Im trying to implement a nice accordion effect on my app. My goal is to "open up" a cell when the user tap on it, diplaying additionnal content (such as text) as the cell height increase.
The perfect sample code for that is the TableView Animations & Gestures sample code provided by Apple. However I am experiencing a strange behavior, that ruins the whole effect.
It appears that depending on the order in which the tableview will display its cells (top --> Bottom or Bottom-->up) the cells textviews will overlap each other or not.
As its a bit difficult to explain with word so here is it with images.
Those screenshots were taken from the TVAnimationsGestures Sample Code, without any changes made to it. It comes from the first version of the sample code without storyboard:
Now the version with the storyboard, first behaved well, but after a while, and without me touching the code it started drawing this :
And I have the exact problem on my custom with my custom cells.
It took me a while to understand what I think the problem comes from. If cells are drawn from the Top cell to the bottom, there is no such problem. However if cells are drawn bottom to the top, they will stack in reverse and therefore overlap each other. I don't think it is possible to control this behavior.
What gave me the hint, is that when I scroll down, forcing the top cell to redraw, they actually redraw nicely, and the screen looks like this:
A Mixture of overlapping cells and "good" cells.
Again, this all comes directly from Apple sample code, without any changes.
Does anyone knows whats going on?
Thanks a lot for your help.
You can increase the cell height by pinching on the cell.
Related
I'm trying to build a custom, reusable UIScrollView that can be added to multiple views. The scroll view is going to be a weight picker. For the life of me, I can't find a decent example for how to implement this neatly or cleanly.
I would love for someone to point me to an existing library or tutorial that shows me how to do this. I've hacked apart a few examples, but so far, nothing is very good or reusable. Please help!!
For what it's worth, I have an image that individual ticks for the weight. So I can select to the tenth of the number (e.g. 160.4). The image has the first tick bold and larger than the remaining 9. I'd like to have the weight/number centered over the large tick. I'll update the points to my label/datasource after scrolling stops.
UPDATE
I need to make this. I have the custom font, background, and ticker image.
I would not do this through an UIScrollView. I think it would be more complex and you would certainly end up having issues when trying to add you custom picker into another scroll view.
What I would do is:
building the picker view by means of a series of CALayers, each one representing a "building block" of your picker view; see attached image:
each building block would represent a specific value by mixing a UILabel (the text) and an image;
use a pan gesture recognizer, or alternatively define touchesBegin/Moved/Ended method to deal with panning;
when a pan is done, you displace the view content to the left or right according to the panning;
when panning, you also add new building blocks to the left or right end of the picker to account for empty areas that would be revealed by the displacement done at point 4.
I think that having a look at another kind of custom control source code would be of great help to you. You would not possibly find your custom picker already implemented, but could get some guidance. Have a look then at cocoa controls.
Hope this helps.
If I were going to implement this, I would create a really wide image that had every weight on it I'd ever need - I would probably create this in code when the app started up. This image is then used as the contentView of your picker. You get all the scrolling features "for free", and you could even update the values shown in the other parts of the view during scrolling (or dragging.
The scrollView is just the area with the tick marks and weight numbers, and resides in a subview above the background, but below the centered vertical line that shows the actual weight.
EDIT: on second thought, forget the image. If you have the code to draw the image, you can do the drawing in a custom UIView. So you get the draw rect, you know the contentOffset, so you can draw just what you need.
I've implemented autoresizing mask in all my the views of my project very successfully. However in the last one, which is the settings and there are a lot of sliders inside tableCells, it seems it doesn't work too well.:
I'm sure I've implemented the thing right
slide.autoresizingMask=UIViewAutoresingFlexibleWidth
for the sliders and flexible left margin for the labels.
I've also implemented table reload when the rotation takes place.
The cells are being reused ok, or at least in portrait mode they work, but when I rotate and go back I got what you see in the picture.
Any ideas on what am I missing?
Thansk in advance!
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've had this issue come up a couple times doing iPhone development now and have yet to find a good solution for it. What I'm looking for is this:
I want to show some text along with an icon and I want the overall display to be centered within its parent view. Specifically, in my current case, I'm looking to display a box that says "Reconnecting..." with a UIActivityIndicatorView to the left of the text.
