString();
messageList.add(new ChatMessage(txt, "self"));
adapter.notifyItemInserted(messageList.size()-1);
editText.setText("");
hideKeyboardFrom(MainActivity.this, view);
}
});
}
public static void hideKeyboardFrom(Context context, View view) {
InputMethodManager imm = (InputMethodManager) context.getSystemService(Activity.INPUT_METHOD_SERVICE);
imm.hideSoftInputFromWindow(view.getWindowToken(), 0);
}
}
model class for messages
package com.example.messageapp;
public class ChatMessage {
public String text;
public String user;
public ChatMessage(String text, String user) {
this.text = text;
this.user = user;
}
}
recycler view adapter
package com.example.messageapp;
import android.content.Context;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.RelativeLayout;
import android.widget.TextView;
import androidx.annotation.NonNull;
import androidx.recyclerview.widget.RecyclerView;
import java.util.List;
public class MessagesAdapter extends RecyclerView.Adapter {
Context context;
List<ChatMessage> messages;
public void setMessages(List<ChatMessage> messages) {
this.messages = messages;
}
public MessagesAdapter(Context context, List<ChatMessage> messages) {
this.context = context;
this.messages = messages;
}
private static class MessageViewHolder extends RecyclerView.ViewHolder{
TextView textView;
RelativeLayout relativeLayout;
public MessageViewHolder(#NonNull View itemView) {
super(itemView);
textView=itemView.findViewById(R.id.messageTextView);
relativeLayout=itemView.findViewById(R.id.item_parent);
}
}
#NonNull
#Override
public RecyclerView.ViewHolder onCreateViewHolder(#NonNull ViewGroup parent, int viewType) {
View v= LayoutInflater.from(context).inflate(R.layout.message_item,parent,false);
return new MessageViewHolder(v);
}
#Override
public void onBindViewHolder(#NonNull RecyclerView.ViewHolder holder, int position) {
ChatMessage message=messages.get(position);
((MessageViewHolder) holder).textView.setText(message.text);
RelativeLayout.LayoutParams params= (RelativeLayout.LayoutParams) ((MessageViewHolder) holder).relativeLayout.getLayoutParams();
if(message.user.equals("self")){
params.addRule(RelativeLayout.ALIGN_PARENT_END);
((MessageViewHolder) holder).relativeLayout.setBackgroundColor(context.getResources().getColor(R.color.teal_200));
}else{
params.addRule(RelativeLayout.ALIGN_PARENT_START);
((MessageViewHolder) holder).relativeLayout.setBackgroundColor(context.getResources().getColor(R.color.purple_200));
}
((MessageViewHolder) holder).relativeLayout.setLayoutParams(params);
}
#Override
public int getItemCount() {
return messages.size();
}
}
<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
xmlns:app="http://schemas.android.com/apk/res-auto"
android:layout_margin="10dp">
<RelativeLayout
android:id="#+id/item_parent"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:background="#color/teal_700">
<TextView
android:padding="10dp"
android:id="#+id/messageTextView"
android:layout_width="wrap_content"
android:layout_height="wrap_content" />
</RelativeLayout>
</RelativeLayout>
<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout
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"
tools:context=".MainActivity">
<Button
android:id="#+id/otherSendBtn"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="send"
android:layout_centerHorizontal="true"/>
<androidx.recyclerview.widget.RecyclerView
android:id="#+id/recyclerView"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:layout_below="#id/otherSendBtn"
tools:listitem="#layout/message_item"/>
<RelativeLayout
android:id="#+id/linear"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:layout_alignParentBottom="true"
android:orientation="horizontal">
<EditText
android:id="#+id/editText"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:layout_toStartOf="#+id/sendBtn"
android:layout_marginEnd="5dp"/>
<Button
android:background="#drawable/ic_baseline_send_24"
android:id="#+id/sendBtn"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_alignParentEnd="true"/>
</RelativeLayout>
</RelativeLayout>

Show data from Firebase in a Recyclerview in a Fragment | Java

How can I take data from Firebase into a recyclerview and show it inside a fragment?
