ios – 如何以编程方式更改或更新NSLayoutConstraint

2020年01月16日作者：佚名

我已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,但每次这个ViewController收到一个Notification,它都会运行：

[self.view layoutIfNeeded];

但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.

解决方法

我认为你有两个选择.

选项1
保留财产

@property (strong,nonatomic)NSLayoutConstraint *constraintToAnimate3;

然后使用此属性

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];

当你想改变

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"

然后搜索以获得约束

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

然后更改常量,如Option1所示

更新：
如果在我发布的代码中使用常量

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

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