如何设置子视图控制器的topLayoutGuide位置
我正在实现一个自定义容器，它与UINavigationController非常相似，除了它不包含整个控制器堆栈。 它有一个UINavigationBar，它受限于容器控制器的topLayoutGuide，它恰好是顶部20px，这没问题。
当我添加一个子视图控制器并将其视图放入层次结构中时，我希望在IB中看到它的topLayoutGuide并用于布置子视图控制器的视图的子视图以显示在导航栏的底部。 在相关文件中记录了要做的事情：
该属性的值特别是查询此属性时返回的对象的length属性的值。 该值受视图控制器或其封闭容器视图控制器（如导航或选项卡栏控制器）的约束，如下所示：
否则指示视图控制器视图的顶部边缘。
但我不太了解如何“限制它的价值”，因为topLayoutGuide和它的长度属性都是只读的。
我试过这段代码来添加一个子视图控制器：
[self addChildViewController:gamePhaseController];
UIView *gamePhaseControllerView = gamePhaseController.view;
gamePhaseControllerView.translatesAutoresizingMaskIntoConstraints = NO;
[self.contentContainer addSubview:gamePhaseControllerView];
NSArray *horizontalConstraints = [NSLayoutConstraint constraintsWithVisualFormat:@"|-0-[gamePhaseControllerView]-0-|"
options:0
metrics:nil
views:NSDictionaryOfVariableBindings(gamePhaseControllerView)];
NSLayoutConstraint *topLayoutGuideConstraint = [NSLayoutConstraint constraintWithItem:gamePhaseController.topLayoutGuide
attribute:NSLayoutAttributeTop
relatedBy:NSLayoutRelationEqual
toItem:self.navigationBar
attribute:NSLayoutAttributeBottom
multiplier:1 constant:0];
NSLayoutConstraint *bottomLayoutGuideConstraint = [NSLayoutConstraint constraintWithItem:gamePhaseController.bottomLayoutGuide
attribute:NSLayoutAttributeBottom
relatedBy:NSLayoutRelationEqual
toItem:self.bottomLayoutGuide
attribute:NSLayoutAttributeTop
multiplier:1 constant:0];
[self.view addConstraint:topLayoutGuideConstraint];
[self.view addConstraint:bottomLayoutGuideConstraint];
[self.contentContainer addConstraints:horizontalConstraints];
[gamePhaseController didMoveToParentViewController:self];
_contentController = gamePhaseController;
在IB中，我为gamePhaseController指定了“Under Top Bars”和“Under Bottom Bars”。 其中一个视图特别限制为顶层布局指南，无论如何，它在设备上似乎距离容器导航栏底部20px ...
用这种行为实现自定义容器控制器的正确方法是什么？
据我几小时的调试后可以看出，布局指南是只读的，并且来自用于基于约束的布局的私有类。 覆盖访问器什么都不做（即使它们被调用），并且这只是令人讨厌的烦人。
（更新：现在可用作cocoapod，请参阅https://github.com/stefreak/TTLayoutSupport）
一个工作解决方案是删除苹果的布局约束和添加自己的约束。 我为此做了一个小类。
这里是代码 - 但我建议cocoapod。 它有单元测试，更有可能是最新的。
//
// UIViewController+TTLayoutSupport.h
//
// Created by Steffen on 17.09.14.
//
#import <UIKit/UIKit.h>
@interface UIViewController (TTLayoutSupport)
@property (assign, nonatomic) CGFloat tt_bottomLayoutGuideLength;
@property (assign, nonatomic) CGFloat tt_topLayoutGuideLength;
@end
-
#import "UIViewController+TTLayoutSupport.h"
#import "TTLayoutSupportConstraint.h"
#import <objc/runtime.h>
@interface UIViewController (TTLayoutSupportPrivate)
// recorded apple's `UILayoutSupportConstraint` objects for topLayoutGuide
@property (nonatomic, strong) NSArray *tt_recordedTopLayoutSupportConstraints;
// recorded apple's `UILayoutSupportConstraint` objects for bottomLayoutGuide
@property (nonatomic, strong) NSArray *tt_recordedBottomLayoutSupportConstraints;
// custom layout constraint that has been added to control the topLayoutGuide
@property (nonatomic, strong) TTLayoutSupportConstraint *tt_topConstraint;
// custom layout constraint that has been added to control the bottomLayoutGuide
@property (nonatomic, strong) TTLayoutSupportConstraint *tt_bottomConstraint;
// this is for NSNotificationCenter unsubscription (we can't override dealloc in a category)
@property (nonatomic, strong) id tt_observer;
@end
@implementation UIViewController (TTLayoutSupport)
- (CGFloat)tt_topLayoutGuideLength
{
return self.tt_topConstraint ? self.tt_topConstraint.constant : self.topLayoutGuide.length;
}
- (void)setTt_topLayoutGuideLength:(CGFloat)length
{
[self tt_ensureCustomTopConstraint];
self.tt_topConstraint.constant = length;
[self tt_updateInsets:YES];
}
- (CGFloat)tt_bottomLayoutGuideLength
{
return self.tt_bottomConstraint ? self.tt_bottomConstraint.constant : self.bottomLayoutGuide.length;
}
- (void)setTt_bottomLayoutGuideLength:(CGFloat)length
{
[self tt_ensureCustomBottomConstraint];
self.tt_bottomConstraint.constant = length;
[self tt_updateInsets:NO];
}
- (void)tt_ensureCustomTopConstraint
{
if (self.tt_topConstraint) {
// already created
return;
}
// recording does not work if view has never been accessed
__unused UIView *view = self.view;
// if topLayoutGuide has never been accessed it may not exist yet
__unused id<UILayoutSupport> topLayoutGuide = self.topLayoutGuide;
self.tt_recordedTopLayoutSupportConstraints = [self findLayoutSupportConstraintsFor:self.topLayoutGuide];
NSAssert(self.tt_recordedTopLayoutSupportConstraints.count, @"Failed to record topLayoutGuide constraints. Is the controller's view added to the view hierarchy?");
[self.view removeConstraints:self.tt_recordedTopLayoutSupportConstraints];
NSArray *constraints =
[TTLayoutSupportConstraint layoutSupportConstraintsWithView:self.view
topLayoutGuide:self.topLayoutGuide];
// todo: less hacky?
