ASP.NET MVC - Html.DropDownList - 值通过ViewData.Model不设置 [英] ASP.NET MVC - Html.DropDownList - Value not set via ViewData.Model

问题描述

刚刚开始使用ASP.NET MVC玩，并绊倒了以下情况。这感觉很像一个错误，但如果它不是，解释将AP preciated：）

Have just started playing with ASP.NET MVC and have stumbled over the following situation. It feels a lot like a bug but if its not, an explanation would be appreciated :)

该视图包含pretty基本的东西

The View contains pretty basic stuff

<%=Html.DropDownList("MyList", ViewData["MyListItems"] as SelectList)%>
<%=Html.TextBox("MyTextBox")%>

当不使用一个模型，价值和选择的项目被设定为预期：

When not using a model, the value and selected item are set as expected:

//works fine
public ActionResult MyAction(){
  ViewData["MyListItems"] = new SelectList(items, "Value", "Text"); //items is an ienumerable of {Value="XXX", Text="YYY"}

  ViewData["MyList"] = "XXX"; //set the selected item to be the one with value 'XXX'
  ViewData["MyTextBox"] = "ABC"; //sets textbox value to 'ABC'

  return View();
}

但是，试图通过模型加载时，文本框具有预期设定的值，但是下拉犯规获得一个选择的项目设置。

But when trying to load via a model, the textbox has the value set as expected, but the dropdown doesnt get a selected item set.

//doesnt work
public ActionResult MyAction(){
  ViewData["MyListItems"] = new SelectList(items, "Value", "Text"); //items is an ienumerable of {Value="XXX", Text="YYY"}

  var model = new {
    MyList = "XXX", //set the selected item to be the one with value 'XXX'
    MyTextBox = "ABC" //sets textbox value to 'ABC'
  }

  return View(model);
}

任何想法？我就可以了目前的想法是，使用模型时，或许，我们仅限于上设置选择列表的构造所选择的项目，而不是使用可视数据（其中正常工作），并与模型通过选择列表中 - 这将有益处清洁code了一点 - 我只是想知道为什么这种方法doesnt工作....

Any ideas? My current thoughts on it are that perhaps when using a model, we're restricted to setting the selected item on the SelectList constructor instead of using the viewdata (which works fine) and passing the selectlist in with the model - which would have the benefit of cleaning the code up a little - I'm just wondering why this method doesnt work....

非常感谢您的任何建议。

Many thanks for any suggestions

推荐答案

一束卷边和hawing后它归结为以下行code的

After a bunch of hemming and hawing it boils down to the following line of code

if (ViewData.ModelState.TryGetValue(key, out modelState))

这意味着MVC正试图通过只看ViewData字典＆LT来解决的价值;>对象，而不是向下遍历到ViewData.Model对象

which means MVC is trying to resolve the value by only looking at the ViewData Dictionary<> object and not traversing down into the ViewData.Model object.

这是否是一个错误，限制或设计决定我不知道。但是，您可以修复它​​通过以下方式：

Whether that's a bug, limitation or design decision I'm not sure. However, you can fix it the following way:

<%= Html.TextBox("MyTextBox", ViewData.Model.MyTextBox) %>

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