I followed This video to create a recyclerview inside a fragment. But in it the data is static. (retrieved from the strings file)
I then tried to incorporate this video to retrieve data from Firebase.
But it doesn't work. Maybe I have to call the functions in a different override??
My Fragment Class (HomeFragemnt.java)
package com.example.foodapp.deliverer;
import android.os.Bundle;
import androidx.annotation.NonNull;
import androidx.annotation.Nullable;
import androidx.fragment.app.Fragment;
import androidx.recyclerview.widget.LinearLayoutManager;
import androidx.recyclerview.widget.RecyclerView;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import com.example.foodapp.R;
import com.google.firebase.database.DataSnapshot;
import com.google.firebase.database.DatabaseError;
import com.google.firebase.database.DatabaseReference;
import com.google.firebase.database.FirebaseDatabase;
import com.google.firebase.database.ValueEventListener;
import java.util.ArrayList;
public class HomeFragment extends Fragment {
private ArrayList<OrderItem> orderItemArrayList;
RecyclerView recyclerview;
DatabaseReference DB;
ItemRecyclerAdapter itemRecyclerAdapter;
#Override
public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
View view = inflater.inflate(R.layout.delivery_fragment_home, container, false);
return view;
}
#Override
public void onViewCreated(#NonNull View view, #Nullable Bundle savedInstanceState) {
super.onViewCreated(view, savedInstanceState);
recyclerview = view.findViewById(R.id.delivery_orders_recyclerView);
DB = FirebaseDatabase.getInstance().getReference("Delivery");
recyclerview.setHasFixedSize(true);
recyclerview.setLayoutManager(new LinearLayoutManager(getContext()));
orderItemArrayList = new ArrayList<>();
itemRecyclerAdapter = new ItemRecyclerAdapter(getContext(), orderItemArrayList);
recyclerview.setAdapter(itemRecyclerAdapter);
DB.addValueEventListener(new ValueEventListener() {
#Override
public void onDataChange(#NonNull DataSnapshot snapshot) {
for(DataSnapshot dataSnapshot: snapshot.getChildren()){
OrderItem item = dataSnapshot.child("Delivery").getValue(OrderItem.class);
orderItemArrayList.add(item);
}
}
#Override
public void onCancelled(#NonNull DatabaseError error) {
}
});
itemRecyclerAdapter.notifyDataSetChanged();
}
}
My Fragment Layout (delivery_fragment_home.xml)
<?xml version="1.0" encoding="utf-8"?>
<androidx.constraintlayout.widget.ConstraintLayout 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"
android:layout_width="match_parent"
android:layout_height="match_parent"
tools:context=".deliverer.HomeFragment" >
<androidx.recyclerview.widget.RecyclerView
android:id="#+id/delivery_orders_recyclerView"
android:layout_width="409dp"
android:layout_height="729dp"
android:background="#CDDC39"
app:layout_constraintBottom_toBottomOf="parent"
app:layout_constraintEnd_toEndOf="parent"
app:layout_constraintStart_toStartOf="parent"
app:layout_constraintTop_toTopOf="parent"
tools:listitem="#layout/delivery_orderitem" />
</androidx.constraintlayout.widget.ConstraintLayout>
Item into Recyclerview class (OrderItem.java)
package com.example.foodapp.deliverer;
public class OrderItem {
private String orderID;
private String Address;
public OrderItem(String orderID, String Address) {
this.orderID = orderID;
this.Address = Address;
}
public String getOrderID() {
return orderID;