Previously, I've just relied on the fact that I know exactly the dimensions of the text and activity indicator, so I can position things absolutely to appear centered. What I'm looking for is something more automatic.
Any ideas?
One of the UIKit additions to NSString will return the pixel size of the text if you give it the font that you're using on the UILabel. So then presumably the total size of the two things together in the layout you describe is:
the difference between label.frame.origin.x and activityIndicatorView.frame.origin.x; plus
the width of the text.
You can then either shuffle both the views appropriately or give them a common parent that's still a subview of the whole thing and shift that.
An activity indicator can be shown in a view just calling a single method.Please click here get SHKActivityIndicator class
I'm trying to make a level-of-detail line chart, where the user can zoom in/out horizontally by using two fingers, and grow the contentSize attribute of the the UIScrollView field. They can also scroll horizontally to shift left or right and see more of the chart (check any stock on Google Finance charts to get an idea of what I'm talking about). Potentially, the scroll view could grow to up to 100x its original size, as the user is zooming in.
My questions are:
- Has anyone had any experience with UIScrollViews that have such large contentSize restrictions? Will it work?
- The view for the scroll view could potentially be really huge, since the user is zooming in. How is this handled in memory?
- Just a thought, but would it be possible to use UITableViewCells, oriented to scroll horizontally, to page in/out the data?
This is kind of an open ended question right now - I'm still brainstorming myself. If anyone has any ideas or has implemented such a thing before, please respond with your experience. Thanks!
This is quite an old topic, but still I want to share some my experiences.
Using such a large UIView (100x than its origin size) in UIScrollView could cause Memory Warning. You should avoid render the entire UIView at once.
A better way to implement this is to render the only area which you can see and the area just around it. So, UIViewScroll can scroll within this area smoothly. But what if user scrolled out of the area that has been rendered? Use delegate to get notified when user scroll out of the pre-rendered area and try to render the new area which is going to be showed.
The basic idea under this implementation is to use 9 UIViews (or more) to tile a bigger area, when user scrolled (or moved) from old position to new position. Just move some UIViews to new place to make sure that one of UIView is the main view which you can see mostly, and other 8 UIViews are just around it.
Hope it is useful.
I have something similar, although probably not to the size your talking about. The UIScrollView isn't a problem. The problem is that if you're drawing UIViews on it (rather than drawing lines yourself) UIViews that are well, well off the screen continue to exist in memory. If you're actually drawing the lines by creating your own UIView and responding to drawRect, it's fine.
Assuming that you're a reasonably experienced programmer, getting a big scroll view working that draws pars of the chart is only a days work, so my recommendation would be to create a prototype for it, and run the prototype under the object allocations tool and see if that indicates any problems.
Sorry for the vagueness of my answer; it's a brainstorming question
But still, this approach (in the example above) is not good enough in some cases. Cause we only rendered a limited area in the UIScrollView.
User can use different gestures in UIScrollView: drag or fling. With drag, the pre-rendered 8 small UIViews is enough for covering the scrolling area in most of the case. But with flinging, UIScrollView could scroll over a very large area when user made a quick movement, and this area is totally blank (cause we didn't render it) while scrolling. Even we can display the right content after the UIScrollView stops scrolling, the blank during scrolling isn't very UI friendly to user.
For some apps, this is Ok, for example Google map. Since the data couldn't be downloaded immediately. Waiting before downloading is reasonable.
But if the data is local, we should eliminate this blank area as possible as we can. So, pre-render the area that is going to be scrolled is crucial. Unlike UITableView, UIScrollView doesn't have the ability to tell us which cell is going to be displayed and which cell is going to be recycled. So, we have to do it ourselves. Method [UIScrollViewDelegate scrollViewWillEndDragging:withVelocity:targetContentOffset:] will be called when UIScrollView starts to decelerating (actually, scrollViewWillBeginDecelerating is the method been called before decelerating, but in this method we don't know the information about what content will be displayed or scrolled). So based on the UIScrollView.contentOffset.x and parameter targetContentOffset, we can know exactly where the UIScrollView starts and where the UIScrollView will stop, then pre-render this area to makes the scrolling more smoothly.