use TruncatedList to prevent rendering hundreds/thousands of DOM nodes

Signed-off-by: Michael Telatynski <7t3chguy@gmail.com>

src/components/views/dialogs/DevtoolsDialog.js

@@ -242,6 +242,8 @@ class SendAccountData extends GenericEditor {
     }
 }
 
+const INITIAL_LOAD_TILES = 20;
+
 class FilteredList extends React.Component {
     static propTypes = {
         children: PropTypes.any,
@@ -249,31 +251,65 @@ class FilteredList extends React.Component {
         onChange: PropTypes.func,
     };
 
+    static filterChildren(children, query) {
+        if (!query) return children;
+        const lcQuery = query.toLowerCase();
+        return children.filter((child) => child.key.toLowerCase().includes(lcQuery));
+    }
+
     constructor(props, context) {
         super(props, context);
-        this.onQuery = this.onQuery.bind(this);
+
+        this.state = {
+            filteredChildren: FilteredList.filterChildren(this.props.children, this.props.query),
+            truncateAt: INITIAL_LOAD_TILES,
+        };
     }
 
-    onQuery(ev) {
+    componentWillReceiveProps(nextProps) {
+        if (this.props.children === nextProps.children && this.props.query === nextProps.query) return;
+        this.setState({
+            filteredChildren: FilteredList.filterChildren(nextProps.children, nextProps.query),
+            truncateAt: INITIAL_LOAD_TILES,
+        });
+    }
+
+    showAll = () => {
+        this.setState({
+            truncateAt: -1,
+        });
+    };
+
+    createOverflowElement = (overflowCount: number, totalCount: number) => {
+        return <button className="mx_DevTools_RoomStateExplorer_button" onClick={this.showAll}>
+            { _t("and %(count)s others...", { count: overflowCount }) }
+        </button>;
+    };
+
+    onQuery = (ev) => {
         if (this.props.onChange) this.props.onChange(ev.target.value);
-    }
+    };
 
-    filterChildren() {
-        if (this.props.query) {
-            const lowerQuery = this.props.query.toLowerCase();
-            return this.props.children.filter((child) => child.key.toLowerCase().includes(lowerQuery));
-        }
-        return this.props.children;
-    }
+    getChildren = (start: number, end: number) => {
+        return this.state.filteredChildren.slice(start, end);
+    };
+
+    getChildCount = (): number => {
+        return this.state.filteredChildren.length;
+    };
 
     render() {
+        const TruncatedList = sdk.getComponent("elements.TruncatedList");
         return <div>
             <input size="64"
                    onChange={this.onQuery}
                    value={this.props.query}
                    placeholder={_t('Filter results')}
                    className="mx_TextInputDialog_input mx_DevTools_RoomStateExplorer_query" />
-            { this.filterChildren() }
+            <TruncatedList getChildren={this.getChildren}
+                           getChildCount={this.getChildCount}
+                           truncateAt={this.state.truncateAt}
+                           createOverflowElement={this.createOverflowElement} />
         </div>;
     }
 }