Use a consumable LiveData event to report the schedule download result to UI in place of LocalBroadcastManager

Use a simple AtomicBoolean instead of a lock to prevent concurrent downloads

app/src/main/java/be/digitalia/fosdem/activities/MainActivity.java

@@ -4,17 +4,10 @@ import android.animation.Animator;
 import android.animation.AnimatorListenerAdapter;
 import android.app.Dialog;
 import android.app.SearchManager;
-import android.content.ActivityNotFoundException;
+import android.content.*;
-import android.content.BroadcastReceiver;
-import android.content.Context;
-import android.content.DialogInterface;
-import android.content.Intent;
-import android.content.IntentFilter;
-import android.content.SharedPreferences;
 import android.graphics.drawable.Animatable;
 import android.graphics.drawable.Drawable;
 import android.net.Uri;
-import android.os.AsyncTask;
 import android.os.Build;
 import android.os.Bundle;
 import android.text.format.DateUtils;
@@ -23,10 +16,6 @@ import android.view.MenuItem;
 import android.view.View;
 import android.widget.ProgressBar;
 import android.widget.TextView;
-
-import com.google.android.material.navigation.NavigationView;
-import com.google.android.material.snackbar.Snackbar;
-
 import androidx.annotation.IdRes;
 import androidx.annotation.NonNull;
 import androidx.annotation.Nullable;
@@ -53,11 +42,11 @@ import be.digitalia.fosdem.R;
 import be.digitalia.fosdem.api.FosdemApi;
 import be.digitalia.fosdem.api.FosdemUrls;
 import be.digitalia.fosdem.db.DatabaseManager;
-import be.digitalia.fosdem.fragments.BookmarksListFragment;
+import be.digitalia.fosdem.fragments.*;
-import be.digitalia.fosdem.fragments.LiveFragment;
+import be.digitalia.fosdem.livedata.SingleEvent;
-import be.digitalia.fosdem.fragments.MapFragment;
+import be.digitalia.fosdem.model.DownloadScheduleResult;
-import be.digitalia.fosdem.fragments.PersonsListFragment;
+import com.google.android.material.navigation.NavigationView;
-import be.digitalia.fosdem.fragments.TracksFragment;
+import com.google.android.material.snackbar.Snackbar;
 
 /**
  * Main entry point of the application. Allows to switch between section fragments and update the database.
@@ -136,24 +125,26 @@ public class MainActivity extends AppCompatActivity {
 
 	private MenuItem searchMenuItem;
 
-	private final BroadcastReceiver scheduleDownloadResultReceiver = new BroadcastReceiver() {
+	private final Observer<SingleEvent<DownloadScheduleResult>> scheduleDownloadResultObserver = new Observer<SingleEvent<DownloadScheduleResult>>() {
 
 		@Override
-		public void onReceive(Context context, Intent intent) {
+		public void onChanged(SingleEvent<DownloadScheduleResult> singleEvent) {
-			int result = intent.getIntExtra(FosdemApi.EXTRA_RESULT, FosdemApi.RESULT_ERROR);
+			final DownloadScheduleResult result = singleEvent.consume();
+			if (result == null) {
+				return;
+			}
 			String message;
-			switch (result) {
+			if (result.isError()) {
-				case FosdemApi.RESULT_ERROR:
+				message = getString(R.string.schedule_loading_error);
-					message = getString(R.string.schedule_loading_error);
+			} else if (result.isUpToDate()) {
-					break;
+				message = getString(R.string.events_download_up_to_date);
-				case FosdemApi.RESULT_UP_TO_DATE:
+			} else {
-					message = getString(R.string.events_download_up_to_date);
+				int eventsCount = result.getEventsCount();
-					break;
+				if (eventsCount == 0) {
-				case 0:
 					message = getString(R.string.events_download_empty);
-					break;
+				} else {
-				default:
+					message = getResources().getQuantityString(R.plurals.events_download_completed, eventsCount, eventsCount);
-					message = getResources().getQuantityString(R.plurals.events_download_completed, result, result);
+				}
 			}
 			Snackbar.make(findViewById(R.id.content), message, Snackbar.LENGTH_LONG).show();
 		}
@@ -172,14 +163,14 @@ public class MainActivity extends AppCompatActivity {
 		@NonNull
 		@Override
 		public Dialog onCreateDialog(Bundle savedInstanceState) {
-			return new AlertDialog.Builder(getActivity())
+			return new AlertDialog.Builder(getContext())
 					.setTitle(R.string.download_reminder_title)
 					.setMessage(R.string.download_reminder_message)
 					.setPositiveButton(android.R.string.ok, new DialogInterface.OnClickListener() {
 
 						@Override
 						public void onClick(DialogInterface dialog, int which) {
-							((MainActivity) getActivity()).startDownloadSchedule();
+							FosdemApi.downloadSchedule(getContext());
 						}
 
 					}).setNegativeButton(android.R.string.cancel, null)
@@ -234,6 +225,9 @@ public class MainActivity extends AppCompatActivity {
 			}
 		});
 
