I´m pretty new to Xcode and playing around with some techniques.
For testing, i am writing an app where i have a detailViewController with three views within.
As soon as i assign constraints to one of the views the layout gets really strange. No matter if i center horizontally or set border distance, the view seems somehow to vanish and the components within the view are placed somehow.
Any idea what i´m doing wrong?
Sure, you need to follow these basic rules. Checkout the auto layout guide. Each view from the top of the scene to the bottom should have constraints (also constraints should exist from side-to-side if you want expansion and contraction, or have height/width if those are important to maintain). Most times you will need to have at least four constraints per view. The auto layout errors will not go away until all the views have constraints applied and adhere to the simple rules I mentioned above.
Related
I am trying to create a custom subclass of UITableViewCell that displays an image and a few labels to the right of the image. I have my UIImageView and UILabels arranged in stack views, the outermost of which I pinned to all four sides of the content view.
But when I run the app in the simulator, I do not see the image views. Debugging the view hierarchy, I see they are getting clipped.
And digging in a little further by focusing on the outermost stack view with "Show Constraints" on, I don't see my auto layout constraints at all (instead I get an ambiguous position runtime warning for each of the outermost stack views).
The text label that expands to the right is set up with 0 lines and the table view gets a constant estimatedRowHeight value and its rowHeight set to UITableViewAutomaticDimension, so I think if these constraints were working, the rows in the table would size to fit the content. Perhaps notably, any width or height auto layout constraint I add does appear when I debug the view hierarchy, so I know some constraints are present at runtime, I just cannot for the life of me figure out why the constraints relative to the content view are not.
After wrestling with this for a long time and having a much more experienced developer look over my project, it seems as if there was nothing wrong with the way it was set up. Recreating the table view cell from scratch with exactly the same layout and constraints and using the exact same code fixed this issue. I had messed around with the stack views and constraints quite a bit before this started happening, so it might be possible to get Xcode into a place where it does not properly set up constraints when you run the app in the simulator.
Try to solve all warnings which are printed into your console log when you run your application and viewing this screen. Because you can not ignore warnings always, many warnings you must have to remove by correcting or solving issues in your constraint. And that is the only solution which helps you most of the time.
I'm 5 years late to the party, but I managed to find a solution to this problem in my project. If any of the views that are contained in the table view cell have a bad subclass set on them, the intializer defaults them back to a regular UIView and without any of the layout constraints. Hopefully that saves someone the hours it took me!
Just for fun I started to play with animations after successfully applying them to some basic background color changes. I have some different images on my "welcome/splash" view that I would like to animate. One image should appear from the bottom, another from the top and so on.
I immediately ran into trouble since I am using auto layout it was not that easy as animating background colors. I found this post How do I animate constraint changes? and after doing what was described at least my image was animating. However, is it correct that the console window should be filled with warnings/info/errors about constraint violations? Also, animating the vertical position of one image causes all the other image to animate too, probably because of some constraint relations.
How are you supposed to deal with that? when animating the "Bottom layout attribute" with a new constant value I expect only the view it belongs to animate, not the whole screen.
And how are you supposed to refer to the constraints? By outlets?
I am creating my views and constraints in storyboard. I deleted my code for animating the image views since it was just a mess. But whats done with the button and textfields in this tutorial is pretty much what I am trying to do with my images. Without animating one image causing the whole view to animate with it. http://www.raywenderlich.com/113674/ios-animation-tutorial-getting-started
However, is it correct that the console window should be filled with warnings/info/errors about constraint violations?
Learning Auto layout can be a challenge which will fill your days with such warnings/info/errors about constraints. Many iOS developer's struggle with Auto Layout at first. Auto layout is an addition to the layout process. The issue here is how are you going to deal with them. I suggest reading the Apple Auto Layout Guide, it contains a section on debugging. Also look at the Debugging Tricks and Tips section.
Here's a great article explaining more of the concepts behind Auto layout.
Build a simply app that has only one view and a subview, so that you can reduce the noise around layout constraint errors in more complicated layouts.
Here is a code snippet of how to animate a constraint.
if myViewTrailingConstraint.constant == -2 {
myViewTrailingConstraint.constant = 200
} else {
myViewTrailingConstraint.constant = -2
}
UIView.animateWithDuration(0.3,
animations: {
self.view.layoutIfNeeded()
},
completion: nil)
How are you supposed to deal with that?
Auto layout is an inter connected system of relationships between your views. A constraint represents a relationship. So you really need to think through your view's layout and plan your constraints first. Why? because if you plan to animate certain views you need to need to make sure that the constraint constant you are going to change will effect only that view in question.
And how are you supposed to refer to the constraints? By outlets?
You can create constraints solely in code or with the interface builder (outlets). I would suggest that you start with interface builder as even when you are comfortable working in code, it is useful and time saving to be able to do your initial layout in interface builder - so learn to use both.
