I have seen in many mapkit examples that we can dequeue a reusable annotation view with the dequeueReusableAnnotationViewWithIdentifier of the map view, but where would this annotation view come from ? Is it created programmatically before ? What is the point of it compared to creating it each time ?
dequeueReusableAnnotationViewWithIdentifier is not creating new AnnotationViews.
It is reCycling. Very much like UITableViewCell deQueue.
For ram saving purposes, annotationViews for annotations which get out of visible border of map are reUsed for visible annotations.
dequeue looks for an annotation view which is out of visible area.
If it finds it, it salvages it and use it. You have to reFurnish the recycled view.
If it can not salvage an old view, it creates a new one and registers it for reCycling with deQueue.
Say u have 20 annotations attached to mapview.
5 is on screen , 15 is out of sight.
There are not 20 annotationviews for 20 annotations if not necessary.
Max 7-8 annotationViews for whole 20 annotations.
Say programatically you created a 21st annotation and it is in sight.
One view out of 8 stolen now. 1 left for backup.
Say u cretaed another 2 which are visible, i view gotten from backup, and 1 view created now.
It is for optimal resource usage.
Related
I have a problem. I want for each record in my core data database to draw an UIImage view on screen. But the problem is that I want to make a sort of grid. On the link below you see what I want to achieve.
picture
So my question is, how do I draw an image on screen in code. And place those images in a sort of a grid. using a collection view is no option, because the app should be running on all IOS devices.
While you could implement a custom UIView and implement the drawRect: method and draw UIImages there, I suggest just using multiple UIImageViews as subviews on your "main" view. Your view might be embedded in a UIScrollView, or you could use a UITableView with custom UITableViewCells. Whichever is easier is probably related to how you can interact with the view.
Building that one huge image view is something that I'd definitely try to avoid - it costs many many (probably unnecessary) memory, and it might be slow as well. Definitely not very flexible to handle, and a pain to update dynamically.
A quick cheat for something like this is to use a Table View and then in each cell to place another TableView but rotated at 90 degrees.
You can then use this second TableView to display the pictures etc...
This will give you a table that scrolls up and down and then each cell can scroll left to right.
I'd suggest subclassing UITableViewCell and setting it up as a UITableViewDelegate and UITableViewDatasource.
You will also have to remember to rotate the content of these "sub"tables by 90 degrees also so that they are the right way up.
This sounds like a lot of work but if you push the management of the sub Tables into the cells then it actually becomes quite easy.
Initially I was under the impression that it uses the table row slideup/down animations while inserting/deleting new rows but I doubt if it's doing that as it does it so fluidly even with thousands of items in the list (otherwise it would take a lot of time for the deletions/insertions to work).
Am I right in my assumption that it's simply attaching a new instance of the News list at the bottom of the screen, shrinking the above one while the one at the bottom expands to fill up space?
UPDATE:
Please see this video of what I mean: http://dl.dropbox.com/u/4960327/ReederAnim.mov
I can not tell you exactly how Silvio Rizzi made this, but as you see in the playback, a list view is added behind the shown list view, and the front list view fades out (.alpha = 0.0;) while the list view behind it expands its height per row.
When you desicate it frame by frame it becomes quite clear what he does, and it is really not that advanced. But I have to admit, with the white "milky" polished interface, it looks quite neat.
In addition, you can see that while animating, the background list view only renders the top 7 entries (hopefully calculated by dividing the view height with the average height of the cells shown) making the list view quick to load. Then afterwards, he can load an extended array of cells once you start scrolling, or in a background thread starting once the animation is complete.
I'm trying to add a way for my app to display data in an easily comprehensible form. I tried doing this with graphs, but found it to be a bit awkward, so I'm off to find a better solution.
Here's a problem:
I want to show up to 30 days of data, with user reported events plotted against a timeline.
The events should align vertically, to visually provide a reference of when certain events cluster together.