+		// Monitor the schedule download result
+		FosdemApi.getDownloadScheduleResult().observe(this, scheduleDownloadResultObserver);
+
 		// Setup drawer layout
 		getSupportActionBar().setDisplayHomeAsUpEnabled(true);
 		drawerLayout = findViewById(R.id.drawer_layout);
@@ -296,7 +290,7 @@ public class MainActivity extends AppCompatActivity {
 		updateLastUpdateTime();
 
 		if (savedInstanceState == null) {
-		    // Select initial section
+			// Select initial section
 			currentSection = Section.TRACKS;
 			String action = getIntent().getAction();
 			if (action != null) {
@@ -375,10 +369,6 @@ public class MainActivity extends AppCompatActivity {
 	protected void onStart() {
 		super.onStart();
 
-		// Monitor the schedule download result
-		LocalBroadcastManager.getInstance(this).registerReceiver(scheduleDownloadResultReceiver,
-				new IntentFilter(FosdemApi.ACTION_DOWNLOAD_SCHEDULE_RESULT));
-
 		// Download reminder
 		long now = System.currentTimeMillis();
 		long time = DatabaseManager.getInstance().getLastUpdateTime();
@@ -404,8 +394,6 @@ public class MainActivity extends AppCompatActivity {
 			searchMenuItem.collapseActionView();
 		}
 
-		LocalBroadcastManager.getInstance(this).unregisterReceiver(scheduleDownloadResultReceiver);
-
 		super.onStop();
 	}
 
@@ -444,35 +432,16 @@ public class MainActivity extends AppCompatActivity {
 					item.setIcon(icon);
 					((Animatable) icon).start();
 				}
-				startDownloadSchedule();
+				FosdemApi.downloadSchedule(this);
 				return true;
 		}
 		return false;
 	}
 
-	public void startDownloadSchedule() {
-		new DownloadScheduleAsyncTask(this).executeOnExecutor(AsyncTask.THREAD_POOL_EXECUTOR);
-	}
-
-	private static class DownloadScheduleAsyncTask extends AsyncTask<Void, Void, Void> {
-
-		private final Context appContext;
-
-		public DownloadScheduleAsyncTask(Context context) {
-			appContext = context.getApplicationContext();
-		}
-
-		@Override
-		protected Void doInBackground(Void... args) {
-			FosdemApi.downloadSchedule(appContext);
-			return null;
-		}
-	}
-
 	// MAIN MENU
 
 	void handleNavigationMenuItem(@NonNull MenuItem menuItem) {
-	    final int menuItemId = menuItem.getItemId();
+		final int menuItemId = menuItem.getItemId();
 		final Section section = Section.fromMenuItemId(menuItemId);
 		if (section != null) {
 			selectMenuSection(section, menuItem);

app/src/main/java/be/digitalia/fosdem/api/FosdemApi.java

@@ -1,24 +1,22 @@
 package be.digitalia.fosdem.api;
 
 import android.content.Context;
-import android.content.Intent;
+import android.os.AsyncTask;
-
-import java.util.Map;
-import java.util.concurrent.locks.Lock;
-import java.util.concurrent.locks.ReentrantLock;
-
 import androidx.annotation.MainThread;
 import androidx.annotation.WorkerThread;
 import androidx.lifecycle.LiveData;
 import androidx.lifecycle.MutableLiveData;
-import androidx.localbroadcastmanager.content.LocalBroadcastManager;
-import be.digitalia.fosdem.BuildConfig;
 import be.digitalia.fosdem.db.DatabaseManager;
+import be.digitalia.fosdem.livedata.SingleEvent;
+import be.digitalia.fosdem.model.DownloadScheduleResult;
 import be.digitalia.fosdem.model.Event;
 import be.digitalia.fosdem.model.RoomStatus;
 import be.digitalia.fosdem.parsers.EventsParser;
 import be.digitalia.fosdem.utils.HttpUtils;
 
+import java.util.Map;
+import java.util.concurrent.atomic.AtomicBoolean;
+
 /**
  * Main API entry point.
  *
@@ -26,31 +24,36 @@ import be.digitalia.fosdem.utils.HttpUtils;
  */
 public class FosdemApi {
 
-	// Local broadcasts parameters
+	private static final AtomicBoolean isLoading = new AtomicBoolean();
-	public static final String ACTION_DOWNLOAD_SCHEDULE_RESULT = BuildConfig.APPLICATION_ID + ".action.DOWNLOAD_SCHEDULE_RESULT";
-	public static final String EXTRA_RESULT = "RESULT";
-
-	public static final int RESULT_ERROR = -1;
-	public static final int RESULT_UP_TO_DATE = -2;
-
-	private static final Lock scheduleLock = new ReentrantLock();
 	private static final MutableLiveData<Integer> progress = new MutableLiveData<>();
+	private static final MutableLiveData<SingleEvent<DownloadScheduleResult>> result = new MutableLiveData<>();
 	private static LiveData<Map<String, RoomStatus>> roomStatuses;
 
