我现在很难理解为什么下面的单元测试在iPad2上失败了。自动布局似乎有点错位(0.5分)
view
在…内
superview
相对于两个布局约束所要求的精确居中。特别奇怪的是,关键的测试(但最后一个断言)在iPhone 5上通过,因此明显的舍入误差只影响一个(iOS 6)平台。这是怎么回事?
更新1
我修改了代码,以确保两个框架在宽度和高度方面都受到足够的约束,即使
translatesAutoresizingMaskIntoConstraints
是
NO
,作为一种可能相关的补救措施
here
然而,这显然并不能改变现状。
#import "BugTests.h"
@implementation BugTests
- (void)testCenteredLayout {
UIView *superview = [[UIView alloc] initWithFrame:CGRectMake(0, 0, 768, 88)];
superview.autoresizingMask = UIViewAutoresizingFlexibleTopMargin | UIViewAutoresizingFlexibleBottomMargin;
superview.translatesAutoresizingMaskIntoConstraints = YES;
UILabel *view = [[UILabel alloc] initWithFrame:CGRectMake(0, 0, 0, 0)];
view.text = @"Single Round against iPad.";
view.autoresizingMask = UIViewAutoresizingFlexibleTopMargin | UIViewAutoresizingFlexibleBottomMargin;
view.translatesAutoresizingMaskIntoConstraints = NO;
[view addConstraint:[NSLayoutConstraint constraintWithItem:view attribute:NSLayoutAttributeWidth relatedBy:NSLayoutRelationEqual toItem:nil attribute:NSLayoutAttributeNotAnAttribute multiplier:0.0 constant:206.0]];
[view addConstraint:[NSLayoutConstraint constraintWithItem:view attribute:NSLayoutAttributeHeight relatedBy:NSLayoutRelationEqual toItem:nil attribute:NSLayoutAttributeNotAnAttribute multiplier:0.0 constant: 21.0]];
[superview addSubview:view];
[superview addConstraint:[NSLayoutConstraint constraintWithItem:superview attribute:NSLayoutAttributeCenterX relatedBy:NSLayoutRelationEqual toItem:view attribute:NSLayoutAttributeCenterX multiplier:1.0 constant:0.0]];
[superview addConstraint:[NSLayoutConstraint constraintWithItem:superview attribute:NSLayoutAttributeCenterY relatedBy:NSLayoutRelationEqual toItem:view attribute:NSLayoutAttributeCenterY multiplier:1.0 constant:0.0]];
STAssertEquals(superview.center, CGPointMake(384, 44), nil); // succeeds
STAssertEquals(view.center, CGPointMake( 0, 0), nil); // succeeds
[superview setNeedsLayout];
[superview layoutIfNeeded];
STAssertTrue(!superview.hasAmbiguousLayout, nil);
STAssertEquals(superview.frame.size, CGSizeMake(768, 88), nil); // succeeds
STAssertEquals(view.frame.size, CGSizeMake(206, 21), nil); // succeeds
STAssertEquals(superview.center, CGPointMake(384, 44), nil); // succeeds
STAssertEquals(superview.center, view.center, nil); // fails: why?
STAssertEquals(view.center, CGPointMake(384, 44.5), nil); // succeeds: why?
}
@end
更新2
我在第二次单元测试中隔离了(显然)相同问题的另一个实例。这一次它涉及顶部(而不是中心)约束,而这一次分数点坐标似乎是触发因素。(该测试也在Retina之前的设备上成功,例如
y = 951
,即奇点坐标。)我检查了各种模拟器配置(在我的物理iPad 2和iPhone 5旁边),出现这种情况似乎确实与没有Ratina显示屏有关。(再次感谢@ArkadiuszHolko的领先。)
我目前从这些测试中得到的感觉是,如果需要在Retina之前的显示器上进行精确的点自动布局,就必须避免奇数高度和分数y坐标。但为什么?
- (void)testNonRetinaAutoLayoutProblem2 {
UIView *superview = [[UIView alloc] initWithFrame:CGRectMake(0, 0, 768, 1004)];
superview.autoresizingMask = UIViewAutoresizingFlexibleRightMargin | UIViewAutoresizingFlexibleBottomMargin;
superview.translatesAutoresizingMaskIntoConstraints = YES;
CGFloat y = 950.5; // see e.g. pageControlTopConstraint
UIView *view = [[UIView alloc] initWithFrame:CGRectMake(0, 0, 0, 0)];
view.translatesAutoresizingMaskIntoConstraints = NO;
[superview addConstraint:[NSLayoutConstraint constraintWithItem:view attribute:NSLayoutAttributeLeading relatedBy:NSLayoutRelationEqual toItem:superview attribute:NSLayoutAttributeLeading multiplier:1.0 constant:0.0]];
[superview addConstraint:[NSLayoutConstraint constraintWithItem:view attribute:NSLayoutAttributeTrailing relatedBy:NSLayoutRelationEqual toItem:superview attribute:NSLayoutAttributeTrailing multiplier:1.0 constant:0.0]];
[superview addConstraint:[NSLayoutConstraint constraintWithItem:view attribute:NSLayoutAttributeTop relatedBy:NSLayoutRelationEqual toItem:superview attribute:NSLayoutAttributeTop multiplier:1.0 constant:y]];
[superview addConstraint:[NSLayoutConstraint constraintWithItem:view attribute:NSLayoutAttributeHeight relatedBy:NSLayoutRelationEqual toItem:nil attribute:NSLayoutAttributeNotAnAttribute multiplier:0.0 constant:8]];
[superview addSubview:view];
[superview setNeedsLayout];
[superview layoutIfNeeded];
STAssertTrue(!superview.hasAmbiguousLayout, nil);
STAssertTrue(!view.hasAmbiguousLayout, nil);
STAssertEquals(superview.frame, CGRectMake(0, 0, 768, 1004), nil); // succeeds
STAssertEquals(view.frame, CGRectMake(0, y, 768, 8), nil); // fails: why?
STAssertEquals(view.frame, CGRectMake(0, y + 0.5, 768, 8), nil); // succeeds: why?
}