Кнопка «Назад» - студия Android

Question

У меня есть навигационный ящик, и я пытаюсь реализовать панель действий с кнопкой «Назад» в упражнении, выбранном из ящика (второе занятие). Я попытался поместить [getSupportActionBar () ...] в первое переопределение во втором действии, но, когда я выбираю действие из ящика, это дает мне сбой.

Спасибо

Это мое первое занятие

package com.progetto.app;

import android.content.Intent;
import android.os.Bundle;
import android.support.design.widget.FloatingActionButton;
import android.support.design.widget.NavigationView;
import android.support.design.widget.Snackbar;
import android.support.v4.view.GravityCompat;
import android.support.v4.widget.DrawerLayout;
import android.support.v7.app.ActionBarDrawerToggle;
import android.support.v7.app.AppCompatActivity;
import android.support.v7.widget.Toolbar;
import android.view.Menu;
import android.view.MenuItem;
import android.view.View;

public class Alarm extends AppCompatActivity
        implements NavigationView.OnNavigationItemSelectedListener {

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_alarm);
        Toolbar toolbar = (Toolbar) findViewById(R.id.toolbar);
        setSupportActionBar(toolbar);

        FloatingActionButton fab = (FloatingActionButton) findViewById(R.id.fab);
        fab.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                Snackbar.make(view, "Replace with your own action", Snackbar.LENGTH_LONG)
                        .setAction("Action", null).show();
            }
        });

        DrawerLayout drawer = (DrawerLayout) findViewById(R.id.drawer_layout);
        ActionBarDrawerToggle toggle = new ActionBarDrawerToggle(
                this, drawer, toolbar, R.string.navigation_drawer_open, R.string.navigation_drawer_close);
        drawer.addDrawerListener(toggle);
        toggle.syncState();

        NavigationView navigationView = (NavigationView) findViewById(R.id.nav_view);
        navigationView.setNavigationItemSelectedListener(this);
    }

    @Override
    public void onBackPressed() {
        DrawerLayout drawer = (DrawerLayout) findViewById(R.id.drawer_layout);
        if (drawer.isDrawerOpen(GravityCompat.START)) {
            drawer.closeDrawer(GravityCompat.START);
        } else {
            super.onBackPressed();
        }
    }

    @Override
    public boolean onCreateOptionsMenu(Menu menu) {
        // Inflate the menu; this adds items to the action bar if it is present.
        getMenuInflater().inflate(R.menu.home, menu);
        return true;
    }

    @Override
    public boolean onOptionsItemSelected(MenuItem item) {
        // Handle action bar item clicks here. The action bar will
        // automatically handle clicks on the Home/Up button, so long
        // as you specify a parent activity in AndroidManifest.xml.
        int id = item.getItemId();

        //noinspection SimplifiableIfStatement
        if (id == R.id.action_settings) {
            return true;
        }

        return super.onOptionsItemSelected(item);
    }

    @SuppressWarnings("StatementWithEmptyBody")
    @Override
    public boolean onNavigationItemSelected(MenuItem item) {
        // Handle navigation view item clicks here.
        int id = item.getItemId();
        switch (id) {

            case R.id.nav_home:
                Intent h = new Intent(Alarm.this, Home.class);
                startActivity(h);
                break;

            case R.id.nav_bt:
                Intent i = new Intent(Alarm.this, BluetoothActivitySetting.class);
                startActivity(i);
                break;

            case R.id.nav_alarm:
                Intent g = new Intent(Alarm.this, AlarmActivity.class);
                startActivity(g);
                break;

            case R.id.nav_tips:
                Intent s = new Intent(Alarm.this, Tips.class);
                startActivity(s);
                break;

        }
        DrawerLayout drawer = (DrawerLayout) findViewById(R.id.drawer_layout);
        drawer.closeDrawer(GravityCompat.START);
        return true;
    }


}

Это мое второе занятие

    package com.progetto.app;

import android.annotation.TargetApi;
import android.app.AlarmManager;
import android.app.PendingIntent;
import android.content.Context;
import android.content.Intent;
import android.os.Build;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.util.Log;
import android.view.View;
import android.widget.Button;
import android.widget.TextView;
import android.widget.TimePicker;
import java.util.Calendar;
import java.util.Random;

import android.annotation.TargetApi;
import android.app.AlarmManager;
import android.app.PendingIntent;
import android.content.Context;
import android.content.Intent;
import android.os.Build;
import android.os.Bundle;
import android.support.design.widget.FloatingActionButton;
import android.support.design.widget.Snackbar;
import android.support.v7.app.AppCompatActivity;
import android.support.v7.widget.Toolbar;
import android.util.Log;
import android.view.View;
import android.view.Menu;
import android.view.MenuItem;
import android.widget.AdapterView;
import android.widget.ArrayAdapter;
import android.widget.Button;
import android.widget.Spinner;
import android.widget.TextView;
import android.widget.TimePicker;
import android.widget.Toast;

import java.util.Calendar;

public class AlarmActivity extends AppCompatActivity {

    //to make our alarm manager
    AlarmManager alarm_manager;
    TimePicker alarm_timepicker;
    TextView update_text;
    Context context;
    PendingIntent pending_intent;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_alarm2);

        getSupportActionBar().setDisplayHomeAsUpEnabled(true);
        getSupportActionBar().setDisplayHomeAsUpEnabled(true);