}
public String getAddress() {
return Address;
}
}
Item into recyclerview layout (delivery_orderItem.xml)
<?xml version="1.0" encoding="utf-8"?>
<androidx.constraintlayout.widget.ConstraintLayout 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="wrap_content">
<TextView
android:id="#+id/textView2"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_marginStart="15dp"
android:layout_marginTop="15dp"
android:text="#string/lbl_orderId"
app:layout_constraintStart_toStartOf="parent"
app:layout_constraintTop_toTopOf="parent" />
<TextView
android:id="#+id/textView3"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_marginStart="15dp"
android:layout_marginTop="8dp"
android:layout_marginBottom="15dp"
android:text="#string/lbl_address"
app:layout_constraintBottom_toBottomOf="parent"
app:layout_constraintStart_toStartOf="parent"
app:layout_constraintTop_toBottomOf="#+id/textView2" />
<TextView
android:id="#+id/lbl_orderId"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_marginStart="12dp"
android:layout_marginTop="15dp"
android:text="TextView"
app:layout_constraintStart_toEndOf="#+id/textView2"
app:layout_constraintTop_toTopOf="parent" />
<TextView
android:id="#+id/lbl_address"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_marginTop="8dp"
android:layout_marginBottom="15dp"
android:text="TextView"
app:layout_constraintBottom_toBottomOf="parent"
app:layout_constraintStart_toStartOf="#+id/lbl_orderId"
app:layout_constraintTop_toBottomOf="#+id/lbl_orderId" />
</androidx.constraintlayout.widget.ConstraintLayout>
Adapter class (ItemRecyclerAdapter.java)
package com.example.foodapp.deliverer;
import android.content.Context;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.TextView;
import androidx.annotation.NonNull;
import androidx.recyclerview.widget.RecyclerView;
import com.example.foodapp.R;
import java.util.ArrayList;
public class ItemRecyclerAdapter extends RecyclerView.Adapter<ItemRecyclerAdapter.DriverItemViewHolder> {
Context context;
ArrayList<OrderItem> itemArrayList;
public ItemRecyclerAdapter(Context context, ArrayList<OrderItem> itemList) {
this.context = context;
this.itemArrayList = itemList;
}
#NonNull
#Override
public DriverItemViewHolder onCreateViewHolder(#NonNull ViewGroup parent, int viewType) {
View v = LayoutInflater.from(context).inflate(R.layout.delivery_orderitem, parent, false);
return new DriverItemViewHolder(v);
}
#Override
public void onBindViewHolder(#NonNull ItemRecyclerAdapter.DriverItemViewHolder holder, int position) {
OrderItem order = itemArrayList.get(position);
holder.orderID.setText(order.getOrderID());
holder.address.setText(order.getAddress());
}
#Override
public int getItemCount() {
return itemArrayList .size();
}
public static class DriverItemViewHolder extends RecyclerView.ViewHolder{
private TextView orderID;
private TextView address;
public DriverItemViewHolder(#NonNull View itemView) {
super(itemView);
this.orderID = itemView.findViewById(R.id.lbl_orderId);
this.address = itemView.findViewById(R.id.lbl_address);
}
}
}
What am I doing wrong?

Android Studio Grid View doesn't show when I run the app

I created a Java class that should display something like this:
But this is what I get when I run the app:
It doesn't show what I wanted and Android Studio doesn't show any error in Logcat, so I don't know why it's not working.