To solve the problem, I thought of using a UITableView with a background which has a scale, and superimpose upon that background a set of "pins", indicating user events. As the table is scrolled, the events would align one under another, providing a good indication historic event development:
I know that this is possible to be done with a UIScrollView, where I can just position a series of rulers and add events as pins. In order to do this efficiently, I'll have to use Tiling, a technique that I don't have much experience with.
I'm interested in knowing if this is possible with a UITableView, where caching and tiling is already done for me.
I tried adding UIImageViews to a tableViewCell.backgroundview , but this does not produce the desired results. I'd like to be able to dynamically add any number of subviews to the table cell. I can do this by adding a certain pre-determined number of images to an .xib and then trying to reposition them, but this does not seem like an ideal solution.
Is what I'm trying to do possible with UITableView, or should I abandon these efforts and look at UIScrollView with tiling?
Thank you!
yes this should be possible. Add the ruler image to the background of the UITableViewCell.
Then create a subclass of UITableViewCell that takes an array of pins objects that it will place within its view. The pin objects would contain the pin image and a horizontal location on the scale. Then in the tableView dataSource method cellForRowAtIndexPath method you set the tableViewCell's pin array to the correct array (or NSSet) of pins.
To make it even more lightweight, you could draw the pins yourself in the UITableViewCell subclasses drawRect method. Then you could just pass the locations of the pins.
Good luck
I think this is a new spin on an old question, but I'm completely stuck here.
In my app, I have a UITableView with 650 cells, each with a custom 16x16 RGB icon. On most recent iOS devices, loading all of those icons into memory before displaying the table works totally fine, but on older hardware, I'd like to implement a lazy load system that only loads icons it needs.
I've implemented the Apple LazyTableImages example, (which uses a UIScrollView delegate to determine when the table stops moving to load the visible icons), but I've run into another snag.
My UITableView also has a section index display (ie the list of labels on the right hand side you can swipe up and down to scroll quickly), and the LazyTableImages example hasn't taken this into account.
If I scroll using the index, the images won't lazy-load. :(
As far as I can see, the scroll index doesn't actually have any delegate events it triggers.
So I'm wondering, has anyone else tried to implement lazy-loading on a table with a scroll index? Is there any way to track the index and find out if the user has interacted with it?
Thanks!
After buzzing around a few of my iOS developer buddies, I came up with a solution that worked well enough.
I set it up so that in addition to the icons being loaded from the UIScrollView delegates, an NSTimer object will periodically call a method that checks the currently visible table cells ([UITableView indexPathsForVisibleRows]) every .5 seconds, and loads any icons on the screen that haven't been loaded yet in a single separate thread.
I tried to make the solution as efficient as possible, so I made sure the timer was only active when the tableView was visible and stationary, and I liked it since it meant that every visible icon regardless was addressed.
One thing I discovered was that if the tableView was reloaded while the thread was looping through the visible cells (rare, but was possible), it would crash. The solution to this was to make sure each cell data source entry was retained while the icon was being loaded.
I got trouble to add slideshow to my application.
Currently, I have a UIView composed of a segmentedControl.
I made two "views" that I hide or display depending on the selected button.
I'm looking to make a simple slideshow in one of my two views. I made a UIImageView because it is simple to display pictures.
So I'd like to display my pictures one by one and it is possible to move from one image to another by sliding your finger to the right or left (just as in the native app "Photos").
I tried to adapt example codes from the documentation, but without succes.
So I'ml looking for help.
Thanks,
jb crestot
SO, I've actually done this and it's fairly easy. The ingredient that you are missing is a UISCrollView. My implementation did exactly what you describe (allow the user to go back and forth between a set of images).
Basically, add a UIScrollView to your View in interface builder and you will be creating the UIImage views with code (a simple for loop) and setting their images the same way. I did this safely with no memories issues with about 15 images (PNG's). There could be a potential performance issue with this message if you are working with a large number of images (say 40?)
I hope this helps, let me know if you need a code sample to see how this works.
You may consider using a custom class, such as iCarousel, linked below. Each of these views could be your image, and then tapping on them could launch a fullscreen view for example.
Keep us posted!
http://cocoacontrols.com/platforms/ios/controls/icarousel
See apple's page control sample application.