I'm encountering a common TableView data reloading problem. I've read many questions on the same subject but the problem was never exactly the same as mine...
I have a navigation based application. In the RootViewController's viewDidLoad method I make a request in order to get JSON data (articles). When the connection has finished loading I create custom Article objects for each entry. The Article class has an initWithDictionnary method which initializes the attributes of the object and most importantly creates a request to download an image. When the connection has finished loading I set the image attribute of the Article object.
The goal is to initialize the cell.imageView.image property with the downloaded image. At that point, you may have guessed what the problem is about.
Images are downloaded after the cell image is rendered so it stays empty until the cell is reloaded (if it gets out of the screen and then back in for example).
I guess I should call reloadData at a certain time but I don't know when. Ideally I would call it when all the cells are loaded but it doesn't seem possible.
I've tried a bunch of crazy things like waiting for a cell to load and the try to reload the previous one but it didn't work.
By reading Q&A out here I learned about Apple's LazyTableImage sample code but I don't understand all of it so I'm not sure I should/could use it.
Please ask me if you need more details.
Thanks in advance for any help.
You have to load the images Asynchronously. Keep in mind that your table data should contain a field per row specifying if the image was loaded so that (if true) you can skip loading and just display cached images.
Look at this question first: Load images async
There are about 10 good Lazy Loading Image UITableView tutorials. Pick one.
You'll get the hang of it by reviewing the tutorials after a while. Stick with it, it's an important concept, not only for this project, but for the rest of your programming career.
Lazy Loading Image UITableView Tutorials that'll make you smarter!
Related
I wish to do asynchronous loading in my UITable cell (I'm using custom cells) as the moment I click on UIButton 'Details', it will hang around 7~8 seconds as it is doing some internet connection for the checking of status. The only thing that requires loading is only the '(2) Book Status' as shown below:
I've done my research but so far I only found solutions such as lazy loading, which is largely meant for loading of images. Would anyone give some advice for how to do asynchronous loading for text, preferably with some examples? Thanks alot in advance :)
Actually u need to do lazy loading for values in uitableviewcell. display value when available.
Refer LazyTableImages a sample project from apple which loads all values in cell along with image Asynchronously
For the Asynchronous load the cell followings are resources where you can get the idea.
NMPaginator
Source Code
I have a table which is made from custom UITableViewCells which contains downloaded images.
Ive found the app crashes after too many images are displayed. How can best stop this? I don't mind deleting the first images, but don't know of the best way to do it.
EDIT
How do I write the images to the device for caching?
Post your cellForRowAtIndexPath code. Sounds like you have a problem there. If you're certain you do not, then when you receive the memory warning, release any objects you do not need, and can easily be loaded again if required. These objects may be in other ViewControllers not on screen or ImageView objects already displayed.
Best we can do unless you post code.
Or read Apple's Memory Management Guide.
I have seen many apps that load data to UITableViews from the internet, and they usually load smoothly. Now it's my turn to load in that kind of data. I am getting different data at the same time, separating categories with ~ and pieces of categories with #. This works great, and I have managed to separate the data in obj-c perfectly.
Everything in my app works, it's just that the loading takes a lot of time.
So, I guess the real question is, how can you load in data for a tableView in the background, showing a label/UIActivityView or something while it is loading?
Thank you.
The simplest way is to add a temporary cell which shows some kind of loading progress (label with 'Loading...' text, or a UIActivityIndicator, etc). When your data is done loading, remove that cell and add your actual cells with your data.
To load data 'in the background' I would recommend having a look at NSURLConnection. It lets you implicitly load the data asynchronously so you don't have to deal with threads.
I am not getting your question clearly. Why don't you use UIActivityIndicator to show the loading. You can do it from your nib or programmatically.
One ting is also possible that you can load the contents From intenet by using NSXMlParsing which will be much quiker and show an activity indiacator until all date gets parsed and filling the table entirely at once.
Do reply if you get this.
I have a table view with all cells having the UITableViewCellStyleSubtitle,
the images of all the cells are got from the server.
However, those images are not changed frequently.
Someone can show me how to improve the user experience? Each time, user scroll down the table, it seems that it goes online to check and download images again.
Or at least, show me some options that are available to achieve the goal.
