自动布局以编程方式修改约束的乘数

Question

如何以编程方式修改约束的乘数？我设置了以下内容:

[self.view addConstraint:[NSLayoutConstraint constraintWithItem:_button attribute:NSLayoutAttributeWidth relatedBy:NSLayoutRelationEqual toItem:self.view attribute:NSLayoutAttributeWidth multiplier:0.5 constant:0.0]];

我需要将其修改为:

[self.view addConstraint:[NSLayoutConstraint constraintWithItem:_button attribute:NSLayoutAttributeWidth relatedBy:NSLayoutRelationEqual toItem:self.view attribute:NSLayoutAttributeWidth multiplier:1.0 constant:0.0]];

Answer 1

您将无法更改乘数,因为它是只读的.您必须存储对约束的引用.然后,当您想要更改乘数时,您将删除约束并添加一个新约束.

您可以在视图控制器实现中包含这样的方法:

- (void)changeMultiplier:(NSLayoutConstraint **)constraint to:(CGFloat)newMultiplier{
    NSLayoutConstraint *newConstraint = [NSLayoutConstraint constraintWithItem:(*constraint).firstItem attribute:(*constraint).firstAttribute relatedBy:(*constraint).relation toItem:(*constraint).secondItem attribute:(*constraint).secondAttribute multiplier:newMultiplier constant:(*constraint).constant];
    [self.view removeConstraint:(*constraint)];
    [self.view addConstraint:newConstraint];
    *constraint = newConstraint;
}

相关问题:

我可以更改NSLayoutConstraint的乘数属性吗？