I have subclassed a UITableViewCell which has a bunch of buttons and labels created in IB which all have outlets. What I'm trying to do is, depending on the content of the cell, a UIButton needs to move slightly up, or remain in its place. I created an outlet for the constraint which needs to change so that I can change it in code.
Inside cellForRowAtIndexPath, I have the following:
[cell.usernameButton.superview removeConstraint:cell.usernameTopConstraint];
int topDistance;
// code to conditionally change topDistance for constraint is omitted here, results in either 5 or 15
cell.usernameTopConstraint = [NSLayoutConstraint constraintWithItem:cell.usernameButton
attribute:NSLayoutAttributeTop
relatedBy:NSLayoutRelationEqual
toItem:cell.usernameButton.superview
attribute:NSLayoutAttributeTop
multiplier:1
constant:topDistance];
[cell.usernameButton.superview addConstraint:cell.usernameTopConstraint];
[cell.usernameButton.superview layoutIfNeeded];
The problem is, the existing constraint must not get removed, because I get the error: "Unable to simultaneously satisfy constraints" - the two it shows me are the two that can get applied above.
Oddly, when I log cell.usernameButton.superview, it's null for every cell until a cell with the non-default topDistance which throws the constraint error. Then it's set for every cell drawn afterwords.
Why isn't the constraint getting removed? I've tried a bunch of different ways of referencing the button's superview, none of which seem to work.
Why don't you change the constant instead of removing and re-adding the constraint?
cell.usernameConstraint.constant = topDistance;
Related
I am having an UIImageView (say imageView1) and a UITextView(say textView1) which have to be displayed vertically (one [imageView1] below the other [textView1]) beginning with the same margin position as of textView1. I have to achieve this through autolayout programmatically.
I know that this can be done by setting the vertical constraints like below for both the views.
NSLayoutConstraint constraintsWithVisualFormat:#"V:|[textView1]"
But the problem I have here is I already have many text views(textView2, textView3) arranged in horizontal before and after this textView1.
I have already added many autolayout constraints to this textView1 through storyboard. Based on the different screen size and orientation the textView1 margin differs as per the constraints that are provided on the storyboard for this.
Now how can I provide the autolayout constraint programmatically in such a way that my imageView1 is to align in par vertically with the same margin as that of textView1?
p.s: imageView1 is created programmatically in code but where as all other views that I mentioned above are created through storyboard.
+ Adding images for easy understanding
In the image, imageView1 is the UI Image. I have created it in storyboard just for understanding purpose but in real it will be created programmatically and this have to be aligned to the margin of UITextView (textView1) present below it.
This is the constraint that I want to create it through programmatically(In case this is the real question here :).
This constraint is to always make sure that imageView1 and textView1 start originating from the same margin.
How to define this constraint programmatically ?
Rather than using the visual format, you can just instantiate a constraint directly, e.g.
[NSLayoutConstraint
constraintWithItem:imageView1 attribute:NSLayoutAttributeLeading
relatedBy:NSLayoutRelationEqual
toItem:textView1 attribute:NSLayoutAttributeLeading
multiplier:1.0 constant:0.0]
Use Masonry for setting constraints programmatically.It is very easy to use and reduce lots of complexities for the user.
https://github.com/SnapKit/Masonry
...you can try to build an UIView, set the constraints that it will need, and use it as a placeholder for your UIImageViews.(later you can add them inside of such a view) or, by the otherside, using an UICollectionView instead.
You can set the options argument in
constraintsWithVisualFormat:options:metrics:views: check Apple Class Reference.
Your code might be as follows
NSString* leadingConstraintsExpression = #"V:[imageView1][textView1]";
NSDictionary* viewsDictionary = NSDictionaryOfVariableBindings(imageView1,textView1);
NSArray* leadingConstraints = [NSLayoutConstraint
constraintsWithVisualFormat:leadingConstraintsExpression
options:NSLayoutFormatAlignAllLeading
metrics:nil
views:viewsDictionary];
[self.view addConstraints:leadingConstraints];
I'm trying to force myself to start using AutoLayout everywhere. I have a scenario that is extremely simple using frames but I can't make it work using Autolayout.
