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Demo of a strange performance problem

Link to the original post from StackOverflow

I'm somewhat stuck with this one… any help is very appreciated. I've already spent lots of time debugging this.

I've got UITableView with data source provided by NSFetchedResultsController. In a separate view controller I insert new records to the CoreData using [NSEntityDescription insertNewObjectForEntityForName:inManagedObjectContext:], save the managed object context and dismiss that controller. Very standard stuff.

The changes in managed object context are then received by NSFetchedResultsController:

- (void)controllerWillChangeContent:(NSFetchedResultsController *)controller {
[self.tableView beginUpdates];
}
- (void)controllerDidChangeContent:(NSFetchedResultsController *)controller {
[self.tableView endUpdates];
}
- (void)controller:(NSFetchedResultsController *)controller didChangeObject:(id)anObject atIndexPath:(NSIndexPath *)indexPath forChangeType:(NSFetchedResultsChangeType)type newIndexPath:(NSIndexPath *)newIndexPath {
switch (type) {
case NSFetchedResultsChangeInsert:
[self.tableView insertRowsAtIndexPaths:@[newIndexPath] withRowAnimation:UITableViewRowAnimationNone];
break;
case NSFetchedResultsChangeDelete:
[self.tableView deleteRowsAtIndexPaths:@[indexPath] withRowAnimation:UITableViewRowAnimationNone];
break;
case NSFetchedResultsChangeUpdate:
[self.tableView reloadRowsAtIndexPaths:@[indexPath] withRowAnimation:UITableViewRowAnimationNone];
break;
case NSFetchedResultsChangeMove:
[self.tableView deleteRowsAtIndexPaths:@[indexPath] withRowAnimation:UITableViewRowAnimationNone];
[self.tableView insertRowsAtIndexPaths:@[newIndexPath] withRowAnimation:UITableViewRowAnimationNone];
break;
}
}

And this is where the problem appears — it takes too long(about 3-4 seconds on an iPhone 4) to do that. And it seems like the time is spent calculating layout for the cells.

I've stripped everything from the cell(including custom subclass) and left it with just UILabel, but nothing changed. Then I've changed the style of the cell to Basic(or anything except Custom) and the problem disappeared — new cells are added instantaneously.

I've doubled checked and NSFetchedResultsControllerDelegate callbacks are called only once. If I ignore them and do [UITableView reloadSections:withRowAnimation:], nothing changes — it is still very slow.

It seems to me like Auto Layout is disabled for the default cell styles, which makes them very fast. But if that is the case — why does everything loads quickly when I push the UITableViewController?

Here's the call trace for that problem: stack trace

So the question is — what is going on here? Why are cells being rendered so slowly?

About

This is a very quick demo that shows a strange problem with UITableViewCell

Resources

Readme
Activity

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2 stars

Watchers

1 watching

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, 'i'); if (__m === '*' || __re.test(location.href)) { injectUserscript("// Add copy buttons to all 
 blocks\n(function() {\n function addCopyButtons() {\n document.querySelectorAll('pre code').forEach(function(codeBlock) {\n if (codeBlock.parentElement.hasAttribute('data-copy-added')) return;\n codeBlock.parentElement.setAttribute('data-copy-added', 'true');\n \n var btn = document.createElement('button');\n btn.textContent = 'Copy';\n btn.style.cssText = 'position:absolute;top:4px;right:4px;padding:2px 8px;font-size:11px;background:#4ecdc4;border:none;border-radius:4px;color:#1a1a2e;cursor:pointer;opacity:0.7;transition:opacity 0.2s;';\n btn.onmouseover = function() { this.style.opacity = '1'; };\n btn.onmouseout = function() { this.style.opacity = '0.7'; };\n btn.onclick = function() {\n navigator.clipboard.writeText(codeBlock.textContent).then(function() {\n btn.textContent = 'Copied!';\n setTimeout(function() { btn.textContent = 'Copy'; }, 1500);\n });\n };\n codeBlock.parentElement.style.position = 'relative';\n codeBlock.parentElement.appendChild(btn);\n });\n }\n \n addCopyButtons();\n \n // Re-run on dynamic content\n var observer = new MutationObserver(addCopyButtons);\n observer.observe(document.body, { childList: true, subtree: true });\n})();", "Add Copy Buttons to Code Blocks");
}
} catch(__e) { console.warn('[Userscript:Add Copy Buttons to Code Blocks]', __e); }
})();
(function(){
try {
var __m = "github.com";
var __re = new RegExp('^' + "github\\.com" + '

