我正在使用UITableViewController。我有一个项目表，如果用户进行更多编辑，用户可以删除这些项目。当他进入编辑模式时，我想显示一个标题，提供删除所有项目的选项。同时，它应该显示一个标签，提供有关使用空间的信息。如果设备进入横向模式，我希望自动调整大小。据我所知，我需要使用autolayout来做到这一点。
我很乐意在故事板中设计的UIView中设置标题，但故事板只允许使用视图控制器，而不是视图。我知道我可以拥有一个XIB文件，但如果可以，我宁愿避免使用它。
首先，我重写了editing属性，以便在编辑模式下可以重绘表格部分。
- (void)setEditing:(BOOL)editing animated:(BOOL)animated
{
[super setEditing:editing animated:animated];
NSIndexSet *set = [NSIndexSet indexSetWithIndex:0];
[self.tableView reloadSections:set withRowAnimation:UITableViewRowAnimationAutomatic];
}
我在适当时使用此代码插入节标题：
- (UIView *)tableView:(UITableView *)tableView viewForHeaderInSection:(NSInteger)section
{
if (self.isEditing)
return [self headerView];
else
return nil;
}
- (CGFloat)tableView:(UITableView *)tableView heightForHeaderInSection:(NSInteger)section
{
if (self.isEditing)
return [self headerView].frame.size.height;
else
return 0;
}
神奇发生在- headerView方法中。它返回UIView *，必要时从缓存中获取它。它添加了按钮和标签，然后放入约束。我在故事板中使用了这些相同的约束，我没有遇到任何问题。
- (UIView *)headerView
{
if (headerView)
return headerView;
float w = [[UIScreen mainScreen] bounds].size.width;
UIButton *deleteAllButton = [UIButton buttonWithType:UIButtonTypeRoundedRect];
[deleteAllButton setTitle:@"Delete All" forState:UIControlStateNormal];
CGRect deleteAllButtonFrame = CGRectMake(8.0, 8.0, 30.0, 30); // The autolayout should resize this.
[deleteAllButton setFrame:deleteAllButtonFrame];
deleteAllButton.translatesAutoresizingMaskIntoConstraints = NO;
[deleteAllButton setContentHuggingPriority:252 forAxis:UILayoutConstraintAxisHorizontal];
[deleteAllButton setContentCompressionResistancePriority:751 forAxis:UILayoutConstraintAxisHorizontal];
CGRect textFrame = CGRectMake(47.0, 8.0, 30.0, 30); // The autolayout should resize this.
UILabel *currSizeText = [[UILabel alloc] initWithFrame:textFrame];
currSizeText.text = @"You have a lot of text here telling you that you have stuff to delete";
currSizeText.translatesAutoresizingMaskIntoConstraints = NO;
currSizeText.adjustsFontSizeToFitWidth = YES;
CGRect headerViewFrame = CGRectMake(0, 0, w, 48);
headerView = [[UIView alloc] initWithFrame:headerViewFrame];
//headerView.autoresizingMask = UIViewAutoresizingNone;//UIViewAutoresizingFlexibleWidth | UIViewAutoresizingFlexibleHeight;
//headerView.translatesAutoresizingMaskIntoConstraints = NO;
[headerView addSubview:deleteAllButton];
[headerView addSubview:currSizeText];
NSDictionary *viewsDictionary = NSDictionaryOfVariableBindings(deleteAllButton, currSizeText);
[headerView addConstraints:[NSLayoutConstraint constraintsWithVisualFormat:@"|-[deleteAllButton]-[currSizeText]-|"
options:0
metrics:nil
views:viewsDictionary]];
[headerView addConstraint:[NSLayoutConstraint constraintWithItem:deleteAllButton
attribute:NSLayoutAttributeHeight
relatedBy:NSLayoutRelationEqual
toItem:headerView
attribute:NSLayoutAttributeHeight
multiplier:0.5
constant:0]];
[headerView addConstraint:[NSLayoutConstraint constraintWithItem:currSizeText
attribute:NSLayoutAttributeHeight
relatedBy:NSLayoutRelationEqual
toItem:headerView
attribute:NSLayoutAttributeHeight
multiplier:0.5
constant:0]];
return headerView;
}
现在，一切都很美好。按钮保持恒定大小（因为拥抱和压缩阻力高于标签），标签将更改其文本以适应可用空间。它在旋转设备时调整大小。垂直居中似乎在标签上，但我现在愿意忽略它。
然而，当我第一次设置节标题时，我收到一个恼人的自动布局警告。
