I'm trying to implement a view that shows a grid of information without using a UITableView, however, since I'm displaying about 36 different statistics, with its label I will have to initialize and use 72 UILabels. Does having so many UILabels mean that my iPhone app's performance will be significantly negatively affected? Is there a way to reuse some of the UILabels to decrease the number of UILabels that must be loaded at one time, or should I just resort to drawing everything on a surface instead?
First of all you should test the interface your thinking of and see if it takes a performance hit. Having a lot of labels all loaded at once will increase your memory footprint but depending on what else is going on in the app, it might not matter.
Secondly, you can't easily reuse the labels but it is possible. However, you would have to constantly monitor the displayed area of the scrollview and move the labels frames around as the view scrolled. I doubt you could do that efficiently. It would take a lot of coding in any case.
Thirdly, any grid like layout can be easily displayed in a table without making it look like a table. For example, the photopicker layout is a table but it looks like a bunch of icons on a white background. Another app I saw used a table to display paragraphs of text but it looked like an ordinary scrolling textview. Every row in a table can be customized to display exactly what you want. In principle, you could use a different cell for every row and they could all be unique in their height and contents.
The advantage of the table is the the table manages what is and is not on screen for you. It does reuse cells and their contents which makes them more efficient. The table also makes it easier to manage a lot of data.
Related
I have an infinite scrollview in which I add images as the user scrolls. Those images have varying heights and I've been trying to come up with the best way of finding a clear space inside the current bounds of the view that would allow me to add the image view.
Is there anything built-in that would make my search more efficient?
The problem is I want the images to be sort of glued to one another with no blank space between them. Making the search through 320x480 pixels tends to be quite a CPU hog. Does anyone know an efficient method to do it?
Thanks!
It seems that you're scrolling this thing vertically (you mentioned varying image heights).
There's nothing built in to UIScrollView that will do this for you. You'll have to track your UIImageView subviews manually. You could simply maintain the max y coordinate occupied by you images as you add them.
You might consider using UITableView instead, and implementing a very customized tableView:heightForRowAtIndexPath: in your delegate. You would probably need to do something special with the actual cells as well, but it would seem to make your job a little easier.
Also, for what it's worth, you might find a way to avoid making your solution infinite. Be careful about your memory footprint! iOS will shut your app off if things get out of hand.
UPDATE
Ok, now I understand what you're going for. I had imagined that you were presenting photographs or something rectangular like that. If I were trying to cover a scroll view with UILeafs (wah wah) I would take a statistical approach. I would 'paint' leaves randomly along horizontal/vertical strips as the user scrolls. Perhaps that's what you're doing already? Whatever you're doing I think it looks good.
Now I guess that the reason you're asking is to prevent the little random white spots that show through - is that right? If I may suggest a different solution: try to color the background of your scroll view to something earthy that looks good if it shows through here and there.
Also, it occurred to me that you could use a larger template image -- something that already has a nice distribution of leaves -- with transparency all along the outside outline of the leaves but nowhere else. Then you could tile these, but with overlap, so that the alpha just shows through to the leaves below. You could have a number of these images so that it doesn't look obvious. This would take away all of the uncertainty and make your retiling very efficient.
Also, consider learning about CoreAnimation (CALayer in particular) and CoreGraphics/Quartz 2D ). Proper use of these libraries will probably yield great improvements in rendering speed.
UPDATE 2:
If your images are all 150px wide, then split your scrollview into columns and add/remove based on those (as discussed in chat).
Good luck!
I have a bit gantt chart that i want to be visible on an iphone.
It is 7200 x 1800px large, and consists of ~600 bars, each of which is a UILabel.
It is to look like this:
Now i've gotten it to work. And at ~100 bars, i can make it run quite smoothly by simply adding them all to the scroll view. However, with the full 600 (or more eventually) it simply crashes when i instantiate all those uilabels and add them all to the scroll view as subviews.
So what i've done is made it create only the uilabels for the currently visible rows, and as the user scrolls up and down it removes the invisible uilabels and adds the newly visible ones.
However, this jerks quite noticeably as you scroll vertically as it crosses each row boundary, and has to render another row and remove the old row.
Does anyone have any suggestions to solve this? Any ideas what is the slow part? Instantiating the uilabels, or adding them as subviews, or anything?
All help will be greatly appreciated.
Apple has some really good demo code that shows how to do this. Check out TiledScrollView.m especially the layoutSubviews method.
Other things you might consider:
If you labels are quite long horizontally you may need to break them into smaller chunks. Quite long in this context is wider than the screen.
Make sure your UILabels are opaque. Scrolling things that require compositing adds extra overhead which may account for some of your issues.
Looking at your screen shot the row and column headers are not opaque and are using alphas. Whereas this is a nice effect it may be worth temporarily making them opaque too just to see if this is contributing to your problems. I don't think this is contributing too much to your problems; the area being composited is quite small.
Just a thought, but could the issue be that even though you are caching and reusing the labels, is the scroll view still retaining them, so even though you may only have a few labels, each is being retained hundreds of times. If this is so then I would think that the scroll view is still effectively trying to manage those hundreds of rows.
So as #Nathon S asked - are you moving them? i.e. building a finite set of labels and just moving them around on the scroll view to match the viewing area. If you are hiding and re-adding to the scroll view then I would suspect a massive set of retains being the slow down. I would think that with a moving label design, you would not need to do any hides and adds after the the initial display. Which should make it very fast and lightweight.
I have an array of scores in my iphone game. All I want is a plain list, just text of these scores.
Do I need to load this into a UITableView then somehow remove the background of the table, so it appears as just text, or is there a different method I can use to get this list as just text?
Thanks.
I think you need to better define what "as a list" means to you. You could construct a multiline string containing those values and disposing in a UILabel or UITextField but I can't tell if that would make sense for your data and your desired UI.
How many scores do you have? Will they all fit on the screen at one? Do you need to be able to scroll the list? Do you want to be able to tap on the scores? Copy them? Format them differently?
You certainly could also create a table view with a tranparent background on the table and it's cells. Just be aware that transparent cells are more expensive to render and will not scroll as smoothly as opaque cells.
i did a text rendering program using UIView and UITableViewController. What i did is before going drawRect method, i just calculate all of the cells height as well as each text start & height,width. So that, i can estimate the cell height approximately and then i draw the text.
I did this for both portrait & landscape mode. My program looks like twitter updates. When the user changed to landscape mode i calculated the same things for landscape mode. Next time, i simply retrieve the stored data for drawing text(Valid before application quits).
Now my problem is, when my inputs are less, it works good. But for the huge input say 100 inputs, it takes some time to show the text. Also, my program's scrolling is somewhat not smooth. Also there is no leak in my application.
Please anyone suggest me the good way to do this application and make it so smooth and faster...
Thanks in Advance,
Rajkanth
The short answer to this is to minimize any computation you do in rendering of the cells. This includes any transparent backgrounds. To achieve the fastest scrolling, ideally you would have very few amounts of non-opaque elements.
The trick is to only have one big opaque element by coalescing all your individual elements into a single view.
http://blog.atebits.com/2008/12/fast-scrolling-in-tweetie-with-uitableview/
I add a PickerView to one of my views in an app, but its size is too small(in height). I find that I cannot drag to make it "longer". How to change its size then?
The only way is by adjusting the pickerView.frame.size.height, but you'll get some pretty bad visual artifacts.
I would think long and hard about attempting to circumvent the established design of this control. If you have so many items or your items are too big for this view, a UITableView is probably what you want to go with. It's far more customizable and can handle items/cells of all different shapes and sizes.