Warnings are not normal - you have to solve them to avoid strange effects.
If animating a constraint value of one image moves other images, then indeed you must have some constraints in place that also change - e.g "equal width" constraints or such. Normally it just works - if it doesn't, you have to show the warnings you get and the constraints you set in order for someone to see what is going wrong.
I've got a UITableViewCell that has a child view, and within it an image view and a label. I am wanting to use the child view as a means of giving some margin around the contents of the cell, thus giving me margins inbetween cells. This seemed to be the way a lot of people online recommended doing it.
I've set up my constraints as shown below:
I have performed a Update Frames on all views in the view controller. The story board shows it exactly as I'm expecting it to be on the phone. When I run it on the phone though, I get this...
I'm completely baffled at this point. I've spent two days of reading and trying to layout a simple UITableViewCell and clearly don't have a good understanding of how auto-layout works still.
I've even just laid everything out along the suggested boundaries (the blue lines) and then told the storyboard to generate suggested constraints. At which point the content of the cell just sent with 50% of it off the right side of the screen and un-viewable.
So two questions:
The storyboard more often than not shows me something that is not accurately represented on my actual device. Is this fairly common in iOS development? Should I not be relying at all on the storyboard auto-layout representation?
What do I have to do to these constraints in order to get the cells to layout on my device, like it is shown in my storyboard at this time? What constraints am I setting wrong?
Storyboard doesn't display the content according to any device by default. You can set it to your current device in its size properties(by default it is "Inferred"). Constraints are used to display the views equal on all devices. They automatically adjust UIelements according to display size. So if you want your app to run on devices of different sizes you have to rely on constraints.
I think you are setting too many constraints. Happens if you are new to auto layout. Try reading this guide. Its very helpful.
This is what I'm trying to do...
I have one view controller that needs to dynamically display different subviews based on the presence of some data.
Here is a simple mockup. Each colored block represents a unique subview.
Sometimes the green block needs to be at the top, sometimes the green block won't display at all, sometimes the light blue block will be something different, etc.
Each subview has interactive elements, so I've been creating and adding them like so:
Defining a new view controller
Defining its view
Calling addChildViewController and didMoveToParentViewController
Calling addSubview on myNewViewController.view
Using SnapKit to make auto layout constraints to position the view
I want to transition to UIStackView because it seems a good support system for this view because all I need to do is stack its subviews. I'm seeing many conflicting constraint errors and unexpected view frames when trying to add subviews with their own inner auto layout constraints.
Question
Am I setting myself up for failure here by embedding the views of 4-6 view controllers in the view of one view controller?
Also, how do I give the added views properties like minimum heights or content sizes without seeing many breaking constraints with UIStackView? (So they can stack, but one of them is say, 400 tall, and the other is 200 tall)
Answer
You can absolutely do this using UIContainerViews combined with UIStackViews and UIScrollViews, it's a complicated setup so here's a starter project to get you started:
https://github.com/Rnorback/ScrollingStackView
Here's what that project looks like:
You want the containers to have different sizes. In order to do that, simply add height constraints to the containers with Autolayout. If you want to change the height of the scrolling. Then you'll need to change the height constraint of the UIStackView.
Brief Explanation
When creating this setup, you have to make sure the UIStackView distribution setting stays in fill. That way you can set height constraints on UIContainerViews.
When setting up anything in a UIScrollView you have to make sure that the object is pinned to the edges of the scroll view and has a defined width and height, otherwise the scrollview will throw a constriant error. I think of it like the scrollview tries to press in on all sides of your content view and if any side gives, the scrollview won't be able to present it properly.
Hope this helps.
Im starting to experiment with storyboard. As you can see I have chosen the storyboard size to be height=regular and width=compact, which says “For all iPhones in portrait”.
The simulator I am using is iPhone6 however when I run everything is slightly off to the right.
Can someone explain what is happening or what I am missing?
The problem is that (as described in the comments) you are positioning the views without AutoLayout. When you just drag and drop the views, it's actually setting the frame's positions and sizes. The main problem with this approach is that it doesn't set the position and size in a proportional and related manner, taking in consideration the container. This is why you're getting the view at the current position. If you run in another simulator, maybe you can get the correct position, or maybe not. What you can do to change this is apply auto layout constraints to those views. There's a special constraint to center views horizontally. With autoLayout you can go further, specifying relation between one or more views, and those views not necessarily need have the same container view.
One quick example:
Notes:
I'm using universal storyboard to take those screenshots. It's more flexible and with AL you don't necessarily have to concern yourself with the size, as views adjust themselves depending on the constraints applied to.
EDIT:
https://developer.apple.com/library/ios/documentation/UserExperience/Conceptual/AutolayoutPG/Introduction/Introduction.html
This is a link to auto layout guide provided by apple, a great tutorial on how to get your hands dirty in this little world.