2014-02-07 11:25:19.770 ErikApp[10704:70b] 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:0xb9a4ad0 H:|-(NSSpace(20))-[UIButton:0xb99e220] (Names: '|':UIView:0xb9a4680 )>",
"<NSLayoutConstraint:0xb9a4bf0 H:[UIButton:0xb99e220]-(NSSpace(8))-[UILabel:0xb99f530]>",
"<NSLayoutConstraint:0xb9a4c20 H:[UILabel:0xb99f530]-(NSSpace(20))-| (Names: '|':UIView:0xb9a4680 )>",
"<NSAutoresizingMaskLayoutConstraint:0xa2d1680 h=--& v=--& H:[UIView:0xb9a4680(0)]>"
)
Will attempt to recover by breaking constraint
<NSLayoutConstraint:0xb9a4bf0 H:[UIButton:0xb99e220]-(NSSpace(8))-[UILabel:0xb99f530]>
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.
我的第一个想法是将返回的UIView属性translatesAutoresizingMaskIntoConstraints更改为NO。当我这样做时，我会发生崩溃而不是警告。不完全是一种改进。
2014-02-07 10:49:13.041 ErikApp[10597:70b] *** Assertion failure in -[UITableView layoutSublayersOfLayer:], /SourceCache/UIKit_Sim/UIKit-2903.23/UIView.m:8540
2014-02-07 10:49:13.383 ErikApp[10597:70b] *** Terminating app due to uncaught exception 'NSInternalInconsistencyException', reason: 'Auto Layout still required after executing -layoutSubviews. UITableView's implementation of -layoutSubviews needs to call super.'
有没有人建议如何摆脱警告？
答案 0 :(得分：4)
似乎当您的部分正在重新加载时，UITableView在某个时刻会引用旧部分标题和新部分标题。如果它是相同的视图，则会出现一些问题。因此，您必须始终提供tableView:viewForHeaderInSection:方法的不同视图。
有时在节标题中显示单个实例非常有用。为此，每次要求提供节标题并将自定义视图放入其中时，您需要创建一个新视图，并适当地配置约束。这是一个例子：
@property (strong, nonatomic) UIView *headerContentView;
- (void)viewDidLoad {
// Create the view, which is to be presented inside the section header
self.headerContentView = [self loadHeaderContentView];
// Note that we have to set the following property to NO to prevent the unsatisfiable constraints
self.headerContentView.translatesAutoresizingMaskIntoConstraints = NO;
}
- (UIView *)loadHeaderContentView {
// Here you instantiate your custom view from a nib
// or create it programmatically. Speaking in terms
// of the OP, it should look like the following. (Note:
// I have removed all the frame-related code as your are
// not supposed to deal with frames directly with auto layout.
// I have also removed the line setting translatesAutoresizingMaskIntoConstraints property
// to NO of the headerContentView object as we do it explicitly in viewDidLoad.
UIButton *deleteAllButton = [UIButton buttonWithType:UIButtonTypeRoundedRect];
[deleteAllButton setTitle:@"Delete All" forState:UIControlStateNormal];
deleteAllButton.translatesAutoresizingMaskIntoConstraints = NO;
[deleteAllButton setContentHuggingPriority:252 forAxis:UILayoutConstraintAxisHorizontal];
[deleteAllButton setContentCompressionResistancePriority:751 forAxis:UILayoutConstraintAxisHorizontal];
UILabel *currSizeText = [[UILabel alloc] init];
currSizeText.text = @"You have a lot of text here telling you that you have stuff to delete";
currSizeText.translatesAutoresizingMaskIntoConstraints = NO;
currSizeText.adjustsFontSizeToFitWidth = YES;
UIView *headerContentView = [[UIView alloc] init];
[headerContentView addSubview:deleteAllButton];
[headerContentView addSubview:currSizeText];
NSDictionary *viewsDictionary = NSDictionaryOfVariableBindings(deleteAllButton, currSizeText);
// In the original post you used to have an ambigious layout
// as the Y position of neither button nor label was set.
