Keep selected application on screen rotation

app/src/main/java/com/github/gotify/messages/MessagesModel.java

@@ -0,0 +1,70 @@
+package com.github.gotify.messages;
+
+import android.app.Activity;
+import androidx.lifecycle.ViewModel;
+import com.github.gotify.Settings;
+import com.github.gotify.api.ClientFactory;
+import com.github.gotify.client.ApiClient;
+import com.github.gotify.client.api.MessageApi;
+import com.github.gotify.messages.provider.ApplicationHolder;
+import com.github.gotify.messages.provider.MessageFacade;
+import com.github.gotify.messages.provider.MessageState;
+import com.github.gotify.picasso.PicassoHandler;
+import com.squareup.picasso.Target;
+import java.util.ArrayList;
+import java.util.List;
+
+public class MessagesModel extends ViewModel {
+    private final Settings settings;
+    private final PicassoHandler picassoHandler;
+    private final ApiClient client;
+    private final ApplicationHolder appsHolder;
+    private final MessageFacade messages;
+
+    // we need to keep the target references otherwise they get gc'ed before they can be called.
+    @SuppressWarnings("MismatchedQueryAndUpdateOfCollection")
+    private final List<Target> targetReferences = new ArrayList<>();
+
+    private long appId = MessageState.ALL_MESSAGES;
+
+    public MessagesModel(Activity parentView) {
+        settings = new Settings(parentView);
+        picassoHandler = new PicassoHandler(parentView, settings);
+        client =
+                ClientFactory.clientToken(settings.url(), settings.sslSettings(), settings.token());
+        appsHolder = new ApplicationHolder(parentView, client);
+        messages = new MessageFacade(client.createService(MessageApi.class), appsHolder);
+    }
+
+    public Settings getSettings() {
+        return settings;
+    }
+
+    public PicassoHandler getPicassoHandler() {
+        return picassoHandler;
+    }
+
+    public ApiClient getClient() {
+        return client;
+    }
+
+    public ApplicationHolder getAppsHolder() {
+        return appsHolder;
+    }
+
+    public MessageFacade getMessages() {
+        return messages;
+    }
+
+    public List<Target> getTargetReferences() {
+        return targetReferences;
+    }
+
+    public long getAppId() {
+        return appId;
+    }
+
+    public void setAppId(long appId) {
+        this.appId = appId;
+    }
+}