UItexfile实时验证输入字符

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

{

NSString * toBeString = [textField.text stringByReplacingCharactersInRange:range withString:string];

UITextField *loginPass = _textArr[1];

if (loginPass == textField) {

if ([toBeString length] > 12) {

textField.text = [toBeString substringToIndex:12];

UIAlertView *alert = [[UIAlertView alloc] initWithTitle:nil message:@"长度不能超过12" delegate:nil cancelButtonTitle:@"ok"
otherButtonTitles:nil, nil];

[alert show];

return NO;

}

}

return YES;

}