// Note passing NSLayoutFormatAlignAllCenterY as an option
[headerContentView addConstraints:[NSLayoutConstraint constraintsWithVisualFormat:@"|-[deleteAllButton]-[currSizeText]-|"
options:NSLayoutFormatAlignAllCenterY
metrics:nil
views:viewsDictionary]];
[headerContentView addConstraint:[NSLayoutConstraint constraintWithItem:deleteAllButton
attribute:NSLayoutAttributeCenterY
relatedBy:NSLayoutRelationEqual
toItem:headerContentView
attribute:NSLayoutAttributeCenterY
multiplier:1
constant:0]];
// Here setting the heights of the subviews
[headerContentView addConstraint:[NSLayoutConstraint constraintWithItem:deleteAllButton
attribute:NSLayoutAttributeHeight
relatedBy:NSLayoutRelationEqual
toItem:headerContentView
attribute:NSLayoutAttributeHeight
multiplier:0.5
constant:0]];
[headerContentView addConstraint:[NSLayoutConstraint constraintWithItem:currSizeText
attribute:NSLayoutAttributeHeight
relatedBy:NSLayoutRelationEqual
toItem:headerContentView
attribute:NSLayoutAttributeHeight
multiplier:0.5
constant:0]];
return headerContentView;
}
- (UIView *)headerView {
UIView *headerView = [[UIView alloc] init];
[headerView addSubview:self.headerContentView];
NSDictionary *views = @{@"headerContentView" : self.headerContentView};
NSArray *hConstraints = [NSLayoutConstraint constraintsWithVisualFormat:@"H:|[headerContentView]|" options:0 metrics:nil views:views];
NSArray *vConstraints = [NSLayoutConstraint constraintsWithVisualFormat:@"V:|[headerContentView]|" options:0 metrics:nil views:views];
[headerView addConstraints:hConstraints];
[headerView addConstraints:vConstraints];
return headerView;
}
- (UIView *)tableView:(UITableView *)tableView viewForHeaderInSection:(NSInteger)section
{
if (self.isEditing)
return [self headerView];
return nil;
}
- (CGFloat)tableView:(UITableView *)tableView heightForHeaderInSection:(NSInteger)section
{
// You need to return a concrete value here
// and not the current height of the header.
if (self.isEditing)
return 48;
return 0;
}
答案 1 :(得分：3)
我在这里为这篇文章创建了一个GitHub回购：https://github.com/bilobatum/AnimatedTableHeaderDemo
此解决方案实现了表标题视图，即self.tableView.tableHeaderView，而不是具有单个部分的表视图的节标题。
表标题视图及其子视图的颜色用于测试目的。选择任意表头高度用于测试目的。
当表视图进入编辑模式时，表头被懒惰地实例化并动画到位。当表格视图退出编辑模式时，动画会隐藏表格标题。
通常，使用自动布局时不应设置帧。但是，表头在某种意义上是一种特殊情况。不要使用“自动布局”来调整表格标题的大小或位置。相反，您必须设置表头的框架（实际上，您只需要设置矩形的高度）。反过来，系统会将表头的帧转换为约束。
但是，可以在表格标题的子视图上使用自动布局。其中一些约束安装在表头视图中。
@interface ViewController ()
@property (nonatomic, strong) NSArray *mockData;
@property (nonatomic, strong) UIButton *deleteAllButton;
@property (nonatomic, strong) UILabel *label;
@property (nonatomic, strong) UIView *headerView;
@end
@implementation ViewController
- (void)viewDidLoad
{
[super viewDidLoad];
self.title = @"Fruit";
self.mockData = @[@"Orange", @"Apple", @"Pear", @"Banana", @"Cantalope"];
self.navigationItem.rightBarButtonItem = self.editButtonItem;
}
- (UIButton *)deleteAllButton
{
if (!_deleteAllButton) {
_deleteAllButton = [[UIButton alloc] init];
_deleteAllButton.backgroundColor = [UIColor grayColor];
[_deleteAllButton setTitle:@"Delete All" forState:UIControlStateNormal];
