Ask for permission to access external storage

app/build.gradle

@@ -5,7 +5,7 @@ android {
     buildToolsVersion "25.0.3"
     defaultConfig {
         applicationId "de.trac.spherical"
-        minSdkVersion 15
+        minSdkVersion 16
         targetSdkVersion 25
         versionCode 1
         versionName "1.0"

app/src/main/java/de/trac/spherical/MainActivity.java

@@ -1,12 +1,15 @@
 package de.trac.spherical;
 
+import android.Manifest;
 import android.content.Intent;
+import android.content.pm.PackageManager;
 import android.graphics.BitmapFactory;
 import android.net.Uri;
 import android.os.Build;
 import android.os.Bundle;
-import android.support.design.widget.AppBarLayout;
 import android.support.design.widget.FloatingActionButton;
+import android.support.v4.app.ActivityCompat;
+import android.support.v4.content.ContextCompat;
 import android.support.v7.app.AppCompatActivity;
 import android.support.v7.widget.Toolbar;
 import android.util.Log;
@@ -38,11 +41,15 @@ public class MainActivity extends AppCompatActivity {
     public static final String MIME_PHOTO_SPHERE = "application/vnd.google.panorama360+jpg";
     public static final String MIME_IMAGE = "image/*";
 
+    private static final int PERMISSION_REQUEST_READ_EXTERNAL_STORAGE = 387;
+
     private SphereSurfaceView surfaceView;
     private Renderer renderer;
     private FloatingActionButton fab;
     private Toolbar toolbar;
 
+    private Intent cachedIntent;
+
     @Override
     protected void onCreate(Bundle savedInstanceState) {
         super.onCreate(savedInstanceState);
@@ -92,11 +99,14 @@ public class MainActivity extends AppCompatActivity {
             }
         });
 
-        Intent intent = getIntent();
+        handleIntent(getIntent());
+    }
+
+    private void handleIntent(Intent intent) {
         switch (intent.getAction()) {
             //Image was sent into the app
             case Intent.ACTION_SEND:
-                handleSentImageIntent(intent);
+                checkPermissionAndHandleSentImage(intent);
                 break;
 
             //App was launched via launcher icon
@@ -106,6 +116,36 @@ public class MainActivity extends AppCompatActivity {
         }
     }
 
+    private void checkPermissionAndHandleSentImage(Intent intent) {
+        int status = ContextCompat.checkSelfPermission(this, Manifest.permission.READ_EXTERNAL_STORAGE);
+        if (status == PackageManager.PERMISSION_GRANTED) {
+            handleSentImageIntent(intent);
+        }
+
+        // Cache intent and request permission
+        this.cachedIntent = intent;
+        ActivityCompat.requestPermissions(this, new String[]{Manifest.permission.READ_EXTERNAL_STORAGE},
+                PERMISSION_REQUEST_READ_EXTERNAL_STORAGE);
+
+    }
+
+    @Override
+    public void onRequestPermissionsResult(int requestCode,
+                                           String permissions[], int[] grantResults) {
+        switch (requestCode) {
+            case PERMISSION_REQUEST_READ_EXTERNAL_STORAGE: {
+                // If request is cancelled, the result arrays are empty.
+                if (grantResults.length > 0
+                        && grantResults[0] == PackageManager.PERMISSION_GRANTED) {
+                    handleSentImageIntent(cachedIntent);
+                } else {
+                    Toast.makeText(this, R.string.missing_permission, Toast.LENGTH_LONG).show();
+                }
+                return;
+            }
+        }
+    }
+
     private void displayUI(boolean display) {
         if (display) {
             fab.show();

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

@@ -6,4 +6,5 @@
     <string name="wow">WOW! SUCH 3D!!!</string>
     <string name="menu_force_sphere">Show as Sphere</string>
     <string name="not_yet_implemented">Not yet implemented!</string>
+    <string name="missing_permission">Cannot display photo: Missing permissions to access external storage.</string>
 </resources>