I have a master/detail app for iPad, with a few sliders on a table view cell to control the XYZ position of an image. Every time I add another cell, another image will show on the screen that can be moved around.
When the app is restarted the table view cells that I added disappear. I already have it set up to record and save the slider values to NSUserDefaults, but I want the cells to stay on the view. How can I save the cells, so they aren't deleted when the app is reloaded? I would also like to save the sliders' positions when the cells reload.
You probably need to add persistence to your app.
Some ideas to get you started are in this StackOverflow post.
You'll want to save the data for each of the cells, and recreate the cells when your TableView reloads upon app launch.
You can update the sliders with the stored values as well.
Posting the code you're using to do this, along with any issues, may help the community help you resolve this.
Related
I am using UITableView to show a list of records. My table allows refresh from top and bottom. On refreshing from top, the old records remain visible until new data is fetched. After the data is fetched, all the records from the array are removed and new records are filled. Then as a final step I refresh the tableview to reflect the newly fetched data.
All works like a charm.
BUT...
Its causing a crash when we do monkey testing. During the top refresh, when the data is being fetched, if I keep scrolling, pulling the tableview, after several attempts there comes an unlucky moment when array is being removed to add the new records but at that time UITableView is also laying out the cells due to constant pulling. This causes the crash.
An easy fix would be to empty the tableview when doing a top refresh but that don't look good as far as the ui aesthetic is concerned. Also if the call fails I won't have anything to show to the user.
I tried by encapsulating the refreshing code in tableview's beginUpdate and endUpdate block but that won't run as there is no change in the tableview itself (i.e. no adding/deleting).
Any help would be appreciated.
Since you say you scroll away and crashes is probably because you try to insert data to indexes that are no longer visible. You should somehow check at what index you are before trying to update the table.
Some code would help me better understand.
I already found entries with that topic on this page and also a website that provides a tutorial for that problem. But nothing worked very well.
The tutorial sad I should double the height of my tableView so cells loaded earlier, but with a higher tableView I never reached the last cells.
My problem is, I use a tableView to display my apps mainpage. This mainPage shows every time a topic and if its necessary for that topic it shows for example a cell with a map, one with pictures and sometimes not. Problem now, if I trying to scroll to my view its always lagging because it loads a map or this pictures. And scrolling back again because the loaded cells already deleted. I used a tableView because of the possibility to switch celltypes(mapCell, pictureCell, textCell) on and off.
I understand this feature, because of memory issues but in my case its not that much and it would be better if all my cells be preloaded and stay in memory until I change the topic.
Is there a swifty way to told my tableView to have this behavior?
Thanks a lot and nice greetings
I would suggest a different approach. Set up your table view controller to install placeholder images in your cells, trigger an async download that you cache to disk, and then update the cell with it's downloaded content if it's still visible when the download is finished.
There are various third party frameworks that do all this housekeeping for you.
Declare a cell array.
Follow these steps whenever change in your topic.
Clear you array
Create and configure all cells add to your array.
Return these cells to datasource methods using row index. Don't use tableview dequeue method here.
I am currently working on a watchkit app and ran into a problem with a flickering table.
The situation is as follows: With the storyboard tool, I created a table containing two row types.
The concept is, that when the data for the table is being downloaded, there is only one row of the first type which will use the whole space to indicate, that data is being downloaded. When the data arrives the second row type is used to display the data.
The problem is, that the table is somehow flickering, while it is being updated with the data. I was able to fix this problem by removing the download indication message und using only the one row type for data.
My question is, if someone did run into a similar problem or if there is any better way/pattern to display this kind of information messages, which show the user whats going on when he is using the app.
The WatchKit Table will flicker when reloading when a visible cell is different size than the other cells. Make sure they are all the same height and width and you will not have a flicker.
The way I did it was to put a group above my table that took up the entire screen with a loading animation inside it. I then hide/show the groups as needed.
I would like to have my UITableView load 3 or 4 cells outside of the table so that any data to be shown there is already loaded when I scroll down.
I have some images, and data that must be downloaded before it can be shown in the cell.
This causes a visible delay before the images are loaded when scrolling.
I can manually trigger loading of this data by doing it in the UITableViewDataSource tableView:cellForRowAtIndexPath: method. I've done this before, but I'm curious if there's an easier way to do it.
Is there any way to expand the reusable cell pool, or adjust how the cells are loaded/recycled?
EDIT:
To clarify, I have lazy loading of images and data in place.
Everything works fine, I just wanted an easy solution to the "prefetching" problem.
Which can be solved in many ways that has nothing to do with the view itself. Right now you can easily see the images load as you scroll. I just wanted them to load right before they become visible.
You may be looking for an asynchronous table view that loads the data asynchronously.
Apple provides a sample app demonstrating this:
LazyTableImages
Of course, you could pre-cache the data and begin downloading data into your datasource before they scroll.
The general idea is that you are loading data into a datasource (that is separate from the UI), so you can do this at any time (and in the background). You can display temporary data or some type of loading image or spinner if the data isn't loaded yet.
If data of the cell will be loaded when cel becomes visible, you can programmatically scroll the table view by scrolling to the bottom cell and go back to the first cell without animation. Another way would be creating all the cells and placing them into array when your view controller is created, and feed the table from that array that contains already created cells. I think there is no way to extend the cell pool as you are asking. Hope this helps, Good Luck!
UITableView Core Data reordering
I'm having troubles with the solution above. If I do updates one by one (ie one move or one delete at a time) it works when back to noedit mode. But with more updates I get application crash. (I'm using a fetchcontroller)
Could someone try this from a tableview not populated :
- create 3 rows
- hit edit mode and move 1st cell to 3rd position, still in edit mode delete the second cell.
- back to noedit mode it crash for me
Besides this I'm trying to make it work in grouped style and with several sections, where you can move cells to any section. Is someone knows an application doing this correctly ?
Thank you
Well after days trying different solutions it seems I finally get what I wanted.
In addition to Ryan Ferretti solution I had to put a flag to bypass tableview updates when commiting moved modifications on CoreData, to get it work with nsfetchedresultcontroller delegate.
It is describe on Apple documentation, see User-Driven Updates : http://developer.apple.com/library/ios/#documentation/CoreData/Reference/NSFetchedResultsControllerDelegate_Protocol/Reference/Reference.html
I now get a tableview grouped style and can move rows from any section to another one, sorted like I want.
So don't forget this flag. :-)