I am just playing a bit with the constraints and auto layout within iOs. I made up a design which caused the interactive elements (except for the buttons) to be disabled. I cannot toggle them.
First they were working, but then I applied a few Views and constraints... I colored the Views underneath the disabled elements. So programmatically I did not make a change.
What did I do wrong?
EDIT
Here the constraints of the back and save button:
Mr #DonMag pointed me at the right thing:
The little Red arrow-circle-icon means you have a conflict with your constraints. That isn't necessarily the reason you cannot interact with objects, but it certainly could be related.
The little Red arrow-circle-icon pointed me at a missing constraint for the height of the underlying elements view. Once I set the height of the View, the elements where enabled again.
Related
I've been doing iOS for a while now, but when it comes to dynamically hiding / showing elements, I'm a bit lost.
Coming from Android, I'm used to being able to simply set views to visibility gone, but this doesn't exist on iOS.
So let's say I have the following scenario:
Basically I want to have a table, but the table should not fill the entire view controller. Instead it should leave place for optionally either a button, a multiline label, or possibly both at the bottom (if visible, these should be fixed, not scroll).
One way to solve this would be to use auto layout and modify constraints, like adding a zero height constraint. But that would make iOS kill one of the other constraints, which would make it hard to change it again. For the label, I wouldn't always want to have a height constraint, because it could be multiline, and should take the size it needs.
Maybe it's easier to skip autolayout here and modify frames instead, I don't know.
My question is: What approach would be best here?
Is there some other way of doing this I haven't thought of, or do I have to try to do what I described above?
I'm not primarily looking for code (code can be ok), but I'm more interested in a description of how it can be done.
I'd like to support iOS 7.
This problem had a variety of solutions, and opinion based, but I'm facing such questions a lot, when I don't know what to choose and what would be the "right thing".
So, I my opinion, the best solution here is using autolayout, you need to set height of label manually, but you have a few methods for this, at least you can play with it and if you don't succeed ask question about it. Using frames, you'll face same problem of calculating height, right? But with auto layout, you only need to set height, vertical space to 0, when you need to hide message.
You can also use constrains with priority lower 1000, and remove completely constraints from message (button, label) if you don't need it at all anymore.
For example, taking your layout image, you can make UIView with subviews: button, label. Top constraint connect to the UITableView, other constraints to the sides.Label and button will calculate the view's height. The only question here is label height.
So in ios assuming that the background of both these objects is opaque only the front most view in the Heirarchy will be visible and interactable, An easy solution would be to change the different frames of these two things you need and make sure they are in the back of your view heirachy, and when you need them to appear use view.bringSubviewToFront(mySubview) and view.pushSubviewToBack(mySubview) to make it disappear again. View obviously would be referring to main view of your view controller.
I have a swift app I have been working on for some time now. I noticed that my init view controller has extra space at the top and the bottom of the view, so much that it allows me to pull up and down on the first view and let go and have it spring back into where it was. I removed all my constraints thinking I had an issue with them, but it's still done the same thing. The size class is set to any any, and all my graphic fit inside the view, yet I still an able to pull up and down.
I also made sure my view, wasn't a scroll view, it's not.
I looked around for similar issues, but couldn't find anything like this.
Thanks for the help!
Here is what my view looks like in IB
When I run the app.
Showing the amount I am able to pull it down from the top.
If you remove all of your constraints, and the storyboard is set to use auto layout, it usually won't show up correctly, as you have seen. You will have to add the constraints to each element in your view controller. To do that, you can control click on each and drag it where you want to connect a constraint. Or, use the pin and align buttons in the bottom right corner of the storyboard view.
There is a good tutorial from apple that I suggest you read. It will help you with the basics of using auto layout. Another option would be to not use auto layout. To turn it off in the Storyboard, go to the file inspector and uncheck the box "Use Auto Layout".
I have issue with autolayout.
I have three different views (could be n views as well). When I pin first one to top of super view and connect one next to the other everything seems fine. But if I want to change height of first one the other two does not follow (they stay on the same position). What I find weird about this is that if I connect only two views this works perfectly.
To have better understanding what I am trying to achieve I made simple, example solution with three views:
http://i.stack.imgur.com/cMwiB.png
So, when I set height of green view to 0 ( can be any other number as well ) and only red view is connected, this works fine, red will move as it should. Blue one is not connected and it remains where it is:
Here is screenshot when I connect blue to red:
What I tried to do:
connect blue one to green as well ( not working)
connect blue only to green ( not working )
"boxing": have boxes with views at the time ( ugly, hard to manage, not working in all cases)
What I would like to know:
what makes this happen? Can I change this kind of behavior?
