add an About activity

app/src/main/AndroidManifest.xml

@@ -39,5 +39,9 @@
                 <action android:name="android.appwidget.action.APPWIDGET_CONFIGURE"/>
             </intent-filter>
         </activity>
+
+        <activity
+            android:name="com.simplemobiletools.calculator.AboutActivity"
+            android:screenOrientation="portrait"/>
     </application>
 </manifest>

app/src/main/java/com/simplemobiletools/calculator/AboutActivity.java

@@ -0,0 +1,14 @@
+package com.simplemobiletools.calculator;
+
+import android.os.Bundle;
+import android.support.v7.app.AppCompatActivity;
+
+public class AboutActivity extends AppCompatActivity {
+
+    @Override
+    protected void onCreate(Bundle savedInstanceState) {
+        super.onCreate(savedInstanceState);
+        setContentView(R.layout.activity_about);
+        setTitle(getResources().getString(R.string.about));
+    }
+}

app/src/main/java/com/simplemobiletools/calculator/MainActivity.java

@@ -1,8 +1,12 @@
 package com.simplemobiletools.calculator;
 
+import android.content.Intent;
 import android.content.res.Resources;
 import android.os.Bundle;
 import android.support.v7.app.AppCompatActivity;
+import android.view.Menu;
+import android.view.MenuInflater;
+import android.view.MenuItem;
 import android.view.View;
 import android.widget.TextView;
 
@@ -28,6 +32,25 @@ public class MainActivity extends AppCompatActivity implements Calculator {
         AutofitHelper.create(result);
     }
 
+    @Override
+    public boolean onCreateOptionsMenu(Menu menu) {
+        MenuInflater inflater = getMenuInflater();
+        inflater.inflate(R.menu.menu, menu);
+        return true;
+    }
+
+    @Override
+    public boolean onOptionsItemSelected(MenuItem item) {
+        switch (item.getItemId()) {
+            case R.id.about:
+                final Intent intent = new Intent(getApplicationContext(), AboutActivity.class);
+                startActivity(intent);
+                return true;
+            default:
+                return super.onOptionsItemSelected(item);
+        }
+    }
+
     private void setupResultView() {
         final Resources res = getResources();
         result.setBackgroundColor(res.getColor(android.R.color.white));

app/src/main/res/layout/activity_about.xml

@@ -0,0 +1,6 @@
+<?xml version="1.0" encoding="utf-8"?>
+<RelativeLayout
+    android:id="@+id/about_holder"
+    xmlns:android="http://schemas.android.com/apk/res/android"
+    android:layout_width="match_parent"
+    android:layout_height="match_parent"/>

app/src/main/res/layout/activity_main.xml

@@ -7,6 +7,7 @@
     android:layout_height="match_parent"
     android:background="@color/dark_grey"
     android:orientation="vertical"
+    android:theme="@style/MainTheme"
     tools:context=".MainActivity">
 
     <TextView

app/src/main/res/menu/menu.xml

@@ -0,0 +1,8 @@
+<?xml version="1.0" encoding="utf-8"?>
+<menu xmlns:android="http://schemas.android.com/apk/res/android"
+      xmlns:app="http://schemas.android.com/apk/res-auto">
+    <item
+        android:id="@+id/about"
+        android:title="@string/about"
+        app:showAsAction="never"/>
+</menu>

app/src/main/res/values/strings.xml

@@ -1,3 +1,4 @@
 <resources>
     <string name="app_name">Simple Calculator</string>
+    <string name="about">About</string>
 </resources>

app/src/main/res/values/styles.xml

@@ -4,6 +4,9 @@
         <item name="colorPrimary">@color/colorPrimary</item>
         <item name="colorPrimaryDark">@color/colorPrimaryDark</item>
         <item name="colorAccent">@color/colorAccent</item>
+    </style>
+
+    <style name="MainTheme" parent="@style/AppTheme">
         <item name="android:textColor">@android:color/white</item>
     </style>