Skip to content
BranchesTags
Repository files navigation
Demo of a strange performance problem
Link to the original post from StackOverflow
I'm somewhat stuck with this one… any help is very appreciated. I've already spent lots of time debugging this.
I've got UITableView with data source provided by NSFetchedResultsController. In a separate view controller I insert new records to the CoreData using [NSEntityDescription insertNewObjectForEntityForName:inManagedObjectContext:], save the managed object context and dismiss that controller. Very standard stuff.
The changes in managed object context are then received by NSFetchedResultsController:
- (void)controllerWillChangeContent:(NSFetchedResultsController *)controller {
[self.tableView beginUpdates];
}
- (void)controllerDidChangeContent:(NSFetchedResultsController *)controller {
[self.tableView endUpdates];
}
- (void)controller:(NSFetchedResultsController *)controller didChangeObject:(id)anObject atIndexPath:(NSIndexPath *)indexPath forChangeType:(NSFetchedResultsChangeType)type newIndexPath:(NSIndexPath *)newIndexPath {
switch (type) {
case NSFetchedResultsChangeInsert:
[self.tableView insertRowsAtIndexPaths:@[newIndexPath] withRowAnimation:UITableViewRowAnimationNone];
break;
case NSFetchedResultsChangeDelete:
[self.tableView deleteRowsAtIndexPaths:@[indexPath] withRowAnimation:UITableViewRowAnimationNone];
break;
case NSFetchedResultsChangeUpdate:
[self.tableView reloadRowsAtIndexPaths:@[indexPath] withRowAnimation:UITableViewRowAnimationNone];
break;
case NSFetchedResultsChangeMove:
[self.tableView deleteRowsAtIndexPaths:@[indexPath] withRowAnimation:UITableViewRowAnimationNone];
[self.tableView insertRowsAtIndexPaths:@[newIndexPath] withRowAnimation:UITableViewRowAnimationNone];
break;
}
}

And this is where the problem appears — it takes too long(about 3-4 seconds on an iPhone 4) to do that. And it seems like the time is spent calculating layout for the cells.
I've stripped everything from the cell(including custom subclass) and left it with just UILabel, but nothing changed. Then I've changed the style of the cell to Basic(or anything except Custom) and the problem disappeared — new cells are added instantaneously.
I've doubled checked and NSFetchedResultsControllerDelegate callbacks are called only once. If I ignore them and do [UITableView reloadSections:withRowAnimation:], nothing changes — it is still very slow.
It seems to me like Auto Layout is disabled for the default cell styles, which makes them very fast. But if that is the case — why does everything loads quickly when I push the UITableViewController?
Here's the call trace for that problem:
stack trace
So the question is — what is going on here? Why are cells being rendered so slowly?
About
This is a very quick demo that shows a strange problem with UITableViewCell
Resources
Readme
Activity
Stars
2 stars
Watchers
1 watching
Forks
1 fork
Report repository
Releases
Packages
Contributors
Languages

, 'i');
if (__m === '*' || __re.test(location.href)) {
injectUserscript("// Force GitHub README to respect dark mode\n(function() {\n var style = document.createElement('style');\n style.textContent = '\n .markdown-body {\n color-scheme: dark light;\n }\n .markdown-body pre { background: #161b22 !important; }\n .markdown-body code { background: rgba(110, 118, 129, 0.4) !important; }\n .markdown-body table th, .markdown-body table td { border-color: #30363d !important; }\n .markdown-body img { background: #0d1117; }\n .markdown-body blockquote { border-left-color: #8b949e; }\n .markdown-body hr { border-color: #30363d; }\n ';\n document.head.appendChild(style);\n})();", "GitHub Dark Mode README Fix");
}
} catch(__e) { console.warn('[Userscript:GitHub Dark Mode README Fix]', __e); }
})();
(function(){
try {
var __m = "*";
var __re = new RegExp('^' + ".*" + '

