ASP.NET MVC从FormCollection中填充ViewModel

Question

我有很多类似的ViewModel：

public class RequestForSalaryVM : StatementViewModel
{
  // RequestForSalaryVM properties
}
public class ReliefVM : StatementViewModel
{
  // ReliefVM properties
}

和许多类似的方法：

[HttpPost]
public ActionResult SaveRelief(User currentUser, ReliefVM statement)
{
    ReliefVM model = (ReliefVM)SaveModel(currentUser, statement);
    if (model == null)
        return RedirectToAction("List");
    return View("Relief", model);
}
[HttpPost]
public ActionResult SaveRequestForSalary(User currentUser, RequestForSalaryVM statement)
{
    RequestForSalaryVM model = (RequestForSalaryVM)SaveModel(currentUser, statement);
    if (model == null)
        return RedirectToAction("List");
    return View("RequestForSalary", model);
}

我想得到这样的东西：

[HttpPost]
public ActionResult SaveStatement(User currentUser, FormCollection statement, string ViewModelName)
{
  Assembly assembly = typeof(SomeKnownType).Assembly;
  Type type = assembly.GetType(ViewModelName);
  object ViewModel = Activator.CreateInstance(type);
  //Fill ViewModel from FormCollection  <= how can I use asp.net mvc binding for this?
  //I do not want to create their own implementation of asp.net mvc binding 
    return View(ViewModelName, ViewModel);
}

Answer 1

您可以尝试controller.updatemodel或controller.tryupdatemodel方法：

[HttpPost]
public ActionResult SaveStatement(User currentUser, FormCollection statement, string ViewModelName)
{
    ...
    object ViewModel = Activator.CreateInstance(type);
    if (TryUpdateModel(viewModel))
    {
        // save the ViewModel
    }   
    return View(ViewModelName, ViewModel);
}

但是，我建议您创建一个自定义模型燃烧器，因为它有责任创建和填充模型属性。

我可以向您展示一个简单的示例，如何实现这一目标：

基础视图

public abstract class StatementViewModel
{
    public abstract StatementType StatementType { get; }
    ...
}
public enum StatementType
{
    Relief,
    RequestForSalary,
    ...
}

ViewModels

public class RequestForSalaryVM : StatementViewModel
{
    public override StatementType StatementType
    {
        get { return StatementType.RequestForSalary; }
    }
    ...
}
public class ReliefVM : StatementViewModel
{
    public override StatementType StatementType
    {
        get { return StatementType.Relief; }
    }
    ...
}

ModelBinder

public class StatementModelBinder : DefaultModelBinder
{
    protected override object CreateModel(ControllerContext controllerContext, ModelBindingContext bindingContext, Type modelType)
    {
        var statementTypeParameter = bindingContext.ValueProvider.GetValue("StatementType");
        if (statementTypeParameter == null)
            throw new InvalidOperationException("StatementType is not specified");
        StatementType statementType;
        if (!Enum.TryParse(statementTypeParameter.AttemptedValue, true, out statementType))
            throw new InvalidOperationException("Incorrect StatementType"); // not sure about the type of exception
        var model = SomeFactoryHelper.GetStatementByType(statementType); // returns an actual model by StatementType parameter
                                                                         // this could be a simple switch statement
        bindingContext.ModelMetadata = ModelMetadataProviders.Current.GetMetadataForType(null, model.GetType());
        bindingContext.ModelMetadata.Model = model;
        return model;
    }
}

之后，在Global.asax中注册模型粘合剂：

ModelBinders.Binders.Add(typeof(StatementViewModel), new StatementModelBinder());

控制器

[HttpPost]
public ActionResult Index(StatementViewModel viewModel)
{
    if (ModelState.IsValid)
    {
        // save the model
    }
    return View(viewModel);
}

Answer 2

您可能可以通过这样的CustomModelBinder解决问题：

public class StatementVMBinder : DefaultModelBinder
{
    // this is the only method you need to override:
    protected override object CreateModel(ControllerContext controllerContext, ModelBindingContext bindingContext, Type modelType)
    {
        if (modelType == typeof(StatementViewModel)) // so it will leave the other VM to the default implementation.
        {
            // this gets the value from the form collection, if it was in an input named "ViewModelName":
            var discriminator = bindingContext.ValueProvider.GetValue("ViewModelName");
            Type instantiationType;
            if (discriminator == "SomethingSomething")
                instantiationType = typeof(ReliefVM);
            else // or do a switch case
                instantiationType = typeof(RequestForSalaryVM);
            var obj = Activator.CreateInstance(instantiationType);
            bindingContext.ModelMetadata = ModelMetadataProviders.Current.GetMetadataForType(null, instantiationType);
            bindingContext.ModelMetadata.Model = obj;
            return obj;
        }
        return base.CreateModel(controllerContext, bindingContext, modelType);
    }
}

您的操作将需要此签名：

public ActionResult SaveStatement(User currentUser, StatementViewModel viewModel)

但是您在该方法中收到的viewModel将是适当的派生类型，因此您应该能够像在单个方法中一样施放它。

唯一剩下的就是在global.asax中注册自定义粘合剂。

Answer 3

您是否尝试使用UpdateModel或tryupdatemodel来从Form Collection初始化模型值？查看下面的代码示例

[HttpPost]
public ActionResult SaveStatement(User currentUser, FormCollection statement, string    ViewModelName)
{
  Assembly assembly = typeof(SomeKnownType).Assembly;
  Type type = assembly.GetType(ViewModelName);
  object ViewModel = Activator.CreateInstance(type);
  if (!TryUpdateModel(ViewModel, statement.ToValueProvider()))
  {
     //some another actions
  }
  return View(ViewModelName, ViewModel);
}

Answer 4

如果我是您，我将使用DTO（数据传输对象）包装视图名称和通过接口访问的ViewModel。然后，您有类似的东西：

[HttpPost]
public ActionResult SaveStatement(User currentUser, VMWrapper wrapper)
{
    IVM model = SaveModel(currentUser, wrapper.Statement);
    if (model == null)
        return RedirectToAction("List");
    return View(wrapper.ViewName, model);
}

，但这认为您的观点可以处理VM之间的差异...