Gracefully hiding and showing views when using autolayout

Question

I thought there might be a way to easily hide and show a button in a row using auto layout so that views could be automatically arranged neatly depending on which are visible.

For example, say I have two buttons that I always want centered in a frame:

// pseudo visual format code:
|-----[star][download]-----|

When I press download I want now to see three buttons: (pause is the download button relabelled; cancel is a previously hidden button)

|--[star][cancel][pause ]--|

I thought I could perhaps have all three buttons always present but perhaps override the width to make the view gracefully animate between states? I thought there might be a more semantic way to achieve the adding and removing of views from the auto layout structure. Any thoughts?

I asked the similar question and got downvoted http://stackoverflow.com/questions/20876664/ios-autolayout-dynamically-adjust-controls/20876746?noredirect=1#comment31327381_20876746 :) — Abhishek, Jan 02 '14 at 12:00

score 0 · Answer 1 · edited May 23 '17 at 10:33

I've put together a small sample showing how this could be done using a custom UIView subclass. In the example below, I've used the AutoLayout framework from this answer and I'd recommend you do the same; it keeps the constraint code clean and legible.

The general approach is that you have to keep pointers to the key constraints that bind the trailing edge of the left-hand buttons to the leading edge of those to the right and then use those pointers to dynamically add/remove constraints. Generally, you don't want to do too much of that because performance will suffer, but a small amount in response to a user action is OK.

My view is declared thus:

@protocol TSDownloadViewDelegate;
@interface TSDownloadView : UIView
  @property (strong, nonatomic)          id<TSDownloadViewDelegate> delegate;
@end

@protocol TSDownloadViewDelegate <NSObject>
  - (void) downloadStartedInDownloadView:(TSDownloadView*)downloadView;
  - (void) downloadPausedInDownloadView:(TSDownloadView *)downloadView;
  - (void) downloadCancelledInDownloadView:(TSDownloadView*)downloadView;
@end

And implemented like this:

#import "UIView+AutoLayout.h"
#import "TSDownloadView.h"

static const CGFloat        kMargin                = 20.0;

@interface TSDownloadView ()

    // Our buttons
    @property (strong, nonatomic)          UIButton *   starButton;
    @property (strong, nonatomic)          UIButton *   cancelButton;
    @property (strong, nonatomic)          UIButton *   downloadButton;

    // State tracking
    @property (nonatomic)                  BOOL         downloading;
    @property (nonatomic)                  BOOL         constraintsUpdated;

    // The constraint governing what's tied to the right hand side of the starButton
    @property (weak, nonatomic)            NSLayoutConstraint *starRightConstraint;

    // The constraint governing what's tied to the left hand side of the downloadButton
    @property (weak, nonatomic)            NSLayoutConstraint *downloadLeftConstraint;

@end

@implementation TSDownloadView

- (void) initializator
{
    _starButton = [UIButton buttonWithType:UIButtonTypeSystem];
    _cancelButton = [UIButton buttonWithType:UIButtonTypeSystem];
    _downloadButton = [UIButton buttonWithType:UIButtonTypeSystem];

    _starButton.translatesAutoresizingMaskIntoConstraints = NO;
    _cancelButton.translatesAutoresizingMaskIntoConstraints = NO;
    _downloadButton.translatesAutoresizingMaskIntoConstraints = NO;

    _starButton.titleLabel.textAlignment = NSTextAlignmentCenter;
    _cancelButton.titleLabel.textAlignment = NSTextAlignmentCenter;
    _downloadButton.titleLabel.textAlignment = NSTextAlignmentCenter;

    [_starButton setTitle:@"Star" forState:UIControlStateNormal];
    [_cancelButton setTitle:@"Cancel" forState:UIControlStateNormal];
    [_downloadButton setTitle:@"Download" forState:UIControlStateNormal];

    [_downloadButton addTarget:self action:@selector(downloadClicked:) forControlEvents:UIControlEventTouchUpInside];

    [self addSubview:_starButton];
    [self addSubview:_cancelButton];
    [self addSubview:_downloadButton];

    _cancelButton.hidden = YES;

}

- (id)initWithFrame:(CGRect)frame
{
    self = [super initWithFrame:frame];
    if (self) {
        // Initialization code
        [self initializator];
    }
    return self;
}

- (id) initWithCoder:(NSCoder *)aDecoder
{
    self = [super initWithCoder:aDecoder];
    if( self )
    {
        [self initializator];
    }
    return self;
}


- (void)downloadClicked:(id)sender
{
    self.downloading = !self.downloading;
    if( self.downloading )
    {
        [self.downloadButton setTitle:@"Pause" forState:UIControlStateNormal];
        self.cancelButton.hidden = NO;