Thanks,
The Three20 library has an ImageView subclass that accepts a URL to your remote image and uses the excellent TTURLRequest/Caching mechanism to fetch images. It maintains an in-memory and on-disk cache and will only download images if they are not cached or have expired. You can configure the default cache-expiration time or use a value from your HTTP response. If you use the TTTableViewController subclass and the appropriate TTTableItem subclass, you will get the appropriate image downloading behavior for free. However, it is not necessary to use every three component to do what you need. If you're integrating into existing code, you could create your own UITableViewCell subclass that uses a TTImageView instead of the standard UIImageView. Then, in your cell configuration methods, you can set a default placeholder image and a URL to load and it will pretty much take care of the rest. As a performance optimization, you should also implement the UIScrollView delegate methods in your tableview controller to suspend the TTURLRequestQueue during scrolling (take a look at the TTTableViewController to see how this is done).
You could try one of the following
Create an dictionary and cache all the fetched images in it using the image name as the key
Cache and reuse the entire UITableView cells in tableView:cellForRowAtIndexPath:
If it is just one image repeating load it one outside tableView:cellForRowAtIndexPath:
You write that the images change on a monthly basis - you could save the images to disk as they are used and just either check if the images have changed on the back burner or at a given daily interval redownload the images. Brian Chapados reply seems interesting .
Depending on your code there is probably a ton of other ways to improve image loading. Hope that helps...
I have some 50 custom cells in my UITableView. I want to display an image and a label in the cells where I get the images from URLs.
I want to do a lazy load of images so the UI does not freeze up while the images are being loaded. I tried getting the images in separate threads but I have to load each image every time a cell becomes visible again (Otherwise reuse of cells shows old images)
Apps like Facebook load images only for cells currently visible and once the images are loaded, they are not loaded again. Can someone please tell me how to duplicate this behavior.
Thanks.
Edit
Trying to cache images in an NSMutableDictionary object creates problems when the user scrolls fast. I am getting images only when scrolling completely stops and clearing out the cache on memory warning. But the app invariably gets a memory warning (due to size of images being cached) and clears the cache before reloading. If scrolling is very fast, it crashes.
Any other suggestions are welcome
Loading the images on a background thread is still a good idea. If you didn't want to reload them each time, I'd suggest setting up an NSMutableDictionary and storing the images in there. You could use some unique identifier, like the row ID or even the name of the image, as the key for each image.
When loading a cell, you'd send an objectForKey: message to the NSMutableDictionary to retrieve the image for that particular cell (based on your unique key for it). If it returns nil, that means that the image is missing from the cache and you need your background image loading thread to go retrieve it. Otherwise, you will get back the appropriate image for your table cell to display. On a memory warning, you could clear out this cache of images with no adverse effects (aside from forcing them to be reloaded again on demand).
I have just successfully tackled the same problem by using a custom NSOperation to load the images in a queing fasion and stored them into a static NSMutableDictionary as a cache. Below is a link to the basis of the code I used to solve the problem.
Loading remote images for UITableViewCell
Best to read all the threads in the forum to help you understand what's actually going on.
lostInTransit,
I am having a similar problem and while exploring the many different possible solutions I found this blog post:
davidgolightly.blogspot.com/2009/02/asynchronous-image-caching-with-iphone.html
I would also suggest that you download the URLCache sample from the apple developer website:
developer.apple.com/iphone/prerelease/library/samplecode/URLCache/
And here is another post on the problem:
www.markj.net/iphone-asynchronous-table-image/
I'd love you to share your findings as well.
Lazy loading is like synchronous type request.. means wait for respond
ego image button is solution for that..
ego image button is asynchronous type request..don't wait for respond..just display data at a time....
you can download folder from github....
add to your project...
in xib..at image view ,change class to ego image button...
make object of it in m file...
you can use.....
For those who are interested, and are lazy like me, I would like to suggest an open source (MIT license) implementation of lazy/cached network of UIImageView images: SDWebImage
UITableView with image caching and resizing/setting in background thread:
http://blog.slaunchaman.com/2011/08/12/gcd-example-updated-now-with-more-speed/
This is Tutorial about NSOperation with example that show how to Lazy load images in UITableViewCell