如何以编程方式更改或更新 NSLayoutConstraint

Question

我已经使用代码以编程方式实现了 AutoLayout：

- (void)addConstraintWithListNavigationViewController:(UIView *)listViewNavigation y:(CGFloat)y height:(CGFloat)height
{
    //WIDTH_ListTableView = 0.4

    //set x = 0;
    NSLayoutConstraint *constraintToAnimate1 = [NSLayoutConstraint constraintWithItem:listViewNavigation
                                                                            attribute:NSLayoutAttributeLeft
                                                                            relatedBy:NSLayoutRelationEqual
                                                                               toItem:self.view
                                                                            attribute:NSLayoutAttributeLeft
                                                                           multiplier:0.00
                                                                             constant:0];
    [self.view addConstraint:constraintToAnimate1];


    //set y = y;
    NSLayoutConstraint *constraintToAnimate2 = [NSLayoutConstraint constraintWithItem:listViewNavigation
                                                                            attribute:NSLayoutAttributeTop
                                                                            relatedBy:NSLayoutRelationEqual
                                                                               toItem:self.view
                                                                            attribute:NSLayoutAttributeBottom
                                                                           multiplier:0.00
                                                                             constant:y];
    [self.view addConstraint:constraintToAnimate2];








    //set Width = self.view.frame.size.width*0.4
    NSLayoutConstraint *constraintToAnimate3 = [NSLayoutConstraint constraintWithItem:listViewNavigation
                                                                            attribute:NSLayoutAttributeWidth
                                                                            relatedBy:NSLayoutRelationEqual
                                                                               toItem:self.view
                                                                            attribute:NSLayoutAttributeWidth
                                                                           multiplier:1-WIDTH_ListTableView
                                                                             constant:0.0];
    [self.view addConstraint:constraintToAnimate3];





    //Set height = height
    NSLayoutConstraint *constraintToAnimate4 = [NSLayoutConstraint constraintWithItem:listViewNavigation
                                                                            attribute:NSLayoutAttributeHeight
                                                                            relatedBy:NSLayoutRelationEqual
                                                                               toItem:nil
                                                                            attribute:NSLayoutAttributeNotAnAttribute
                                                                           multiplier:0.00
                                                                             constant:height];
    [self.view addConstraint:constraintToAnimate4];
}

这很完美，但是每次 ViewController 收到 Notification 时，它都会运行:

[self.view layoutIfNeeded];

但是我想根据连接的布尔变量设置listViewNavigation的宽度。

if(connected){
        listViewNavigation.view.frame.size.width = 0.4 * self.view.frame.size.width;
    }
    else{
        listViewNavigation.view.frame.size.width = 0.6 * self.view.frame.size.width;
    }

但我不知道如何更新 NSLayoutConstraint :

NSLayoutConstraint *constraintToAnimate3 = [NSLayoutConstraint constraintWithItem:PreView
                                                                            attribute:NSLayoutAttributeWidth
                                                                            relatedBy:NSLayoutRelationEqual
                                                                               toItem:self.view
                                                                            attribute:NSLayoutAttributeWidth
                                                                           multiplier:1 - WIDTH_ListTableView
                                                                             constant:0.0];
[self.view addConstraint:constraintToAnimate3];

当此 ViewController 收到 通知时 。

Answer 1

好的，我知道了。

[self.view removeConstraint:self.constraintOld];
[self.view addConstraint:self.constraintNew];

[UIView animateWithDuration:time animations:^{
    [self.view layoutIfNeeded];
}];

Answer 2

我想你有两个选择。

选项 1 保留一个属性

@property (strong,nonatomic)NSLayoutConstraint *constraintToAnimate3;

然后用这个属性到

self.constraintToAnimate3 = [NSLayoutConstraint constraintWithItem:PreView
                                                                        attribute:NSLayoutAttributeWidth
                                                                        relatedBy:NSLayoutRelationEqual
                                                                           toItem:self.view
                                                                        attribute:NSLayoutAttributeWidth
                                                                       multiplier:1
                                                                         constant:-1 * 0.4 * self.view.frame.size.width];
[self.view addConstraint:self.constraintToAnimate3];

想换的时候

if(connected){
    self.constraintToAnimate3.constant = -1 *0.6 * self.view.frame.size.width;
}
else{
    self.constraintToAnimate3.constant = -1 *0.4 * self.view.frame.size.width;
}
[UIView animateWithDuration:yourduration animations:^{
    [self.view layoutIfNeeded];
}];

选项 2 设置 constraintToAnimate3

的标识符

constraintToAnimate3.identifier = @"1234"

然后搜索得到约束

NSLayoutConstraint * constraint3 = nil;
NSArray * constraints = self.view.constraints;
for (NSLayoutConstraint * constraint in constraints) {
    if ([constraint.identifier isEqualToString:@"1234"]) {
        constraint3 = constraint;
        break;
    }
}

然后如Option1所示改变常量

更新： 如果在代码中使用常量 I post

PreView.frame.size.with = self.view.size.width * multiplier + constant

Answer 3

重要的是，您不仅要将约束添加到您的视图中，而且还要记住它们。

如果您只需要更改其常量，那么更改约束是最简单的 - 常量是约束中唯一可以稍后重复更改的部分。为此，您需要单独存储约束。

否则您需要删除旧约束并添加新约束。由于您通常有多个约束，因此存储包含可能需要替换的约束集的数组，然后更新整个数组。您还可以使用 activateConstraints 和 deactivateConstraints 方法。

如何以编程方式更改或更新 NSLayoutConstraint

How to change or update NSLayoutConstraint programmatically

objective-c

ios

nslayoutconstraint