Merge pull request #2842 from matrix-org/bwindels/bacat-scrolling-merged-develop

BACAT Scrolling

src/utils/ResizeNotifier.js

@@ -0,0 +1,59 @@
+/*
+Copyright 2019 New Vector Ltd
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+*/
+
+/**
+ * Fires when the middle panel has been resized.
+ * @event module:utils~ResizeNotifier#"middlePanelResized"
+ */
+import { EventEmitter } from "events";
+import { throttle } from "lodash";
+
+export default class ResizeNotifier extends EventEmitter {
+    constructor() {
+        super();
+        // with default options, will call fn once at first call, and then every x ms
+        // if there was another call in that timespan
+        this._throttledMiddlePanel = throttle(() => this.emit("middlePanelResized"), 200);
+    }
+
+    notifyBannersChanged() {
+        this.emit("leftPanelResized");
+        this.emit("middlePanelResized");
+    }
+
+    // can be called in quick succession
+    notifyLeftHandleResized() {
+        // don't emit event for own region
+        this._throttledMiddlePanel();
+    }
+
+    // can be called in quick succession
+    notifyRightHandleResized() {
+        this._throttledMiddlePanel();
+    }
+
+    // can be called in quick succession
+    notifyWindowResized() {
+        // no need to throttle this one,
+        // also it could make scrollbars appear for
+        // a split second when the room list manual layout is now
+        // taller than the available space
+        this.emit("leftPanelResized");
+
+        this._throttledMiddlePanel();
+    }
+}
+