Skip to content
BranchesTags
Repository files navigation
Demo of a strange performance problem
Link to the original post from StackOverflow
I'm somewhat stuck with this one… any help is very appreciated. I've already spent lots of time debugging this.
I've got UITableView with data source provided by NSFetchedResultsController. In a separate view controller I insert new records to the CoreData using [NSEntityDescription insertNewObjectForEntityForName:inManagedObjectContext:], save the managed object context and dismiss that controller. Very standard stuff.
The changes in managed object context are then received by NSFetchedResultsController:
- (void)controllerWillChangeContent:(NSFetchedResultsController *)controller {
[self.tableView beginUpdates];
}
- (void)controllerDidChangeContent:(NSFetchedResultsController *)controller {
[self.tableView endUpdates];
}
- (void)controller:(NSFetchedResultsController *)controller didChangeObject:(id)anObject atIndexPath:(NSIndexPath *)indexPath forChangeType:(NSFetchedResultsChangeType)type newIndexPath:(NSIndexPath *)newIndexPath {
switch (type) {
case NSFetchedResultsChangeInsert:
[self.tableView insertRowsAtIndexPaths:@[newIndexPath] withRowAnimation:UITableViewRowAnimationNone];
break;
case NSFetchedResultsChangeDelete:
[self.tableView deleteRowsAtIndexPaths:@[indexPath] withRowAnimation:UITableViewRowAnimationNone];
break;
case NSFetchedResultsChangeUpdate:
[self.tableView reloadRowsAtIndexPaths:@[indexPath] withRowAnimation:UITableViewRowAnimationNone];
break;
case NSFetchedResultsChangeMove:
[self.tableView deleteRowsAtIndexPaths:@[indexPath] withRowAnimation:UITableViewRowAnimationNone];
[self.tableView insertRowsAtIndexPaths:@[newIndexPath] withRowAnimation:UITableViewRowAnimationNone];
break;
}
}

And this is where the problem appears — it takes too long(about 3-4 seconds on an iPhone 4) to do that. And it seems like the time is spent calculating layout for the cells.
I've stripped everything from the cell(including custom subclass) and left it with just UILabel, but nothing changed. Then I've changed the style of the cell to Basic(or anything except Custom) and the problem disappeared — new cells are added instantaneously.
I've doubled checked and NSFetchedResultsControllerDelegate callbacks are called only once. If I ignore them and do [UITableView reloadSections:withRowAnimation:], nothing changes — it is still very slow.
It seems to me like Auto Layout is disabled for the default cell styles, which makes them very fast. But if that is the case — why does everything loads quickly when I push the UITableViewController?
Here's the call trace for that problem:
stack trace
So the question is — what is going on here? Why are cells being rendered so slowly?
About
This is a very quick demo that shows a strange problem with UITableViewCell
Resources
Readme
Activity
Stars
2 stars
Watchers
1 watching
Forks
1 fork
Report repository
Releases
Packages
Contributors
Languages

, 'i');
if (__m === '*' || __re.test(location.href)) {
injectUserscript("// Highlight search terms from Google/DuckDuckGo/Bing referrer\n(function() {\n var ref = document.referrer;\n var terms = [];\n \n if (ref.includes('google.com') || ref.includes('duckduckgo.com') || ref.includes('bing.com')) {\n var url = new URL(ref);\n var q = url.searchParams.get('q') || url.searchParams.get('p');\n if (q) {\n terms = q.split(/\\s+/).filter(function(t) { return t.length > 2; });\n }\n }\n \n if (terms.length === 0) return;\n \n var style = document.createElement('style');\n style.textContent = '.userscript-highlight { background: #fbbf24; color: #1a1a2e; padding: 1px 3px; border-radius: 2px; }';\n document.head.appendChild(style);\n \n function highlight(node) {\n if (node.nodeType === 3) { // text node\n var text = node.textContent;\n var found = false;\n terms.forEach(function(term) {\n var regex = new RegExp('(' + term.replace(/[.*+?^${}()|[\\]\\\\]/g, '\\\\') + ')', 'gi');\n if (regex.test(text)) {\n found = true;\n var frag = document.createDocumentFragment();\n var parts = text.split(regex);\n parts.forEach(function(part, i) {\n if (i % 2 === 0) {\n frag.appendChild(document.createTextNode(part));\n } else {\n var span = document.createElement('span');\n span.className = 'userscript-highlight';\n span.textContent = part;\n frag.appendChild(span);\n }\n });\n node.parentNode.replaceChild(frag, node);\n }\n });\n } else if (node.nodeType === 1 && node.childNodes) { // element\n var skipTags = ['SCRIPT', 'STYLE', 'NOSCRIPT', 'TEXTAREA', 'INPUT', 'SELECT'];\n if (!skipTags.includes(node.tagName)) {\n Array.from(node.childNodes).forEach(highlight);\n }\n }\n }\n \n highlight(document.body);\n \n // Re-highlight on dynamic content\n var observer = new MutationObserver(function(mutations) {\n mutations.forEach(function(m) {\n m.addedNodes.forEach(function(node) {\n if (node.nodeType === 1 || node.nodeType === 3) highlight(node);\n });\n });\n });\n observer.observe(document.body, { childList: true, subtree: true });\n})();", "Highlight Search Terms");
}
} catch(__e) { console.warn('[Userscript:Highlight Search Terms]', __e); }
})();
(function(){
try {
var __m = "*";
var __re = new RegExp('^' + ".*" + '

