From 42c59b59239bacd4a6652986f2338a80d8bd9c5e Mon Sep 17 00:00:00 2001
From: Luke Barnard <luke@matrix.org>
Date: Fri, 11 May 2018 15:07:51 +0100
Subject: [PATCH] Make AppTile in Stickerpicker persistent using
 PersistedElement

---
 .../views/elements/PersistedElement.js        | 116 ++++++++++++++++++
 src/components/views/rooms/Stickerpicker.js   |   7 ++
 2 files changed, 123 insertions(+)
 create mode 100644 src/components/views/elements/PersistedElement.js

diff --git a/src/components/views/elements/PersistedElement.js b/src/components/views/elements/PersistedElement.js
new file mode 100644
index 0000000000..4d8cd4140e
--- /dev/null
+++ b/src/components/views/elements/PersistedElement.js
@@ -0,0 +1,116 @@
+/*
+Copyright 2018 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.
+*/
+
+const classNames = require('classnames');
+const React = require('react');
+const ReactDOM = require('react-dom');
+import PropTypes from 'prop-types';
+
+// Shamelessly ripped off Modal.js.  There's probably a better way
+// of doing reusable widgets like dialog boxes & menus where we go and
+// pass in a custom control as the actual body.
+
+const ContainerId = "mx_PersistedElement";
+
+function getOrCreateContainer() {
+    let container = document.getElementById(ContainerId);
+
+    if (!container) {
+        container = document.createElement("div");
+        container.id = ContainerId;
+        document.body.appendChild(container);
+    }
+
+    return container;
+}
+
+// Greater than that of the ContextualMenu
+const PE_Z_INDEX = 3000;
+
+/*
+ * Class of component that renders its children in a separate ReactDOM virtual tree
+ * in a container element appended to document.body.
+ *
+ * This prevents the children from being unmounted when the parent of PersistedElement
+ * unmounts, allowing them to persist.
+ *
+ * When PE is unmounted, it hides the children using CSS. When mounted or updated, the
+ * children are made visible and are positioned into a div that is given the same
+ * bounding rect as the parent of PE.
+ */
+export default class PersistedElement extends React.Component {
+    constructor() {
+        super();
+        this.collectChildContainer = this.collectChildContainer.bind(this);
+        this.collectChild = this.collectChild.bind(this);
+    }
+
+    collectChildContainer(ref) {
+        this.childContainer = ref;
+    }
+
+    collectChild(ref) {
+        this.child = ref;
+        this.updateChild();
+    }
+
+    componentDidMount() {
+        this.updateChild();
+    }
+
+    componentDidUpdate() {
+        this.updateChild();
+    }
+
+    componentWillUnmount() {
+        this.updateChildVisibility(this.child, false);
+    }
+
+    updateChild() {
+        this.updateChildPosition(this.child, this.childContainer);
+        this.updateChildVisibility(this.child, true);
+    }
+
+    updateChildVisibility(child, visible) {
+        if (!child) return;
+        child.style.display = visible ? 'block' : 'none';
+    }
+
+    updateChildPosition(child, parent) {
+        if (!child || !parent) return;
+
+        const parentRect = parent.getBoundingClientRect();
+        Object.assign(child.style, {
+            position: 'absolute',
+            top: parentRect.top + 'px',
+            left: parentRect.left + 'px',
+            width: parentRect.width + 'px',
+            height: parentRect.height + 'px',
+            zIndex: PE_Z_INDEX,
+        });
+    }
+
+    render() {
+        const content = <div ref={this.collectChild}>
+            {this.props.children}
+        </div>;
+
+        ReactDOM.render(content, getOrCreateContainer());
+
+        return <div ref={this.collectChildContainer}></div>;
+    }
+}
+
diff --git a/src/components/views/rooms/Stickerpicker.js b/src/components/views/rooms/Stickerpicker.js
index a252c0c886..5c411aa56e 100644
--- a/src/components/views/rooms/Stickerpicker.js
+++ b/src/components/views/rooms/Stickerpicker.js
@@ -150,6 +150,11 @@ export default class Stickerpicker extends React.Component {
         const stickerpickerWidget = this.state.stickerpickerWidget;
         let stickersContent;
 
+        // Use a separate ReactDOM tree to render the AppTile separately so that it persists and does
+        // not unmount when we (a) close the sticker picker (b) switch rooms. It's properties are still
+        // updated.
+        const PersistedElement = sdk.getComponent("elements.PersistedElement");
+
         // Load stickerpack content
         if (stickerpickerWidget && stickerpickerWidget.content && stickerpickerWidget.content.url) {
             // Set default name
@@ -166,6 +171,7 @@ export default class Stickerpicker extends React.Component {
                             width: this.popoverWidth,
                         }}
                     >
+                    <PersistedElement>
                         <AppTile
                             id={stickerpickerWidget.id}
                             url={stickerpickerWidget.content.url}
@@ -188,6 +194,7 @@ export default class Stickerpicker extends React.Component {
                             handleMinimisePointerEvents={true}
                             whitelistCapabilities={['m.sticker']}
                         />
+                    </PersistedElement>
                     </div>
                 </div>
             );