新进的公司, 新接手的项目, 新的代码, 发现了好多输入框, 但是都没做长度限制........., 一个个限制, 我觉得我会疯掉. 突然想到了神奇的Runtime. 之前有看到过一篇, 使用Runtime 拿到文件的button, 加事件的. 或许是一个思路

经过了一个上午加中午的实验, 终于成功了

直接上代码

  #import "UITextField+Length.h"
  #import <objc/runtime.h>
  @implementation UITextField (Length)


  + (void)load
  {
static dispatch_once_t onceToken;
dispatch_once(&onceToken, ^{
    Method oldMethod = class_getInstanceMethod([self class], @selector(setDelegate:));
    Method newMethod = class_getInstanceMethod([self class], @selector(hook_setDelegate:));
    method_exchangeImplementations(oldMethod, newMethod);
});
  }
  #pragma mark - 交换代理方法

  - (void)hook_setDelegate:(id<UITextFieldDelegate>)delegate
  {
SEL oldSelector = @selector(textField:shouldChangeCharactersInRange:replacementString:);
SEL newSelector = @selector(hook_textField:shouldChangeCharactersInRange:replacementString:);
Method oldMethod_del = class_getInstanceMethod([delegate class], oldSelector);
Method oldMethod_self = class_getInstanceMethod([self class], oldSelector);
Method newMethod = class_getInstanceMethod([self class], newSelector);

// 若未实现代理方法，则先添加代理方法
BOOL isSuccess = class_addMethod([delegate class], oldSelector, class_getMethodImplementation([self class], newSelector), method_getTypeEncoding(newMethod));
if (isSuccess) {
    class_replaceMethod([delegate class], newSelector, class_getMethodImplementation([self class], oldSelector), method_getTypeEncoding(oldMethod_self));
} else {
    // 若已实现代理方法，则添加 hook 方法并进行交换
    BOOL isVictory = class_addMethod([delegate class], newSelector, class_getMethodImplementation([delegate class], oldSelector), method_getTypeEncoding(oldMethod_del));
    if (isVictory) {
        class_replaceMethod([delegate class], oldSelector, class_getMethodImplementation([self class], newSelector), method_getTypeEncoding(newMethod));
    }
}
[self hook_setDelegate:delegate];
  }

  #pragma mark - 交换的方法
    


  - (BOOL)hook_textField:(UITextField *)textField shouldChangeCharactersInRange:(NSRange)range replacementString:(NSString *)string{
if (textField.keyboardType == UIKeyboardTypeNumberPad ) {
    if (textField.text.length > 10) {
        textField.text = [textField.text substringToIndex:10];
         return  [self hook_textField:textField shouldChangeCharactersInRange:range replacementString:string];
    }
    
}
if (textField.text.length > 30) {
    textField.text = [textField.text substringToIndex:30];
    return  [self hook_textField:textField shouldChangeCharactersInRange:range replacementString:string];
    
}


return   YES;
}


  - (BOOL)textField:(UITextField *)textField shouldChangeCharactersInRange:(NSRange)range replacementString:(NSString *)string{
return [self textField:textField shouldChangeCharactersInRange:range replacementString:string];
  }


  @end