I have a StoryBoard I can't touch because it belongs to a library. When the ViewController related to the storyboard loads I want to programmatically add a View. So I created a UIView in the viewDidLoad, added the constraints for height and width and also two other constraints to position them. Everything worked fine BUT the width, I want to have the same width as an other view. How should I do this?
I logged the size of the "other view" in the viewDidLoad and the size is not right, I also logged the self.view.frame.size.width, and is not correct either.
I read that the correct sizes are not set until viewDidLayoutSubviews, so I tried to add my code there but I get in a loop of calls to viewDidLayoutSubviews that never ends. What am I doing wrong?
Try putting the code in viewDidAppear. Check if the subview is already a descendent of the view and if no, then add the subview with the constraints.
If you want two views to have the same width, you should do that with
constraintWithItem:attribute:relatedBy:toItem:attribute:multiplier:constant:. You can do this in viewDidLoad.
NSLayoutConstraint *widthCon = [NSLayoutConstraint constraintWithItem:view1 attribute:NSLayoutAttributeWidth relatedBy: NSLayoutRelationEqual toItem:view2 attribute:NSLayoutAttributeWidth multiplier:1 constant:0];
This assumes that the view that comes from the library storyboard was made using constraints.
You can surely use this method of UIViewController's,
- (void)updateViewConstraints
{
[super updateViewConstraints] ;
// now update your subviews contraints or log your view sizes
}
As you are using constraint based layout and wants to update the subviews constraints depending to UIViewController's constraints then you should always use the following method.
I'm experimenting with how to use UIScrollView. After much trouble, I finally got the hang of it. But now I've seem to hit another snag.
In this simple app, I have a scroll view with and in order for it to work, I have to set the view's bottom space to scrollview constraint to 0 as described here and it works fine. I'm doing it through the IB.
Now I've come across a scenario where I have to do that part programmatically. I've added the below code in the viewDidLoad method.
NSLayoutConstraint *bottomSpaceConstraint = [NSLayoutConstraint constraintWithItem:self.view
attribute:NSLayoutAttributeBottom
relatedBy:NSLayoutRelationEqual
toItem:self.scrollView
attribute:NSLayoutAttributeBottom
multiplier:1.0
constant:0.0];
[self.view addConstraint:bottomSpaceConstraint];
But it doesn't seem to work. It outputs the following message in the console window adn i don't know what to make of it.
Unable to simultaneously satisfy constraints.
Probably at least one of the constraints in the following list is one you don't want. Try this: (1) look at each constraint and try to figure out which you don't expect; (2) find the code that added the unwanted constraint or constraints and fix it. (Note: If you're seeing NSAutoresizingMaskLayoutConstraints that you don't understand, refer to the documentation for the UIView property translatesAutoresizingMaskIntoConstraints)
(
"",
""
)
Can someone please tell me how to do this? I've also attached a demo project here so that you can get a better idea on the issue.
UPDATE:
First off thanks for the responses. Using the ways mentioned in the answers I was able to get it working. However ina slightly different scenario its not. Now I'm trying to load a view onto a viewcontroller programatically.
If I may explain further. There are 2 view controllers. First one being a UITableViewController and the second one a UIViewController. Inside that a UIScrollView. Also There are multiple UIViews and some of those views' height exceeds the normal height of the screen.
The UITableViewController displays a list of options. Based on the user's selection, a particular UIView out of the lot will be loaded into the UIViewController with the UIScrollView.
In this scenario, the above method doesn't work. The scrolling isn't happening. Do I have to do something different since I'm loading the view separately?
I've uploaded a demo project here so that you can see it in action. Please see the Email.xib and select Email from the table view list.
Based upon a review of your code, a few comments:
You generally don't need to adjust constraints when a view appears. If you find yourself doing this, it often means that you haven't configured your storyboard correctly (or at least, not efficiently). The only time you really need to set/create constraints is either (a) you're adding views programmatically (which I'm suggesting is more work than it's worth); or (b) you need to do some runtime adjustment of constraints (see third bullet under point 3, below).
I don't mean to belabor it, but your project had a bunch of redundant code. E.g.
