BuyFilter.java + activity_buy_filter.xml

package com.example.chat;

import android.content.DialogInterface;
import android.content.Intent;
import android.support.annotation.NonNull;
import android.support.design.widget.FloatingActionButton;
import android.support.design.widget.NavigationView;
import android.support.v4.widget.DrawerLayout;
import android.support.v7.app.ActionBarDrawerToggle;
import android.support.v7.app.AlertDialog;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.view.MenuItem;
import android.view.View;
import android.widget.AdapterView;
import android.widget.ArrayAdapter;
import android.widget.Button;
import android.widget.SeekBar;
import android.widget.Spinner;
import android.widget.TextView;
import android.widget.Toast;

public class BuyFilter extends AppCompatActivity implements AdapterView.OnItemSelectedListener {
    Spinner category;
    TextView priceText;
    SeekBar priceBar;
    Button find;
    FloatingActionButton add;
    String categorySelect;
    int progressValue;

    private NavigationView nav_view;
    private DrawerLayout dl;
    private ActionBarDrawerToggle t;

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

        //spinner
        category = findViewById(R.id.buySellSpinner);
        ArrayAdapter<CharSequence> adapter = ArrayAdapter.createFromResource(this, R.array.buySellCategories, android.R.layout.simple_spinner_item);
        adapter.setDropDownViewResource(android.R.layout.simple_spinner_dropdown_item);
        category.setAdapter(adapter);
        category.setOnItemSelectedListener(this);
        //seek bar
        seekBar();
        //add and delete buttons
        addButtonActions();
        findButtonActions();
        addNavigationDrawer();

    }

    public void findButtonActions() {
        find = findViewById(R.id.buyButton);
        find.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                Intent intent = new Intent(BuyFilter.this, OnSalePage.class);
                //create item and add extra to intent
                //Item item = new Item(categorySelect, progressValue);
                //intent.putExtra("item", item);
                startActivity(intent);
            }
        });
    }

    public void addButtonActions() {
        add = findViewById(R.id.floatingActionButton);
        add.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                Intent addingPage = new Intent(BuyFilter.this, SellAddItem.class);
                startActivity(addingPage);
            }
        });
    }

    public void seekBar() {
        priceBar = findViewById(R.id.priceBar);
        priceText = findViewById(R.id.priceTag);
        //to make the time bar max 1 month the max value is set to 30
        priceBar.setMax(1000);
        priceBar.setOnSeekBarChangeListener(
                new SeekBar.OnSeekBarChangeListener() {

                    @Override
                    public void onProgressChanged(SeekBar seekBar, int progress, boolean fromUser) {
                        progressValue = progress;
                        priceText.setText("Upper Limit: " + progressValue + " TL");

                    }

                    @Override
                    public void onStartTrackingTouch(SeekBar seekBar) {
                    }

                    @Override
                    public void onStopTrackingTouch(SeekBar seekBar) {
                        priceText.setText("Upper Limit: " + progressValue + " TL");
                    }
                }
        );

    }


    @Override
    public void onItemSelected(AdapterView<?> parent, View view, int position, long id) {
        categorySelect = parent.getItemAtPosition(position).toString();
        //THE SELECTED CATEGORY INFORMATION
    }

    @Override
    public void onNothingSelected(AdapterView<?> parent) {
    }

    @Override
    public void onPointerCaptureChanged(boolean hasCapture) {

    }

    private void addNavigationDrawer() {
        dl = (DrawerLayout) findViewById(R.id.activity_main);
        t = new ActionBarDrawerToggle(BuyFilter.this, dl, R.string.Open, R.string.Close);

        dl.addDrawerListener(t);
        t.syncState();

        nav_view = (NavigationView) findViewById(R.id.nv);
        nav_view.setNavigationItemSelectedListener(new NavigationView.OnNavigationItemSelectedListener() {
            @Override
            public boolean onNavigationItemSelected(@NonNull MenuItem item) {
                int id = item.getItemId();
                switch (id) {
                    case R.id.logout:
                        Toast.makeText(BuyFilter.this, "Logout", Toast.LENGTH_SHORT).show();
                        break;
                    case R.id.buy_sell:
                        Toast.makeText(BuyFilter.this, "Buy / Sell", Toast.LENGTH_SHORT).show();
                        dl.closeDrawers();
                        break;
                    case R.id.lost_found:
                        Toast.makeText(BuyFilter.this, "Lost & Found", Toast.LENGTH_SHORT).show();
                        startActivity(new Intent(BuyFilter.this, LostFilter.class));
                        finish();
                        break;
                    case R.id.chats:
                        Toast.makeText(BuyFilter.this, "Chats", Toast.LENGTH_SHORT).show();
                        startActivity(new Intent(BuyFilter.this, ChatActivity.class));
                        finish();
                        break;
                    case R.id.settings:
                        Toast.makeText(BuyFilter.this, "Settings", Toast.LENGTH_SHORT).show();
                        startActivity(new Intent(BuyFilter.this, SettingsActivity.class));
                        finish();
                        break;
                    default:
                        dl.closeDrawers();
                        return true;
                }
                return true;
            }
        });
    }
}



