1.UITextField 的基本设置

   UITextField *passTf = [[UITextField alloc]init];//初始化
    passTf.placeholder = @"密码";//填充背景提示
    passTf.secureTextEntry = YES; //设置为密码格式，默认是明文格式
    passTf.delegate = self;//设置代理，能够使用协议中的方法实现操作
    passTf.clearButtonMode = UITextFieldViewModeWhileEditing;//编辑时尾部出现 x , 能够清空文本
    [父视图 addSubview:passTf]; //添加视图
    [passTf mas_makeConstraints:^(MASConstraintMaker *make) {//此处运用了Masonry第三方框架实现自动布局
       make.edges.mas_equalTo(UIEdgeInsetsMake(0, 20, 0, 20));
    }];

 textField.returnKeyType = UIReturnKeyDefault;//默认是return

2.UITextField的文本限制 以及 字符长度

//定义字符类型kAlphaNum

#define kAlphaNum @"ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789"

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

  //限制字符类型

    NSCharacterSet *cs;
    cs = [[NSCharacterSet characterSetWithCharactersInString:kAlphaNum]invertedSet];
    
    NSString *filtered = [[string componentsSeparatedByCharactersInSet:cs]componentsJoinedByString:@""]; //按cs分离出数组,数组按@""分离出字符串
    
    BOOL canChange = [string isEqualToString:filtered];
    
    if (!canChange) {
        UIAlertController *alert = [UIAlertController alertControllerWithTitle:@"⚠️警告" message:@"输入错误！请输入字母或数字" preferredStyle:UIAlertControllerStyleAlert];
        [alert addAction:[UIAlertAction actionWithTitle:@"确定" style:UIAlertActionStyleDefault handler:^(UIAlertAction * _Nonnull action) {
            
        }]];
        [self presentViewController:alert animated:YES completion:nil];
    }
    //限制字符长度
    NSString * toBeString = [textField.text stringByReplacingCharactersInRange:range withString:string]; //得到输入框的内容
    if ([string isEqualToString:@""]) {
        return YES;
    }
    BOOL islength = [toBeString length] < 10;
    if (!islength) {
        textField.text = [toBeString substringToIndex:[toBeString length] -1];
        UIAlertController *alert = [UIAlertController alertControllerWithTitle:@"⚠️警告" message:@"用户名和密码不能超过10个字符！" preferredStyle:UIAlertControllerStyleAlert];
        [alert addAction:[UIAlertAction actionWithTitle:@"确定" style:UIAlertActionStyleDefault handler:^(UIAlertAction * _Nonnull action) {
            
        }]];
        [self presentViewController:alert animated:YES completion:nil];
        
    }
    
    return canChange && islength;
}

3.return 按键对应的协议方法

#pragma UITextFieldDelegate
-(BOOL)textFieldShouldReturn:(UITextField *)textField {
    [textField resignFirstResponder];//放弃第一响应者，收起键盘
    textField.text = @"";  //将文本内容置空
    return YES;
}