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Ios UICollectionView 动态单元格高度

我需要显示一组具有不同高度的集合ViewCells.视图太复杂了，我不想手动计算预期高度.我要强制自动布局以计算单元格高度

在cellForItemAtIndexPath之外调用dequeueReusableCellWithReuseIdentifier会中断集合视图并导致其崩溃

另一个问题是该单元格不在单独的XIB中，因此我不能手动实例化一个临时单元格并将其用于高度计算.

对此有什么解决方案吗？

public func collectionView(collectionView: UICollectionView, layout collectionViewLayout: UICollectionViewLayout, sizeForItemAtIndexPath indexPath: NSIndexPath) -> CGSize {
    
    var cell = collectionView.dequeueReusableCellWithReuseIdentifier(cellIdentifier, forIndexPath: indexPath) as UICollectionViewCell
    configureCell(cell, item: items[indexPath.row])
    
    cell.contentView.setNeedsLayout()
    cell.contentView.layoutIfNeeded()
    
    return cell.contentView.systemLayoutSizeFittingSize(UILayoutFittingCompressedSize)
}

EDIT:

一叫dequeueReusableCellWithReuseIdentifier，就会发生坠机.如果我不调用该方法，而是返回一个大小，那么一切都很好，单元格显示时没有计算出的大小

流布局中不支持负大小或零大小

2015-01-26 18:24:34.231 [13383:9752256] *** Terminating app due to uncaught exception 'NSRangeException', reason: '*** -[__NSArrayM objectAtIndex:]: index 1 beyond bounds [0 .. 0]'
*** First throw call stack:
(
    0   CoreFoundation                      0x00000001095aef35 __exceptionPreprocess + 165
    1   libobjc.A.dylib                     0x0000000109243bb7 objc_exception_throw + 45
    2   CoreFoundation                      0x0000000109499f33 -[__NSArrayM objectAtIndex:] + 227
    3   UIKit                               0x0000000107419d9c -[UICollectionViewFlowLayout _getSizingInfos] + 842
    4   UIKit                               0x000000010741aca9 -[UICollectionViewFlowLayout _fetchItemsInfoForRect:] + 526
    5   UIKit                               0x000000010741651f -[UICollectionViewFlowLayout prepareLayout] + 257
    6   UIKit                               0x000000010742da10 -[UICollectionViewData _prepareToLoadData] + 67
    7   UIKit                               0x00000001074301c6 -[UICollectionViewData layoutAttributesForItemAtIndexPath:] + 44
    8   UIKit                               0x00000001073fddb1 -[UICollectionView _dequeueReusableViewOfKind:withIdentifier:forIndexPath:viewCategory:] + 248
    9                                       0x00000001042b824c _TFC1228BasePaginatingViewController14collectionViewfS0_FTCSo16UICollectionView6layoutCSo22UICollectionViewLayout22sizeForItemAtIndexPathCSo11NSIndexPath_VSC6CGSize + 700
    10                                     0x00000001042b83d4 _TToFC1228BasePaginatingViewController14collectionViewfS0_FTCSo16UICollectionView6layoutCSo22UICollectionViewLayout22sizeForItemAtIndexPathCSo11NSIndexPath_VSC6CGSize + 100
    11  UIKit                               0x0000000107419e2e -[UICollectionViewFlowLayout _getSizingInfos] + 988
    12  UIKit                               0x000000010741aca9 -[UICollectionViewFlowLayout _fetchItemsInfoForRect:] + 526
    13  UIKit                               0x000000010741651f -[UICollectionViewFlowLayout prepareLayout] + 257
    14  UIKit                               0x000000010742da10 -[UICollectionViewData _prepareToLoadData] + 67
    15  UIKit                               0x000000010742e0e9 -[UICollectionViewData validateLayoutInRect:] + 54
    16  UIKit                               0x00000001073f67b8 -[UICollectionView layoutSubviews] + 170
    17  UIKit                               0x0000000106e3c973 -[UIView(CALayerDelegate) layoutSublayersOfLayer:] + 521
    18  QuartzCore                          0x0000000106b0fde8 -[CALayer layoutSublayers] + 150
    19  QuartzCore                          0x0000000106b04a0e _ZN2CA5Layer16layout_if_neededEPNS_11TransactionE + 380
    20  QuartzCore                          0x0000000106b0487e _ZN2CA5Layer28layout_and_display_if_neededEPNS_11TransactionE + 24
    21  QuartzCore                          0x0000000106a7263e _ZN2CA7Context18commit_transactionEPNS_11TransactionE + 242
    22  QuartzCore                          0x0000000106a7374a _ZN2CA11Transaction6commitEv + 390
    23  QuartzCore                          0x0000000106a73db5 _ZN2CA11Transaction17observer_callbackEP19__CFRunLoopObservermPv + 89
    24  CoreFoundation                      0x00000001094e3dc7 __CFRUNLOOP_IS_CALLING_OUT_TO_AN_OBSERVER_CALLBACK_FUNCTION__ + 23
    25  CoreFoundation                      0x00000001094e3d20 __CFRunLoopDoObservers + 368
    26  CoreFoundation                      0x00000001094d9b53 __CFRunLoopRun + 1123
    27  CoreFoundation                      0x00000001094d9486 CFRunLoopRunSpecific + 470
    28  GraphicsServices                    0x000000010be869f0 GSEventRunModal + 161
    29  UIKit                               0x0000000106dc3420 UIApplicationMain + 1282
    30                                      0x000000010435c709 main + 169
    31  libdyld.dylib                       0x000000010a0f2145 start + 1
)
libc++abi.dylib: terminating with uncaught exception of type NSException

推荐答案

下面是一个Ray Wenderlich tutorial，演示如何使用AutoLayout动态调整UITableViewCell的大小.我想UICollectionViewCell年也一样.

