我可以更改 NSLayoutConstraint 的乘数属性吗? [英] Can I change multiplier property for NSLayoutConstraint?

问题描述

我在一个超级视图中创建了两个视图，然后在视图之间添加了约束:

I created two views in one superview, and then added constraints between views:

_indicatorConstrainWidth = [NSLayoutConstraint constraintWithItem:self.view1 attribute:NSLayoutAttributeWidth relatedBy:NSLayoutRelationEqual toItem:self.view2 attribute:NSLayoutAttributeWidth multiplier:1.0f constant:0.0f];
[_indicatorConstrainWidth setPriority:UILayoutPriorityDefaultLow];
_indicatorConstrainHeight = [NSLayoutConstraint constraintWithItem:self.view1 attribute:NSLayoutAttributeHeight relatedBy:NSLayoutRelationEqual toItem:self.view2 attribute:NSLayoutAttributeHeight multiplier:1.0f constant:0.0f];
[_indicatorConstrainHeight setPriority:UILayoutPriorityDefaultLow];
[self addConstraint:_indicatorConstrainWidth];
[self addConstraint:_indicatorConstrainHeight];

现在我想用动画更改 multiplier 属性，但我不知道如何更改 multiler 属性.(我在头文件 NSLayoutConstraint.h 的私有属性中发现了 _coefficient，但它是私有的.)

Now I want to change multiplier property with animation, but I can't figure out how to change the multipler property. (I found _coefficient in private property in header file NSLayoutConstraint.h, but it private.)

如何更改multipler 属性?

How do I change multipler property?

我的解决方法是删除旧约束并添加具有不同 multipler 值的新约束.

My workaround is to remove the old constraint and add the new one with a different value for multipler.

推荐答案

如果您只有两组需要应用的乘数，从 iOS8 开始，您可以添加两组约束和随时决定哪个应该处于活动状态:

If you have only have two sets of multipliers that need to be applied, from iOS8 onwards you can add both sets of constraints and decide which should be active at any time:

NSLayoutConstraint *standardConstraint, *zoomedConstraint;

// ...
// switch between constraints
standardConstraint.active = NO; // this line should always be the first line. because you have to deactivate one before activating the other one. or they will conflict.
zoomedConstraint.active = YES;
[self.view layoutIfNeeded]; // or using [UIView animate ...]

Swift 5.0 版本

var standardConstraint: NSLayoutConstraint!
var zoomedConstraint: NSLayoutConstraint!

// ...

// switch between constraints
standardConstraint.isActive = false // this line should always be the first line. because you have to deactivate one before activating the other one. or they will conflict.
zoomedConstraint.isActive = true
self.view.layoutIfNeeded() // or using UIView.animate

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