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!
Related
I have a custom section header in my UITableView that contains A UICollectionView of some avatar images. The data is sourced once and cached for the images (images change so infrequently that it doesn't warrant real time updates).
I was hoping to make it so this header never redraws again even if the UITableView refresh is called. The reasoning for this is every time you take action, it causes the images to flicker as they're being redrawn from their default anonymous silhouette to the actual image of the person. The images are cached, but it doesn't matter because
I assume this is not possible by design - a UITableView will destroy everything and reload it all over again every time the refresh is called, correct?
I just wish I could hook into the refresh and preserve the section header, and reload the rows only.
Thanks for any ideas/guidance, I know this is a little uncommon but I don't want to move the header out into its own view because i'm using a UITableViewController directly, and it would be a real pain to have to embed it in a containerview and all that.
Yes, even you cached the image and set by local or something, it will take time to load. If you are using lazy loading, it will be splash ( for sure :) ). So, the only possible thing is, you have to update your tableView after refreshing is using tableView.beginUpdates and tableView.endUpdates. Input some add cell or remove cell base on the data after refreshing
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.
All,
I hope most of you know that with ios7 there is not need to do a null check for tableview reuse
if (cell == nil) {
But unfortunately, because of that the cells are always reinitialized, as we put the code in the same method for initializing values. The problem is only with text fields inside the tableview though.
Let me explain the scenario. I have a table view with multiple rows, and some rows contain multiple text boxes. I populate the textboxes with data from server when the page is loaded. Since the cells are always re-initialized as i explained above, whatever I enter in the field goes away and the server data is re populated once i scroll down and come back to the initial stage. This is because the populating the data code is also in the same place. After fetching a reusable cell it populates the data.
Previously till ios6, we used if(cell==nil) and hence we loaded server data inside the cell and when reusing the cell, this piece of code will never be called.
I have other dirty solutions, but would like to know if someone else has a graceful way of dealing this. Please help.
You just don't store any data in the table view cell but in the model that fills the table cell. This is always the way it should be done.
Looking from the MVC standpoint than the UITableViewCell is a view. Since it is reused by iOS you should use a model to the view.
Yes, this is the expected behavior of UITableView. For performance reasons, cells are reused. Thus, it is your responsibility to populate the views in a Table View Cell every time tableView:cellForRowAtIndexPath: is called.
The thing I don't understand from your question - are you making a network call every single time a cell comes into view? If so, cache the results somewhere. Or, if it's a small amount of data, consider just doing it all in one shot at the beginning (still need to be asynchronous though).
One thing I see a lot of developers do is move a lot of code into UITableViewCell subclasses, which sounds like a good idea because it's modular, but makes solutions for problems like this more difficult. Have the Table View Data Source manage the network calls.
If you need some inspiration, look at Apple's LazyTableImages sample.
Right now my table view presents 5 cells at the same time. I load them all up into an array so the "flow" of the UITableView is easier. But since there quite a few objects, the initial load can take quite a bit.
So my question is, is there a way to present the initial 5-7 cells while the rest are loading? Or what would be the practice for this?
The idea: for the first few cells to come up as fast possible, even while we are loading a bunch in the background so the user isn't sitting there waiting for 100+ cells to load.
Also, I am loading this cells with parse (I am getting the user's info including an image).
Thanks!
This may not work depending on where your data comes from and when it gets into your app, but this is what I would do. Allow your array to fill up with the first 5-7 items. Then call reloadData on your table view. Assuming your datasource is hooked up to your array properly, it will load the first few items. Then let your array continue to load until it's complete, and call reloadData again. You could even use this strategy repetitively to continually load new data. Good luck!
I'm trying to create a custom view that can display a large amount of data, similar to the way UITableView is able to display many rows of data. Right now I'm displaying the data in a UIScrollView, but after I reload the data several times my app starts to receive memory warnings.
What's the right way to design a custom view to display a large amount of data, and how can I avoid these memory warnings?
It doesn't. UITableView loads only as many rows as it can fit on the screen. When it needs more rows it asks the data source for them. This gives the appearance that the table contains all the data without all the overhead of copying everything at once.
When your tableView cell is too heavy means, it has imageView and more than one text label better create a custom cell by subclassing the UITableView.
Make sure that in custom cell the subview should be added only once and reused for cells. Just you need to sent the image of imageview or text of label. Even if you have so many cells in tableview the performance will be good.
And also make sure that if you are loading images from server don't fetch every time when you are setting image for cell. use image cache.
The following link might me useful for loading data to table view from server.
http://www.raywenderlich.com/4295/multithreading-and-grand-central-dispatch-on-ios-for-beginners-tutorial