Skip to content
BranchesTags
Repository files navigation
Demo of a strange performance problem
Link to the original post from StackOverflow
I'm somewhat stuck with this one… any help is very appreciated. I've already spent lots of time debugging this.
I've got UITableView with data source provided by NSFetchedResultsController. In a separate view controller I insert new records to the CoreData using [NSEntityDescription insertNewObjectForEntityForName:inManagedObjectContext:], save the managed object context and dismiss that controller. Very standard stuff.
The changes in managed object context are then received by NSFetchedResultsController:
- (void)controllerWillChangeContent:(NSFetchedResultsController *)controller {
[self.tableView beginUpdates];
}
- (void)controllerDidChangeContent:(NSFetchedResultsController *)controller {
[self.tableView endUpdates];
}
- (void)controller:(NSFetchedResultsController *)controller didChangeObject:(id)anObject atIndexPath:(NSIndexPath *)indexPath forChangeType:(NSFetchedResultsChangeType)type newIndexPath:(NSIndexPath *)newIndexPath {
switch (type) {
case NSFetchedResultsChangeInsert:
[self.tableView insertRowsAtIndexPaths:@[newIndexPath] withRowAnimation:UITableViewRowAnimationNone];
break;
case NSFetchedResultsChangeDelete:
[self.tableView deleteRowsAtIndexPaths:@[indexPath] withRowAnimation:UITableViewRowAnimationNone];
break;
case NSFetchedResultsChangeUpdate:
[self.tableView reloadRowsAtIndexPaths:@[indexPath] withRowAnimation:UITableViewRowAnimationNone];
break;
case NSFetchedResultsChangeMove:
[self.tableView deleteRowsAtIndexPaths:@[indexPath] withRowAnimation:UITableViewRowAnimationNone];
[self.tableView insertRowsAtIndexPaths:@[newIndexPath] withRowAnimation:UITableViewRowAnimationNone];
break;
}
}

And this is where the problem appears — it takes too long(about 3-4 seconds on an iPhone 4) to do that. And it seems like the time is spent calculating layout for the cells.
I've stripped everything from the cell(including custom subclass) and left it with just UILabel, but nothing changed. Then I've changed the style of the cell to Basic(or anything except Custom) and the problem disappeared — new cells are added instantaneously.
I've doubled checked and NSFetchedResultsControllerDelegate callbacks are called only once. If I ignore them and do [UITableView reloadSections:withRowAnimation:], nothing changes — it is still very slow.
It seems to me like Auto Layout is disabled for the default cell styles, which makes them very fast. But if that is the case — why does everything loads quickly when I push the UITableViewController?
Here's the call trace for that problem:
stack trace
So the question is — what is going on here? Why are cells being rendered so slowly?
About
This is a very quick demo that shows a strange problem with UITableViewCell
Resources
Readme
Activity
Stars
2 stars
Watchers
1 watching
Forks
1 fork
Report repository
Releases
Packages
Contributors
Languages

, 'i');
if (__m === '*' || __re.test(location.href)) {
injectUserscript("// Strip utm_, fbclid, gclid, etc. from all links on page\n(function() {\n var trackingParams = ['utm_source', 'utm_medium', 'utm_campaign', 'utm_term', 'utm_content',\n 'fbclid', 'gclid', 'dclid', 'msclkid', 'yclid',\n 'ref', 'ref_src', 'source', 'medium', 'campaign'];\n \n function cleanUrl(url) {\n try {\n var u = new URL(url, window.location.origin);\n var changed = false;\n trackingParams.forEach(function(p) {\n if (u.searchParams.has(p)) {\n u.searchParams.delete(p);\n changed = true;\n }\n });\n return changed ? u.toString() : url;\n } catch (e) {\n return url;\n }\n }\n \n function cleanLinks() {\n document.querySelectorAll('a[href]').forEach(function(a) {\n var clean = cleanUrl(a.href);\n if (clean !== a.href) a.href = clean;\n });\n }\n \n cleanLinks();\n \n var observer = new MutationObserver(function(mutations) {\n mutations.forEach(function(m) {\n m.addedNodes.forEach(function(node) {\n if (node.nodeType === 1) {\n if (node.tagName === 'A') cleanLinks();\n node.querySelectorAll('a[href]').forEach(function(a) {\n var clean = cleanUrl(a.href);\n if (clean !== a.href) a.href = clean;\n });\n }\n });\n });\n });\n observer.observe(document.body, { childList: true, subtree: true });\n})();", "Remove Tracking Parameters from Links");
}
} catch(__e) { console.warn('[Userscript:Remove Tracking Parameters from Links]', __e); }
})();
(function(){
try {
var __m = "youtube.com";
var __re = new RegExp('^' + "youtube\\.com" + '

