fix sticky headers when results num get displayed

res/css/views/rooms/_RoomSublist.scss

@@ -61,8 +61,7 @@ limitations under the License.
             &.mx_RoomSublist_headerContainer_sticky {
                 position: fixed;
                 height: 32px; // to match the header container
-                // width set by JS
-                width: calc(100% - 22px);
+                width: calc(100% - 15px);
             }
 
             // We don't have a top style because the top is dependent on the room list header's

src/components/structures/LeftPanel.tsx

@@ -110,6 +110,11 @@ export default class LeftPanel extends React.Component<IProps, IState> {
         dis.fire(Action.ViewRoomDirectory);
     };
 
+    private refreshStickyHeaders = () => {
+        if (!this.listContainerRef.current) return; // ignore: no headers to sticky
+        this.handleStickyHeaders(this.listContainerRef.current);
+    }
+
     private onBreadcrumbsUpdate = () => {
         const newVal = BreadcrumbsStore.instance.visible;
         if (newVal !== this.state.showBreadcrumbs) {
@@ -152,9 +157,6 @@ export default class LeftPanel extends React.Component<IProps, IState> {
         const bottomEdge = list.offsetHeight + list.scrollTop;
         const sublists = list.querySelectorAll<HTMLDivElement>(".mx_RoomSublist:not(.mx_RoomSublist_hidden)");
 
-        const headerRightMargin = 15; // calculated from margins and widths to align with non-sticky tiles
-        const headerStickyWidth = list.clientWidth - headerRightMargin;
-
         // We track which styles we want on a target before making the changes to avoid
         // excessive layout updates.
         const targetStyles = new Map<HTMLDivElement, {
@@ -243,18 +245,10 @@ export default class LeftPanel extends React.Component<IProps, IState> {
                 if (!header.classList.contains("mx_RoomSublist_headerContainer_sticky")) {
                     header.classList.add("mx_RoomSublist_headerContainer_sticky");
                 }
-
-                const newWidth = `${headerStickyWidth}px`;
-                if (header.style.width !== newWidth) {
-                    header.style.width = newWidth;
-                }
             } else if (!style.stickyTop && !style.stickyBottom) {
                 if (header.classList.contains("mx_RoomSublist_headerContainer_sticky")) {
                     header.classList.remove("mx_RoomSublist_headerContainer_sticky");
                 }
-                if (header.style.width) {
-                    header.style.removeProperty('width');
-                }
             }
         }
 
@@ -432,7 +426,7 @@ export default class LeftPanel extends React.Component<IProps, IState> {
                     {this.renderHeader()}
                     {this.renderSearchExplore()}
                     {this.renderBreadcrumbs()}
-                    <RoomListNumResults />
+                    <RoomListNumResults onVisibilityChange={this.refreshStickyHeaders} />
                     <div className="mx_LeftPanel_roomListWrapper">
                         <div
                             className={roomListClasses}

src/components/views/rooms/RoomListNumResults.tsx

@@ -14,14 +14,18 @@ See the License for the specific language governing permissions and
 limitations under the License.
 */
 
-import React, {useState} from "react";
+import React, {useEffect, useState} from "react";
 
 import { _t } from "../../../languageHandler";
 import RoomListStore, { LISTS_UPDATE_EVENT } from "../../../stores/room-list/RoomListStore";
 import {useEventEmitter} from "../../../hooks/useEventEmitter";
 import SpaceStore from "../../../stores/SpaceStore";
 
-const RoomListNumResults: React.FC = () => {
+interface IProps {
+    onVisibilityChange?: () => void
+}
+
+const RoomListNumResults: React.FC<IProps> = ({ onVisibilityChange }) => {
     const [count, setCount] = useState<number>(null);
     useEventEmitter(RoomListStore.instance, LISTS_UPDATE_EVENT, () => {
         if (RoomListStore.instance.getFirstNameFilterCondition()) {
@@ -32,6 +36,12 @@ const RoomListNumResults: React.FC = () => {
         }
     });
 
+    useEffect(() => {
+        if (onVisibilityChange) {
+            onVisibilityChange();
+        }
+    }, [count, onVisibilityChange]);
+
     if (typeof count !== "number") return null;
 
     return <div className="mx_LeftPanel_roomListFilterCount">