[android] Use DataFetcherFactory to create data fetchers and allow cancelling loads

briar-android/src/main/java/org/briarproject/briar/android/conversation/ConversationModule.java

@@ -0,0 +1,19 @@
+package org.briarproject.briar.android.conversation;
+
+import org.briarproject.briar.android.activity.ActivityScope;
+import org.briarproject.briar.android.conversation.glide.BriarDataFetcherFactory;
+
+import dagger.Module;
+import dagger.Provides;
+
+@Module
+public class ConversationModule {
+
+	@ActivityScope
+	@Provides
+	BriarDataFetcherFactory provideBriarDataFetcherFactory(
+			BriarDataFetcherFactory dataFetcherFactory) {
+		return dataFetcherFactory;
+	}
+
+}

briar-android/src/main/java/org/briarproject/briar/android/conversation/glide/BriarDataFetcher.java

@@ -35,17 +35,18 @@ class BriarDataFetcher implements DataFetcher<InputStream> {
 	private final MessagingManager messagingManager;
 	@DatabaseExecutor
 	private final Executor dbExecutor;
+	private final AttachmentItem attachment;
 
-	@Nullable
-	private AttachmentItem attachment;
 	@Nullable
 	private volatile InputStream inputStream;
+	private volatile boolean cancel = false;
 
 	@Inject
 	public BriarDataFetcher(MessagingManager messagingManager,
-			@DatabaseExecutor Executor dbExecutor) {
+			@DatabaseExecutor Executor dbExecutor, AttachmentItem attachment) {
 		this.messagingManager = messagingManager;
 		this.dbExecutor = dbExecutor;
+		this.attachment = attachment;
 	}
 
 	@Override
@@ -53,6 +54,7 @@ class BriarDataFetcher implements DataFetcher<InputStream> {
 			DataCallback<? super InputStream> callback) {
 		MessageId id = requireNonNull(attachment).getMessageId();
 		dbExecutor.execute(() -> {
+			if (cancel) return;
 			try {
 				inputStream = messagingManager.getAttachment(id).getStream();
 				callback.onDataReady(inputStream);
@@ -76,7 +78,7 @@ class BriarDataFetcher implements DataFetcher<InputStream> {
 
 	@Override
 	public void cancel() {
-		// does it make sense to cancel a database load?
+		cancel = true;
 	}
 
 	@Override
@@ -89,8 +91,4 @@ class BriarDataFetcher implements DataFetcher<InputStream> {
 		return LOCAL;
 	}
 
-	public void setAttachment(AttachmentItem attachment) {
-		this.attachment = attachment;
-	}
-
 }

briar-android/src/main/java/org/briarproject/briar/android/conversation/glide/BriarDataFetcherFactory.java

@@ -0,0 +1,30 @@
+package org.briarproject.briar.android.conversation.glide;
+
+import org.briarproject.bramble.api.db.DatabaseExecutor;
+import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
+import org.briarproject.briar.android.conversation.AttachmentItem;
+import org.briarproject.briar.api.messaging.MessagingManager;
+
+import java.util.concurrent.Executor;
+
+import javax.inject.Inject;
+
+@NotNullByDefault
+public class BriarDataFetcherFactory {
+
+	private final MessagingManager messagingManager;
+	@DatabaseExecutor
+	private final Executor dbExecutor;
+
+	@Inject
+	public BriarDataFetcherFactory(MessagingManager messagingManager,
+			@DatabaseExecutor Executor dbExecutor) {
+		this.messagingManager = messagingManager;
+		this.dbExecutor = dbExecutor;
+	}
+
+	BriarDataFetcher createBriarDataFetcher(AttachmentItem model) {
+		return new BriarDataFetcher(messagingManager, dbExecutor, model);
+	}
+
+}

briar-android/src/main/java/org/briarproject/briar/android/conversation/glide/BriarModelLoader.java

@@ -19,21 +19,19 @@ import javax.inject.Inject;
 public final class BriarModelLoader
 		implements ModelLoader<AttachmentItem, InputStream> {
 
-	private final BriarApplication app;
-
 	@Inject
-	BriarDataFetcher dataFetcher;
+	BriarDataFetcherFactory dataFetcherFactory;
 
 	public BriarModelLoader(BriarApplication app) {
-		this.app = app;
+		app.getApplicationComponent().inject(this);
 	}
 
 	@Override
 	public LoadData<InputStream> buildLoadData(AttachmentItem model, int width,
 			int height, Options options) {
-		app.getApplicationComponent().inject(this);
 		ObjectKey key = new ObjectKey(model.getMessageId());
-		dataFetcher.setAttachment(model);
+		BriarDataFetcher dataFetcher =
+				dataFetcherFactory.createBriarDataFetcher(model);
 		return new LoadData<>(key, dataFetcher);
 	}