You were setting the frame for the scroll view, but that is governed by constraints, so that does nothing (i.e. when the constraints are applied, any manually set frame settings will be replaced). In general, in auto layout, don't try changing frame directly: Edit the constraints. But, no changing of constraints is needed at all anyway, so the point is moot.
You were setting the content size for the scroll view, but in auto layout, that, too, is governed by constraints (of the subviews), so that was unnecessary.
You were setting constraints for the scrollview (which were already zero), but then you weren't adding the view from the NIB into the scrollview, defeating any intent there, too. The original question was how to change the bottom constraint of the scroll view. But the bottom constraint for that is already zero, so I see no reason to set it to zero again.
I'd suggest a more radical simplification of your project:
You're making life much harder on yourself by storing your views in NIBs. It's much easier if you stay within the the storyboard world. We can help you do the NIB stuff if you really need to, but why make life so hard on yourself?
Use cell prototypes to facilitate the design of the cells in your table. You can also define the segues to go from the cells to the next scene. This eliminates any need to write any didSelectRowAtIndexPath or prepareForSegue code. Clearly, if you have something you need to pass to the next scene, by all means use prepareForSegue, but nothing you've presented thus far requires that, so I've commented it out in my examples.
Assuming you were looking for a practical example of programmatically changing constraints, I've set up the scene so that the text view will change its height programmatically, based upon the text in the text view. As always, rather than iterating through the constraints to find the one in question, when altering an existing constraint that IB created for me, I think it's far more efficient to set up an IBOutlet for the constraint, and edit the constant property for the constraint directly, so that's what I've done. So I set up the view controller to be the delegate of the text view, and wrote a textViewDidChange that updated the text view's height constraint:
#pragma mark - UITextViewDelegate
- (void)textViewDidChange:(UITextView *)textView
{
self.textViewHeightConstraint.constant = textView.contentSize.height;
[self.scrollView layoutIfNeeded];
}
Note, my text view has two height constraints, a mandatory minimum height constraint, and a medium priority constraint that I change above based upon the amount of text. The main point is that it illustrates a practical example of changing constraints programmatically. You shouldn't have to muck around with the scrollview's bottom constraint at all, but this is shows a real-world example of when you might want to adjust a constraint.
When you add a scrollview in IB, it will automatically get all the constraints you need. You probably don't want to be adding a constraint programmatically (at least not without removing the existing bottom constraint).
Two approaches might be simpler:
Create an IBOutlet for your existing bottom constraint, say scrollViewBottomConstraint. Then you can just do
self.scrollViewBottomConstraint.constant = 0.0;
Or create your view initially in IB where the bottom constraint is 0.0 and then you don't have to do anything programmatically at all. If you want to layout a long scrollview and it's subviews, select the controller, set it's simulated metrics from "inferred" to "free form". Then you can change the size of the view, set the scrollview's top and bottom constraints to be zero, layout everything you want inside the scroll view, and then when the view is presented at runtime, the view will be resized appropriately, and because you've defined the scrollview's top and bottom constraints to be 0.0, it will be resized properly. It looks a bit odd in IB, but it works like a charm when the app runs.
If you're determined to add a new constraint, you could either programmatically remove the old bottom constraint, or set the old bottom constraints' priority down as low as possible, and that way your new constraint (with higher priority) will take precedence, and the old, low-priority bottom constraint will gracefully not be applied.
But you definitely don't want to just add a new constraint.
It's possible to create outlets to represent layout constraints in your view controller. Just select the constraint you want in interface builder (e.g. via "select and edit" on the measurements pane of the view you are arranging). Then go to the outlets pane and drag a "New Referencing Outlet" to your code file (.h or .m). This will bind the constraint to an NSLayoutConstraint instance that you can access from your controller and adjust dynamically on the fly (generally via the constant property, which is poorly named because it's not a constant at all).
(Note that in XCode 6 you can double-click the constraint to select it for editing.)
Be careful when adjusting the layout in interface builder, however, as you may end up deleting the constraint and have to re-bind it to the outlet.
Looking at the console information, i feel that you are creating ambiguity when you add two same type of constraint.
