From 4a8c08c8bfd5ee37c45f0804879680025be87f33 Mon Sep 17 00:00:00 2001
From: infinite-persistence
 <64950861+infinite-persistence@users.noreply.github.com>
Date: Mon, 16 Aug 2021 13:45:04 -0700
Subject: [PATCH] Fix scroll position not restored when doing Back on Desktop
 (#6842)

## Ticket
6743: Desktop: "Back" in Following Page no longer restores scroll position

## Issue
This was a side-effect of "6609 claimListDiscover: don't re-render until query is done". That PR did not handle the case of navigating backwards, which typically would just need to display past results. It ended up always starting with a blank list on mount, so the scroll position could not be restored correctly.

I don't know why it still worked on Web/Chrome -- maybe the latest browser knows how to move to desired scroll position when the height is available.

## Change
If navigating backwards, initialize the final URI list with the previous result. It is almost always correct, and if not, will be corrected in the effects. This saves us one re-render when navigating backwards too.
---
 ui/component/claimListDiscover/view.jsx | 19 ++++++++++++++++++-
 1 file changed, 18 insertions(+), 1 deletion(-)

diff --git a/ui/component/claimListDiscover/view.jsx b/ui/component/claimListDiscover/view.jsx
index 0b18272e6..42a2557da 100644
--- a/ui/component/claimListDiscover/view.jsx
+++ b/ui/component/claimListDiscover/view.jsx
@@ -141,7 +141,6 @@ function ClaimListDiscover(props: Props) {
   const { search } = location;
   const [page, setPage] = React.useState(1);
   const [forceRefresh, setForceRefresh] = React.useState();
-  const [finalUris, setFinalUris] = React.useState([]);
   const isLargeScreen = useIsLargeScreen();
   const [orderParamEntry, setOrderParamEntry] = usePersistedState(`entry-${location.pathname}`, CS.ORDER_BY_TRENDING);
   const [orderParamUser, setOrderParamUser] = usePersistedState(`orderUser-${location.pathname}`, CS.ORDER_BY_TRENDING);
@@ -387,6 +386,9 @@ function ClaimListDiscover(props: Props) {
     : undefined;
   const livestreamSearchResult = livestreamSearchKey && claimSearchByQuery[livestreamSearchKey];
 
+  const [finalUris, setFinalUris] = React.useState(
+    getFinalUrisInitialState(history.action === 'POP', claimSearchResult)
+  );
   const [prevOptions, setPrevOptions] = React.useState(null);
 
   if (!isJustScrollingToNewPage(prevOptions, options)) {
@@ -448,6 +450,10 @@ function ClaimListDiscover(props: Props) {
     </div>
   );
 
+  // **************************************************************************
+  // Helpers
+  // **************************************************************************
+
   // Returns true if the change in 'options' indicate that we are simply scrolling
   // down to a new page; false otherwise.
   function isJustScrollingToNewPage(prevOptions, options) {
@@ -500,6 +506,17 @@ function ClaimListDiscover(props: Props) {
     return prev.length === next.length && prev.every((value, index) => value === next[index]);
   }
 
+  function getFinalUrisInitialState(isNavigatingBack, claimSearchResult) {
+    if (isNavigatingBack && claimSearchResult && claimSearchResult.length > 0) {
+      return claimSearchResult;
+    } else {
+      return [];
+    }
+  }
+
+  // **************************************************************************
+  // **************************************************************************
+
   React.useEffect(() => {
     if (shouldPerformSearch) {
       const searchOptions = JSON.parse(optionsStringForEffect);