如何在Autolayout可视化格式语言中使用NSNumber或CGFloat常量？

Question

我正在尝试使用可视格式语言将顶部和底部填充设置为Autolayout中的视图.如果我将可视格式字符串中的填充写为整数,代码将编译并运行,但是当我尝试用常量替换它时它会失败.这是我得到的错误:

由于未捕获的异常'NSInvalidArgumentException'而终止应用程序,原因:'无法解析约束格式:无法设置等于视图宽度或高度的空间.也许您想使用视图作为间隔？[view1] [spacer(== view1)] [view2] V:| -kTopAndBottomPadding- [messageTextView] -kTopAndBottomPadding- |

这是我的代码.

CGFloat const SPMTVC_kTopAndBottomPadding = 5.0;
// ...

// Create my own NSDictionary of variable bindings.
NSDictionary *variableBindings = @{@"messageTextView" : _messageTextView,
    @"contentView" : self.contentView,
    @"kTopAndBottomPadding" : [NSNumber numberWithFloat:SPMTVC_kTopAndBottomPadding]};

// Constraints in the horizontal axis.
// Basically just pins the view to the left and right of superview.
NSMutableArray *constraints = [[NSLayoutConstraint
    constraintsWithVisualFormat:@"H:|-0-[messageTextView(==contentView)]-0-|"
    options:NSLayoutFormatAlignAllLeading
    metrics:nil
    views:variableBindings] mutableCopy];

// Constraints in vertical axis, give 5-point padding from superview's top & bottom.
[constraints addObjectsFromArray:[NSLayoutConstraint
    constraintsWithVisualFormat:@"V:|-kTopAndBottomPadding-[messageTextView]-kTopAndBottomPadding-|"
    options:NSLayoutFormatAlignAllTop
    metrics:nil
    views:variableBindings]];

for (NSLayoutConstraint *constraint in constraints) {
    [self.contentView addConstraint:constraint];
}

我认为错误消息意味着编译器认为kTopAndBottomPadding是a UIView,当它NSNumber是字典中定义的时候.有没有办法做到这一点？

Answer 1

这就是指标字典的用途.因此,例如,如果要在VFL字符串中使用"填充"作为常量,请执行以下操作:

[constraints addObjectsFromArray:[NSLayoutConstraint
    constraintsWithVisualFormat:@"V:|-padding-[messageTextView]-kTopAndBottomPadding-|"
    options:NSLayoutFormatAlignAllTop
    metrics:@{@"padding":@5}
    views:variableBindings]];