方法1: 

(1)给TextField添加和Button一样的方法,forControlEvents选择UIControlEventEditingChanged;

(2)执行方法;

如下图 : 限制最大长度为6字符,每输入一个字符就打印一次,当输到第6个或超过第6个的时候,就只截取前6位字符.

方法2:

(1)UITextField签订协议

(2)利用系统的方法,黄色框里的是想用哪个TextField上.

附上上图代码:

#pragma mark - UITextFieldDelegate限制最多输入6个字符串

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

{

if(textField ==self.smsField||textField ==self.setNewPasswordField||textField ==self.confirmPasswordField) {

if(string.length==0)returnYES;

NSIntegerexistedLength = textField.text.length;

NSIntegerselectedLength = range.length;

NSIntegerreplaceLength = string.length;

if(existedLength - selectedLength + replaceLength >6) {

returnNO;

}

}

returnYES;

}