Use `getRealMetrics` for display metrics. Closes #4934

Summary:
Fixes https://github.com/facebook/react-native/issues/4934.

Since API level 17, there has a `Display.getRealMetrics` method. This allows us to get the actual sizes of the screen (including soft menu bar and other system decor elements).

See: http://developer.android.com/reference/android/view/Display.html#getRealMetrics(android.util.DisplayMetrics)

I'm not sure if there is a good way to write unit or integration tests for this. Please let me know if there are any suggestions or concerns.
Closes https://github.com/facebook/react-native/pull/4935

Reviewed By: svcscm

Differential Revision: D2811091

Pulled By: bestander

fb-gh-sync-id: fed4e357db7eb36d638eebabd8ced4bdffd766a4

ReactAndroid/src/main/java/com/facebook/react/uimanager/UIManagerModule.java

@@ -11,11 +11,17 @@ package com.facebook.react.uimanager;
 
 import javax.annotation.Nullable;
 
+import java.lang.reflect.InvocationTargetException;
+import java.lang.reflect.Method;
 import java.util.Arrays;
 import java.util.List;
 import java.util.Map;
 
+import android.content.Context;
+import android.os.Build;
 import android.util.DisplayMetrics;
+import android.view.Display;
+import android.view.WindowManager;
 
 import com.facebook.csslayout.CSSLayoutContext;
 import com.facebook.infer.annotation.Assertions;
@@ -84,7 +90,9 @@ public class UIManagerModule extends ReactContextBaseJavaModule implements
       UIImplementation uiImplementation) {
     super(reactContext);
     mEventDispatcher = new EventDispatcher(reactContext);
-    DisplayMetrics displayMetrics = reactContext.getResources().getDisplayMetrics();
+
+    DisplayMetrics displayMetrics = getDisplayMetrics();
+
     DisplayMetricsHolder.setDisplayMetrics(displayMetrics);
     mModuleConstants = createConstants(displayMetrics, viewManagerList);
     mUIImplementation = uiImplementation;
@@ -452,4 +460,39 @@ public class UIManagerModule extends ReactContextBaseJavaModule implements
   public void sendAccessibilityEvent(int tag, int eventType) {
     mUIImplementation.sendAccessibilityEvent(tag, eventType);
   }
+
+  private DisplayMetrics getDisplayMetrics() {
+    Context context = getReactApplicationContext();
+
+    DisplayMetrics displayMetrics = context.getResources().getDisplayMetrics();
+    WindowManager wm = (WindowManager) context.getSystemService(Context.WINDOW_SERVICE);
+    Display display = wm.getDefaultDisplay();
+
+    // Get the real display metrics if we are using API level 17 or higher.
+    // The real metrics include system decor elements (e.g. soft menu bar).
+    //
+    // See: http://developer.android.com/reference/android/view/Display.html#getRealMetrics(android.util.DisplayMetrics)
+    if (Build.VERSION.SDK_INT >= 17){
+      display.getRealMetrics(displayMetrics);
+
+    } else {
+      // For 14 <= API level <= 16, we need to invoke getRawHeight and getRawWidth to get the real dimensions.
+      // Since react-native only supports API level 16+ we don't have to worry about other cases.
+      //
+      // Reflection exceptions are rethrown at runtime.
+      //
+      // See: http://stackoverflow.com/questions/14341041/how-to-get-real-screen-height-and-width/23861333#23861333
+      try {
+        Method mGetRawH = Display.class.getMethod("getRawHeight");
+        Method mGetRawW = Display.class.getMethod("getRawWidth");
+        displayMetrics.widthPixels = (Integer) mGetRawW.invoke(display);
+        displayMetrics.heightPixels = (Integer) mGetRawH.invoke(display);
+      } catch (InvocationTargetException | IllegalAccessException | NoSuchMethodException e) {
+        throw new RuntimeException("Error getting real dimensions for API level < 17", e);
+      }
+    }
+
+    return displayMetrics;
+  }
+
 }