How do you make a UIButton's vertical distance equivalent to a UIButton's horizontal distance in AutoLayout.
Using Visual Format Language, I can currently make all UIButtons have the equivalent height or width, but I don't know how to specify those to be the same.
I also do not want this distance to be predefined which I know is possible through setting metrics.
You can't use vfl for this.
You have to use the method...
AddConstraintForItem:attribute:relation:toItem:attribute:multiplier:constant.
Or something like that anyway.
Both items can be the same and the two attributes set one to width and one to height.
Figured out a solution to this. You can't use Visual Format Language, but rather need to use NSLayoutConstraint constraintWithItem
NSLayoutConstraint *constraint = [NSLayoutConstraint constraintWithItem:forwardButton attribute:NSLayoutAttributeHeight relatedBy:NSLayoutRelationEqual toItem:forwardButton attribute:NSLayoutAttributeWidth multiplier:1.0 constant:0];
[self.view addConstraint:constraint];
Related
I'm struggling to figure out how to use VFL to accomplish this. I always want the button to be 50 points above the bottom of its superview. I don't want to specify the distance between the top of the bottom and the top of its superview because that will vary across devices.
I was only able to find other similar questions using interface builder, but my project does not use interface builder or swift, but I would like to do this programmatically, in Objective-C.
Thanks in advance.
If you have no idea about how to use VFL, I think you should check the document:https://developer.apple.com/library/ios/documentation/UserExperience/Conceptual/AutolayoutPG/VisualFormatLanguage/VisualFormatLanguage.html
button.translatesAutoresizingMaskIntoConstraints=NO;
NSArray *constraints=[NSLayoutConstraint constraintsWithVisualFormat:#"V:[button]-50-|" options:0 metrics:nil views:NSDictionaryOfVariableBindings(button)];
// add more constraints to satisfy auto layout
[superview addConstraints:constraints];
BTW, I recommend to use Masonry, https://github.com/SnapKit/Masonry, it's more elegant.
Use something like this:
[yourSuperView addConstraint:[NSLayoutConstraint constraintWithItem:yourButton
attribute:NSLayoutAttributeBottom
relatedBy:NSLayoutRelationEqual
toItem:yourSuperView
attribute:NSLayoutAttributeBottomMargin
multiplier:1.0
constant:-50.0]];
You can read more on this here: Working with Auto Layout Programmatically
I have a tableViewCell with a label inside. Lets say I dont want to create an IBOutlet in this case. I want to add a constraint to the label based on a condition so that label moves 10pixels down if the condition is true. To be more precise, I want to achieve the constraint in the image below by code.
I have tried
NSLayoutConstraint *myConstraint = [NSLayoutConstraint constraintWithItem:amountLabel attribute:NSLayoutAttributeTop
relatedBy:NSLayoutRelationEqual toItem:cell.superview attribute:NSLayoutAttributeTop
multiplier:1.0 constant:+10];
[amountLabel addConstraint:myConstraint];
but to no effect. Any help would be appreciated. :)
I think you would have to add that constraint to the superview to get it to work (always add constraints to the topmost view, or to the nearest common ancestor view).
I've found that working with constraints in code is WAY easier using a category library. My favorite is the one made by Richard Turton: https://github.com/jrturton/UIView-Autolayout
I think you will find adding constraints is much more intuitive using this.
Example
[amountLabel pinEdge:NSLayoutAttributeTop toEdge:NSLayoutAttributeTop ofView:superView inset:10];
I’m beginning to implement AutoLayout, and I’m trying to piece together how I can hook up one of my custom UITableViewCell classes properly. It usually has two UILabel objects, one on top of another, much like the standard subtitle class. I’d like these two labels to be centred in the cell, regardless of the cell’s height, with a given padding between the two.
I assume I can do this by doing something like add the heights of the two labels, add the padding, then subtract that from the height of the cell, and divide by two. However, I’m curious semantically whether this is correct, since I’d be constraining them from the top and bottom of the cell, rather than from each other. Am I missing a trick here?
Secondly, there’s sometimes a third label stacked in there too, so three on top of one another. In that instance, I’d need two sets of the padding, etc., but the question becomes even more relevant: shouldn’t I be constraining them to each other, rather than to the top and bottom of the cell?
So, question is more of a semantic one: if I want to constrain multiple elements vertically inside a parent view, is there a smarter way to do this than the method I suggested above?
