NewPipe/app/src/main/java/org/schabi/newpipe/download/DownloadActivity.java

package org.schabi.newpipe.download;

import android.app.FragmentTransaction;
import android.content.Intent;
import android.os.Bundle;
import androidx.appcompat.app.ActionBar;
import androidx.appcompat.app.AppCompatActivity;
import androidx.appcompat.widget.Toolbar;
import android.view.Menu;
import android.view.MenuInflater;
import android.view.MenuItem;
import android.view.ViewTreeObserver;

import org.schabi.newpipe.R;
import org.schabi.newpipe.settings.SettingsActivity;
import org.schabi.newpipe.util.ThemeHelper;

import us.shandian.giga.service.DownloadManagerService;
import us.shandian.giga.ui.fragment.MissionsFragment;

public class DownloadActivity extends AppCompatActivity {

    private static final String MISSIONS_FRAGMENT_TAG = "fragment_tag";

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        // Service
        Intent i = new Intent();
        i.setClass(this, DownloadManagerService.class);
        startService(i);

        ThemeHelper.setTheme(this);
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_downloader);

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

        ActionBar actionBar = getSupportActionBar();
        if (actionBar != null) {
            actionBar.setDisplayHomeAsUpEnabled(true);
            actionBar.setTitle(R.string.downloads_title);
            actionBar.setDisplayShowTitleEnabled(true);
        }

        getWindow().getDecorView().getViewTreeObserver().addOnGlobalLayoutListener(new ViewTreeObserver.OnGlobalLayoutListener() {
            @Override
            public void onGlobalLayout() {
                updateFragments();
                getWindow().getDecorView().getViewTreeObserver().removeOnGlobalLayoutListener(this);
            }
        });
    }

    private void updateFragments() {
        MissionsFragment fragment = new MissionsFragment();

        getSupportFragmentManager().beginTransaction()
                .replace(R.id.frame, fragment, MISSIONS_FRAGMENT_TAG)
                .setTransition(FragmentTransaction.TRANSIT_FRAGMENT_FADE)
                .commit();
    }

    @Override
    public boolean onCreateOptionsMenu(Menu menu) {
        super.onCreateOptionsMenu(menu);
        MenuInflater inflater = getMenuInflater();

        inflater.inflate(R.menu.download_menu, menu);

        return true;
    }

    @Override
    public boolean onOptionsItemSelected(MenuItem item) {
        switch (item.getItemId()) {
            case android.R.id.home: {
                onBackPressed();
                return true;
            }
            case R.id.action_settings: {
                Intent intent = new Intent(this, SettingsActivity.class);
                startActivity(intent);
                return true;
            }
            default:
                return super.onOptionsItemSelected(item);
        }
    }
}