ios - 在父 View 上更新 NSLayoutConstraint

Question

如何更改/更新父 View 上的约束。

我使用 CodeBlock 的尝试:

//
//  CollectionViewController.m
//  FloatingButton
//

#import <QuartzCore/QuartzCore.h>
#import "CollectionViewController.h"
#import "MyCollectionViewCell.h"

#import "FloatingView.h"

#define CircleWidthAndHight 80

@interface CollectionViewController ()

@end

@implementation CollectionViewController{
    FloatingView *floatingView;
    CGRect rectOrigin;
    NSLayoutConstraint *hightConstraint;

}

static NSString * const reuseIdentifier = @"Cell";

- (void)viewDidLoad {
    [super viewDidLoad];

    self.collectionView.scrollEnabled = YES;

//    CGFloat hightOfFloatingView = self.collectionView.frame.size.height - (self.collectionView.frame.size.height - 100);
//    CGFloat yPositionOfFloatingView = self.collectionView.frame.size.height - (hightOfFloatingView + 10);


    floatingView = [[FloatingView alloc] initWithCircleSize:CircleWidthAndHight];
    floatingView.backgroundColor = [UIColor greenColor];
    __block id myself = self;
    floatingView.compare = ^{
        [myself showFloatingButtons];

    };

    [self.view addSubview:floatingView];
    [self.view bringSubviewToFront:floatingView];


    // Uncomment the following line to preserve selection between presentations
    // self.clearsSelectionOnViewWillAppear = NO;

    // Register cell classes
//    [self.collectionView registerClass:[MyCollectionViewCell class] forCellWithReuseIdentifier:reuseIdentifier];

    // Do any additional setup after loading the view.
}

- (void)createTabBar{

}

- (void)viewDidLayoutSubviews{
    [self setConstraints];
}

- (void) showFloatingButtons{

    hightConstraint.constant = 200;

    [self.view layoutIfNeeded];

//    [self.view removeConstraint:hightConstraint];
//
//    hightConstraint = [NSLayoutConstraint
//                       constraintWithItem:floatingView
//                       attribute:NSLayoutAttributeHeight
//                       relatedBy:NSLayoutRelationEqual
//                       toItem:nil
//                       attribute:NSLayoutAttributeNotAnAttribute
//                       multiplier:1.0
//                       constant:CircleWidthAndHight +200];
//    
//    
//    
//    [self.view addConstraint:hightConstraint];


}

- (void)setConstraints{

    floatingView.translatesAutoresizingMaskIntoConstraints = NO;

    [self.view addConstraint:[NSLayoutConstraint
                              constraintWithItem:floatingView
                              attribute:NSLayoutAttributeWidth
                              relatedBy:NSLayoutRelationEqual
                              toItem:self.view
                              attribute:NSLayoutAttributeWidth
                              multiplier:1.0
                              constant:CircleWidthAndHight]];

    hightConstraint = [NSLayoutConstraint
                              constraintWithItem:floatingView
                              attribute:NSLayoutAttributeHeight
                              relatedBy:NSLayoutRelationEqual
                              toItem:nil
                              attribute:NSLayoutAttributeNotAnAttribute
                              multiplier:1.0
                              constant:CircleWidthAndHight +20];



    [self.view addConstraint:hightConstraint];
//    floatingView.parentHightConstraint = hightConstraint;

    [self.view addConstraint:[NSLayoutConstraint constraintWithItem:self.view attribute:NSLayoutAttributeCenterX relatedBy:NSLayoutRelationEqual toItem:floatingView attribute:NSLayoutAttributeCenterX multiplier:1.0 constant:0]];

    NSLayoutConstraint *yConstraint = [NSLayoutConstraint constraintWithItem:self.view attribute:NSLayoutAttributeBottom relatedBy:NSLayoutRelationEqual toItem:floatingView attribute:NSLayoutAttributeBottom multiplier:1.0 constant:0];

    [self.view addConstraint:yConstraint];

//    floatingView.parentYConstraint = yConstraint;

    [floatingView setConstraints];
}



- (void)viewDidAppear:(BOOL)animated{
}

- (void)didReceiveMemoryWarning {
    [super didReceiveMemoryWarning];
    // Dispose of any resources that can be recreated.
}

/*
#pragma mark - Navigation

// In a storyboard-based application, you will often want to do a little preparation before navigation
- (void)prepareForSegue:(UIStoryboardSegue *)segue sender:(id)sender {
    // Get the new view controller using [segue destinationViewController].
    // Pass the selected object to the new view controller.
}
*/

#pragma mark <UICollectionViewDataSource>

- (NSInteger)numberOfSectionsInCollectionView:(UICollectionView *)collectionView {
    return 1;
}

