Java tutorial
/*********************************************************************************************************************** * ========================================== * * Copyright (C) 2013 by Paul Oremland * http://www.linkedin.com/in/pauloremland * https://github.com/poremland * *********************************************************************************************************************** * * Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file except in compliance with * the License. You may obtain a copy of the License at * * http://www.apache.org/licenses/LICENSE-2.0 * * Unless required by applicable law or agreed to in writing, software distributed under the License is distributed on * an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the License for the * specific language governing permissions and limitations under the License. * ***********************************************************************************************************************/ package net.oremland.rss.reader; import android.os.*; import android.support.v4.app.*; import android.support.v7.app.*; import android.text.*; import android.view.*; import android.widget.*; import java.util.*; import net.oremland.rss.reader.fragments.*; import net.oremland.rss.reader.helpers.*; import net.oremland.rss.reader.models.*; public class MainActivity extends ActionBarActivity implements AddFeedFragment.OnFeedListChangedListener, FeedsListFragment.OnFeedSelectedListener, FeedItemsListFragment.OnFeedItemSelectedListener { private int optionsMenuId = this.getDefaultOptionsMenuId(); protected interface FragmentLifecycleHelper<T extends Fragment> { T create(int id); void update(T fragment); void addToFragmentTransaction(FragmentTransaction transaction); boolean shouldIncludeMainMenuItems(); } /** Called when the activity is first created. */ @Override public void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.main); if (savedInstanceState == null) { this.showDefaultFragment(); } } @Override public boolean onCreateOptionsMenu(Menu menu) { MenuInflater minflater = getMenuInflater(); minflater.inflate(this.optionsMenuId, menu); return true; } @Override public boolean onOptionsItemSelected(MenuItem item) { return this.handledHome(item) || this.handledAdd(item) || super.onOptionsItemSelected(item); } private boolean handledHome(MenuItem item) { if (item.getItemId() == android.R.id.home) { this.popBackStack(); return true; } return false; } private boolean handledAdd(MenuItem item) { if (item.getItemId() == R.id.menu_add) { this.displayAddFeedFragment(); return true; } return false; } @Override public void onResume() { super.onResume(); this.updateHomeButton(); } @Override public void onBackPressed() { if (!this.popBackStack()) { this.finish(); } } @Override public void onSaveInstanceState(Bundle outState) { super.onSaveInstanceState(outState); outState.putInt("optionsMenuId", this.optionsMenuId); } @Override public void onRestoreInstanceState(Bundle savedInstanceState) { super.onRestoreInstanceState(savedInstanceState); this.optionsMenuId = savedInstanceState.getInt("optionsMenuId", this.getDefaultOptionsMenuId()); this.restoreFragmentInstanceState(); } private void restoreFragmentInstanceState() { Fragment addFeedFragment = this.getFragment(R.id.add_feed_fragment); Fragment browserFragment = this.getFragment(R.id.browser_fragment); int id = addFeedFragment == null ? browserFragment == null ? -1 : R.id.browser_fragment : R.id.add_feed_fragment; FragmentManager manager = getSupportFragmentManager(); if (id != -1 && manager != null) { FragmentTransaction transaction = manager.beginTransaction(); this.hideFragmentInLayout(R.id.feeds_list_fragment, transaction); this.hideFragmentInLayout(R.id.feed_items_list_fragment, transaction); transaction.commit(); } } @Override public void onFeedListChanged() { Fragment fragment = this.getFragment(R.id.feeds_list_fragment); if (fragment != null) { ((FeedsListFragment) fragment).load(); } } @Override public void onFeedSelected(Feed feed) { this.displayFeedItemsListFragment(feed); } @Override public void onFeedItemSelected(FeedItem item) { this.displayBrowserFragment(item); } private void showDefaultFragment() { this.displayFeedsListFragment(); if (this.shouldDisplayAddFeedFragment()) { this.displayAddFeedFragment(); } } private boolean shouldDisplayAddFeedFragment() { FeedHelper helper = new FeedHelper(); return helper.getFeeds().size() == 0; } private void displayAddFeedFragment() { this.displayFragment(R.id.add_feed_fragment, new FragmentLifecycleHelper<AddFeedFragment>() { public void addToFragmentTransaction(FragmentTransaction transaction) { hideFragmentInLayout(R.id.feeds_list_fragment, transaction); hideFragmentInLayout(R.id.feed_items_list_fragment, transaction); } public AddFeedFragment create(int id) { return new AddFeedFragment(); } public boolean shouldIncludeMainMenuItems() { return false; } public void update(AddFeedFragment fragment) { } }); } private void displayFeedsListFragment() { this.displayFragment(R.id.feeds_list_fragment, new FragmentLifecycleHelper<FeedsListFragment>() { public void addToFragmentTransaction(FragmentTransaction transaction) { } public FeedsListFragment create(int id) { FeedsListFragment fragment = new FeedsListFragment(); return fragment; } public boolean shouldIncludeMainMenuItems() { return true; } public void update(FeedsListFragment fragment) { } }); } private void displayFeedItemsListFragment(final Feed feed) { this.displayFragment(R.id.feed_items_list_fragment, new FragmentLifecycleHelper<FeedItemsListFragment>() { public void addToFragmentTransaction(FragmentTransaction transaction) { } public FeedItemsListFragment create(int id) { FeedItemsListFragment fragment = new FeedItemsListFragment(); fragment.setFeed(feed); return fragment; } public boolean shouldIncludeMainMenuItems() { return true; } public void update(FeedItemsListFragment fragment) { fragment.setFeed(feed); fragment.load(); LinearLayout.LayoutParams parameters = (LinearLayout.LayoutParams) fragment.getView() .getLayoutParams(); parameters.weight = 2f; fragment.getView().setLayoutParams(parameters); } }); } private void displayBrowserFragment(final FeedItem item) { this.displayFragment(R.id.browser_fragment, new FragmentLifecycleHelper<BrowserFragment>() { public void addToFragmentTransaction(FragmentTransaction transaction) { hideFragmentInLayout(R.id.feeds_list_fragment, transaction); hideFragmentInLayout(R.id.feed_items_list_fragment, transaction); } public BrowserFragment create(int id) { BrowserFragment fragment = new BrowserFragment(); fragment.setFeedItem(item); return fragment; } public boolean shouldIncludeMainMenuItems() { return false; } public void update(BrowserFragment fragment) { fragment.setFeedItem(item); fragment.loadFeed(); } }); } private void hideFragmentInLayout(int id, FragmentTransaction transaction) { Fragment fragment = this.getFragment(id); if (fragment != null && transaction != null && fragment.isInLayout()) { transaction.hide(fragment); } } protected FeedsListFragment.OnFeedSelectedListener getOnFeedSelectedListener() { return this; } protected FeedItemsListFragment.OnFeedItemSelectedListener getOnFeedItemSelectedListener() { return this; } private void displayFragment(int id, FragmentLifecycleHelper helper) { Fragment fragment = this.createOrUpdateFragment(id, helper); this.addFragmentToBackStack(fragment, id, helper); this.updateHomeButton(id); this.optionsMenuId = helper.shouldIncludeMainMenuItems() ? getDefaultOptionsMenuId() : R.menu.empty_menu; this.invalidateOptionsMenu(); } private Fragment createOrUpdateFragment(int id, FragmentLifecycleHelper helper) { Fragment fragment = this.getFragment(id); if (fragment == null) { return helper.create(id); } helper.update(fragment); return fragment; } private Fragment getFragment(int id) { FragmentManager