IOS TextField 输入银行卡号格式化（每四位中间空一格）

-(BOOL)textField:(UITextField *)textField shouldChangeCharactersInRange:(NSRange)range replacementString:(NSString *)string{

if (textField == self.text_cardno) {
NSString *text = [self.text_cardno text];

NSCharacterSet *characterSet = [NSCharacterSet characterSetWithCharactersInString:@"0123456789\b"];
string = [string stringByReplacingOccurrencesOfString:@" " withString:@""];
if ([string rangeOfCharacterFromSet:[characterSet invertedSet]].location != NSNotFound) {
return NO;
}

text = [text stringByReplacingCharactersInRange:range withString:string];
text = [text stringByReplacingOccurrencesOfString:@" " withString:@""];

NSString *newString = @"";
while (text.length > 0) {
NSString *subString = [text substringToIndex:MIN(text.length, 4)];
newString = [newString stringByAppendingString:subString];
if (subString.length == 4) {
newString = [newString stringByAppendingString:@" "];
}
text = [text substringFromIndex:MIN(text.length, 4)];
}

newString = [newString stringByTrimmingCharactersInSet:[characterSet invertedSet]];

// 限制长度
if (newString.length >= 24) {
return NO;
}

[self.text_cardno setText:newString];

return NO;

}
return YES;
}

// 银行卡号转正常号 － 去除4位间的空格
-(NSString *)bankNumToNormalNum
{
return [self.text_cardno.text stringByReplacingOccurrencesOfString:@" " withString:@""];
}