When I click on Listview to open another Aciticity the app hangs and Fexa

Question

I’m creating an App that looks for nearby wifi networks and then can connect to them, but locked at the beginning, because I can make it scan, but when I click on some network of the list, which would redirect me to another Acitiviry, the app hangs and Fexa, why? Mainacitivity.java

package com.emanuel.testes;

import android.content.BroadcastReceiver;
import android.content.Context;
import android.content.Intent;
import android.content.IntentFilter;
import android.net.wifi.ScanResult;
import android.net.wifi.WifiManager;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.view.View;
import android.widget.AdapterView;
import android.widget.ArrayAdapter;
import android.widget.Button;
import android.widget.ListView;
import android.widget.Toast;
import java.util.ArrayList;
import java.util.List;

public class MainActivity extends AppCompatActivity {

    private WifiManager wifiManager;
    private ListView listView;
    private Button buttonScan;
    private List<ScanResult> results;
    private ArrayList<String> arrayList = new ArrayList<>();
    private ArrayAdapter adapter;
    private boolean f = false;

    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        buttonScan = findViewById(R.id.scanBtn);
        buttonScan.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                scanWifi();
            }
        });

        listView = findViewById(R.id.wifiList);
        wifiManager = (WifiManager) getApplicationContext().getSystemService(Context.WIFI_SERVICE);

        if (!wifiManager.isWifiEnabled()) {
            Toast.makeText(this, "Wifi está desativado. Eu vou ativa-lo por você.", Toast.LENGTH_LONG).show();
            wifiManager.setWifiEnabled(true);
        }

        adapter = new ArrayAdapter(this, android.R.layout.simple_list_item_1, arrayList);
        listView.setAdapter(adapter);
        scanWifi();

        listView.setOnItemClickListener(new AdapterView.OnItemClickListener() {
            @Override
            public void onItemClick(AdapterView<?> adapterView, View view, int i, long l) {
                Intent intent = new Intent(MainActivity.this, Element.class);
                startActivity(intent);
                f = true;
            }

        });
        if(f) {
            this.finish();
        }
    }


    private void scanWifi() {
        arrayList.clear();
        registerReceiver(wifiReceiver, new IntentFilter(WifiManager.SCAN_RESULTS_AVAILABLE_ACTION));
        wifiManager.startScan();
        Toast.makeText(this, "Procurando ESPs...", Toast.LENGTH_LONG).show();
    }

    BroadcastReceiver wifiReceiver = new BroadcastReceiver() {
        @Override
        public void onReceive(Context context, Intent intent) {
            results = wifiManager.getScanResults();
            unregisterReceiver(this);

            for (ScanResult scanResult : results) {
                arrayList.add(scanResult.SSID);
                adapter.notifyDataSetChanged();
            }
        }
    };
}

Element.java

package com.emanuel.testes;

import android.os.Bundle;
import android.support.v7.app.AppCompatActivity;

public class Element extends AppCompatActivity {
    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.content_main);
    }
}

activity_main

<?xml version="1.0" encoding="utf-8"?>
<android.support.constraint.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=".MainActivity">

    <Button
        android:id="@+id/scanBtn"
        android:layout_width="0dp"
        android:layout_height="wrap_content"
        android:layout_marginBottom="8dp"
        android:layout_marginEnd="8dp"
        android:layout_marginStart="8dp"
        android:layout_marginTop="4dp"
        android:text="@string/procurar_esps"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toBottomOf="@+id/wifiList" />

    <ListView
        android:id="@+id/wifiList"
        android:layout_width="368dp"
        android:layout_height="439dp"
        android:layout_marginBottom="4dp"
        android:layout_marginEnd="8dp"
        android:layout_marginStart="8dp"
        android:layout_marginTop="8dp"
        app:layout_constraintBottom_toTopOf="@+id/scanBtn"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toTopOf="parent" />
</android.support.constraint.ConstraintLayout>

content_main

<?xml version="1.0" encoding="utf-8"?>
<android.support.constraint.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">

    <TextView
        android:id="@+id/textView"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_marginBottom="8dp"
        android:layout_marginEnd="8dp"
        android:layout_marginStart="8dp"
        android:layout_marginTop="8dp"
        android:text="FUNCIONA POR FAVOR"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toTopOf="parent" />
</android.support.constraint.ConstraintLayout>

Answer 1

You should include your new "Activity" in the "Androidmanifest.xml" file"

<application
    android:allowBackup="true"
    android:icon="@mipmap/ic_launcher"
    android:label="@string/app_name"
    android:roundIcon="@mipmap/ic_launcher_round"
    android:supportsRtl="true"
    android:theme="@style/AppTheme"
    android:usesCleartextTraffic="true">
    <activity android:name=".MainActivity">
        <intent-filter>
            <action android:name="android.intent.action.MAIN" />

            <category android:name="android.intent.category.LAUNCHER" />
        </intent-filter>
    </activity>
    <activity android:name=".ui.activity.Sua_Activity"></activity>

</application>