- (NSInteger)collectionView:(UICollectionView *)collectionView numberOfItemsInSection:(NSInteger)section {
    return 10;
}

- (UICollectionViewCell *)collectionView:(UICollectionView *)collectionView cellForItemAtIndexPath:(NSIndexPath *)indexPath {
    MyCollectionViewCell *cell = (MyCollectionViewCell*)[collectionView dequeueReusableCellWithReuseIdentifier:reuseIdentifier forIndexPath:indexPath];


    cell.label.textColor = [UIColor blackColor];
    cell.label.text = @"Hello there!";

    cell.layer.borderWidth=1.0f;
    cell.layer.borderColor=[UIColor blueColor].CGColor;

    // Configure the cell

    return cell;
}

- (CGSize)collectionView:(UICollectionView *)collectionView layout:(UICollectionViewLayout*)collectionViewLayout sizeForItemAtIndexPath:(NSIndexPath *)indexPath {
    return CGSizeMake(self.collectionView.frame.size.width, 100);
}

#pragma mark ScrollView

- (void)scrollViewDidScroll:(UIScrollView *)scrollView{
//    CGRect collBounds = self.collectionView.bounds;
//    CGRect floatFrame = floatingView.frame;
//    floatingView.frame = CGRectMake(rectOrigin.origin.x,
//                                    rectOrigin.origin.y + collBounds.origin.y,
//                                    floatFrame.size.width,
//                                    floatFrame.size.height);
//    
//    [self.view bringSubviewToFront:floatingView];
}

#pragma mark <UICollectionViewDelegate>

/*
// Uncomment this method to specify if the specified item should be highlighted during tracking
- (BOOL)collectionView:(UICollectionView *)collectionView shouldHighlightItemAtIndexPath:(NSIndexPath *)indexPath {
    return YES;
}
*/

/*
// Uncomment this method to specify if the specified item should be selected
- (BOOL)collectionView:(UICollectionView *)collectionView shouldSelectItemAtIndexPath:(NSIndexPath *)indexPath {
    return YES;
}
*/

/*
// Uncomment these methods to specify if an action menu should be displayed for the specified item, and react to actions performed on the item
- (BOOL)collectionView:(UICollectionView *)collectionView shouldShowMenuForItemAtIndexPath:(NSIndexPath *)indexPath {
    return NO;
}

- (BOOL)collectionView:(UICollectionView *)collectionView canPerformAction:(SEL)action forItemAtIndexPath:(NSIndexPath *)indexPath withSender:(id)sender {
    return NO;
}

- (void)collectionView:(UICollectionView *)collectionView performAction:(SEL)action forItemAtIndexPath:(NSIndexPath *)indexPath withSender:(id)sender {

}
*/

@结束

这不起作用，并给出了一个:

Unable to simultaneously satisfy constraints.

我试过“layoutIfNeeded”和“setNeedsDisplay”和“needsUpdateConstraints”。而且没有效果？我在约束(hightConstrint)工作后立即更改它，但不是从 CodeBlock。

也试过这个:

hightConstraint.active = false;
hightConstraint.constant = 400;
hightConstraint.active = true;

终端记录如下:

2016-11-02 13:10:36.900317 FloatingButton[32486:1582882] [LayoutConstraints] 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. 
(
    "<NSLayoutConstraint:0x60800008ac30 FloatingView:0x7f98adc0a670.height == 100   (active)>",
    "<NSLayoutConstraint:0x600000087580 FloatingView:0x7f98adc0a670.height == 400   (active)>"
)

Will attempt to recover by breaking constraint 
<NSLayoutConstraint:0x600000087580 FloatingView:0x7f98adc0a670.height == 400   (active)>

Make a symbolic breakpoint at UIViewAlertForUnsatisfiableConstraints to catch this in the debugger.
The methods in the UIConstraintBasedLayoutDebugging category on UIView listed in <UIKit/UIView.h> may also be helpful.

Answer 1

当您更改约束的值(在您的情况下是常量)时，您必须在该约束适用的 super View 上调用 layoutIfNeeded 。

我假设 floatingView 是约束所附加的，在这种情况下，调用 [self.view layoutIfNeeded]。

虽然根据我在您的回答中看到的代码(也许我遗漏了一些东西)您还有 3 个问题:

1. 永远不要将 floatingView 添加到 View Controller 的 View 中。
2. 永远不要将约束添加到 floatingView。
3. 您有其他限制条件，这些限制条件与您对该限制条件所做的不一致。我建议检查所有约束的逻辑，如果需要，请将它们绘制在白板等物理表面上(总是对我有帮助)。