 	/**
 	 * Download & store the schedule to the database.
 	 * Only one thread at a time will perform the actual action, the other ones will return immediately.
-	 * The result will be sent back in the form of a local broadcast with an ACTION_DOWNLOAD_SCHEDULE_RESULT action.
+	 * The result will be sent back in the consumable Result LiveData.
 	 */
-	@WorkerThread
+	@MainThread
 	public static void downloadSchedule(Context context) {
-		if (!scheduleLock.tryLock()) {
+		if (!isLoading.compareAndSet(false, true)) {
 			// If a download is already in progress, return immediately
 			return;
 		}
+		final Context appContext = context.getApplicationContext();
+		AsyncTask.THREAD_POOL_EXECUTOR.execute(new Runnable() {
+			@Override
+			public void run() {
+				downloadScheduleInternal(appContext);
+				isLoading.set(false);
+			}
+		});
+	}
 
+	@WorkerThread
+	private static void downloadScheduleInternal(Context context) {
 		progress.postValue(-1);
-		int result = RESULT_ERROR;
+		DownloadScheduleResult res = DownloadScheduleResult.error();
 		try {
 			DatabaseManager dbManager = DatabaseManager.getInstance();
 			HttpUtils.HttpResult httpResult = HttpUtils.get(
@@ -64,13 +67,14 @@ public class FosdemApi {
 					});
 			if (httpResult.inputStream == null) {
 				// Nothing to parse, the result is up-to-date.
-				result = RESULT_UP_TO_DATE;
+				res = DownloadScheduleResult.upToDate();
 				return;
 			}
 
 			try {
 				Iterable<Event> events = new EventsParser().parse(httpResult.inputStream);
-				result = dbManager.storeSchedule(events, httpResult.lastModified);
+				int count = dbManager.storeSchedule(events, httpResult.lastModified);
+				res = DownloadScheduleResult.success(count);
 			} finally {
 				try {
 					httpResult.inputStream.close();
@@ -80,12 +84,10 @@ public class FosdemApi {
 
 		} catch (Exception e) {
 			e.printStackTrace();
+			res = DownloadScheduleResult.error();
 		} finally {
 			progress.postValue(100);
-			Intent resultIntent = new Intent(ACTION_DOWNLOAD_SCHEDULE_RESULT)
+			result.postValue(new SingleEvent<>(res));
-					.putExtra(EXTRA_RESULT, result);
-			LocalBroadcastManager.getInstance(context).sendBroadcast(resultIntent);
-			scheduleLock.unlock();
 		}
 	}
 
@@ -99,6 +101,10 @@ public class FosdemApi {
 		return progress;
 	}
 
+	public static LiveData<SingleEvent<DownloadScheduleResult>> getDownloadScheduleResult() {
+		return result;
+	}
+
 	@MainThread
 	public static LiveData<Map<String, RoomStatus>> getRoomStatuses() {
 		if (roomStatuses == null) {

app/src/main/java/be/digitalia/fosdem/livedata/SingleEvent.java

@@ -0,0 +1,28 @@
+package be.digitalia.fosdem.livedata;
+
+import androidx.annotation.NonNull;
+import androidx.annotation.Nullable;
+
+/**
+ * Encapsulates data that can only be consumed once.
+ */
+public class SingleEvent<T> {
+
+	private T content;
+
+	public SingleEvent(@NonNull T content) {
+		this.content = content;
+	}
+
+	/**
+	 * @return The content, or null if it has already been consumed.
+	 */
+	@Nullable
+	public T consume() {
+		final T previousContent = content;
+		if (previousContent != null) {
+			content = null;
+		}
+		return previousContent;
+	}
+}

app/src/main/java/be/digitalia/fosdem/model/DownloadScheduleResult.java

@@ -0,0 +1,41 @@
+package be.digitalia.fosdem.model;
+
+public class DownloadScheduleResult {
+
+	private static final DownloadScheduleResult RESULT_ERROR = new DownloadScheduleResult(0);
+	private static final DownloadScheduleResult RESULT_UP_TO_DATE = new DownloadScheduleResult(0);
+
+	private final int eventsCount;
+
+	private DownloadScheduleResult(int eventsCount) {
+		this.eventsCount = eventsCount;
+	}
+
+	public static DownloadScheduleResult success(int eventsCount) {
+		return new DownloadScheduleResult(eventsCount);
+	}
+
+	public static DownloadScheduleResult error() {
+		return RESULT_ERROR;
+	}
+
+	public static DownloadScheduleResult upToDate() {
+		return RESULT_UP_TO_DATE;
+	}
+
+	public boolean isSuccess() {
+		return this != RESULT_ERROR && this != RESULT_UP_TO_DATE;
+	}
+
+	public boolean isError() {
+		return this == RESULT_ERROR;
+	}
+
+	public boolean isUpToDate() {
+		return this == RESULT_UP_TO_DATE;
+	}
+
+	public int getEventsCount() {
+		return eventsCount;
+	}
+}