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<?xml version="1.0" encoding="utf-8"?>

<android.support.v4.widget.DrawerLayout
    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/activity_main"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:background="@color/colorAccent"
    tools:context=".MainActivity">

<android.support.constraint.ConstraintLayout
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    tools:context=".BuyFilter">

    <android.support.constraint.Guideline
        android:id="@+id/guideline"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:orientation="horizontal"
        app:layout_constraintGuide_begin="20dp" />

    <android.support.constraint.Guideline
        android:id="@+id/guideline2"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:orientation="vertical"
        app:layout_constraintGuide_begin="20dp" />

    <TextView
        android:id="@+id/sellText"
        android:layout_width="223dp"
        android:layout_height="45dp"
        android:text="I WANT TO SELL AN ITEM"
        android:textColor="#000000"
        android:textSize="18sp"
        android:textStyle="bold|italic"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toTopOf="parent"
        app:layout_constraintVertical_bias="0.113"
        tools:text="I WANT TO SELL AN ITEM" />

    <TextView
        android:id="@+id/filterTitle"
        android:layout_width="316dp"
        android:layout_height="51dp"
        android:text="WANT TO BUY SOMETHING?"
        android:textColor="#050505"
        android:textSize="24sp"
        android:textStyle="bold"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintHorizontal_bias="0.6"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toTopOf="parent"
        app:layout_constraintVertical_bias="0.242"
        tools:text="WANT TO BUY SOMETHING?" />

    <TextView
        android:id="@+id/categoriesLost"
        android:layout_width="119dp"
        android:layout_height="31dp"
        android:text="CATEGORIES:"
        android:textColor="#030303"
        android:textSize="18sp"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintHorizontal_bias="0.236"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toTopOf="parent"
        app:layout_constraintVertical_bias="0.38"
        tools:text="CATEGORIES:" />

    <TextView
        android:id="@+id/priceRange"
        android:layout_width="146dp"
        android:layout_height="21dp"
        android:text="Price Range:"
        android:textSize="18sp"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintHorizontal_bias="0.241"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toTopOf="parent" />

    <TextView
        android:id="@+id/minPrice"
        android:layout_width="85dp"
        android:layout_height="26dp"
        android:text="0 TL"
        android:textSize="18sp"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintHorizontal_bias="0.248"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toTopOf="parent"
        app:layout_constraintVertical_bias="0.673" />

    <TextView
        android:id="@+id/maxPrice"
        android:layout_width="85dp"
        android:layout_height="27dp"
        android:text="1000 TL"
        android:textSize="18sp"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintHorizontal_bias="0.828"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toTopOf="parent"
        app:layout_constraintVertical_bias="0.673" />

    <android.support.design.widget.FloatingActionButton
        android:id="@+id/floatingActionButton"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:clickable="true"
        android:focusable="true"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintHorizontal_bias="0.892"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toTopOf="parent"
        app:layout_constraintVertical_bias="0.115"
        app:srcCompat="@android:drawable/ic_input_add" />

    <SeekBar
        android:id="@+id/priceBar"
        android:layout_width="267dp"
        android:layout_height="23dp"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toTopOf="parent"
        app:layout_constraintVertical_bias="0.737" />

    <Button
        android:id="@+id/buyButton"
        android:layout_width="106dp"
        android:layout_height="52dp"
        android:text="Let's Buy!"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintHorizontal_bias="0.498"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toTopOf="parent"
        app:layout_constraintVertical_bias="0.854" />

    <TextView
        android:id="@+id/priceTag"
        android:layout_width="246dp"
        android:layout_height="39dp"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintHorizontal_bias="0.563"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toTopOf="parent"
        app:layout_constraintVertical_bias="0.57" />

    <Spinner
        android:id="@+id/buySellSpinner"
        android:layout_width="168dp"
        android:layout_height="52dp"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintHorizontal_bias="0.783"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toTopOf="parent"
        app:layout_constraintVertical_bias="0.391" />

</android.support.constraint.ConstraintLayout>
    <android.support.design.widget.NavigationView
        android:id="@+id/nv"
        android:layout_width="wrap_content"
        android:layout_height="match_parent"
        android:layout_gravity="start"
        android:fitsSystemWindows="true"

        app:headerLayout="@layout/nav_header"
        app:menu="@menu/nav_menu">

    </android.support.design.widget.NavigationView>
</android.support.v4.widget.DrawerLayout>