self.tt_topConstraint = [constraints firstObject];
[self.view addConstraints:constraints];
// this fixes a problem with iOS7.1 (GH issue #2), where the contentInset
// of a scrollView is overridden by the system after interface rotation
// this should be safe to do on iOS8 too, even if the problem does not exist there.
__weak typeof(self) weakSelf = self;
self.tt_observer = [[NSNotificationCenter defaultCenter] addObserverForName:UIDeviceOrientationDidChangeNotification
object:nil
queue:[NSOperationQueue mainQueue]
usingBlock:^(NSNotification *note) {
__strong typeof(self) self = weakSelf;
[self tt_updateInsets:NO];
}];
}
- (void)tt_ensureCustomBottomConstraint
{
if (self.tt_bottomConstraint) {
// already created
return;
}
// recording does not work if view has never been accessed
__unused UIView *view = self.view;
// if bottomLayoutGuide has never been accessed it may not exist yet
__unused id<UILayoutSupport> bottomLayoutGuide = self.bottomLayoutGuide;
self.tt_recordedBottomLayoutSupportConstraints = [self findLayoutSupportConstraintsFor:self.bottomLayoutGuide];
NSAssert(self.tt_recordedBottomLayoutSupportConstraints.count, @"Failed to record bottomLayoutGuide constraints. Is the controller's view added to the view hierarchy?");
[self.view removeConstraints:self.tt_recordedBottomLayoutSupportConstraints];
NSArray *constraints =
[TTLayoutSupportConstraint layoutSupportConstraintsWithView:self.view
bottomLayoutGuide:self.bottomLayoutGuide];
// todo: less hacky?
self.tt_bottomConstraint = [constraints firstObject];
[self.view addConstraints:constraints];
}
- (NSArray *)findLayoutSupportConstraintsFor:(id<UILayoutSupport>)layoutGuide
{
NSMutableArray *recordedLayoutConstraints = [[NSMutableArray alloc] init];
for (NSLayoutConstraint *constraint in self.view.constraints) {
// I think an equality check is the fastest check we can make here
// member check is to distinguish accidentally created constraints from _UILayoutSupportConstraints
if (constraint.firstItem == layoutGuide && ![constraint isMemberOfClass:[NSLayoutConstraint class]]) {
[recordedLayoutConstraints addObject:constraint];
}
}
return recordedLayoutConstraints;
}
- (void)tt_updateInsets:(BOOL)adjustsScrollPosition
{
// don't update scroll view insets if developer didn't want it
if (!self.automaticallyAdjustsScrollViewInsets) {
return;
}
UIScrollView *scrollView;
if ([self respondsToSelector:@selector(tableView)]) {
scrollView = ((UITableViewController *)self).tableView;
} else if ([self respondsToSelector:@selector(collectionView)]) {
scrollView = ((UICollectionViewController *)self).collectionView;
} else {
scrollView = (UIScrollView *)self.view;
}
if ([scrollView isKindOfClass:[UIScrollView class]]) {
CGPoint previousContentOffset = CGPointMake(scrollView.contentOffset.x, scrollView.contentOffset.y + scrollView.contentInset.top);
UIEdgeInsets insets = UIEdgeInsetsMake(self.tt_topLayoutGuideLength, 0, self.tt_bottomLayoutGuideLength, 0);
scrollView.contentInset = insets;
scrollView.scrollIndicatorInsets = insets;
if (adjustsScrollPosition && previousContentOffset.y == 0) {
scrollView.contentOffset = CGPointMake(previousContentOffset.x, -scrollView.contentInset.top);
}
}
}
@end
@implementation UIViewController (TTLayoutSupportPrivate)
- (NSLayoutConstraint *)tt_topConstraint
{
return objc_getAssociatedObject(self, @selector(tt_topConstraint));
}