        Toolbar toolbar = (Toolbar) findViewById(R.id.toolbar);
        this.context = this;



        // initialize our alarm manager
        alarm_manager = (AlarmManager) getSystemService(ALARM_SERVICE);

        //initialize our timepicker
        alarm_timepicker = (TimePicker) findViewById(R.id.time_picker);

        //initialize our text update box
        update_text = (TextView) findViewById(R.id.update_text);

        // create an instance of a calendar
        final Calendar calendar = Calendar.getInstance();

        // create an intent to the Alarm Receiver class
        final Intent my_intent = new Intent(this.context, Alarm_Receiver.class);


        // initialize start button
        Button alarm_on = (Button) findViewById(R.id.alarm_on);

        // create an onClick listener to start the alarm
        alarm_on.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {

                // setting calendar instance with the hour and minute that we picked
                // on the time picker
                calendar.set(Calendar.HOUR_OF_DAY, alarm_timepicker.getHour());
                calendar.set(Calendar.MINUTE, alarm_timepicker.getMinute());

                // get the int values of the hour and minute
                int hour = alarm_timepicker.getHour();
                int minute = alarm_timepicker.getMinute();

                // convert the int values to strings
                String hour_string = String.valueOf(hour);
                String minute_string = String.valueOf(minute);


                // method that changes the update text Textbox
                set_alarm_text("Alarm set to: " + hour_string + ":" + minute_string);

                // put in extra string into my_intent
                // tells the clock that you pressed the "alarm on" button
                my_intent.putExtra("extra", "alarm on");


                // create a pending intent that delays the intent
                // until the specified calendar time
                pending_intent = PendingIntent.getBroadcast(AlarmActivity.this, 0,
                        my_intent, PendingIntent.FLAG_UPDATE_CURRENT);

                // set the alarm manager
                alarm_manager.set(AlarmManager.RTC_WAKEUP, calendar.getTimeInMillis(),
                        pending_intent);

            }


        });


        // initialize the stop button
        Button alarm_off = (Button) findViewById(R.id.alarm_off);
        // create an onClick listener to stop the alarm or undo an alarm set

        alarm_off.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {

                // method that changes the update text Textbox
                set_alarm_text("Alarm off!");

                // cancel the alarm
                alarm_manager.cancel(pending_intent);

                my_intent.putExtra("extra", "alarm off");


                // stop the ringtone
                sendBroadcast(my_intent);


            }
        });


    }

    private void set_alarm_text(String output) {
        update_text.setText(output);
    }


    @Override
    public boolean onOptionsItemSelected(MenuItem item){
        int id = item.getItemId();

        if (id== android.R.id.home){
            this.finish();
        }
        return super.onOptionsItemSelected(item);

    }
    @Override
    public void onDestroy() {
        super.onDestroy();

        Log.e("MyActivity", "on Destroy");
    }
}

Это xml для второго действия

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:orientation="vertical">

    <TimePicker
        android:id="@+id/time_picker"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:layout_alignParentStart="true"
        android:layout_alignParentTop="true"
        android:timePickerMode="clock" />

    <Button
        android:id="@+id/alarm_on"
        android:layout_width="181dp"
        android:layout_height="wrap_content"
        android:layout_alignParentBottom="true"
        android:layout_alignParentStart="true"
        android:layout_marginBottom="66dp"
        android:text="@string/AlarmOn" />

    <Button
        android:id="@+id/alarm_off"
        android:layout_width="180dp"
        android:layout_height="wrap_content"
        android:layout_alignParentBottom="true"
        android:layout_alignParentEnd="true"
        android:layout_marginBottom="55dp"
        android:text="@string/AlarmOff" />

    <TextView
        android:id="@+id/update_text"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:layout_alignParentStart="true"
        android:layout_below="@+id/time_picker"
        android:text="@string/SetAlarm"
        android:textAlignment="center"
        android:textSize="24sp" />

</RelativeLayout>

Answer 1

Во-первых, вы не включили панель инструментов в свой второй макет деятельности. Вам необходимо включить панель инструментов. Это решение, которое я использую, и оно работает без проблем.

Добавьте это в свой onCreate

initUI();

И добавить это позже, после создания

@Override
public boolean onNavigateUp() {
    onBackPressed();
    return true;
}

public void initUI() {
    toolbar = findViewById(R.id.toolbar);
    setSupportActionBar(toolbar);
    getSupportActionBar().setDisplayHomeAsUpEnabled(true);
    getSupportActionBar().setHomeButtonEnabled(true);
    getSupportActionBar().setDisplayShowTitleEnabled(false);
    toolbar.setNavigationOnClickListener(v -> onNavigateUp());
}

Дайте мне знать, если у вас есть какие-либо проблемы.