This is the code for the class SetsActivity:
package com.example.myquiz;
import androidx.annotation.NonNull;
import androidx.appcompat.app.AppCompatActivity;
import android.os.Bundle;
import android.view.MenuItem;
import android.widget.GridView;
import android.widget.Toolbar;
public class SetsActivity extends AppCompatActivity {
private GridView sets_grid;
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_sets);
androidx.appcompat.widget.Toolbar toolbar = findViewById(R.id.set_toolbar);
//setSupportActionBar(toolbar);
String title = getIntent().getStringExtra("CATEGORY");
getSupportActionBar().setTitle(title);
getSupportActionBar().setDisplayHomeAsUpEnabled(true);
sets_grid = findViewById(R.id.sets_gridview);
SetsAdapter adapter = new SetsAdapter(2);
sets_grid.setAdapter(adapter);
}
#Override
public boolean onOptionsItemSelected(#NonNull MenuItem item) {
if(item.getItemId() == android.R.id.home)
{
SetsActivity.this.finish();
}
return super.onOptionsItemSelected(item);
}
}
I also created an adapter class SetsAdapter so I'm gonna post the code for it as well:
package com.example.myquiz;
import android.content.Intent;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.BaseAdapter;
import android.widget.TextView;
public class SetsAdapter extends BaseAdapter {
private int numOfSets;
public SetsAdapter(int numOfSets) {
this.numOfSets = numOfSets;
}
#Override
public int getCount() {
return 0;
}
#Override
public Object getItem(int position) {
return null;
}
#Override
public long getItemId(int position) {
return 0;
}
#Override
public View getView(int position, View convertView, ViewGroup parent) {
View view;
if (convertView == null) {
view = LayoutInflater.from(parent.getContext()).inflate(R.layout.set_item_layout, parent, false);
} else {
view = convertView;
}
view.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View v) {
Intent intent = new Intent(parent.getContext(),QuestionActivity.class);
parent.getContext().startActivity(intent);
}
});
((TextView) view.findViewById(R.id.setNo_tv)).setText(String.valueOf(position + 1));
return view;
}
}
And here is the code for the XML file:
<?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"
tools:context=".SetsActivity"
android:orientation="vertical">
<androidx.appcompat.widget.Toolbar
android:id="#+id/set_toolbar"
android:layout_width="match_parent"
android:layout_height="?attr/actionBarSize"
android:background="#color/colorPrimary"
android:theme="#style/ThemeOverlay.AppCompat.Dark"
></androidx.appcompat.widget.Toolbar>
<TextView
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:text="Sets"
android:textSize="26sp"
android:textStyle="bold"
android:padding="16dp" />
<GridView
android:layout_width="match_parent"
android:layout_height="0dp"
android:id="#+id/sets_gridview"
android:layout_weight="1"
android:gravity="center"
android:horizontalSpacing="16dp"
android:verticalSpacing="16dp"
android:padding="16dp"
android:columnWidth="100dp"
android:numColumns="auto_fit"
></GridView>
</LinearLayout>
Here is the code for the XML file set_item_layout:
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout
xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="100dp"
android:layout_height="100dp"
android:orientation="vertical"
android:gravity="center"
android:background="#drawable/round_corner"
android:backgroundTint="#FFC3C3"
>
<TextView
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="1"
android:id="#+id/setNo_tv"
android:textStyle="bold"
android:textColor="#android:color/black"
android:textSize="45sp"></TextView>
</LinearLayout>

The getCount() method in the SetsAdapter should return numOfSets not 0.
#Override
public int getCount() {
return numOfSets;
}

Android Studio RecyclerView wont show my data when i add toolbar at my `layout.xml` file

I created a page where it will show the firebase data in a RecyclerView. It work but I decided to put a toolbar at the top of the page to have a back function. After I put the toolbar in my layout file, the RecyclerView is not showing any data anymore. I think that my layout XML file is wrong. Thanks in advance for anyone helping.