        // Remove previous constraints
        [self removeConstraint:self.starRightConstraint];
        [self removeConstraint:self.downloadLeftConstraint];

        // |--[star][cancel][pause ]--|
        self.starRightConstraint = [self.starButton autoPinEdge:ALEdgeRight toEdge:ALEdgeLeft ofView:self.cancelButton withOffset:-kMargin];
        self.downloadLeftConstraint = [self.downloadButton autoPinEdge:ALEdgeLeft toEdge:ALEdgeRight ofView:self.cancelButton withOffset:kMargin];

        // Tell delegate what's happened
        if( self.delegate )
            [self.delegate downloadStartedInDownloadView:self];
    }
    else
    {
        [self.downloadButton setTitle:@"Download" forState:UIControlStateNormal];
        self.cancelButton.hidden = YES;

        // Remove previous constraints
        [self removeConstraint:self.starRightConstraint];
        [self removeConstraint:self.downloadLeftConstraint];

        // |-----[star][download]-----|
        self.starRightConstraint = [self.starButton autoPinEdge:ALEdgeRight toEdge:ALEdgeLeft ofView:self.downloadButton withOffset:-kMargin];
        self.downloadLeftConstraint = nil;

        // Tell delegate what's happened
        if( self.delegate )
            [self.delegate downloadPausedInDownloadView:self];
    }

}

- (void) updateConstraints
{
    [super updateConstraints];
    if( self.constraintsUpdated ) return;
        self.constraintsUpdated = YES;

    // Now put our constraints in place

    // Make sure the button hugs the label and doesn't get stretched
    // just because there's space available
    [self.starButton setContentHuggingPriority:UILayoutPriorityRequired forAxis:UILayoutConstraintAxisHorizontal];

    // Pin the starButton to the top, left and bottom edges of its superview
    [self.starButton autoPinEdgeToSuperviewEdge:ALEdgeTop withInset:kMargin];
    [self.starButton autoPinEdgeToSuperviewEdge:ALEdgeLeft withInset:kMargin];
    [self.starButton autoPinEdgeToSuperviewEdge:ALEdgeBottom withInset:kMargin];

    // Repeat for the other buttons

    [self.cancelButton setContentHuggingPriority:UILayoutPriorityRequired forAxis:UILayoutConstraintAxisHorizontal];
    [self.cancelButton autoPinEdgeToSuperviewEdge:ALEdgeTop withInset:kMargin];
    [self.cancelButton autoPinEdgeToSuperviewEdge:ALEdgeBottom withInset:kMargin];

    [self.downloadButton setContentHuggingPriority:UILayoutPriorityRequired forAxis:UILayoutConstraintAxisHorizontal];
    [self.downloadButton autoPinEdgeToSuperviewEdge:ALEdgeTop withInset:kMargin];
    [self.downloadButton autoPinEdgeToSuperviewEdge:ALEdgeBottom withInset:kMargin];
    [self.downloadButton autoPinEdgeToSuperviewEdge:ALEdgeRight withInset:kMargin];


    // These two are special. We keep a reference to them so we can replace
    // them later. Note that since the cancelButton is hidden at the start,
    // the initial value for downloadLeftConstraint is simply nil.

    self.starRightConstraint = [self.starButton autoPinEdge:ALEdgeRight toEdge:ALEdgeLeft ofView:self.downloadButton withOffset:-kMargin];
    self.downloadLeftConstraint = nil;
}
@end

There's a lot more work to do to make the view really functional, but hopefully you can see the general approach to take.

score 0 · Answer 2 · answered Aug 11 '14 at 08:53

Design the (5) buttons one over the other using Autolayout.

//on ViewDidLoad: set cancel & pause button to hide

-(void) viewDidLoad
{
   [_pauseBtn setHidden:YES];
   [_cancelBtn setHidden:YES];
}

//on Downlaod action

-(IBAction) downloadClick (UIButton *) sender
{
    [_pauseBtn setHidden:NO];
    [_cancelBtn setHidden:NO];
    [sender setHidden:YES];
}

score -3 · Answer 3 · answered Mar 20 '13 at 08:59

-3

this can only be achieve handling constraints from code: http://www.techotopia.com/index.php/Implementing_iOS_6_Auto_Layout_Constraints_in_Code

answered Mar 20 '13 at 08:59

Vaibhav Saran

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1

Did you find any way to achieve this? I am also stucked on the same. – Akshay Shah Sep 01 '13 at 06:43

Gracefully hiding and showing views when using autolayout

3 Answers3