不过，基本上，你最终会排队，配置一个原型单元，并获取其高度.读完本文后，我决定实现这个方法，只需编写一些清晰、明确的大小代码.

以下是我认为整个文章的"秘密酱":

- (CGFloat)tableView:(UITableView *)tableView heightForRowAtIndexPath:(NSIndexPath *)indexPath {
    return [self heightForBasicCellAtIndexPath:indexPath];
}

- (CGFloat)heightForBasicCellAtIndexPath:(NSIndexPath *)indexPath {
    static RWBasicCell *sizingCell = nil;
    static dispatch_once_t onceToken;
    dispatch_once(&onceToken, ^{
        sizingCell = [self.tableView dequeueReusableCellWithIdentifier:RWBasicCellIdentifier];
    });

    [self configureBasicCell:sizingCell atIndexPath:indexPath];
    return [self calculateHeightForConfiguredSizingCell:sizingCell];
}

- (CGFloat)calculateHeightForConfiguredSizingCell:(UITableViewCell *)sizingCell {
    [sizingCell setNeedsLayout];
    [sizingCell layoutIfNeeded];

    CGSize size = [sizingCell.contentView systemLayoutSizeFittingSize:UILayoutFittingCompressedSize];
    return size.height + 1.0f; // Add 1.0f for the cell separator height
}

EDIT: I did some research into your crash and decided that there is no way to get this done without a custom XIB. While that is a bit frustrating, you should be able to cut and paste from your Storyboard to a custom, empty XIB.

一旦您做到了这一点，下面这样的代码就可以让您开始工作了:

//  ViewController.m
#import "ViewController.h"
#import "CollectionViewCell.h"
@interface ViewController () <UICollectionViewDataSource, UICollectionViewDelegate, UICollectionViewDelegateFlowLayout> {

}
@property (weak, nonatomic) IBOutlet CollectionViewCell *cell;
@property (weak, nonatomic) IBOutlet UICollectionView   *collectionView;
@end
@implementation ViewController
- (void)viewDidLoad {
    [super viewDidLoad];
    self.view.backgroundColor = [UIColor lightGrayColor];
    [self.collectionView registerNib:[UINib nibWithNibName:@"CollectionViewCell" bundle:nil] forCellWithReuseIdentifier:@"cell"];
}
- (void)viewDidAppear:(BOOL)animated {
    [super viewDidAppear:animated];
    NSLog(@"viewDidAppear...");
}
- (NSInteger)numberOfSectionsInCollectionView:(UICollectionView *)collectionView {
    return 1;
}
- (NSInteger)collectionView:(UICollectionView *)collectionView numberOfItemsInSection:(NSInteger)section {
    return 50;
}
- (CGFloat)collectionView:(UICollectionView *)collectionView layout:(UICollectionViewLayout *)collectionViewLayout minimumInteritemSpacingForSectionAtIndex:(NSInteger)section {
    return 10.0f;
}
- (CGFloat)collectionView:(UICollectionView *)collectionView layout:(UICollectionViewLayout *)collectionViewLayout minimumLineSpacingForSectionAtIndex:(NSInteger)section {
    return 10.0f;
}
- (CGSize)collectionView:(UICollectionView *)collectionView layout:(UICollectionViewLayout *)collectionViewLayout sizeForItemAtIndexPath:(NSIndexPath *)indexPath {
    return [self sizingForRowAtIndexPath:indexPath];
}
- (CGSize)sizingForRowAtIndexPath:(NSIndexPath *)indexPath {
    static NSString *title                  = @"This is a long title that will cause some wrapping to occur. This is a long title that will cause some wrapping to occur.";
    static NSString *subtitle               = @"This is a long subtitle that will cause some wrapping to occur. This is a long subtitle that will cause some wrapping to occur.";
    static NSString *buttonTitle            = @"This is a really long button title that will cause some wrapping to occur.";
    static CollectionViewCell *sizingCell   = nil;
    static dispatch_once_t onceToken;
    dispatch_once(&onceToken, ^{
        sizingCell                          = [[NSBundle mainBundle] loadNibNamed:@"CollectionViewCell" owner:self options:nil][0];
    });
    [sizingCell configureWithTitle:title subtitle:[NSString stringWithFormat:@"%@: Number %d.", subtitle, (int)indexPath.row] buttonTitle:buttonTitle];
    [sizingCell setNeedsLayout];
    [sizingCell layoutIfNeeded];
    CGSize cellSize = [sizingCell.contentView systemLayoutSizeFittingSize:UILayoutFittingCompressedSize];
    NSLog(@"cellSize: %@", NSStringFromCGSize(cellSize));
    return cellSize;
}
- (UICollectionViewCell *)collectionView:(UICollectionView *)collectionView cellForItemAtIndexPath:(NSIndexPath *)indexPath {
    static NSString *title                  = @"This is a long title that will cause some wrapping to occur. This is a long title that will cause some wrapping to occur.";
    static NSString *subtitle               = @"This is a long subtitle that will cause some wrapping to occur. This is a long subtitle that will cause some wrapping to occur.";
    static NSString *buttonTitle            = @"This is a really long button title that will cause some wrapping to occur.";
    CollectionViewCell *cell                = [collectionView dequeueReusableCellWithReuseIdentifier:@"cell" forIndexPath:indexPath];
    [cell configureWithTitle:title subtitle:[NSString stringWithFormat:@"%@: Number %d.", subtitle, (int)indexPath.row] buttonTitle:buttonTitle];
    return cell;
}
@end

上面的代码(以及一个非常基本的UICollectionViewCell子类和相关的XIB)告诉我:

在此处输入图像描述

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