(I’m currently implementing AutoLayout entirely in code (using Masonry) since this cell in question has no XIB and isn’t in a Storyboard).
The correct approach is to use a container view, which derives its height from its subviews. The container view is then pinned to the centre of the cell - you wouldn't have any constraints linking the container to the top and bottom edges of the cell.
Within the container, the vertical constraints would be |[label1]-[label2]|, which would make the container the height of the two labels plus the space, and the centre of the container view would be between the two labels.
If you added three labels, it would be |[label1]-[label2]-[label3]| and the centre of the container would be in the centre of the middle label.
In each case the centre of the container would be at the centre of the cell, and you don't need to calculate anything.
Using Interface Builder, I'm able to vertically center multiple UIViews using the following steps. My use case is that I want these multiple UIViews to behave like a group as much as possible but I don't want to introduce any further views in order to achieve that.
Firstly, I select what I consider to be my default Form Factor using the button along the bottom (Form Factor being 3.5 inch or 4 inch retina). Then, I position the buttons in the center of the view by dragging one at a time, and I use the auto-snapping with blue guidelines to help with this.
Once the buttons are in place, I select them one at a time to apply their constraints. Click on a button, then select the Align Constraints menu from the floating buttons at the bottom right in Interface Builder (I see a set of 4, and the Align is the one on the left, next to the Form Factor button).
In this menu, check the Vertical Center In Container checkbox, then click to open the dropdown menu next to the value, which is probably 0. From that list, choose Use Current Canvas Value. Then, hit the Add Constraints button (possibly labelled Add 1 Constraint).
As you do this, you'll probably know it's working if you see the values next to Vertical Center In Container becoming set to Y-offset values you might guess are correct by glancing back to your arrangement of UIViews.
Apologies if you don't want to use Interface Builder, but I had trouble achieving this myself and wanted to mention these steps. You could always use IB as a one-off, and programmatically log out the constraints in a test, then take them and apply in your code-only solution.
Assuming you have label1, label2, label3, and cell
// Center the labels
[NSLayoutConstraint constraintWithItem:label1 attribute:NSLayoutAttributeCenterX relatedBy:NSLayoutRelationEqual
toItem:cell.contentView attribute:NSLayoutAttributeCenterX
multiplier:1.0 constant:0]
[NSLayoutConstraint constraintWithItem:label2 attribute:NSLayoutAttributeCenterX relatedBy:NSLayoutRelationEqual
toItem:cell.contentView attribute:NSLayoutAttributeCenterX
multiplier:1.0 constant:0]
[NSLayoutConstraint constraintWithItem:label3 attribute:NSLayoutAttributeCenterX relatedBy:NSLayoutRelationEqual
toItem:cell.contentView attribute:NSLayoutAttributeCenterX
multiplier:1.0 constant:0]
// Vertical alignment/spacing of 8 between each label
[NSLayoutConstraint constraintWithItem:label1 attribute:NSLayoutAttributeTop relatedBy:NSLayoutRelationEqual
toItem:cell.contentView attribute:NSLayoutAttributeTop
multiplier:1.0 constant:0]
[NSLayoutConstraint constraintWithItem:label2 attribute:NSLayoutAttributeTop relatedBy:NSLayoutRelationEqual
toItem:label1 attribute:NSLayoutAttributeBottom
multiplier:1.0 constant:8]
[NSLayoutConstraint constraintWithItem:label3 attribute:NSLayoutAttributeTop relatedBy:NSLayoutRelationEqual
toItem:label2 attribute:NSLayoutAttributeBottom
multiplier:1.0 constant:8]
You can nest everything inside a for() loop I guess so you won't have to repeat the constraints
No code. Just edit in the storyboard.
I just read few information about how to manipulates constraints number programatically, but I think I need to see it visually using Xcode. So I decided to put a UIView like this and see what's going on with Constraints :
automatically it will create 4 constraints :
after modifying the number, I got what's the meaning of all this. there we have 2 vertical space and 2 horizontal space. but let's focus on vertical first...
one of vertical space measured from top of the screen (superview, I guess), I give this number 30. and other vertical space measured from the bottom, I give -50.
now, when it turns into code, I really don't understand how to give this 2 numbers. as far as I know, here's how to set constraint with code :
NSLayoutConstraint *myConstraint =[NSLayoutConstraint
constraintWithItem:_screenView
attribute:NSLayoutAttributeHeight
relatedBy:NSLayoutRelationEqual
toItem:_container
attribute:NSLayoutAttributeHeight
multiplier:20
constant:200];
[_screenView addConstraint: myConstraint];
let's assume _screenView is a superview and _container is UIView placed on top of it. I have 3 questions :
How to set both vertical space (30 and -50) manually with code? because from storyboard I don't see any different name or ID of vertical space. they both have same name. do I have to create 2 NSLayoutConstraint ?
