我在情节提要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。但是在 ios 7 和例如 iphone 4 上，应用程序在尝试加载包含此控件的视图控制器时崩溃。调试器突出显示这一行：
typeof(self) loadedView = self.viewFromNib;
我的控制.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