Implement MotionObservable in android.

Reviewers: featherless, O2 Material Motion, O6 Material Motion Android platform reviewers

Reviewed By: featherless, O2 Material Motion, O6 Material Motion Android platform reviewers

Subscribers: featherless

Tags: #material_motion

Differential Revision: http://codereview.cc/D2150

library/build.gradle

@@ -36,6 +36,7 @@ android {
 
 dependencies {
   // If you are developing any dependencies locally, also list them in local.dependencies.
+  compile 'com.github.material-motion:indefinite-observable-android:1.0.0'
 
   testCompile 'com.google.truth:truth:0.28'
   testCompile 'junit:junit:4.12'

library/src/main/java/com/google/android/material/motion/streams/MotionObservable.java

@@ -0,0 +1,80 @@
+/*
+ * Copyright 2016-present The Material Motion Authors. All Rights Reserved.
+ *
+ * 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 com.google.android.material.motion.streams;
+
+import android.support.annotation.IntDef;
+
+import com.google.android.material.motion.observable.IndefiniteObservable;
+import com.google.android.material.motion.observable.Observer;
+import com.google.android.material.motion.streams.MotionObservable.MotionObserver;
+
+import java.lang.annotation.Retention;
+import java.lang.annotation.RetentionPolicy;
+
+/**
+ * A MotionObservable is a type of <a href="http://reactivex.io/documentation/observable.html">Observable</a>
+ * that specializes in motion systems that can be either active or at rest.
+ * <p>
+ * Throughout this documentation we will treat the words "observable" and "stream" as synonyms.
+ *
+ * @see <a href="https://material-motion.github.io/material-motion/starmap/specifications/streams/MotionObservable">The
+ * motion observable specification</a>
+ */
+public class MotionObservable<T> extends IndefiniteObservable<MotionObserver<T>> {
+
+  /**
+   * The stream is at rest.
+   */
+  public static final int AT_REST = 0;
+
+  /**
+   * The stream is currently active.
+   */
+  public static final int ACTIVE = 1;
+
+  public MotionObservable(Subscriber<MotionObserver<T>> subscriber) {
+    super(subscriber);
+  }
+
+  /**
+   * The possible states that a stream can be in.
+   * <p>
+   * What "active" means is stream-dependant. The stream is active if you can answer yes to any of
+   * the following questions: <ul> <li>Is my animation currently animating?</li> <li>Is my
+   * physical simulation still moving?</li> <li>Is my gesture recognizer in the .began or .changed
+   * state?</li> </ul> Momentary events such as taps may emit {@link #ACTIVE} immediately followed
+   * by {@link #AT_REST}.
+   */
+  @IntDef({AT_REST, ACTIVE})
+  @Retention(RetentionPolicy.SOURCE)
+  public @interface MotionState {
+
+  }
+
+  /**
+   * An observer with an additional {@link #state(int)} method.
+   */
+  public interface MotionObserver<T> extends Observer<T> {
+
+    @Override
+    void next(T value);
+
+    /**
+     * A method to handle new state values from upstream.
+     */
+    void state(@MotionState int state);
+  }
+}

sample/src/main/java/com/google/android/material/motion/streams/sample/MainActivity.java

@@ -15,24 +15,112 @@
  */
 package com.google.android.material.motion.streams.sample;
 
-import com.google.android.material.motion.streams.Library;
-
+import android.graphics.Color;
 import android.os.Bundle;
+import android.support.annotation.Nullable;
 import android.support.v7.app.AppCompatActivity;
+import android.view.View;
+import android.widget.Button;
 import android.widget.TextView;
 
+import com.google.android.material.motion.observable.IndefiniteObservable.Subscriber;
+import com.google.android.material.motion.observable.IndefiniteObservable.Subscription;
+import com.google.android.material.motion.observable.IndefiniteObservable.Unsubscriber;
+import com.google.android.material.motion.streams.MotionObservable;
+import com.google.android.material.motion.streams.MotionObservable.MotionObserver;
+import com.google.android.material.motion.streams.MotionObservable.MotionState;
+
+import static com.google.android.material.motion.streams.MotionObservable.ACTIVE;
+import static com.google.android.material.motion.streams.MotionObservable.AT_REST;
+
 /**
  * Streams for Android sample Activity.
  */
 public class MainActivity extends AppCompatActivity {
 
+  private static final String[] values = new String[]{
+    "foo", "bar", "baz", "qux"
+  };
+
+  private MotionObserver<String> callback;
+  private int index = 0;
+
   @Override
   protected void onCreate(Bundle savedInstanceState) {
     super.onCreate(savedInstanceState);
 
     setContentView(R.layout.main_activity);
 
-    TextView text = (TextView) findViewById(R.id.text);
-    text.setText(Library.LIBRARY_NAME);
+    final TextView text = (TextView) findViewById(R.id.text);
+    Button nextButton = (Button) findViewById(R.id.next_button);
+    Button unsubscribeButton = (Button) findViewById(R.id.unsubscribe_button);
+
+    MotionObservable<String> observable = new MotionObservable<>(
+      new Subscriber<MotionObserver<String>>() {
+        @Nullable
+        @Override
+        public Unsubscriber subscribe(MotionObserver<String> observer) {
+          registerButtonCallback(observer);
+          return new Unsubscriber() {
+            @Override
+            public void unsubscribe() {
+              unregisterButtonCallback();
+            }
+          };
+        }
+      });
+
+    final Subscription subscription = observable.subscribe(new MotionObserver<String>() {
+      @Override
+      public void next(String value) {
+        text.setText(value);
+      }
+
+      @Override
+      public void state(@MotionState int state) {
+        switch (state) {
+          case AT_REST:
+            text.setTextColor(Color.BLACK);
+            break;
+          case ACTIVE:
+            text.setTextColor(Color.RED);
+            break;
+        }
+      }
+    });
+
+    nextButton.setOnClickListener(new View.OnClickListener() {
+      @Override
+      public void onClick(View v) {
+        if (callback != null) {
+          if (index < values.length) {
+            callback.next(values[index]);
+          }
+
+          if (index + 1 < values.length) {
+            callback.state(ACTIVE);
+          } else {
+            callback.state(AT_REST);
+          }
+
+          index++;
+        }
+      }
+    });
+
+    unsubscribeButton.setOnClickListener(new View.OnClickListener() {
+      @Override
+      public void onClick(View v) {
+        subscription.unsubscribe();
+      }
+    });
+  }
+
+  private void registerButtonCallback(MotionObserver<String> observer) {
+    callback = observer;
+  }
+
+  private void unregisterButtonCallback() {
+    callback = null;
   }
 }

sample/src/main/res/layout/main_activity.xml

@@ -14,12 +14,26 @@
   ~ See the License for the specific language governing permissions and
   ~ limitations under the License.
 -->
-<FrameLayout xmlns:android="http://schemas.android.com/apk/res/android"
+<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
   android:layout_width="match_parent"
-  android:layout_height="match_parent">
+  android:layout_height="match_parent"
+  android:orientation="vertical">
+
   <TextView
     android:id="@+id/text"
     android:layout_width="wrap_content"
     android:layout_height="wrap_content"
     android:text="Hello, World!"/>
-</FrameLayout>
+
+  <Button
+    android:id="@+id/next_button"
+    android:layout_width="wrap_content"
+    android:layout_height="wrap_content"
+    android:text="Next"/>
+
+  <Button
+    android:id="@+id/unsubscribe_button"
+    android:layout_width="wrap_content"
+    android:layout_height="wrap_content"
+    android:text="Unsubscribe"/>
+</LinearLayout>