Xib的UIControl在ios 7.1上崩潰

Question

我在情節提要中創建了一個自定義UIControl（MyControl）。 在ios 8和ios 9上，一切正常，我的應用程序沒有崩潰。 但是在ios 7（例如iphone 4）上，嘗試加載包含此控件的視圖控制器時，應用程序崩潰。 調試器突出顯示以下行：

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

檢查約束屬性，並與此處的列表進行比較。 以下屬性是在iOS 8中添加的，如果在xib或代碼中引用，則會在iOS 7（或更早版本）上崩潰。

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