My Activity is restarts when i press back button

Question

*UPDATE! About this link - Android close app on back button - I have tried code from answers, but nothing is changing. I think my problem is in Activity A. When user open my app, Activity A check does there is a value in preferences. If value is missing, Activity A doesn't refer user to Activity B. If value is present Activity A refer user to Activity B. So it is a vicious cycle: User open my app ---> He is get to Activity A ---> Activity A checks value in preferences ---> Activity A refer user to Activity B ---> When user clicks back button, Activity A is is opening ---> Activity A refer user to Activity B ---> and so on

Please help me to solve my problem)

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I have two activities - A and B. Activity A have a button, when I click it, it refer me to the settings. But if it is a value in the settings, then Activity A refer me to Activity B using Intent. Activity B is activity with content, and when I press back button Activity B restarts. But I want to close the app, when back button is clicked. How I can do that?

My code:

AActivity.java:

public class AActivityextends AppCompatActivity implements View.OnClickListener {

Button btn_select;
SharedPreferences sp;

/**
 * Called when the activity is first created.
 */
public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_a);
    btn_select = (Button) findViewById(R.id.btn_select);
    sp = PreferenceManager.getDefaultSharedPreferences(this);
    String select_class = sp.getString("select_class", "");
    if (select_class.equals("") || select_class.equals("0")) {
        btn_select.setVisibility(View.VISIBLE);
    }
}

protected void onResume() {
    String select_class = sp.getString("select_class", "");
    tvInfo.setText(select_class);
    if (select_class.equals("") || select_class.equals("0")) {
        btn_select.setVisibility(View.VISIBLE);
    } else {
        btn_select.setVisibility(View.INVISIBLE);
        Intent intent = new Intent(this, BActivity.class);
        startActivity(intent);
    }
    super.onResume();
}

}

BActivity.java:

public class BActivity extends AppCompatActivity {

private Toolbar toolbar;
private TabLayout tabLayout;
private ViewPager viewPager;
SharedPreferences sp;

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

    sp = PreferenceManager.getDefaultSharedPreferences(this);
    String select_class = sp.getString("select_class", "");

    toolbar = (Toolbar) findViewById(R.id.toolbar);
    setSupportActionBar(toolbar);

    viewPager = (ViewPager) findViewById(R.id.viewpager);
    setupViewPager(viewPager);

    tabLayout = (TabLayout) findViewById(R.id.tabs);
    tabLayout.setupWithViewPager(viewPager);
}

private void setupViewPager(ViewPager viewPager) {
    ViewPagerAdapter adapter = new ViewPagerAdapter(getSupportFragmentManager());
    adapter.addFragment(new MondayFragment(), "ПН");
    adapter.addFragment(new TuesdayFragment(), "ВТ");
    adapter.addFragment(new WednesdayFragment(), "СР");
    adapter.addFragment(new ThursdayFragment(), "ЧТ");
    adapter.addFragment(new FridayFragment(), "ПТ");
    viewPager.setAdapter(adapter);
}

class ViewPagerAdapter extends FragmentPagerAdapter {
    private final List<Fragment> mFragmentList = new ArrayList<>();
    private final List<String> mFragmentTitleList = new ArrayList<>();

    public ViewPagerAdapter(FragmentManager manager) {
        super(manager);
    }

    @Override
    public Fragment getItem(int position) {
        return mFragmentList.get(position);
    }

    @Override
    public int getCount() {
        return mFragmentList.size();
    }

    public void addFragment(Fragment fragment, String title) {
        mFragmentList.add(fragment);
        mFragmentTitleList.add(title);
    }

    @Override
    public CharSequence getPageTitle(int position) {
        return mFragmentTitleList.get(position);
    }
}

@Override
public boolean onCreateOptionsMenu(Menu menu) {
    // Inflate the menu; this adds items to the action bar if it is present.
    getMenuInflater().inflate(R.menu.menu, 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) {
        Intent intent = new Intent(BActivity.this, SettingsActivity.class);
        intent.putExtra("fwflag","from_menu_item");
        startActivity(intent);
    }

    return super.onOptionsItemSelected(item);
}

}

My AndroidManifest.xml:

<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
package="com.x.x">

<application
    android:allowBackup="true"
    android:icon="@mipmap/ic_launcher"
    android:label="@string/app_name">
    <activity android:name=".AActivity"
        android:theme="@style/MyMaterialTheme">
        <intent-filter>
            <action android:name="android.intent.action.MAIN" />

            <category android:name="android.intent.category.LAUNCHER" />
        </intent-filter>
    </activity>
    <activity android:name=".SettingsActivity"
        android:theme="@style/MyMTheme.Base" />
    <activity android:name=".BActivity"
        android:theme="@style/MyMTheme">
    </activity>
</application>

My Activity C code:

public class CActivity extends AppCompatActivity {

Toolbar toolbar;
@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.toolbar);
    toolbar = (Toolbar) findViewById(R.id.toolbar);
    //toolbar.setNavigationIcon(R.drawable.abc_ic_ab_back_mtrl_am_alpha);
    setSupportActionBar(toolbar);
    getSupportActionBar().setDisplayHomeAsUpEnabled(true);
    toolbar.setNavigationOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View v) {
            onBackPressed();
        }

    });
    getFragmentManager().beginTransaction().replace(R.id.fragment_container,
            new PrefFragment()).commit();
}

public class PrefFragment extends PreferenceFragment
{
    @Override
    public void onCreate(final Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        addPreferencesFromResource(R.xml.pref);
        Intent intent = getIntent();
        String flag_from_where = intent.getStringExtra("fwflag");
        if (flag_from_where.equals("from_btn_select")) {
            PreferenceScreen main = (PreferenceScreen) findPreference(getString(R.string.pref_screen));
            main.onItemClick(null, null, 0, 0);
        } else if (flag_from_where.equals("from_menu_item")) {
        }
        final ListPreference list = (ListPreference) getPreferenceScreen().findPreference("listpref");
        list.setOnPreferenceChangeListener(new Preference.OnPreferenceChangeListener() {
            public boolean onPreferenceChange(Preference preference, Object newValue) {
                Intent intent = new Intent(CActivity.this, BActivity.class);
                startActivity(intent);
                finish();
                return true;
            }
        });
    }

}

}

Answer 1

You need to "finish" each activity right after you call to start a new activity.

So after every startActivity(intent) you should add finish() right below it.

That should take care of your problem.