Add runtime permission support to gallery sample.

checkstyle.xml

@@ -127,7 +127,9 @@
 
         <!-- Checks for blocks. -->
         <!-- See http://checkstyle.sourceforge.net/config_blocks.html -->
-        <module name="AvoidNestedBlocks" />
+        <module name="AvoidNestedBlocks">
+          <property name="allowInSwitchCase" value="true" />
+        </module>
         <module name="EmptyBlock" >
             <property name="option" value="text"/>
         </module>

samples/gallery/src/main/java/com/bumptech/glide/samples/gallery/MainActivity.java

 package com.bumptech.glide.samples.gallery;
 
+import android.Manifest.permission;
+import android.annotation.TargetApi;
+import android.content.pm.PackageManager;
+import android.os.Build;
 import android.os.Bundle;
+import android.support.annotation.NonNull;
+import android.support.v4.app.ActivityCompat;
+import android.support.v4.app.Fragment;
 import android.support.v4.app.FragmentActivity;
+import android.support.v4.content.ContextCompat;
+import android.widget.Toast;
 import com.bumptech.glide.MemoryCategory;
 
 /**
@@ -9,10 +18,53 @@ import com.bumptech.glide.MemoryCategory;
  */
 public class MainActivity extends FragmentActivity {
 
-    @Override
-    protected void onCreate(Bundle savedInstanceState) {
-        super.onCreate(savedInstanceState);
-        setContentView(R.layout.main_activity);
-        GlideApp.get(this).setMemoryCategory(MemoryCategory.HIGH);
+  private static final int REQUEST_READ_STORAGE = 0;
+
+  @Override
+  protected void onCreate(Bundle savedInstanceState) {
+    super.onCreate(savedInstanceState);
+    setContentView(R.layout.main_activity);
+    GlideApp.get(this).setMemoryCategory(MemoryCategory.HIGH);
+    if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.M
+        && ContextCompat.checkSelfPermission(this, permission.READ_EXTERNAL_STORAGE)
+        != PackageManager.PERMISSION_GRANTED) {
+      requestStoragePermission();
+    } else {
+      replaceFragment();
+    }
+  }
+
+  @TargetApi(Build.VERSION_CODES.JELLY_BEAN)
+  private void requestStoragePermission() {
+     ActivityCompat.requestPermissions(this,
+        new String[]{permission.READ_EXTERNAL_STORAGE},
+        REQUEST_READ_STORAGE);
+  }
+
+  private void replaceFragment() {
+    Fragment fragment = new HorizontalGalleryFragment();
+    getSupportFragmentManager()
+        .beginTransaction()
+        .replace(R.id.fragment_container, fragment)
+        .commit();
+  }
+
+  @Override
+  public void onRequestPermissionsResult(int requestCode, @NonNull String[] permissions,
+      @NonNull int[] grantResults) {
+    super.onRequestPermissionsResult(requestCode, permissions, grantResults);
+    switch (requestCode) {
+      case REQUEST_READ_STORAGE: {
+        // If request is cancelled, the result arrays are empty.
+        if (grantResults.length > 0
+            && grantResults[0] == PackageManager.PERMISSION_GRANTED) {
+          replaceFragment();
+        } else {
+          Toast.makeText(this, "Storage permission is required", Toast.LENGTH_LONG)
+              .show();
+          requestStoragePermission();
+        }
+      }
     }
+  }
 }

samples/gallery/src/main/res/layout/main_activity.xml

 <?xml version="1.0" encoding="utf-8"?>
-<merge xmlns:android="http://schemas.android.com/apk/res/android">
-    <fragment
-            android:name="com.bumptech.glide.samples.gallery.HorizontalGalleryFragment"
-            android:layout_width="match_parent"
-            android:layout_height="match_parent"
-            android:id="@+id/horizontal_gallery_fragment"/>
-</merge>
+<FrameLayout
+  xmlns:android="http://schemas.android.com/apk/res/android"
+  android:id="@+id/fragment_container"
+  android:layout_width="match_parent"
+  android:layout_height="match_parent">
+</FrameLayout>