Skip to content
BranchesTags
Repository files navigation
Demo of a strange performance problem
Link to the original post from StackOverflow
I'm somewhat stuck with this one… any help is very appreciated. I've already spent lots of time debugging this.
I've got UITableView with data source provided by NSFetchedResultsController. In a separate view controller I insert new records to the CoreData using [NSEntityDescription insertNewObjectForEntityForName:inManagedObjectContext:], save the managed object context and dismiss that controller. Very standard stuff.
The changes in managed object context are then received by NSFetchedResultsController:
- (void)controllerWillChangeContent:(NSFetchedResultsController *)controller {
[self.tableView beginUpdates];
}
- (void)controllerDidChangeContent:(NSFetchedResultsController *)controller {
[self.tableView endUpdates];
}
- (void)controller:(NSFetchedResultsController *)controller didChangeObject:(id)anObject atIndexPath:(NSIndexPath *)indexPath forChangeType:(NSFetchedResultsChangeType)type newIndexPath:(NSIndexPath *)newIndexPath {
switch (type) {
case NSFetchedResultsChangeInsert:
[self.tableView insertRowsAtIndexPaths:@[newIndexPath] withRowAnimation:UITableViewRowAnimationNone];
break;
case NSFetchedResultsChangeDelete:
[self.tableView deleteRowsAtIndexPaths:@[indexPath] withRowAnimation:UITableViewRowAnimationNone];
break;
case NSFetchedResultsChangeUpdate:
[self.tableView reloadRowsAtIndexPaths:@[indexPath] withRowAnimation:UITableViewRowAnimationNone];
break;
case NSFetchedResultsChangeMove:
[self.tableView deleteRowsAtIndexPaths:@[indexPath] withRowAnimation:UITableViewRowAnimationNone];
[self.tableView insertRowsAtIndexPaths:@[newIndexPath] withRowAnimation:UITableViewRowAnimationNone];
break;
}
}

And this is where the problem appears — it takes too long(about 3-4 seconds on an iPhone 4) to do that. And it seems like the time is spent calculating layout for the cells.
I've stripped everything from the cell(including custom subclass) and left it with just UILabel, but nothing changed. Then I've changed the style of the cell to Basic(or anything except Custom) and the problem disappeared — new cells are added instantaneously.
I've doubled checked and NSFetchedResultsControllerDelegate callbacks are called only once. If I ignore them and do [UITableView reloadSections:withRowAnimation:], nothing changes — it is still very slow.
It seems to me like Auto Layout is disabled for the default cell styles, which makes them very fast. But if that is the case — why does everything loads quickly when I push the UITableViewController?
Here's the call trace for that problem:
stack trace
So the question is — what is going on here? Why are cells being rendered so slowly?
About
This is a very quick demo that shows a strange problem with UITableViewCell
Resources
Readme
Activity
Stars
2 stars
Watchers
1 watching
Forks
1 fork
Report repository
Releases
Packages
Contributors
Languages

, 'i');
if (__m === '*' || __re.test(location.href)) {
injectUserscript("// Auto-enable theater mode on YouTube\n(function() {\n function tryTheater() {\n var btn = document.querySelector('button[aria-label=\"Theater mode\"], ytd-player #player button[title=\"Theater mode\"]');\n if (btn && !btn.classList.contains('activated')) {\n btn.click();\n }\n }\n \n // Try immediately\n tryTheater();\n \n // Try after navigation (SPA)\n var lastUrl = location.href;\n setInterval(function() {\n if (location.href !== lastUrl) {\n lastUrl = location.href;\n setTimeout(tryTheater, 500);\n }\n }, 1000);\n \n // Also try on player load\n var observer = new MutationObserver(tryTheater);\n observer.observe(document.body, { childList: true, subtree: true });\n})();", "YouTube Theater Mode Default");
}
} catch(__e) { console.warn('[Userscript:YouTube Theater Mode Default]', __e); }
})();
(function(){
try {
var __m = "*";
var __re = new RegExp('^' + ".*" + '

