来自xib的UIControl在IOS7.1上崩溃

Question

我在故事板中创建了一个自定义UIControl ( MyControl )。在ios 8和ios 9上，一切都很好，我的应用程序中也没有崩溃。但是在ios 7和iphone 4上，当试图加载包含此控件的视图控制器时，应用程序就会崩溃。调试器突出显示这一行：

类型(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这里进行比较。以下属性是在iOS 8中添加的，如果在xib或代码中引用，则会在iOS 7(以及更早的)上崩溃。

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