- (void)setTt_topConstraint:(NSLayoutConstraint *)constraint
{
objc_setAssociatedObject(self, @selector(tt_topConstraint), constraint, OBJC_ASSOCIATION_RETAIN_NONATOMIC);
}
- (NSLayoutConstraint *)tt_bottomConstraint
{
return objc_getAssociatedObject(self, @selector(tt_bottomConstraint));
}
- (void)setTt_bottomConstraint:(NSLayoutConstraint *)constraint
{
objc_setAssociatedObject(self, @selector(tt_bottomConstraint), constraint, OBJC_ASSOCIATION_RETAIN_NONATOMIC);
}
- (NSArray *)tt_recordedTopLayoutSupportConstraints
{
return objc_getAssociatedObject(self, @selector(tt_recordedTopLayoutSupportConstraints));
}
- (void)setTt_recordedTopLayoutSupportConstraints:(NSArray *)constraints
{
objc_setAssociatedObject(self, @selector(tt_recordedTopLayoutSupportConstraints), constraints, OBJC_ASSOCIATION_RETAIN_NONATOMIC);
}
- (NSArray *)tt_recordedBottomLayoutSupportConstraints
{
return objc_getAssociatedObject(self, @selector(tt_recordedBottomLayoutSupportConstraints));
}
- (void)setTt_recordedBottomLayoutSupportConstraints:(NSArray *)constraints
{
objc_setAssociatedObject(self, @selector(tt_recordedBottomLayoutSupportConstraints), constraints, OBJC_ASSOCIATION_RETAIN_NONATOMIC);
}
- (void)setTt_observer:(id)tt_observer
{
objc_setAssociatedObject(self, @selector(tt_observer), tt_observer, OBJC_ASSOCIATION_RETAIN_NONATOMIC);
}
- (id)tt_observer
{
return objc_getAssociatedObject(self, @selector(tt_observer));
}
-
//
// TTLayoutSupportConstraint.h
//
// Created by Steffen on 17.09.14.
//
#import <UIKit/UIKit.h>
@interface TTLayoutSupportConstraint : NSLayoutConstraint
+ (NSArray *)layoutSupportConstraintsWithView:(UIView *)view topLayoutGuide:(id<UILayoutSupport>)topLayoutGuide;
+ (NSArray *)layoutSupportConstraintsWithView:(UIView *)view bottomLayoutGuide:(id<UILayoutSupport>)bottomLayoutGuide;
@end
-
//
// TTLayoutSupportConstraint.m
//
// Created by Steffen on 17.09.14.
//
#import "TTLayoutSupportConstraint.h"
@implementation TTLayoutSupportConstraint
+ (NSArray *)layoutSupportConstraintsWithView:(UIView *)view topLayoutGuide:(id<UILayoutSupport>)topLayoutGuide
{
return @[
[TTLayoutSupportConstraint constraintWithItem:topLayoutGuide
attribute:NSLayoutAttributeHeight
relatedBy:NSLayoutRelationEqual
toItem:nil
attribute:NSLayoutAttributeNotAnAttribute
multiplier:1.0
constant:0.0],
[TTLayoutSupportConstraint constraintWithItem:topLayoutGuide
attribute:NSLayoutAttributeTop
relatedBy:NSLayoutRelationEqual
toItem:view
attribute:NSLayoutAttributeTop
multiplier:1.0
constant:0.0],
];
}
+ (NSArray *)layoutSupportConstraintsWithView:(UIView *)view bottomLayoutGuide:(id<UILayoutSupport>)bottomLayoutGuide
{
return @[
[TTLayoutSupportConstraint constraintWithItem:bottomLayoutGuide
attribute:NSLayoutAttributeHeight
relatedBy:NSLayoutRelationEqual
toItem:nil
attribute:NSLayoutAttributeNotAnAttribute
multiplier:1.0
constant:0.0],
[TTLayoutSupportConstraint constraintWithItem:bottomLayoutGuide
attribute:NSLayoutAttributeBottom
relatedBy:NSLayoutRelationEqual
toItem:view
attribute:NSLayoutAttributeBottom
multiplier:1.0
constant:0.0],
];
}
@end
我认为他们的意思是你应该使用自动布局约束布局指南，即NSLayoutConstraint对象，而不是手动设置长度属性。 长度属性可供选择不使用自动布局的类使用，但似乎使用自定义容器视图控制器，您没有此选择。
我认为最好的做法是在容器视图控制器中将约束的优先级设置为将length属性的值“设置”为UILayoutPriorityRequired 。
我不确定你会绑定什么布局属性，无论是NSLayoutAttributeHeight还是NSLayoutAttributeBottom 。
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