ASP Net Core MVC创建实例控制器System.MissingMethodException：'为此对象未定义无参数构造函数。

Question

How can I fix this issue System.MissingMethodException: 'No parameterless constructor defined for this object.' I followed this code from codeproject CodeProject Code .

Already tried adding blank constructor in Controller but it's giving me another error. InvalidOperationException: Multiple constructors accepting all given argument types have been found in type 'SlhSd18.Controllers.FunctionsController'. There should only be one applicable constructor.

Here is my model code:

    namespace SlhSd18.Models
{
    public class Function
    {
        public int Id { get; set; }

        [Required, StringLength(10)]
        [CustomRemoteValidation("IsFunctionIdExist", "Functions", AdditionalFields = "Id",
            ErrorMessage = "Function Id already exist.")]
        public string FunctionId { get; set; }

Controller Code:

    namespace SlhSd18.Controllers
{
    public class FunctionsController : Controller
    {
        private readonly SlhSd18Context _context;

        public FunctionsController(SlhSd18Context context)
        {
            _context = context;
        }

        public IActionResult IsFunctionIdExist(string functionId, int ? Id)
        {
            bool validate = _context.Function.Any
                (x => x.FunctionId == functionId && x.Id != Id);

            if (validate ==true)
            {
                return Json(false);
            }
            else
            {
                return Json(true);
            }
        }

CustomRemoteValidation Code:

SlhSd18 Class Code

    namespace SlhSd18.Models
{
    public class SlhSd18Context : DbContext
    {
        public SlhSd18Context (DbContextOptions<SlhSd18Context> options)
            : base(options)
        {
        }

        public DbSet<SlhSd18.Models.Movie> Movie { get; set; }

        public DbSet<SlhSd18.Models.ChartofAccount> ChartofAccount { get; set; }

        public DbSet<SlhSd18.Models.Function> Function { get; set; }

    }
}

Answer 1

I don't know setup of your DI, but I suggest to use this method to create controller instance:

private object TryCreateController(ValidationContext context, string controllerName) {
    Type controllerType = Assembly.GetExecutingAssembly().GetTypes().Single(x => x.Name.ToString().ToLower() == controllerName+"Controller");
    if (controllerType == null) {
        return null;
    }
    foreach (var constructor in controllerType.GetConstructors()) {
        var parameters = constructor.GetParameters();
        var args = new dynamic[parameters.Length];
        for (int i = 0; i < parameters.Length; i++) {
            args[i] = context.GetService(parameters[i].ParameterType);
        }

        try {
            var instance = Activator.CreateInstance(controllerType, args);
            if (instance != null) {
                return instance;
            }
        }
        catch {
            continue;
        }

    }

    return null;
}

And you can change the highlighted line to the next:

object instance = TryCreateController(validationContext, this.RouteData["controller"].ToString().ToLower());