#pragma mark - UITextFieldDelegate UITextField鍵入字符后調(diào)用
- (BOOL)textField:(UITextField *)textField shouldChangeCharactersInRange:(NSRange)range replacementString:(NSString *)string {
 //拿到為改變前的字符串
 NSString *text = [textField text];
 //鍵入字符集，\b標(biāo)示刪除鍵
 NSCharacterSet *characterSet = [NSCharacterSet characterSetWithCharactersInString:@"0123456789\b"];
 //對(duì)當(dāng)前鍵入字符進(jìn)行空格過濾
 string = [string stringByReplacingOccurrencesOfString:@" " withString:@""];
 //invertedSet會(huì)對(duì)當(dāng)前結(jié)果集取反，檢查當(dāng)前鍵入字符是否在字符集合中，如果不在則直接返回NO 不改變textField值
 if ([string rangeOfCharacterFromSet:[characterSet invertedSet]].location != NSNotFound) {
 return NO;
 }
 //增加當(dāng)前鍵入字符在改變前的字符串尾部
 text = [text stringByReplacingCharactersInRange:range withString:string];
 //再次確認(rèn)去掉字符串中空格
 text = [text stringByReplacingOccurrencesOfString:@" " withString:@""];
 //初始化字符用來保存格式化后的字符串
 NSString *newString = @"";
 //while中對(duì)text進(jìn)行格式化
 while (text.length > 0) {
 //按4位字符進(jìn)行截取，如果當(dāng)前字符不足4位則按照當(dāng)前字符串的最大長度截取
 NSString *subString = [text substringToIndex:MIN(text.length, 4)];
 //將截取后的字符放入需要格式化的字符串中
 newString = [newString stringByAppendingString:subString];
 if (subString.length == 4) {
  //截取的字符串長度滿4位則在后面增加一個(gè)空格符
  newString = [newString stringByAppendingString:@" "];
 }
 //將text中截取掉字符串去掉
 text = [text substringFromIndex:MIN(text.length, 4)];
 }
 //再次確認(rèn)過濾掉除指定字符以外的字符
 newString = [newString stringByTrimmingCharactersInSet:[characterSet invertedSet]];
 //國內(nèi)銀行卡一般為16~19位 格式化后增加4個(gè)空格 也就是最多23個(gè)字符
 if (newString.length > 23) {
 return NO;
 }
 //手動(dòng)對(duì)textField賦值
 [textField setText:newString];
 //返回NO 則不通過委托自動(dòng)往當(dāng)前字符后面增加字符，達(dá)到格式化效果
 return NO;
}