So instead of creating and adding new constraint, try updating the previous constraint that is already in the constraints array.
for(NSLayoutConstraint *constraint in self.view.constraints)
{
if(constraint.firstAttribute == NSLayoutAttributeBottom && constraint.secondAttribute == NSLayoutAttributeBottom &&
constraint.firstItem == self.view && constraint.secondItem == self.scrollView)
{
constraint.constant = 0.0;
}
}
Hope this helps
Even Rob's answer will work!
You can use https://github.com/SnapKit/Masonry for adding constraints programmatically.
It is power of AutoLayout NSLayoutConstraints with a simplified, chainable and expressive syntax. Supports iOS and OSX Auto Layout.
UIView *superview = self.view;
UIView *view1 = [[UIView alloc] init];
view1.translatesAutoresizingMaskIntoConstraints = NO;
view1.backgroundColor = [UIColor greenColor];
[superview addSubview:view1];
UIEdgeInsets padding = UIEdgeInsetsMake(10, 10, 10, 10);
[superview addConstraints:#[
//view1 constraints
[NSLayoutConstraint constraintWithItem:view1
attribute:NSLayoutAttributeTop
relatedBy:NSLayoutRelationEqual
toItem:superview
attribute:NSLayoutAttributeTop
multiplier:1.0
constant:padding.top],
[NSLayoutConstraint constraintWithItem:view1
attribute:NSLayoutAttributeLeft
relatedBy:NSLayoutRelationEqual
toItem:superview
attribute:NSLayoutAttributeLeft
multiplier:1.0
constant:padding.left],
[NSLayoutConstraint constraintWithItem:view1
attribute:NSLayoutAttributeBottom
relatedBy:NSLayoutRelationEqual
toItem:superview
attribute:NSLayoutAttributeBottom
multiplier:1.0
constant:-padding.bottom],
[NSLayoutConstraint constraintWithItem:view1
attribute:NSLayoutAttributeRight
relatedBy:NSLayoutRelationEqual
toItem:superview
attribute:NSLayoutAttributeRight
multiplier:1
constant:-padding.right],]];
in just few lines
Heres the same constraints created using MASConstraintMaker
UIEdgeInsets padding = UIEdgeInsetsMake(10, 10, 10, 10);
[view1 mas_makeConstraints:^(MASConstraintMaker *make) {
make.top.equalTo(superview.mas_top).with.offset(padding.top); //with is an optional semantic filler
make.left.equalTo(superview.mas_left).with.offset(padding.left);
make.bottom.equalTo(superview.mas_bottom).with.offset(-padding.bottom);
make.right.equalTo(superview.mas_right).with.offset(-padding.right);
}];
Or even shorter
[view1 mas_makeConstraints:^(MASConstraintMaker *make) {
make.edges.equalTo(superview).with.insets(padding);
}];
do your best is sort ;)
I can't find a way to create a 'square' constraint, meaning 'width equals height' in Interface Builder. I guess it's possible to add such constraint programmatically. Is there something I can do in IB? Maybe I just don't see it? It seems trivial, yet I can't find it.
Update Xcode 5.1b5
Ctrl+click and drag from a view and release while the pointer is over the view. Select "Aspect Ratio". It will create a constraint where the first and second item is the view.
Before Xcode 5.1
You can't because the width/height editor lacks the fields to relate to another property or set the ratio:
Therefore, you can't express the following code in Interface Builder:
CGFloat ratio = 1.0;
NSLayoutConstraint *constraint = [NSLayoutConstraint
constraintWithItem:myView
attribute:NSLayoutAttributeWidth
relatedBy:NSLayoutRelationEqual
toItem:myView
attribute:NSLayoutAttributeHeight
multiplier:ratio
constant:0];
constraint.priority = 1000;
[myView.superview addConstraint:constraint];
Please add a new constraint, aspect ratio to 1:1 on the UI element as in the image.
To start, control drag diagonally from the button to itself. A contextual menu will appear, where you can add width and height constraints. Shift+Click on each; a checkmark will appear indicating that you have added the constraint. (If you accidentally dismiss the dialog before adding both, that’s OK, just repeat the drag step and set the other one):
When first added, these constraints take on the current width and height of the button, so you’ll need to adjust each constraint to give it a more appropriate value. We’ll have to do this one at a time, although our image is square, so be sure to use the same constant value in both constraints to resize the button proportionally. Double-click on the constraint, and enter a smaller value in its constant field:
I'm playing around with AutoLayout and am really banging my head against the wall for what seems like it ought to be an extremely simple solution.