Actity file
package com.example.attendanceappvqyfyp;
import androidx.appcompat.app.AlertDialog;
import androidx.appcompat.app.AppCompatActivity;
import androidx.recyclerview.widget.LinearLayoutManager;
import androidx.recyclerview.widget.RecyclerView;
import android.content.DialogInterface;
import android.os.Bundle;
import android.view.LayoutInflater;
import android.view.MenuItem;
import android.view.View;
import android.widget.EditText;
import android.widget.TextView;
import android.widget.Toast;
import android.widget.Toolbar;
import com.example.attendanceappvqyfyp.Interface.itemClickListener;
import com.example.attendanceappvqyfyp.Common.Common;
import com.example.attendanceappvqyfyp.Model.LecturerClass;
import com.example.attendanceappvqyfyp.Model.News;
import com.example.attendanceappvqyfyp.Model.Timetable;
import com.firebase.ui.database.FirebaseRecyclerAdapter;
import com.google.firebase.database.DatabaseReference;
import com.google.firebase.database.FirebaseDatabase;
import com.example.attendanceappvqyfyp.Common.Common;
public class LecturerClassList extends AppCompatActivity {
RecyclerView recyclerView;
RecyclerView.LayoutManager layoutManager;
FirebaseDatabase database;
DatabaseReference lecturerclass;
DatabaseReference news;
FirebaseRecyclerAdapter<LecturerClass,LecturerClassViewHolder> adapter;
TextView newscourse, newsclass;
EditText newsdescription;
Toolbar toolbar;
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_lecturer_class_list);
//Firebase
database = FirebaseDatabase.getInstance();
lecturerclass = database.getReference("Class");
news = database.getReference("News");
recyclerView = (RecyclerView)findViewById(R.id.recycler_lecturerclass);
recyclerView.setHasFixedSize(true);
layoutManager = new LinearLayoutManager(this);
recyclerView.setLayoutManager(layoutManager);
//Toolbar code
toolbar = findViewById(R.id.toolbar);
toolbar.setTitle("Class List");
toolbar.setNavigationIcon(R.drawable.ic_arrow_back_black_24dp);
loadLecturerClass(Common.currentLecturer.getName());
}
private void loadLecturerClass(String Lecturer) {
adapter = new FirebaseRecyclerAdapter<LecturerClass, LecturerClassViewHolder>(LecturerClass.class, R.layout.lecturerclass_item, LecturerClassViewHolder.class, lecturerclass.orderByChild("lecturer").equalTo(Lecturer)) {
#Override
protected void populateViewHolder(LecturerClassViewHolder lecturerClassViewHolder, LecturerClass lecturerClass, int i) {
lecturerClassViewHolder.lclasstitle.setText("Class :" + adapter.getRef(i).getKey());
lecturerClassViewHolder.ldate.setText("Day :" + lecturerClass.getDay());
lecturerClassViewHolder.ltime.setText("Time :" + lecturerClass.getTime());
lecturerClassViewHolder.lclassroom.setText("Classroom :" + lecturerClass.getClassroom());
lecturerClassViewHolder.lcourse.setText(lecturerClass.getCourse());
lecturerClassViewHolder.setItemClickListener(new itemClickListener() {
#Override
public void onClick(View view, int position, boolean isLongClick) {
//code later
}
});
}
};
recyclerView.setAdapter(adapter);
}
#Override
public boolean onContextItemSelected(MenuItem item) {
if(item.getTitle().equals(Common.News))
{
showNewsDialog(adapter.getRef(item.getOrder()).getKey(),adapter.getItem(item.getOrder()));
}
return super.onContextItemSelected(item);
}
private void showNewsDialog(final String course, final LecturerClass item) {
AlertDialog.Builder alertDialog = new AlertDialog.Builder(LecturerClassList.this);
alertDialog.setTitle("Make Announcement");
alertDialog.setMessage("Make announcement about this class.");
LayoutInflater inflater = this.getLayoutInflater();
View lecturer_make_news = inflater.inflate(R.layout.activity_lecturer_make_news, null);
newscourse = lecturer_make_news.findViewById(R.id.NewsCourse);
newsclass = lecturer_make_news.findViewById(R.id.NewsClass);
newsdescription = lecturer_make_news.findViewById(R.id.NewsDescription);
newscourse.setText("Course: "+item.getCourse());
newsclass.setText("Subject: " + course);
alertDialog.setView(lecturer_make_news);
alertDialog.setPositiveButton("Post", new DialogInterface.OnClickListener() {
#Override
public void onClick(DialogInterface dialog, int i) {
if(newsdescription.getText().toString().isEmpty()){
Toast.makeText(LecturerClassList.this, "Post cancel, description cannot be empty.", Toast.LENGTH_SHORT).show();
}
else {
News lnews = new News(
item.getCourse(),
course,
newsdescription.getText().toString()
);
news.child(String.valueOf(System.currentTimeMillis())).setValue(lnews);
