如何修复键盘来来去去时的“UICollectionViewFlowLayout未定义”

最终起作用的是,从键盘开始移动到完全隐藏,抑制使布局无效的消息。目标应用程序是Objective-C,但转换为Swift并不重要。

@interface SSCollectionViewFlowLayout : UICollectionViewFlowLayout
@property (nonatomic, assign) BOOL shouldSuppress;
@end

@implementation SSCollectionViewFlowLayout
- (instancetype)initWithCoder:(NSCoder *)coder {
    self = [super initWithCoder:coder];

    [[NSNotificationCenter defaultCenter] addObserver:self
                                             selector:@selector(keyboardUp)
                                                 name:UIKeyboardWillShowNotification
                                               object:nil];
    [[NSNotificationCenter defaultCenter] addObserver:self
                                             selector:@selector(keyboardDown)
                                                 name:UIKeyboardWillHideNotification
                                               object:nil];
    return self;
}

- (void)keyboardUp {
    self.shouldSuppress = YES;
}

- (void)keyboardDown {
    self.shouldSuppress = NO;
}

- (void)prepareLayout {
    if(self.shouldSuppress) { return; }
    [super prepareLayout];
}

- (void)invalidateLayout {
    if(self.shouldSuppress) { return; }
    [super invalidateLayout];
}

- (void)invalidateLayoutWithContext:(UICollectionViewLayoutInvalidationContext *)context {
    if(self.shouldSuppress) { return; }
    [super invalidateLayoutWithContext:context];
}

- (void)dealloc {
    [[NSNotificationCenter defaultCenter] removeObserver:self];
}
@end

两者 invalidate 消息已发送到此对象。