新建一个类继承UITextField，然后实现canPerformAction方法：
.h

import <UIKit/UIKit.h>

@interface NoCopyTextField : UITextField
@end
.m

import "NoCopyTextField.h"

@implementation NoCopyTextField

• (id)initWithFrame:(CGRect)frame
  {
  self = [super initWithFrame:frame];
  if (self) {
  // Initialization code
  }
  return self;
  }

• (BOOL)canPerformAction:(SEL)action withSender:(id)sender {
  UIMenuController *menuController = [UIMenuController sharedMenuController];
  if (menuController) {
  [UIMenuController sharedMenuController].menuVisible = NO;
  }
  return NO;
  }

用hook机制对canPerformAction 检测就好了, 很简单