manager = getSupportFragmentManager(); Fragment fragment = manager.findFragmentByTag(this.getFragmentIdAsString(id)); if (fragment == null) { fragment = manager.findFragmentById(id); } return fragment; } protected void addFragmentToBackStack(Fragment fragment, int id, FragmentLifecycleHelper helper) { FragmentManager manager = getSupportFragmentManager(); if (fragment != null && manager != null && !fragment.isInLayout()) { FragmentTransaction transaction = manager.beginTransaction(); transaction.setTransition(FragmentTransaction.TRANSIT_ENTER_MASK); // alternatively you can have more control over the fragment // lifecycle by choosing to hide/show fragments by calling // transaction.add instead of replace. Calling replace forces // each fragment through it's lifecycle. helper.addToFragmentTransaction(transaction); transaction.replace(R.id.fragment_container, fragment, this.getFragmentIdAsString(id)); transaction.addToBackStack(this.getFragmentIdAsString(id)); transaction.commit(); } } private String getFragmentIdAsString(int id) { return Integer.toString(id); } private boolean popBackStack() { boolean wasBackStackPopped = false; FragmentManager manager = getSupportFragmentManager(); if (manager != null) { if (this.shouldPopBackStack(manager)) { this.popBackStack(manager); wasBackStackPopped = true; } this.optionsMenuId = this.getDefaultOptionsMenuId(); this.invalidateOptionsMenu(); } int id = this.idForPreviousBackStackEntry(manager); this.updateHomeButton(id); return wasBackStackPopped; } private boolean shouldPopBackStack(FragmentManager manager) { return manager.getBackStackEntryCount() > this.initialBackStackCount(); } private int initialBackStackCount() { boolean isTablet = this.getResources().getBoolean(R.bool.isTablet); return isTablet ? 0 : 1; } private int idForPreviousBackStackEntry(FragmentManager manager) { int entryCount = manager.getBackStackEntryCount(); int initialCount = this.initialBackStackCount(); if (entryCount > initialCount) { FragmentManager.BackStackEntry entry = manager.getBackStackEntryAt(entryCount - initialCount); return Integer.parseInt(entry.getName()); } return R.id.feeds_list_fragment; } public void invalidateOptionsMenu() { if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.HONEYCOMB) { super.invalidateOptionsMenu(); } } private int getDefaultOptionsMenuId() { return R.menu.main_menu; } private void popBackStack(FragmentManager manager) { try { manager.popBackStackImmediate(); } catch (Exception e) { // TODO: set flag to pop on resume? e.printStackTrace(); } } private void updateHomeButton() { FragmentManager manager = getSupportFragmentManager(); if (manager != null) { int id = this.fragmentIdFromBackStackEntry(manager); this.updateHomeButton(id); } } private int fragmentIdFromBackStackEntry(FragmentManager manager) { int backStackEntryCount = manager.getBackStackEntryCount(); if (backStackEntryCount > 0) { String name = manager.getBackStackEntryAt(backStackEntryCount - 1).getName(); if (!TextUtils.isEmpty(name)) { return Integer.parseInt(name); } } return R.id.feeds_list_fragment; } private void updateHomeButton(int id) { FragmentManager manager = getSupportFragmentManager(); if (manager != null) { String name = this.getFragmentIdAsString(id); boolean isTablet = this.getResources().getBoolean(R.bool.isTablet); boolean isOnFeedsList = name.equals(this.getFragmentIdAsString(R.id.feeds_list_fragment)); boolean isNotTabletAndNotOnFirstFragment = !isTablet && !isOnFeedsList; boolean isInLayout = this.getFragment(id) != null && this.getFragment(id).isInLayout(); boolean isTabletAndOnFragmentNotInLayout = isTablet && !isInLayout; this.updateHomeButton(isNotTabletAndNotOnFirstFragment || isTabletAndOnFragmentNotInLayout); } } private void updateHomeButton(boolean enableHomeButton) { getSupportActionBar().setDisplayHomeAsUpEnabled(enableHomeButton); getSupportActionBar().setHomeButtonEnabled(enableHomeButton); } }