随着iOS 13的发布，公司的项目也势必要着手适配了。现汇总一下iOS 13的各种坑

1. KVC访问私有属性

这次iOS 13系统升级，影响范围最广的应属KVC访问修改私有属性了，直接禁止开发者获取或直接设置私有属性。而KVC的初衷是允许开发者通过Key名直接访问修改对象的属性值，为其中最典型的 UITextField 的 _placeholderLabel、UISearchBar 的 _searchField。

造成影响：在iOS 13下App闪退

错误代码：

// placeholderLabel私有属性访问
[textField setValue:[UIColor redColor] forKeyPath:@"_placeholderLabel.textColor"];
[textField setValue:[UIFont boldSystemFontOfSize:16] forKeyPath:@"_placeholderLabel.font"];
// searchField私有属性访问
UISearchBar *searchBar = [[UISearchBar alloc] init];
UITextField *searchTextField = [searchBar valueForKey:@"_searchField"];

解决方案:

使用 NSMutableAttributedString 富文本来替代KVC访问 UITextField 的 _placeholderLabel

textField.attributedPlaceholder = [[NSAttributedString alloc] initWithString:@"placeholder" attributes:@{NSForegroundColorAttributeName: [UIColor darkGrayColor], NSFontAttributeName: [UIFont systemFontOfSize:13]}];

因此，可以为UITextFeild创建Category，专门用于处理修改placeHolder属性提供方法

#import "UITextField+ChangePlaceholder.h"

@implementation UITextField (Change)

- (void)setPlaceholderFont:(UIFont *)font {

 [self setPlaceholderColor:nil font:font];
}

- (void)setPlaceholderColor:(UIColor *)color {

 [self setPlaceholderColor:color font:nil];
}

- (void)setPlaceholderColor:(nullable UIColor *)color font:(nullable UIFont *)font {

 if ([self checkPlaceholderEmpty]) {
  return;
 }

 NSMutableAttributedString *placeholderAttriString = [[NSMutableAttributedString alloc] initWithString:self.placeholder];
 if (color) {
  [placeholderAttriString addAttribute:NSForegroundColorAttributeName value:color range:NSMakeRange(0, self.placeholder.length)];
 }
 if (font) {
  [placeholderAttriString addAttribute:NSFontAttributeName value:font range:NSMakeRange(0, self.placeholder.length)];
 }

 [self setAttributedPlaceholder:placeholderAttriString];
}

- (BOOL)checkPlaceholderEmpty {
 return (self.placeholder == nil) || ([[self.placeholder stringByTrimmingCharactersInSet:[NSCharacterSet whitespaceAndNewlineCharacterSet]] length] == 0);
}

关于 UISearchBar，可遍历其所有子视图，找到指定的 UITextField 类型的子视图，再根据上述 UITextField 的通过富文本方法修改属性。

#import "UISearchBar+ChangePrivateTextFieldSubview.h"

@implementation UISearchBar (ChangePrivateTextFieldSubview)

/// 修改SearchBar系统自带的TextField
- (void)changeSearchTextFieldWithCompletionBlock:(void(^)(UITextField *textField))completionBlock {

 if (!completionBlock) {
  return;
 }
 UITextField *textField = [self findTextFieldWithView:self];
 if (textField) {
  completionBlock(textField);
 }
}

/// 递归遍历UISearchBar的子视图，找到UITextField
- (UITextField *)findTextFieldWithView:(UIView *)view {

 for (UIView *subview in view.subviews) {
  if ([subview isKindOfClass:[UITextField class]]) {
   return (UITextField *)subview;
  }else if (subview.subviews.count > 0) {
   return [self findTextFieldWithView:subview];
  }
 }
 return nil;
}
@end