iOSUITextField限制输入长度

#import "ViewController.h"@interface ViewController ()<UITextFieldDelegate> {        UITextField *currentTextFeild;    UIButton    *touchButton;}@end@implementation ViewController- (void)viewDidLoad {    [super viewDidLoad];    // Do any additional setup after loading the view, typically from a nib.        UITextField *textFields = [[UITextField alloc] initWithFrame:CGRectMake(15, 50, self.view.bounds.size.width-15*2, 40)];    textFields.backgroundColor = [UIColor brownColor];    textFields.layer.cornerRadius = 5;    textFields.leftView = [[UIView alloc] initWithFrame:CGRectMake(0, 0, 10, 40)];    textFields.leftViewMode = UITextFieldViewModeAlways;//这两行是为了不让Text太贴textField的左边    textFields.placeholder = @"请输入手机号";    textFields.delegate = self;    [self.view addSubview:textFields];    currentTextFeild = textFields;        UIButton *enableButton = [UIButton buttonWithType:UIButtonTypeCustom];    enableButton.frame = CGRectMake(15, 100, self.view.bounds.size.width-15*2, 40);    enableButton.layer.cornerRadius = 5;    enableButton.backgroundColor = [UIColor grayColor];    [enableButton setTitle:@"没内容不可点击" forState:UIControlStateNormal];    [enableButton setTitle:@"可以按了" forState:UIControlStateSelected];    [enableButton setTitle:@"按下去了" forState:UIControlStateHighlighted];    enableButton.enabled = NO;    [enableButton addTarget:self action:@selector(btnClick) forControlEvents:UIControlEventTouchUpInside];    [self.view addSubview:enableButton];    touchButton = enableButton;}- (void)btnClick {        }

#PRagma mark -  UITextFieldDelegate- (BOOL)textFieldShouldBeginEditing:(UITextField *)textField {        return YES;}- (void)textFieldDidEndEditing:(UITextField *)textField {        }- (BOOL)textField:(UITextField *)textField shouldChangeCharactersInRange:(NSRange)range replacementString:(NSString *)string {        //用来判断是否可以继续输入， - range.length是为了判断是否可以删除    NSInteger currentLength = textField.text.length - range.length + string.length;    if (currentLength > 11) {                return NO;    }        //判断按钮是否可以enable = YES    if (currentTextFeild.text && currentTextFeild.text.length > 0 && currentLength > 0) {                touchButton.enabled = YES;        touchButton.selected = YES;    }else {                touchButton.enabled = NO;        touchButton.selected = NO;    }        if (currentLength <= 0) {                touchButton.enabled = NO;        touchButton.selected = NO;    }        return YES;}- (BOOL)textFieldShouldClear:(UITextField *)textField {        if (currentTextFeild.tag == 11 || currentTextFeild.tag == 12) {        //手机号        touchButton.enabled = NO;        touchButton.selected = NO;;    }        return YES;}- (BOOL)textFieldShouldReturn:(UITextField *)textField {        [textField resignFirstResponder];        return YES;}