ios - 无法用代码获取到NSLayoutAttributeTrailing的值为什么？

Question

我在storyboard中使用了autolayout，因此不能通过更改frame的值来更改控件的位置，使用如下方法：

-(void)replaceView:(UIView *)view constrainWithConstant:(CGFloat)constant attribute:(NSLayoutAttribute)attribute{

for (NSLayoutConstraint *constraint in view.superview.constraints) {
    if (constraint.firstItem == view && constraint.firstAttribute == attribute) {
        constraint.constant = constant;
    }
}

}
可以获取到NSLayoutAttributeLeading以及NSLayoutAttributeTop的值，并在代码中更改。但是无法获取到NSLayoutAttributeTrailing的值，请问我该如何用代码获取到NSLayoutAttributeTrailing的值并加以更改呢？

Answer 1

If trailing is set up in the storyboard, you should be able to get it (notice that you only judged the firstAttribute, maybe it is a problem with the order of adding it during the connection? Check the second and try it), if it is not set, just add it, no need to replace