What is the best practice to have flexible length for height (Besides UITableView)
Thanks in advance.
Ok, I think you're falling into the same trap I did, when I investigated autolayout some time ago. It's tricky to explain, but I'll do my best. When you work with autolayouts, you need to forget completely about setting a view's frame at all. And that, my friend, includes changing size and positioning. When you use autolayout, you define some constraints, some "rules", that the view tries to respect when rendering the screen, so the more specific the rules are, the less random will be the behavior of the view. I mean, if you just define the spacing between views, you're implying that the height of the views doesn't matter, so it's possible that some views grow or shrink when the re-layout is called (that is, if you don't specify a constraint for size. You probably want to always specify the size of some views in every layout...)
By the way, you're allowed to violate the constraints by manually changing the frame of an element AFTER a re-layout is called, but when the re-layout method is called again, the constraints will be forced so the size and positioning of the views will change. Quick tip: an easy way to force the re-layout method is to change orientation (command+left / command+right in the simulator).
So after saying that, I have to say that the layout you provided is completely working as intended, at least to me. When you change orientations the constraints you specified are ALWAYS being respected. If you want, you can try to apply some frame-setting in the viewDidAppear method, because this one is called AFTER the autolayout (and thus, you're able to violate the constraints temporally). After doing this, your view will be broken but once you change orientation the constraints should be respected again. Make sure it's that way.
From here I can only wish you luck ;) Oh, and refer to the documentation, it was a life saver to me when I looked at this half a year ago. https://developer.apple.com/library/ios/documentation/UserExperience/Conceptual/AutolayoutPG/Introduction/Introduction.html It might seem a classic, but it's a pretty nice doc.
EDIT: one last thing. I have the impression that constraints are not designed to be dynamic. You define them once, and they're there always. Their main purpose is to ensure that subviews are rendered as intended in every screen resolution without fail, so if I were to make an application with moving views, I would leave them outside of the autolayout, or avoid using it at all. Just a personal impression though :)
I've read quite a bit about spacer views - they seem very handy in utilising all this auto layout stuff.
I understand all of the concepts behind them, that's fine... I'm looking to practice with them now but before I could even get started I've found myself getting stuck on a more fundamental issue that's really doing my head in... maybe I'm too tired.
How do I actually place a spacer view? I'm looking for some drag and drop, native kind of thingy... but I can't see any "spacer view" in the object browser.. do I have to create this view myself? Where does it come from?
Spacer views are just standard UIViews.
If you want to make them easier to use in IB then give them a coloured background and make them visible but in the runtime attributes give them a Boolean...
Hidden = YES;
That will hide them in the actual app.
The reason they are used with auto layout is because you can't create equal spaces. A space is the gap between two objects. It isn't an object itself so you can make two spaces equal (for example).
But you can replace the spaces by instances of UIView and now you can give these UIViews equal widths or heights. Make them hidden and the constraints still act on them but they cannot be seen.
There's a simple "UIView" widget you can drag and drop from the lower-right corner area of Interface Builder. I don't believe there's any official "spacer view" terminology in Apple's kit...
After reading about UIView's autoresizingMask on SO and developer.apple.com I'm still unclear what the purpose is. What's a situation where setting this property is necessary?
Yes, it is often necessary to set it if you don't want to resize the views manually. Note that it is mostly useful for subviews (i.e. those views that don't take the whole screen) rather then the main view of your app.
Views typically may need resizing if:
the device is rotated
an extra view (say, an ad) is added to the view, so the existing subviews have less available space.
For example, suppose if you have a view with two buttons on it, one in the top-left corner, another in the top-right corner. In order for the buttons to get wider when the view transitions from portrait to landscape, you need to set the FlexibleLeftMargin to the right button, FlexibleRightMargin to the left button.
Edit: autoresizingMask is also the first thing to look at if you see weird holes or overlaps when device is rotated or a new subview is added. Quite often the proper setting of these masks for subviews can get you a nice looking view in both orientations without having to lay out subviews manually - but usually it takes some experimenting.
Edit2: (since this is still gathering upvotes) Autoresizing masks are now mostly superseded with "Auto Layout", which allows for much more flexible constraints on views' sizes and positions. That being said, translatesAutoresizingMaskIntoConstraints is still occasionally useful for dynamically added views.
The purpose is that UIView properly shifts and resizes when its superview changes due to resizing, orientation change, showing editing controls in tableview cells etc.