add Camera open / release

app/src/main/AndroidManifest.xml

@@ -2,13 +2,21 @@
 <manifest package="com.simplemobiletools.camera"
           xmlns:android="http://schemas.android.com/apk/res/android">
 
+    <uses-feature
+        android:name="android.hardware.camera"
+        android:required="true"/>
+
+    <uses-permission android:name="android.permission.CAMERA"/>
+
     <application
         android:allowBackup="true"
         android:icon="@mipmap/ic_launcher"
         android:label="@string/app_name"
         android:supportsRtl="true"
         android:theme="@style/AppTheme">
-        <activity android:name=".MainActivity">
+        <activity
+            android:name=".MainActivity"
+            android:screenOrientation="portrait">
             <intent-filter>
                 <action android:name="android.intent.action.MAIN"/>
 
@@ -16,5 +24,4 @@
             </intent-filter>
         </activity>
     </application>
-
 </manifest>

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

@@ -1,13 +1,49 @@
 package com.simplemobiletools.camera;
 
-import android.support.v7.app.AppCompatActivity;
+import android.hardware.Camera;
 import android.os.Bundle;
+import android.support.v7.app.AppCompatActivity;
+import android.util.Log;
 
 public class MainActivity extends AppCompatActivity {
+    private static final String TAG = MainActivity.class.getSimpleName();
+    private Camera camera;
+    private boolean isOpen;
 
     @Override
     protected void onCreate(Bundle savedInstanceState) {
         super.onCreate(savedInstanceState);
         setContentView(R.layout.activity_main);
     }
+
+    @Override
+    protected void onResume() {
+        super.onResume();
+        openCamera();
+    }
+
+    @Override
+    protected void onPause() {
+        super.onPause();
+        releaseCamera();
+    }
+
+    private void openCamera() {
+        isOpen = false;
+
+        try {
+            releaseCamera();
+            camera = Camera.open();
+            isOpen = (camera != null);
+        } catch (Exception e) {
+            Log.e(TAG, "openCamera exception " + e.getMessage());
+        }
+    }
+
+    private void releaseCamera() {
+        if (camera != null) {
+            camera.release();
+            camera = null;
+        }
+    }
 }