asp.MCV如何将字符串转换为布尔标志

本文关键字：转换 布尔 标志 字符串 MCV asp | 更新日期: 2023-09-27 18:15:34

我正在尝试做一个登录页面。但是当我按F5页面这一行给出了一个错误:

flag = Convert.ToBoolean(cmd.ExecuteScalar());

Login.cs 

using System;
using System.Collections.Generic;
using System.ComponentModel.DataAnnotations;
using System.Configuration;
using System.Data.SqlClient;
using System.Linq;
using System.Web;
namespace LoginFormApp.Models
{
public class Login
{
    [Required(ErrorMessage = "Username is required")] 
    [Display(Name = "Username")]   
    public string username { get; set; }
    [Required(ErrorMessage = "Password is required")]
    [Display(Name = "Password")]
    public string password { get; set; }
    public bool checkUser(string username, string password) 
    { 
        bool flag = false;
        string connString =        ConfigurationManager.ConnectionStrings["MyDatabaseEntities"].ConnectionString    ; 
        using (SqlConnection conn = new SqlConnection(connString))
        {
            conn.Open();
            SqlCommand cmd = new SqlCommand("Select count(*) from Login     where username='" + username + "' and password='" + password + "'", conn);
            flag = Convert.ToBoolean(cmd.ExecuteScalar());
            return flag;
        }
    } 
}
}

Index.cshtml 

@model LoginFormApp.Models.Login
@{
 Layout = null;
}
 <!DOCTYPE html>
<html>
<head>
<meta name="viewport" content="width=device-width" />
<title>DNDB Login</title>
</head>
<body>
<div style="margin:0 auto; text-align: center; border: 2px; border-style:   solid; width:400px;background-color:lightgrey">
    @using (Html.BeginForm())
    {
        <table>
            <tr>
                <td>@Html.LabelFor(m => m.username)</td> 
                <td>@Html.TextBoxFor(m => m.username)</td> 
                <td>@Html.ValidationMessageFor(m => m.username)</td> 
            </tr>
            <tr>
                <td>@Html.LabelFor(m => m.password)</td> 
                <td>@Html.PasswordFor(m => m.password)</td> 
                <td>@Html.ValidationMessageFor(m => m.password)</td> 
            </tr>
            <tr>
                <td></td>
                <td>
                    <input type="submit" value="Submit" />
                </td> 
            </tr>
            <tr>
                <td></td>
                <td>
                    @ViewBag.Message
                </td>
            </tr>
        </table>
    }
</div>
</body>
</html>

show.cshtml 

@model LoginFormApp.Models.Login
@{
Layout = null;
}
<!DOCTYPE html>
 <html>
 <head>
<meta name="viewport" content="width=device-width" />
<title>Show</title>
</head>
<body>
<div>
    <h3> Hi! @Model.username</h3> 
</div>
</body>
</html>

Homecontroller.cs 

using LoginFormApp.Models;
using System;
using System.Collections.Generic;
using System.Configuration;
using System.Data.SqlClient;
using System.Linq;
using System.Web;
using System.Web.Mvc;
namespace LoginFormApp.Controllers
{
public class HomeController : Controller
{
    //
    // GET: /Home/
    [HttpGet]
    public ActionResult Index()
    {
        return View();
    }
    [HttpPost]
    public ViewResult Index(Login login)
    {
        if (ModelState.IsValid) 
        {
            if (login.checkUser(login.username, login.password)) 
            {
                return View("Show", login); 
            }
            else
            {
                ViewBag.Message = "Invalid Username or Password";
                return View(); 
            }
        }
        else
        {
            return View(); 
        }
    }
}
}

asp.MCV如何将字符串转换为布尔标志

你做错了，ExecuteScalar()总是返回第一列的值，所以在您的情况下，它返回总数，不能直接转换为布尔值。

int totalCount = Convert.ToInt32(cmd.ExecuteScalar());
flag = totalCount > 0;

可以使用

flag = (int)cmd.ExecuteScalar() == 1;
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