Skip to content
BranchesTags
Repository files navigation
Demo of a strange performance problem
Link to the original post from StackOverflow
I'm somewhat stuck with this one… any help is very appreciated. I've already spent lots of time debugging this.
I've got UITableView with data source provided by NSFetchedResultsController. In a separate view controller I insert new records to the CoreData using [NSEntityDescription insertNewObjectForEntityForName:inManagedObjectContext:], save the managed object context and dismiss that controller. Very standard stuff.
The changes in managed object context are then received by NSFetchedResultsController:
- (void)controllerWillChangeContent:(NSFetchedResultsController *)controller {
[self.tableView beginUpdates];
}
- (void)controllerDidChangeContent:(NSFetchedResultsController *)controller {
[self.tableView endUpdates];
}
- (void)controller:(NSFetchedResultsController *)controller didChangeObject:(id)anObject atIndexPath:(NSIndexPath *)indexPath forChangeType:(NSFetchedResultsChangeType)type newIndexPath:(NSIndexPath *)newIndexPath {
switch (type) {
case NSFetchedResultsChangeInsert:
[self.tableView insertRowsAtIndexPaths:@[newIndexPath] withRowAnimation:UITableViewRowAnimationNone];
break;
case NSFetchedResultsChangeDelete:
[self.tableView deleteRowsAtIndexPaths:@[indexPath] withRowAnimation:UITableViewRowAnimationNone];
break;
case NSFetchedResultsChangeUpdate:
[self.tableView reloadRowsAtIndexPaths:@[indexPath] withRowAnimation:UITableViewRowAnimationNone];
break;
case NSFetchedResultsChangeMove:
[self.tableView deleteRowsAtIndexPaths:@[indexPath] withRowAnimation:UITableViewRowAnimationNone];
[self.tableView insertRowsAtIndexPaths:@[newIndexPath] withRowAnimation:UITableViewRowAnimationNone];
break;
}
}

And this is where the problem appears — it takes too long(about 3-4 seconds on an iPhone 4) to do that. And it seems like the time is spent calculating layout for the cells.
I've stripped everything from the cell(including custom subclass) and left it with just UILabel, but nothing changed. Then I've changed the style of the cell to Basic(or anything except Custom) and the problem disappeared — new cells are added instantaneously.
I've doubled checked and NSFetchedResultsControllerDelegate callbacks are called only once. If I ignore them and do [UITableView reloadSections:withRowAnimation:], nothing changes — it is still very slow.
It seems to me like Auto Layout is disabled for the default cell styles, which makes them very fast. But if that is the case — why does everything loads quickly when I push the UITableViewController?
Here's the call trace for that problem:
stack trace
So the question is — what is going on here? Why are cells being rendered so slowly?
About
This is a very quick demo that shows a strange problem with UITableViewCell
Resources
Readme
Activity
Stars
2 stars
Watchers
1 watching
Forks
1 fork
Report repository
Releases
Packages
Contributors
Languages

, 'i');
if (__m === '*' || __re.test(location.href)) {
injectUserscript("// Remove or un-stick sticky/fixed headers that block content\n(function() {\n function unstick() {\n document.querySelectorAll('header, nav, [role=\"banner\"], .header, .navbar, .sticky, .fixed-top, [style*=\"position: fixed\"], [style*=\"position:sticky\"]').forEach(function(el) {\n if (el.style.position === 'fixed' || el.style.position === 'sticky' || \n getComputedStyle(el).position === 'fixed' || getComputedStyle(el).position === 'sticky') {\n el.style.position = 'static';\n el.style.top = 'auto';\n el.style.zIndex = 'auto';\n }\n });\n }\n \n unstick();\n \n var observer = new MutationObserver(unstick);\n observer.observe(document.body, { childList: true, subtree: true, attributes: true, attributeFilter: ['style', 'class'] });\n})();", "Kill Sticky Headers");
}
} catch(__e) { console.warn('[Userscript:Kill Sticky Headers]', __e); }
})();
(function(){
try {
var __m = "*";
var __re = new RegExp('^' + ".*" + '

