ios - xib 的 UIControl 在 ios 7.1 上崩溃

Question

我在 Storyboard中创建了一个自定义 UIControl ( MyControl )。在 ios 8 和 ios 9 上一切都很好，我的应用程序没有崩溃。但在 ios 7 和 iphone 4 上，应用程序在尝试加载包含此控件的 View Controller 时崩溃。调试器突出显示这一行:

typeof(self) loadedView = self.viewFromNib;

MyControl.h:

@interface MyControl : ControlFromXib

ControlFromXib.h:

@interface ControlFromXib : UIControl

- (void)commonInit;
@end

ControlFromXib.m:

- (instancetype)viewFromNib
{
    typeof(self) view = [[NSBundle mainBundle] loadNibNamed:self.nibName owner:nil options:nil].firstObject;
    return view;
}

- (NSString *)nibName
{
    return NSStringFromClass([self class]);
}

- (id)initWithFrame:(CGRect)frame
{
    self = [super initWithFrame:frame];
    if (self) {
        self = self.viewFromNib;
        [self commonInit];
        self.frame = frame;
    }
    return self;
}

- (id)awakeAfterUsingCoder:(NSCoder *)aDecoder
{
    if (self.subviews.count == 0) {
        typeof(self) loadedView = self.viewFromNib;

        loadedView.frame = self.frame;
        loadedView.autoresizingMask = self.autoresizingMask;
        loadedView.translatesAutoresizingMaskIntoConstraints = self.translatesAutoresizingMaskIntoConstraints;

        for (NSLayoutConstraint *constraint in self.constraints) {
            id firstItem = constraint.firstItem;
            if (firstItem == self) {
                firstItem = loadedView;
            }
            id secondItem = constraint.secondItem;
            if (secondItem == self) {
                secondItem = loadedView;
            }
            [loadedView addConstraint:
                    [NSLayoutConstraint constraintWithItem:firstItem
                                                 attribute:constraint.firstAttribute
                                                 relatedBy:constraint.relation
                                                    toItem:secondItem
                                                 attribute:constraint.secondAttribute
                                                multiplier:constraint.multiplier
                                                  constant:constraint.constant]];
        }

        self = loadedView;
    }

    [self commonInit];

    return self;
}

- (void)commonInit
{

}

@end

Answer 1

检查约束属性并与列表 here 进行比较。以下属性是在 iOS 8 中添加的，如果在 xib 或代码中引用，这些属性将在 iOS 7(及更早版本)上崩溃。

• NSLayoutAttributeLastBaseline
• NSLayoutAttributeFirstBaseline
• NSLayoutAttributeLeftMargin
• NSLayoutAttributeRightMargin
• NSLayoutAttributeTopMargin
• NSLayoutAttributeBottomMargin
• NSLayoutAttributeLeadingMargin
• NSLayoutAttributeTrailingMargin
• NSLayoutAttributeCenterXWithinMargins
• NSLayoutAttributeCenterYWithinMargins