Java tutorial
package org.schabi.newpipe.util; import android.app.Activity; import android.content.Context; import android.content.Intent; import android.os.Bundle; import android.support.v4.app.NavUtils; import android.support.v7.app.AppCompatActivity; import android.util.Log; import org.schabi.newpipe.ChannelActivity; import org.schabi.newpipe.MainActivity; import org.schabi.newpipe.detail.VideoItemDetailActivity; import org.schabi.newpipe.detail.VideoItemDetailFragment; import org.schabi.newpipe.extractor.NewPipe; import org.schabi.newpipe.extractor.StreamingService; import java.util.ArrayList; import java.util.Stack; /** * Created by Christian Schabesberger on 16.02.17. * * Copyright (C) Christian Schabesberger 2016 <chris.schabesberger@mailbox.org> * NavStack.java is part of NewPipe. * * NewPipe is free software: you can redistribute it and/or modify * it under the terms of the GNU General Public License as published by * the Free Software Foundation, either version 3 of the License, or * (at your option) any later version. * * NewPipe is distributed in the hope that it will be useful, * but WITHOUT ANY WARRANTY; without even the implied warranty of * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the * GNU General Public License for more details. * * You should have received a copy of the GNU General Public License * along with NewPipe. If not, see <http://www.gnu.org/licenses/>. */ /** * class helps to navigate within the app * IMPORTAND: the top of the stack is the current activity !!! */ public class NavStack { private static final String TAG = NavStack.class.toString(); public static final String SERVICE_ID = "service_id"; public static final String URL = "url"; private static final String NAV_STACK = "nav_stack"; private enum ActivityId { CHANNEL, DETAIL } private class NavEntry { public NavEntry(String url, int serviceId) { this.url = url; this.serviceId = serviceId; } public String url; public int serviceId; } private static NavStack instance = new NavStack(); private Stack<NavEntry> stack = new Stack<NavEntry>(); private NavStack() { } public static NavStack getInstance() { return instance; } private void addEntry(String url, Class ac, int serviceId) { stack.push(new NavEntry(url, serviceId)); } public void navBack(Activity activity) throws Exception { if (stack.size() == 0) { // if stack is already empty here, activity was probably called // from another app activity.finish(); return; } stack.pop(); // remove curent activty, since we dont want to return to itself if (stack.size() == 0) { openMainActivity(activity); // if no more page is on the stack this means we are home return; } NavEntry entry = stack.pop(); // this element will reapear, since by calling the old page // this element will be pushed on top again try { StreamingService service = NewPipe.getService(entry.serviceId); switch (service.getLinkTypeByUrl(entry.url)) { case STREAM: openDetailActivity(activity, entry.url, entry.serviceId); break; case CHANNEL: openChannelActivity(activity, entry.url, entry.serviceId); break; case NONE: throw new Exception("Url not known to service. service=" + Integer.toString(entry.serviceId) + " url=" + entry.url); default: openMainActivity(activity); } } catch (Exception e) { e.printStackTrace(); } } public void openChannelActivity(Context context, String url, int serviceId) { openActivity(context, url, serviceId, ChannelActivity.class); } public void openDetailActivity(Context context, String url, int serviceId) { openActivity(context, url, serviceId, VideoItemDetailActivity.class); } private void openActivity(Context context, String url, int serviceId, Class acitivtyClass) { stack.push(new NavEntry(url, serviceId)); Intent i = new Intent(context, acitivtyClass); i.putExtra(SERVICE_ID, serviceId); i.putExtra(URL, url); context.startActivity(i); } public void openMainActivity(Activity a) { stack.clear(); Intent i = new Intent(a, MainActivity.class); i.addFlags(Intent.FLAG_ACTIVITY_CLEAR_TOP); NavUtils.navigateUpTo(a, i); } public void onSaveInstanceState(Bundle state) { ArrayList<String> sa = new ArrayList<>(); for (NavEntry entry : stack) { sa.add(entry.url); } state.putStringArrayList(NAV_STACK, sa); } public void restoreSavedInstanceState(Bundle state) { ArrayList<String> sa = state.getStringArrayList(NAV_STACK); for (String url : sa) { stack.push(new NavEntry(url, NewPipe.getServiceByUrl(url).getServiceId())); } } }