Android AppState

Summary: Closes https://github.com/facebook/react-native/pull/5152

Reviewed By: svcscm

Differential Revision: D2850250

Pulled By: mkonicek

fb-gh-sync-id: 0b5063fa7121d4e304a70da8573c9ba1d05a757c

ReactAndroid/src/main/java/com/facebook/react/modules/appstate/AppStateModule.java

@@ -0,0 +1,76 @@
+/**
+ * Copyright (c) 2015-present, Facebook, Inc.
+ * All rights reserved.
+ *
+ * This source code is licensed under the BSD-style license found in the
+ * LICENSE file in the root directory of this source tree. An additional grant
+ * of patent rights can be found in the PATENTS file in the same directory.
+ */
+
+package com.facebook.react.modules.appstate;
+
+import com.facebook.react.bridge.Arguments;
+import com.facebook.react.bridge.Callback;
+import com.facebook.react.bridge.LifecycleEventListener;
+import com.facebook.react.bridge.ReactApplicationContext;
+import com.facebook.react.bridge.ReactContextBaseJavaModule;
+import com.facebook.react.bridge.ReactMethod;
+import com.facebook.react.bridge.WritableMap;
+import com.facebook.react.modules.core.DeviceEventManagerModule.RCTDeviceEventEmitter;
+
+public class AppStateModule extends ReactContextBaseJavaModule
+        implements LifecycleEventListener {
+
+  public static final String APP_STATE_ACTIVE = "active";
+  public static final String APP_STATE_BACKGROUND = "background";
+
+  private String mAppState = "uninitialized";
+
+  public AppStateModule(ReactApplicationContext reactContext) {
+    super(reactContext);
+  }
+
+  @Override
+  public String getName() {
+    return "AppState";
+  }
+
+  @Override
+  public void initialize() {
+    getReactApplicationContext().addLifecycleEventListener(this);
+  }
+
+  @ReactMethod
+  public void getCurrentAppState(Callback success, Callback error) {
+    success.invoke(createAppStateEventMap());
+  }
+
+  @Override
+  public void onHostResume() {
+    mAppState = APP_STATE_ACTIVE;
+    sendAppStateChangeEvent();
+  }
+
+  @Override
+  public void onHostPause() {
+    mAppState = APP_STATE_BACKGROUND;
+    sendAppStateChangeEvent();
+  }
+
+  @Override
+  public void onHostDestroy() {
+    // do not set state to destroyed, do not send an event. By the current implementation, the
+    // catalyst instance is going to be immediately dropped, and all JS calls with it.
+  }
+
+  private WritableMap createAppStateEventMap() {
+    WritableMap appState = Arguments.createMap();
+    appState.putString("app_state", mAppState);
+    return appState;
+  }
+
+  private void sendAppStateChangeEvent() {
+    getReactApplicationContext().getJSModule(RCTDeviceEventEmitter.class)
+            .emit("appStateDidChange", createAppStateEventMap());
+  }
+}