Toast.makeText(LecturerClassList.this, "Announcement post successfully.", Toast.LENGTH_SHORT).show();
finish();
}
}
});
alertDialog.setNegativeButton("Cancel", new DialogInterface.OnClickListener() {
#Override
public void onClick(DialogInterface dialog, int which) {
dialog.dismiss();;
}
});
alertDialog.show();
}
}
Activity file for viewholder
package com.example.attendanceappvqyfyp;
import android.view.ContextMenu;
import android.view.View;
import android.widget.TextView;
import com.example.attendanceappvqyfyp.Common.Common;
import androidx.recyclerview.widget.RecyclerView;
import com.example.attendanceappvqyfyp.Interface.itemClickListener;
public class LecturerClassViewHolder extends RecyclerView.ViewHolder implements View.OnClickListener,View.OnCreateContextMenuListener {
public TextView lclasstitle, ldate, ltime, lclassroom, lcourse;
private itemClickListener itemClickListener;
public LecturerClassViewHolder(View itemView) {
super(itemView);
lclasstitle = (TextView)itemView.findViewById(R.id.lclasstitle);
ldate = (TextView)itemView.findViewById(R.id.ldate);
ltime = (TextView)itemView.findViewById(R.id.ltime);
lclassroom = (TextView)itemView.findViewById(R.id.lclassroom);
lcourse = (TextView)itemView.findViewById(R.id.lcourse);
itemView.setOnCreateContextMenuListener(this);
itemView.setOnClickListener(this);
}
public void setItemClickListener(itemClickListener itemClickListener) {
this.itemClickListener = itemClickListener;
}
#Override
public void onClick(View view) {
itemClickListener.onClick(view, getAdapterPosition(), false);
}
public void onCreateContextMenu(ContextMenu menu, View v, ContextMenu.ContextMenuInfo menuInfo) {
menu.setHeaderTitle("Select");
menu.add(0,0,getAdapterPosition(), Common.News);
}
}
Layout file for recyclerview
<?xml version="1.0" encoding="utf-8"?>
<androidx.constraintlayout.widget.ConstraintLayout 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"
tools:context=".LecturerClassList">
<android.widget.Toolbar
android:id="#+id/toolbar"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:background="?attr/colorPrimary"
android:minHeight="?attr/actionBarSize"
app:layout_constraintStart_toStartOf="parent"
app:layout_constraintTop_toTopOf="parent"
app:theme="#style/ThemeOverlay.AppCompat.Dark" />
<androidx.recyclerview.widget.RecyclerView
android:id="#+id/recycler_lecturerclass"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:scrollbars="vertical"
app:layout_constraintTop_toBottomOf="#+id/toolbar" />
</androidx.constraintlayout.widget.ConstraintLayout>
Layout file for itemview
<?xml version="1.0" encoding="utf-8"?>
<androidx.cardview.widget.CardView xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:app="http://schemas.android.com/apk/res-auto"
android:orientation="vertical"
android:layout_width="match_parent"
android:layout_height="160dp"
app:cardElevation="4dp"
android:layout_marginBottom="8dp"
>
<RelativeLayout
android:layout_width="match_parent"
android:layout_height="match_parent">
<TextView
android:id="#+id/lclasstitle"
android:layout_width="match_parent"
android:layout_height="40dp"
android:gravity="center"
android:text=""
android:textColor="#android:color/black"
android:textSize="20sp" />
<TextView
android:id="#+id/ldate"
android:layout_width="match_parent"
android:layout_height="40dp"
android:layout_alignBottom="#id/lclasstitle"
android:layout_marginBottom="-40dp"
android:gravity="center"
android:text=""
android:textColor="#android:color/black"
android:textSize="20sp" />
<TextView
android:id="#+id/ltime"
android:layout_width="match_parent"
android:layout_height="40dp"
android:layout_alignBottom="#id/ldate"
android:layout_marginBottom="-40dp"
android:gravity="center"
android:text=""
android:textColor="#android:color/black"
android:textSize="20sp" />
<TextView
android:id="#+id/lclassroom"
android:layout_width="match_parent"
android:layout_height="40dp"
android:layout_alignParentBottom="true"
android:gravity="center"
android:text=""
android:textColor="#android:color/black"
android:textSize="20sp" />
<TextView
android:id="#+id/lcourse"
android:layout_width="match_parent"
android:layout_height="40dp"
android:layout_alignParentBottom="true"
android:gravity="center"
android:text=""
android:visibility="invisible"
android:textColor="#android:color/black"
android:textSize="20sp" />
</RelativeLayout>
</androidx.cardview.widget.CardView>
Thanks to ZeePee for giving this link Display Back Arrow on Toolbar, although the toolbar didnt work for me, i change it back to actionbar and use the code from the link and it work.