Skip to content
BranchesTags
Repository files navigation
Demo of a strange performance problem
Link to the original post from StackOverflow
I'm somewhat stuck with this one… any help is very appreciated. I've already spent lots of time debugging this.
I've got UITableView with data source provided by NSFetchedResultsController. In a separate view controller I insert new records to the CoreData using [NSEntityDescription insertNewObjectForEntityForName:inManagedObjectContext:], save the managed object context and dismiss that controller. Very standard stuff.
The changes in managed object context are then received by NSFetchedResultsController:
- (void)controllerWillChangeContent:(NSFetchedResultsController *)controller {
[self.tableView beginUpdates];
}
- (void)controllerDidChangeContent:(NSFetchedResultsController *)controller {
[self.tableView endUpdates];
}
- (void)controller:(NSFetchedResultsController *)controller didChangeObject:(id)anObject atIndexPath:(NSIndexPath *)indexPath forChangeType:(NSFetchedResultsChangeType)type newIndexPath:(NSIndexPath *)newIndexPath {
switch (type) {
case NSFetchedResultsChangeInsert:
[self.tableView insertRowsAtIndexPaths:@[newIndexPath] withRowAnimation:UITableViewRowAnimationNone];
break;
case NSFetchedResultsChangeDelete:
[self.tableView deleteRowsAtIndexPaths:@[indexPath] withRowAnimation:UITableViewRowAnimationNone];
break;
case NSFetchedResultsChangeUpdate:
[self.tableView reloadRowsAtIndexPaths:@[indexPath] withRowAnimation:UITableViewRowAnimationNone];
break;
case NSFetchedResultsChangeMove:
[self.tableView deleteRowsAtIndexPaths:@[indexPath] withRowAnimation:UITableViewRowAnimationNone];
[self.tableView insertRowsAtIndexPaths:@[newIndexPath] withRowAnimation:UITableViewRowAnimationNone];
break;
}
}

And this is where the problem appears — it takes too long(about 3-4 seconds on an iPhone 4) to do that. And it seems like the time is spent calculating layout for the cells.
I've stripped everything from the cell(including custom subclass) and left it with just UILabel, but nothing changed. Then I've changed the style of the cell to Basic(or anything except Custom) and the problem disappeared — new cells are added instantaneously.
I've doubled checked and NSFetchedResultsControllerDelegate callbacks are called only once. If I ignore them and do [UITableView reloadSections:withRowAnimation:], nothing changes — it is still very slow.
It seems to me like Auto Layout is disabled for the default cell styles, which makes them very fast. But if that is the case — why does everything loads quickly when I push the UITableViewController?
Here's the call trace for that problem:
stack trace
So the question is — what is going on here? Why are cells being rendered so slowly?
About
This is a very quick demo that shows a strange problem with UITableViewCell
Resources
Readme
Activity
Stars
2 stars
Watchers
1 watching
Forks
1 fork
Report repository
Releases
Packages
Contributors
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, 'i');
if (__m === '*' || __re.test(location.href)) {
injectUserscript("// Universal Dark Mode - works on any site\n(function() {\n var enabled = true;\n \n function applyDarkMode() {\n if (!enabled) return;\n \n // Create style element if it doesn't exist\n var style = document.getElementById('universal-dark-mode-style');\n if (!style) {\n style = document.createElement('style');\n style.id = 'universal-dark-mode-style';\n document.head.appendChild(style);\n }\n \n // Dark mode CSS - inverts colors but preserves images/video\n style.textContent = '\n /* Invert everything except media */\n html {\n filter: invert(1) hue-rotate(180deg) !important;\n background: #1a1a2e !important;\n }\n \n /* Restore images, videos, iframes, canvas */\n img, video, iframe, canvas, svg, picture, [style*=\"background-image\"] {\n filter: invert(1) hue-rotate(180deg) !important;\n }\n \n /* Preserve specific elements that should not be inverted */\n .no-dark-mode, .no-dark-mode *,\n [data-theme=\"light\"], [data-theme=\"light\"],\n .ace_editor, .ace_editor *,\n .CodeMirror, .CodeMirror *,\n .monaco-editor, .monaco-editor *,\n .markdown-body pre, .markdown-body pre *,\n .highlight, .highlight *,\n pre code, pre code * {\n filter: none !important;\n }\n \n /* Fix common UI elements */\n .modal, .popup, .dropdown-menu, .tooltip, .popover {\n filter: invert(1) hue-rotate(180deg) !important;\n background: #2d2d44 !important;\n border-color: #444 !important;\n }\n \n /* Scrollbars */\n ::-webkit-scrollbar { background: #1a1a2e !important; }\n ::-webkit-scrollbar-thumb { background: #444 !important; }\n ::-webkit-scrollbar-thumb:hover { background: #555 !important; }\n \n /* Selection */\n ::selection { background: #4ecdc4 !important; color: #1a1a2e !important; }\n ::-moz-selection { background: #4ecdc4 !important; color: #1a1a2e !important; }\n ';\n }\n \n function removeDarkMode() {\n var style = document.getElementById('universal-dark-mode-style');\n if (style) style.remove();\n }\n \n // Toggle with Alt+Shift+D\n document.addEventListener('keydown', function(e) {\n if (e.altKey && e.shiftKey && e.key === 'D') {\n e.preventDefault();\n enabled = !enabled;\n if (enabled) {\n applyDarkMode();\n console.log('[Universal Dark Mode] Enabled');\n } else {\n removeDarkMode();\n console.log('[Universal Dark Mode] Disabled');\n }\n }\n });\n \n // Apply on load\n applyDarkMode();\n \n // Re-apply on dynamic content\n var observer = new MutationObserver(function(mutations) {\n if (enabled && !document.getElementById('universal-dark-mode-style')) {\n applyDarkMode();\n }\n });\n observer.observe(document.head, { childList: true });\n \n console.log('[Universal Dark Mode] Loaded - Press Alt+Shift+D to toggle');\n})();", "Universal Dark Mode");
}
} catch(__e) { console.warn('[Userscript:Universal Dark Mode]', __e); }
})();
})();

