From 810a5cf37d4947a8bcc2c94fb1001be0152b36df Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Pekka=20Maanp=C3=A4=C3=A4?= <pekkamaa@vaadin.com>
Date: Wed, 5 Jun 2019 15:18:58 +0300
Subject: [PATCH] fix: reposition overlay after first page load (#814)

only if the number of items to render has increased from a previous rendering

fix https://github.com/vaadin/vaadin-combo-box-flow/issues/250
---
 src/vaadin-combo-box-data-provider-mixin.html |  4 ++++
 test/lazy-loading.html                        | 17 +++++++++++++++++
 2 files changed, 21 insertions(+)

diff --git a/src/vaadin-combo-box-data-provider-mixin.html b/src/vaadin-combo-box-data-provider-mixin.html
index 935564677..5dc62e2f8 100644
--- a/src/vaadin-combo-box-data-provider-mixin.html
+++ b/src/vaadin-combo-box-data-provider-mixin.html
@@ -156,6 +156,10 @@
             if (Object.keys(this._pendingRequests).length === 0) {
               this.loading = false;
             }
+            if (page === 0 && this.__repositionOverlayDebouncer && items.length > (this.__maxRenderedItems || 0)) {
+              setTimeout(() => this.__repositionOverlayDebouncer.flush());
+              this.__maxRenderedItems = items.length;
+            }
           }
         };
         this._pendingRequests[page] = callback;
diff --git a/test/lazy-loading.html b/test/lazy-loading.html
index a50f53a7a..baa44a9dc 100644
--- a/test/lazy-loading.html
+++ b/test/lazy-loading.html
@@ -258,6 +258,23 @@
               comboBox.open();
               expect(dp).to.be.calledOnce;
             });
+
+            it('should render all visible items after delayed response', done => {
+              const items = [...Array(10)].map((_, i) => 'item ' + i);
+              comboBox.dataProvider = (params, callback) => {
+                setTimeout(() => {
+                  callback(items, 10);
+                  setTimeout(() => {
+                    const renderedTexts = Array.from(comboBox.$.overlay._selector
+                      .querySelectorAll('vaadin-combo-box-item'))
+                      .map(i => i.shadowRoot.querySelector('#content').innerText);
+                    expect(renderedTexts).to.eql(items);
+                    done();
+                  });
+                }, 50);
+              };
+              comboBox.open();
+            });
           });
 
           describe('when selecting item', () => {