feat: add example for polling a server constantly

Kaushik Gopal · Kaushik Gopal · commit f3579c33ec2f · 2014-10-02T15:37:57.000-07:00
diff --git a/README.md b/README.md
@@ -60,6 +60,11 @@ Auto-updating views are a pretty cool thing. If you've dealt with Angular JS bef
 
 While the example here is pretty rudimentary, the technique used to achieve the double binding using a `Publish Subject` is much more interesting.
 
+### Polling with Schedulers
+
+This is an example of polling using RxJava Schedulers. This is useful in cases, where you want to constantly poll a server and possibly get new data. The network call is "simulated" so it forces a delay before return a resultant string.
+
+
 ## Work in Progress:
 
 Examples that I would like to have here, but haven't found the time yet to flush out.
diff --git a/app/src/main/java/com/morihacky/android/rxjava/PollingFragment.java b/app/src/main/java/com/morihacky/android/rxjava/PollingFragment.java
@@ -10,26 +10,33 @@
 import android.view.View;
 import android.view.ViewGroup;
 import android.widget.ArrayAdapter;
-import android.widget.Button;
 import android.widget.ListView;
 import butterknife.ButterKnife;
 import butterknife.InjectView;
 import butterknife.OnClick;
 import com.morihacky.android.rxjava.app.R;
 import java.util.ArrayList;
 import java.util.List;
+import java.util.concurrent.TimeUnit;
+import rx.Observable;
+import rx.Subscriber;
+import rx.functions.Action0;
+import rx.functions.Action1;
+import rx.schedulers.Schedulers;
 import rx.subscriptions.CompositeSubscription;
 import timber.log.Timber;
 
 public class PollingFragment
     extends Fragment {
 
+  public static final int INITIAL_DELAY = 0;
+  public static final int POLLING_INTERVAL = 1000;
   @InjectView(R.id.list_threading_log) ListView _logsList;
-  @InjectView(R.id.btn_start_simple_polling) Button _btnSimplePolling;
 
   private LogAdapter _adapter;
   private List<String> _logs;
   private CompositeSubscription _subscriptions;
+  private int _counter = 0;
 
   @Override
   public void onDestroy() {
@@ -40,6 +47,7 @@ public void onDestroy() {
   @Override
   public void onActivityCreated(@Nullable Bundle savedInstanceState) {
     super.onActivityCreated(savedInstanceState);
+    _subscriptions = new CompositeSubscription();
     _setupLogger();
   }
 
@@ -54,21 +62,39 @@ public View onCreateView(LayoutInflater inflater,
 
   @OnClick(R.id.btn_start_simple_polling)
   public void onStartSimplePollingClicked() {
-    
+    _subscriptions.add(Observable.create(new Observable.OnSubscribe<String>() {
+      @Override
+      public void call(final Subscriber<? super String> observer) {
+
+        Schedulers.newThread().createWorker() //
+            .schedulePeriodically(new Action0() {
+              @Override
+              public void call() {
+                observer.onNext(_doNetworkCallAndGetStringResult());
+              }
+            }, INITIAL_DELAY, POLLING_INTERVAL, TimeUnit.MILLISECONDS);
+      }
+    }).take(10).subscribe(new Action1<String>() {
+      @Override
+      public void call(String s) {
+        _log(String.format("String polling - %s", s));
+      }
+    }));
   }
 
-
   // -----------------------------------------------------------------------------------
   // Method that help wiring up the example (irrelevant to RxJava)
 
-  private void _doSomeLongOperation_thatBlocksCurrentThread() {
-    _log("performing long operation");
+  private String _doNetworkCallAndGetStringResult() {
 
     try {
       Thread.sleep(3000);
     } catch (InterruptedException e) {
       Timber.d("Operation was interrupted");
     }
+    _counter++;
+
+    return String.valueOf(_counter);
   }
 
   private void _log(String logMsg) {
diff --git a/app/src/main/res/layout/fragment_polling.xml b/app/src/main/res/layout/fragment_polling.xml
@@ -25,6 +25,14 @@
             android:layout_marginLeft="20dp"
             android:textSize="16sp"
             android:text="Start simple polling"/>
+
+        <Button
+            android:id="@+id/btn_start_increasingly_delayed_polling"
+            android:layout_height="wrap_content"
+            android:layout_width="wrap_content"
+            android:layout_marginLeft="20dp"
+            android:textSize="16sp"
+            android:text="Start increasingly delayed polling"/>
     </LinearLayout>
 
     <ListView
diff --git a/app/src/main/res/values/strings.xml b/app/src/main/res/values/strings.xml
@@ -11,7 +11,7 @@
     <string name="msg_demo_timeout">This is a demo of terminating events, that take too long to process. Events in this demo should timeout in 3 seconds. Button 1 is an event that takes 2s to process, and Button 2 is a n event that takes 5s to process. Hit Button 2, and see in the logs that it\'s been cancelled, while this is not the case for Button 1.</string>
     <string name="msg_demo_retrofit">Retrofit from Square is a super easy networking helper library. It works really well with RxJava and these are examples taken from Jake Wharton\'s talk at Netflix (see README). Really the only interesting bits here are in the code and logs.</string>
     <string name="msg_demo_doublebinding">Watch how the result gloriously auto-updates based on your changing inputs. Using a technique like this, you could achieve the two-way binding in Angular Js, or more efficiently use a pattern like the Presentation View Model.</string>
-    <string name="msg_demo_polling">This is demo of polling or making a call repeatedly with RxJava. \n\nSimple polling: Notice in the logs how a network call (simulated) is repeatedly made in the background. \n\nExponential backoff polling: We start polling but in increasing time intervals depending on a provided condition.</string>
+    <string name="msg_demo_polling">This is demo of polling or making a call repeatedly with RxJava. \n\nSimple polling: Notice in the logs how a network call (simulated) is repeatedly made in the background.</string>
 
     <string name="btn_demo_schedulers">bg work (schedulers &amp; concurrency)</string>
     <string name="btn_demo_buffer">accumulate calls (buffer)</string>