Try adding horizontal constraints for Toolbar and Recycler View. After that you need to specify where do you want your single item widgets in Relative layout

How to add the ListView element to be referenced in the individual Activity files

The app crashes as soon as any of the list Activities are launched:
NullPointerException: Attempt to invoke virtual method 'void android.widget.ListView.setAdapter' on a null object reference
My instructor says its happening because the layouts haven't been configured correctly. Right now, the list_item is being inflated as the Activity layout. Please create a separate layout, such as activity_list and add the ListView element there to be referenced in the individual Activity files
Here's the code
MainActivity
package com.example.tourguide;
import android.content.Intent;
import android.net.Uri;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.view.View;
import android.widget.*;
public class MainActivity extends AppCompatActivity {
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
Button event = (Button) findViewById(R.id.events);
Button mall = (Button) findViewById(R.id.malls);
Button resturant = (Button) findViewById(R.id.resturants);
Button university = (Button) findViewById(R.id.uinversities);
event.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View v) {
Intent event = new Intent(MainActivity.this, events.class);
startActivity(event); }
});
mall.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View v) {
Intent mall = new Intent(MainActivity.this, malls.class);
startActivity(mall);
}
});
resturant.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View v) {
Intent resturant = new Intent(MainActivity.this, resturants.class);
startActivity(resturant);
}
});
university.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View v) {
Intent university = new Intent(MainActivity.this, universities.class);
startActivity(university);
}
});
}}
WordAdapter.java
package com.example.tourguide;
import android.app.Activity;
import android.content.Context;
import android.support.annotation.LayoutRes;
import android.support.annotation.NonNull;
import android.support.annotation.Nullable;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.ArrayAdapter;
import android.widget.ImageView;
import android.widget.TextView;
import java.util.ArrayList;
public class WordAdapter extends ArrayAdapter<listitem> {
public WordAdapter(Activity context, ArrayList<listitem> listitems) {
super(context, 0, listitems);
}
public View getView(int position, View convertView, ViewGroup parent) {
View listItemView = convertView;
if(listItemView == null) {
listItemView = LayoutInflater.from(getContext()).inflate(
R.layout.list_item, parent, false);
}
listitem currentItem = getItem(position);
TextView name = (TextView) listItemView.findViewById(R.id.text1);
name.setText(currentItem.getName());
ImageView image = (ImageView) listItemView.findViewById(R.id.image1);
image.setImageResource(currentItem.getImage());
TextView dist = (TextView) listItemView.findViewById(R.id.text2);
dist.setText(currentItem.getDist());
TextView price = (TextView) listItemView.findViewById(R.id.text2);
price.setText(currentItem.getPrice());
return listItemView;
}
}
listitem.java
package com.example.tourguide;
import android.widget.ImageView;
public class listitem {
private String name="";
private int image;
private String dist="";
private String price="";
public listitem(String namea, int imagea, String dista, String pricea){
name = namea;
imagea = image;
dist= dista;
price=pricea;
}
/*********** Set Methods ******************/
public void setName(String name)
{
this.name = name;
}
public void setImage(int image)
{
this.image = image;
}
public void setDist(String dist)
{
this.dist = dist;
}
public void setPrice(String price)
{
this.price = price;
}
/*********** Get Methods ****************/
public String getName()
{
return this.name;
}
public int getImage()
{
return this.image;
}
public String getDist()
{
return this.dist;
}
public String getPrice()
{
return this.price;
}
}
Univerisities.java
package com.example.tourguide;
import android.app.Activity;
