我在视图控制器的根视图上有以下自动布局约束:
(lldb) po [superview constraints]
<__NSArrayM 0x9e65ba0>(
<NSLayoutConstraint:0x9e67d10 H:[HeaderView:0x9e6a1b0]-(0)-| (Names: '|':UIView:0x9e69040 )>,
<NSLayoutConstraint:0x9e67ce0 H:|-(0)-[HeaderView:0x9e6a1b0] (Names: '|':UIView:0x9e69040 )>,
<NSLayoutConstraint:0x9e67cb0 V:|-(0)-[HeaderView:0x9e6a1b0] (Names: '|':UIView:0x9e69040 )>,
<NSLayoutConstraint:0x9e67c80 H:|-(0)-[RadialGradientView:0x9e685c0] (Names: '|':UIView:0x9e69040 )>,
<NSLayoutConstraint:0x9e67c50 V:[RadialGradientView:0x9e685c0]-(0)-| (Names: '|':UIView:0x9e69040 )>,
<NSLayoutConstraint:0x9e67c20 H:[RadialGradientView:0x9e685c0]-(0)-| (Names: '|':UIView:0x9e69040 )>,
<NSLayoutConstraint:0x9e67bf0 V:[HeaderView:0x9e6a1b0]-(0)-[RadialGradientView:0x9e685c0]>,
<NSLayoutConstraint:0x10c89830 HeaderView:0x9e6a1b0.height == UIView:0x9e69040.height + 35>
)
当我添加高度约束(最后一个)时,我得到一个autolayout模糊布局错误:
2013-10-16 16:18:43.121 Application[26038:a0b] Unable to simultaneously satisfy constraints.
Probably at least one of the constraints in the following list is one you don't want. Try this: (1) look at each constraint and try to figure out which you don't expect; (2) find the code that added the unwanted constraint or constraints and fix it. (Note: If you're seeing NSAutoresizingMaskLayoutConstraints that you don't understand, refer to the documentation for the UIView property translatesAutoresizingMaskIntoConstraints)
(
"<NSLayoutConstraint:0xb016da0 V:|-(0)-[HeaderView:0xb0192a0] (Names: '|':UIView:0xb018130 )>",
"<NSLayoutConstraint:0xb016d40 V:[RadialGradientView:0xb0176b0]-(0)-| (Names: '|':UIView:0xb018130 )>",
"<NSLayoutConstraint:0xb016ce0 V:[HeaderView:0xb0192a0]-(0)-[RadialGradientView:0xb0176b0]>",
"<NSLayoutConstraint:0xb00c3f0 HeaderView:0xb0192a0.height == UIView:0xb018130.height + 35>"
)
Will attempt to recover by breaking constraint
<NSLayoutConstraint:0xb016ce0 V:[HeaderView:0xb0192a0]-(0)-[RadialGradientView:0xb0176b0]>
Break on objc_exception_throw to catch this in the debugger.
The methods in the UIConstraintBasedLayoutDebugging category on UIView listed in <UIKit/UIView.h> may also be helpful.
RadialGradientView是UIView的子类,它只覆盖drawRect:方法。 HeaderView也是UIView的子类,代码如下:
@implementation HeaderView
{
NSLayoutConstraint * heightConstraint;
}
static UINib * headerViewNib = nil;
- (id)awakeAfterUsingCoder:(NSCoder *)aDecoder
{
if (![[self subviews] count])
{
if (headerViewNib == nil)
headerViewNib = [UINib frameworkNibWithNibName: @"HeaderView"];
SMDFHeaderView * headerView = [[headerViewNib instantiateWithOwner: nil options: nil] lastObject];
[headerView setTranslatesAutoresizingMaskIntoConstraints: NO];
[self removeConstraints: [self constraints]];
return headerView;
}
return self;
}
- (void)layoutSubviews
{
if (!heightConstraint)
[self setNeedsUpdateConstraints];
[super layoutSubviews];
}
- (void)updateConstraints
{
if (!heightConstraint)
{
UIView * superview = [self superview];
heightConstraint = [NSLayoutConstraint constraintWithItem: self attribute: NSLayoutAttributeHeight relatedBy: NSLayoutRelationEqual toItem: superview attribute:NSLayoutAttributeHeight multiplier: 1.0 constant: 35.0];
[superview addConstraint: heightConstraint];
}
[super updateConstraints];
}
/* Tried that, but it does not change anything.
- (CGSize)intrinsicContentSize
{
return CGSizeMake([[super superview] frame].size.width, 35);
}*/
@end
PS:问题似乎与笔尖替换技巧无关,即使我评论了awakeAfterUsingCoder方法,它也会做同样的事情。
答案 0 :(得分:2)
你误解了这条线是如何工作的:
heightConstraint = [NSLayoutConstraint constraintWithItem: self attribute: NSLayoutAttributeHeight relatedBy: NSLayoutRelationEqual toItem: superview attribute:NSLayoutAttributeHeight multiplier: 1.0 constant: 35.0];
这样做会使self
等于superview
的高度,乘以1加上35.这意味着您要求子视图比超级视图高35点,并且另外,在其他地方,要求子视图适合超级视图。那不行。
要将视图限制到特定高度,您需要使用以下内容:
heightConstraint = [NSLayoutConstraint constraintWithItem: self attribute: NSLayoutAttributeHeight relatedBy: NSLayoutRelationEqual toItem: nil attribute:NSLayoutAttributenNotAnAttribute multiplier: 1.0 constant: 35.0];
这只是将视图限制在特定高度。