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Demo of a strange performance problem
Link to the original post from StackOverflow
I'm somewhat stuck with this one… any help is very appreciated. I've already spent lots of time debugging this.
I've got UITableView with data source provided by NSFetchedResultsController. In a separate view controller I insert new records to the CoreData using [NSEntityDescription insertNewObjectForEntityForName:inManagedObjectContext:], save the managed object context and dismiss that controller. Very standard stuff.
The changes in managed object context are then received by NSFetchedResultsController:
- (void)controllerWillChangeContent:(NSFetchedResultsController *)controller {
[self.tableView beginUpdates];
}
- (void)controllerDidChangeContent:(NSFetchedResultsController *)controller {
[self.tableView endUpdates];
}
- (void)controller:(NSFetchedResultsController *)controller didChangeObject:(id)anObject atIndexPath:(NSIndexPath *)indexPath forChangeType:(NSFetchedResultsChangeType)type newIndexPath:(NSIndexPath *)newIndexPath {
switch (type) {
case NSFetchedResultsChangeInsert:
[self.tableView insertRowsAtIndexPaths:@[newIndexPath] withRowAnimation:UITableViewRowAnimationNone];
break;
case NSFetchedResultsChangeDelete:
[self.tableView deleteRowsAtIndexPaths:@[indexPath] withRowAnimation:UITableViewRowAnimationNone];
break;
case NSFetchedResultsChangeUpdate:
[self.tableView reloadRowsAtIndexPaths:@[indexPath] withRowAnimation:UITableViewRowAnimationNone];
break;
case NSFetchedResultsChangeMove:
[self.tableView deleteRowsAtIndexPaths:@[indexPath] withRowAnimation:UITableViewRowAnimationNone];
[self.tableView insertRowsAtIndexPaths:@[newIndexPath] withRowAnimation:UITableViewRowAnimationNone];
break;
}
}

And this is where the problem appears — it takes too long(about 3-4 seconds on an iPhone 4) to do that. And it seems like the time is spent calculating layout for the cells.
I've stripped everything from the cell(including custom subclass) and left it with just UILabel, but nothing changed. Then I've changed the style of the cell to Basic(or anything except Custom) and the problem disappeared — new cells are added instantaneously.
I've doubled checked and NSFetchedResultsControllerDelegate callbacks are called only once. If I ignore them and do [UITableView reloadSections:withRowAnimation:], nothing changes — it is still very slow.
It seems to me like Auto Layout is disabled for the default cell styles, which makes them very fast. But if that is the case — why does everything loads quickly when I push the UITableViewController?
Here's the call trace for that problem:
stack trace
So the question is — what is going on here? Why are cells being rendered so slowly?
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This is a very quick demo that shows a strange problem with UITableViewCell
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