Then how to add it into _screenView? do I have to create this : [_screenView addConstraint: myConstraint]; twice?
what multiplier used for? because I don't see that option in storyboard.
thank you very much.
I think it's important to think of this formula from Apple's Auto Layout Guide when working with constraints:
y = m*x + b, where:
y and x are attributes of views.
m and b are floating point values.
You can think the constraint for the top of _container like this:
_containter.top = m*_screenView.top + b
When you are creating a constraint using NSLayoutConstraint constraintWithItem:... the multiplier argument is "m" and constant is "b" in this formula. To create a constraint that keeps the top of _container 30 points below the top of _screenView you would do this:
NSLayoutConstraint *myConstraint =[NSLayoutConstraint
constraintWithItem:_container
attribute:NSLayoutAttributeTop
relatedBy:NSLayoutRelationEqual
toItem:_screenView
attribute:NSLayoutAttributeTop
multiplier:1.0
constant:30.0];
The bottom constraint would be:
NSLayoutConstraint *myConstraint =[NSLayoutConstraint
constraintWithItem:_container
attribute:NSLayoutAttributeBottom
relatedBy:NSLayoutRelationEqual
toItem:_screenView
attribute:NSLayoutAttributeBottom
multiplier:1.0
constant:-50.0];
Also keep in mind that in the UIKit coordinate system X values go up from left to right and Y values go up from top to bottom. In other words, 0,0 is at the top-left of screen and the values go up from there.
If you want to create the four contraints you show above you will have to create them all individually. You could also use the constraintsWithVisualFormat:options:metrics:views: method of NSLayoutConstraint to make multiple at once. I find it more clear to write them out the way I did above.
I'd like to map dots along a line.
The line length depends on device and orientation and is always stretched across the whole screen. Therfore it would make most sense to me to position the dots using a relative percentage value.
So far I only found constraints being defined in some sort of point value (Doc)
Is it possible to use percentage values as constraints as well? Any ideas on how to position these dots in a scalable way ... or do I need do this conversion/positioning "manually"?
Yes, you can position the dot as a fraction of the view's width. The NSLayoutConstraint method, constraintWithItem:attribute:relatedBy:toItem:attribute:multiplier:constant:, has that multiplier parameter that lets you use a fractional relationship between a superview and its subview. The superview's right edge will be the width of that view (the screen if its a full width view), so if you create a constraint like below, the dot will be positioned at a fractional distance along the line:
-(void)viewDidLoad {
[super viewDidLoad];
[self.view removeConstraint:self.leftConDark];
[self.view removeConstraint:self.leftConLight];
NSLayoutConstraint *lcd = [NSLayoutConstraint constraintWithItem:self.darkButton
attribute:NSLayoutAttributeCenterX
relatedBy:NSLayoutRelationEqual
toItem:self.view
attribute:NSLayoutAttributeRight
multiplier:.5
constant:0];
NSLayoutConstraint *lcl = [NSLayoutConstraint constraintWithItem:self.lightButton
attribute:NSLayoutAttributeCenterX
relatedBy:NSLayoutRelationEqual
toItem:self.view
attribute:NSLayoutAttributeRight
multiplier:.9
constant:0];
[self.view addConstraints:#[lcd,lcl]];
}
In this example I'm positioning two UIButtons (info type dark and light). I added them in IB, and made IBOutlets to their constraints they have to the left side of the view (that's what the system gave me, it could have been to the right side -- it doesn't matter since you just delete them anyway. If you are making the dots in code, you wouldn't need to do this). In code I remove those constraints, then add new ones that will put the center of the buttons at 50% and 90% of the way across the screen.
I'm not an auto-layout expert (or even competent yet!) but as of XCode 6, you seem to be able to do this in IB.
Select the object.
Show the size inspector (click on ruler)
Double-click on the constraint rectangle (not obvious! "Edit" takes you somewhere else)
Here you can set the multiplier just like in the answer above.