I've got a vertical column of controls: 1 label and 3 buttons.
I want the label to be 40 pixels(points) tall and auto-size its width based on the width of its superview (standard spacing on left, top and right).
I want the 3 buttons to line up vertically below that label.
I would like their widths to auto-size just like the label.
I would like their spacing to be standard (aqua?) spacing (8 points, right?).
I would like the 3 buttons to be the same height.
I can get what I want to happen to work, but I keep getting errors in the console at runtime, and I'd like to figure out WHY I'm getting them and HOW to avoid getting them. I've watched the WWDC videos on AutoLayout, and here's what I've tried so far:
UILabel *label = [self Label];
MMGlossyButton *button1 = ...
MMGlossyButton *button2 = ...
MMGlossyButton *button3 = ...
[[self view] addConstraints:
[NSLayoutConstraint constraintsWithVisualFormat:#"H:|-[label]-|"
options:0
metrics:nil
views:NSDictionaryOfVariableBindings(label)]];
[[self view] addConstraints:
[NSLayoutConstraint constraintsWithVisualFormat:#"H:|-[button1]-|"
options:0
metrics:nil
views:NSDictionaryOfVariableBindings(new)]];
[[self view] addConstraints:
[NSLayoutConstraint constraintsWithVisualFormat:#"H:|-[button2]-|"
options:0
metrics:nil
views:NSDictionaryOfVariableBindings(existing)]];
[[self view] addConstraints:
[NSLayoutConstraint constraintsWithVisualFormat:#"H:|-[button3]-|"
options:0
metrics:nil
views:NSDictionaryOfVariableBindings(provider)]];
[[self view] addConstraints:
[NSLayoutConstraint constraintsWithVisualFormat:#"V:|-[label(40)]-[button1(>=25)]-[button2(==button1)]-[button3(==button1)]-|"
options:0
metrics:nil
views:NSDictionaryOfVariableBindings(label, button1, button2, button3)]];
So, this works for displaying the view in a dynamically-sized way, but the following error pops up in the console:
Unable to simultaneously satisfy constraints.
Probably at least one of the constraints in the following list is one you don't want.
Try this:
(1) look at each constraint and try to figure out which you don't expect;
(2) find the code that added the unwanted constraint or constraints and fix it.
(Note: If you're seeing NSAutoresizingMaskLayoutConstraints that you
don't understand, refer to the documentation for the UIView
property translatesAutoresizingMaskIntoConstraints)
// A whole bunch of constraint stuff that doesn't appear to be important...
Will attempt to recover by breaking constraint
<NSLayoutConstraint:0x7554c40 V:[MMGlossyButton:0x7554b40(99)]>
So, the last bit appears to indicate that the first button I have on the view is statically sized to 99 points tall.
Which is the size it has on the view.
Which is completely arbitrary.
Which I don't want assigned, but can't figure out a way to un-assign it.
Although I'm getting what I want (sort of, eventually), it seems to be a REALLY roundabout way to accomplish something that's pretty simple. Am I missing something basic about AutoLayout, or does its power require such complexity?
You are encountering errors because you are mixing and matching constraints generated in code with constraints added by interface builder. Interface builder doesn't let you generate an ambiguous layout, so almost by definition if you add additional constraints, you will get an "Unable to simultaneously satisfy" error, which is the downfall of many a marriage.
To resolve this you either need to define all the constraints you need in interface builder, or you need to mark specific ones as outlets and remove them in code before adding your own.
In your case, the constraints are simple enough to create in IB.
You can pin to a specific height by using this button in IB while your label is selected:
The one in the middle, that looks like a girder. This gives you the following useful menu:
Choosing one of these allows you to create a new constraint against the label, which you can then edit by selecting it:
You can then add your buttons, select all three of them and, using the same menu, create an equal heights constraint.
The constraints created in IB aren't particularly flexible, so if you do decide you need to create or modify them in code, it is best to create outlets to the particular constraints, and then either remove and re-create them, or modify the constant value at run time.