Issue #2446783 by mpdonadio, dawehner, koence: Views preview not working without saving new display

core/modules/views/src/Form/ViewsForm.php

@@ -14,6 +14,7 @@ use Drupal\Core\DependencyInjection\DependencySerializationTrait;
 use Drupal\Core\Form\FormInterface;
 use Drupal\Core\Form\FormStateInterface;
 use Drupal\Core\Routing\UrlGeneratorInterface;
+use Drupal\Core\Url;
 use Drupal\views\ViewExecutable;
 use Symfony\Component\DependencyInjection\ContainerInterface;
 use Symfony\Component\HttpFoundation\RequestStack;

core/modules/views/src/ViewExecutable.php

@@ -21,6 +21,7 @@ use Drupal\views\ViewEntityInterface;
 use Drupal\Component\Utility\Tags;
 use Symfony\Component\HttpFoundation\Request;
 use Symfony\Component\HttpFoundation\Response;
+use Symfony\Component\Routing\Exception\RouteNotFoundException;
 
 /**
  * Represents a view as a whole.
@@ -1763,6 +1764,17 @@ class ViewExecutable implements \Serializable {
       return FALSE;
     }
 
+    // Look up the route name to make sure it exists.  The name may exist, but
+    // not be available yet in some instances when editing a view and doing
+    // a live preview.
+    $provider = \Drupal::service('router.route_provider');
+    try {
+      $provider->getRouteByName($display_handler->getRouteName());
+    }
+    catch (RouteNotFoundException $e) {
+      return FALSE;
+    }
+
     return TRUE;
   }
 

core/modules/views_ui/src/Tests/UnsavedPreviewTest.php

@@ -0,0 +1,84 @@
+<?php
+
+/**
+ * @file
+ * Contains of \Drupal\views_ui\Tests\UnsavedPreviewTest.
+ */
+
+namespace Drupal\views_ui\Tests;
+
+use Drupal\views\Tests\ViewTestBase;
+
+/**
+ * Tests covering Preview of unsaved Views.
+ *
+ * @group views_ui
+ */
+class UnsavedPreviewTest extends ViewTestBase {
+
+  /**
+    * Views used by this test.
+    *
+    * @var array
+    */
+  public static $testViews = ['content'];
+
+  /**
+   * An admin user with the 'administer views' permission.
+   *
+   * @var \Drupal\user\UserInterface
+   */
+  protected $adminUser;
+
+  /**
+   * {@inheritdoc}
+   */
+  public static $modules = array('node', 'views_ui');
+
+  /**
+   * Sets up a Drupal site for running functional and integration tests.
+   */
+  protected function setUp() {
+    parent::setUp(FALSE);
+
+    $this->adminUser = $this->drupalCreateUser(['administer views']);
+    $this->drupalLogin($this->adminUser);
+  }
+
+  /**
+   * Tests previews of unsaved new page displays.
+   */
+  public function testUnsavedPageDisplayPreview() {
+    $this->drupalCreateContentType(['type' => 'page']);
+    for ($i = 0; $i < 5; $i++) {
+      $this->drupalCreateNode();
+    }
+
+    $this->drupalGet('admin/structure/views/view/content');
+    $this->assertResponse(200);
+
+    $this->drupalPostForm(NULL, [], t('Add Page'));
+    $this->assertResponse(200);
+
+    $this->drupalGet('admin/structure/views/nojs/display/content/page_2/path');
+    $this->assertResponse(200);
+
+    $this->drupalPostForm(NULL, ['path' => 'foobarbaz'], t('Apply'));
+    $this->assertResponse(200);
+
+    $this->drupalPostForm(NULL, [], t('Update preview'));
+    $this->assertResponse(200);
+    $this->assertText(t('This display has no path'));
+
+    $this->drupalGet('admin/structure/views/view/content/edit/page_2');
+    $this->assertResponse(200);
+
+    $this->drupalPostForm(NULL, [], t('Save'));
+    $this->assertResponse(200);
+
+    $this->drupalPostForm(NULL, [], t('Update preview'));
+    $this->assertResponse(200);
+    $this->assertLinkByHref('foobarbaz');
+  }
+
+}

core/modules/views_ui/src/ViewUI.php

@@ -598,7 +598,7 @@ class ViewUI implements ViewEntityInterface {
       $executable->setArguments($args);
 
       // Store the current view URL for later use:
-      if ($executable->display_handler->getOption('path')) {
+      if ($executable->hasUrl() && $executable->display_handler->getOption('path')) {
         $path = $executable->getUrl();
       }