import android.os.Bundle;
import android.widget.ImageView;
import android.widget.ListView;
import java.util.ArrayList;
public class universities extends Activity {
protected void onCreate(Bundle bundle) {
super.onCreate(bundle);
setContentView(R.layout.list_item);
ArrayList<listitem> listitemArrayList = new ArrayList<listitem>();
listitemArrayList.add(new listitem("Prince Sultan University", R.drawable.u1, "AlNarjes Dist", "$"));
listitemArrayList.add(new listitem("Princess Nourah University", R.drawable.u2, "AlNarjes Dist", "$"));
listitemArrayList.add(new listitem("King Saud University", R.drawable.u3, "AlNarjes Dist", "$"));
WordAdapter adapter = new WordAdapter(this, listitemArrayList);
ListView listView = (ListView) findViewById(R.id.list);
listView.setAdapter(adapter);
}
}
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"
tools:context="com.example.tourguide.MainActivity"
android:orientation="vertical"
android:layout_width="match_parent"
android:layout_height="match_parent">
<TextView
android:id="#+id/text1"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:textSize="29sp"
android:textColor="#3DC195"
android:textAlignment="center"
android:text="Tour Guide App" />
<TextView
android:id="#+id/text2"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:textColor="#6AA13F"
android:textSize="18sp"
android:text="Tour Guide App is designed to help you discover Riyadh city sightseeings including events, malls, resturants and universities.the app will be developed periodically to add more features... stay tuned" />
<Button
android:id="#+id/events"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:text="Events"
android:onClick="onClickEvent"/>
<Button
android:id="#+id/malls"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:text="Malls"
android:onClick="onClickMall"/>
<Button
android:id="#+id/resturants"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:text="Resturants"
android:onClick="onClickRest"/>
<Button
android:id="#+id/uinversities"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:text="Universities"
android:onClick="onClickUniv"/>
</LinearLayout>
activity_list.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">
<ListView
android:id="#+id/list"
android:layout_width="match_parent"
android:layout_height="match_parent" />
</LinearLayout>
list_item.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">
<LinearLayout
android:layout_width="match_parent"
android:layout_height="match_parent"
android:orientation="horizontal">
<ImageView
android:id="#+id/image1"
android:layout_width="163dp"
android:layout_height="96dp"
android:layout_marginLeft="15dp"
android:layout_marginTop="15dp"
/>
<LinearLayout
android:layout_width="match_parent"
android:layout_height="68dp"
android:layout_marginTop="30dp"
android:orientation="vertical">
<TextView
android:id="#+id/text1"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:textColor="#DB0BA4"
android:textSize="20sp"
/>
<TextView
android:id="#+id/text2"
android:layout_width="113dp"
android:layout_height="wrap_content"
android:textColor="#456233"
android:textSize="15sp"
/>
<TextView
android:id="#+id/text3"
android:layout_width="113dp"
android:layout_height="wrap_content"
android:textColor="#C1B03D"
android:textSize="15sp"
/>
</LinearLayout>
</LinearLayout>
</LinearLayout>

In the file Univerisities.java you should change your layout file to activity_list.xml.
Line
setContentView(R.layout.list_item);
Must be changed to :
setContentView(R.layout.activity_list);

Bro,
First you are trying to inflate the ListView item into you activity, which is wrong:
Change the setContentView(R.layout.list_item) to setContentView(R.layout.activity_list);
Also please check out the ViewHolder pattern for ListView's since the your adapter's getView method should be improved by that to make scrolling even more smooth:
View listItemView = convertView;
if(listItemView == null) {
listItemView = LayoutInflater.from(getContext()).inflate(
R.layout.list_item, parent, false);
}
and if no items are appearing in the list, you should also override the getItemCount on adatpterto return the size of the list.