_deleteAllButton.translatesAutoresizingMaskIntoConstraints = NO;
[_deleteAllButton addTarget:self action:@selector(handleDeleteAll) forControlEvents:UIControlEventTouchUpInside];
}
return _deleteAllButton;
}
- (UILabel *)label
{
if (!_label) {
_label = [[UILabel alloc] init];
_label.backgroundColor = [UIColor yellowColor];
_label.text = @"Delete all button prompt";
_label.translatesAutoresizingMaskIntoConstraints = NO;
}
return _label;
}
- (UIView *)headerView
{
if (!_headerView) {
_headerView = [[UIView alloc] init];
// WARNING: do not set translatesAutoresizingMaskIntoConstraints to NO
_headerView.backgroundColor = [UIColor orangeColor];
_headerView.clipsToBounds = YES;
[_headerView addSubview:self.label];
[_headerView addSubview:self.deleteAllButton];
[_headerView addConstraints:[NSLayoutConstraint constraintsWithVisualFormat:@"H:|-[_deleteAllButton]-[_label]-|" options:NSLayoutFormatAlignAllCenterY metrics:0 views:NSDictionaryOfVariableBindings(_label, _deleteAllButton)]];
[_headerView addConstraint:[NSLayoutConstraint constraintWithItem:self.deleteAllButton attribute:NSLayoutAttributeCenterY relatedBy:NSLayoutRelationEqual toItem:_headerView attribute:NSLayoutAttributeCenterY multiplier:1.0f constant:0.0f]];
}
return _headerView;
}
- (void)setEditing:(BOOL)editing animated:(BOOL)animated
{
[super setEditing:editing animated:animated];
if (self.editing) {
self.tableView.tableHeaderView = self.headerView;
[self.tableView layoutIfNeeded];
}
[UIView animateWithDuration:1.0 animations:^{
CGRect rect = self.headerView.frame;
if (editing) {
rect.size.height = 60.0f; // arbitrary; for testing purposes
} else {
rect.size.height = 0.0f;
}
self.headerView.frame = rect;
self.tableView.tableHeaderView = self.headerView;
[self.tableView layoutIfNeeded];
} completion:^(BOOL finished) {
if (!editing) {
self.tableView.tableHeaderView = nil;
}
}];
}
- (void)handleDeleteAll
{
NSLog(@"handle delete all");
}
#pragma mark - Table view data source
- (NSInteger)tableView:(UITableView *)tableView numberOfRowsInSection:(NSInteger)section
{
return [self.mockData count];
}
- (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath
{
static NSString *CellIdentifier = @"Cell";
UITableViewCell *cell = [tableView dequeueReusableCellWithIdentifier:CellIdentifier forIndexPath:indexPath];
cell.textLabel.text = self.mockData[indexPath.row];
return cell;
}
@end
答案 2 :(得分：2)
你问这个问题已经有好几次了，但也许答案对你（或其他人）有帮助。
Autolayout（自动）为整个节头宽度（调试输出约束列表中的最后一个）添加了约束。这当然应该没有问题，因为在计算子视图的帧时会考虑宽度。 但有时在帧的计算中似乎存在舍入错误......
只需为其中一个子视图宽度值添加较低的优先级即可解决问题：
<强> ... @＆＃34; | - [deleteAllButton（30.0@999）] - [currSizeText] - |＆＃34;
如果按钮宽度不恒定，请使用... deleteAllButton（＆gt; = 30 @ 999）...
答案 3 :(得分：0)
我尝试使用的解决方法是跳过部分标题内容并直接转到tableHeaderView。我已将editing属性替换为：
- (void)setEditing:(BOOL)editing animated:(BOOL)animated
{
[super setEditing:editing animated:animated];
if (editing)
self.tableView.tableHeaderView = [self headerView];
else
self.tableView.tableHeaderView = nil;
}
它的动画效果与节标题不同，但现在这样做。
这并没有真正解决实际问题（因此“解决方法”）所以我不会接受这个解决方案。