Refactor some render computations to local state

Summary: The goal of this stack is to gradually expand large data trees, rather than all at once. To enable that, we need to be able to distinguish 'expandability' vs. 'being expanded'. By moving computations from render to the component hooks and store the results locally, we get a step closer to that.

Reviewed By: jknoxville

Differential Revision: D21301927

fbshipit-source-id: cfb617214d4b2005796b33b41c1abe0032e41847

desktop/app/src/ui/components/data-inspector/DataInspector.tsx

@@ -298,13 +298,23 @@ function isComponentExpanded(
   return false;
 }
 
+type DataInspectorState = {
+  isExpanded: boolean;
+  isExpandable: boolean;
+  res: any;
+  resDiff: any;
+};
+
 /**
  * An expandable data inspector.
  *
  * This component is fairly low level. It's likely you're looking for
  * [`<ManagedDataInspector>`]().
  */
-export default class DataInspector extends Component<DataInspectorProps> {
+export default class DataInspector extends Component<
+  DataInspectorProps,
+  DataInspectorState
+> {
   static defaultProps: {
     expanded: DataInspectorExpanded;
     depth: number;
@@ -322,6 +332,12 @@ export default class DataInspector extends Component<DataInspectorProps> {
   constructor(props: DataInspectorProps) {
     super(props);
     this.interaction = reportInteraction('DataInspector', props.path.join(':'));
+    this.state = {
+      isExpandable: false,
+      isExpanded: false,
+      res: undefined,
+      resDiff: undefined,
+    };
   }
 
   static isExpandable(data: any) {
@@ -364,8 +380,46 @@ export default class DataInspector extends Component<DataInspectorProps> {
     );
   }
 
-  isExpanded(pathParts: Array<string>) {
-    const {expanded} = this.props;
+  static getDerivedStateFromProps(
+    nextProps: DataInspectorProps,
+    _currentState: DataInspectorState,
+  ): DataInspectorState {
+    const {data, depth, diff, expandRoot, path} = nextProps;
+
+    const res = DataInspector.extractValue(nextProps, data, depth);
+    const resDiff = DataInspector.extractValue(nextProps, diff, depth);
+
+    if (!res) {
+      return {
+        isExpanded: false,
+        isExpandable: false,
+        res,
+        resDiff,
+      };
+    }
+
+    const isExpandable = DataInspector.isExpandable(res.value);
+    const isExpanded =
+      isExpandable &&
+      (resDiff != null
+        ? isComponentExpanded(
+            res.value,
+            resDiff.type,
+            resDiff.value,
+            expandRoot === true || DataInspector.isExpanded(nextProps, path),
+          )
+        : expandRoot === true || DataInspector.isExpanded(nextProps, path));
+
+    return {
+      isExpanded,
+      isExpandable,
+      res,
+      resDiff,
+    };
+  }
+
+  static isExpanded(props: DataInspectorProps, pathParts: Array<string>) {
+    const {expanded} = props;
 
     // if we no expanded object then expand everything
     if (expanded == null) {
@@ -380,7 +434,7 @@ export default class DataInspector extends Component<DataInspectorProps> {
     }
 
     // check if all paths are collapsed
-    if (this.props.collapsed === true) {
+    if (props.collapsed === true) {
       return false;
     }
 
@@ -403,7 +457,7 @@ export default class DataInspector extends Component<DataInspectorProps> {
   }
 
   handleClick = () => {
-    const isExpanded = this.isExpanded(this.props.path);
+    const isExpanded = DataInspector.isExpanded(this.props, this.props.path);
     this.interaction(isExpanded ? 'collapsed' : 'expanded');
     this.setExpanded(this.props.path, !isExpanded);
   };
@@ -417,10 +471,10 @@ export default class DataInspector extends Component<DataInspectorProps> {
     onDelete(path);
   };
 
-  extractValue = (data: any, depth: number) => {
+  static extractValue(props: DataInspectorProps, data: any, depth: number) {
     let res;
 
-    const {extractValue} = this.props;
+    const {extractValue} = props;
     if (extractValue) {
       res = extractValue(data, depth);
     }
@@ -430,6 +484,10 @@ export default class DataInspector extends Component<DataInspectorProps> {
     }
 
     return res;
+  }
+
+  extractValue = (data: any, depth: number) => {
+    return DataInspector.extractValue(this.props, data, depth);
   };
 
   render(): any {
@@ -449,42 +507,21 @@ export default class DataInspector extends Component<DataInspectorProps> {
       tooltips,
     } = this.props;
 
-    // the data inspector makes values read only when setValue isn't set so we just need to set it
-    // to null and the readOnly status will be propagated to all children
-    let {setValue} = this.props;
+    const {resDiff, isExpandable, isExpanded, res} = this.state;
 
-    const res = this.extractValue(data, depth);
-    const resDiff = this.extractValue(diff, depth);
-
-    let type;
-    let value;
-    let extra;
-    if (res) {
-      if (!res.mutable) {
-        setValue = null;
-      }
-
-      ({type, value, extra} = res);
-    } else {
+    if (!res) {
       return null;
     }
 
+    // the data inspector makes values read only when setValue isn't set so we just need to set it
+    // to null and the readOnly status will be propagated to all children
+    const setValue = res.mutable ? this.props.setValue : null;
+    const {type, value, extra} = res;
+
     if (ancestry.includes(value)) {
       return <RecursiveBaseWrapper>Recursive</RecursiveBaseWrapper>;
     }
 
-    const isExpandable = DataInspector.isExpandable(value);
-    const isExpanded =
-      isExpandable &&
-      (resDiff != null
-        ? isComponentExpanded(
-            value,
-            resDiff.type,
-            resDiff.value,
-            expandRoot === true || this.isExpanded(path),
-          )
-        : expandRoot === true || this.isExpanded(path));
-
     let expandGlyph = '';
     if (isExpandable) {
       if (isExpanded) {