asp.net-mvc 如何使用默认值创建一个空的下拉列表？
声明：本页面是StackOverFlow热门问题的中英对照翻译，遵循CC BY-SA 4.0协议，如果您需要使用它，必须同样遵循CC BY-SA许可，注明原文地址和作者信息，同时你必须将它归于原作者（不是我）：StackOverFlow
原文地址: http://stackoverflow.com/questions/15640275/
Warning: these are provided under cc-by-sa 4.0 license. You are free to use/share it, But you must attribute it to the original authors (not me):
StackOverFlow
How to create an empty dropdown list with default value?
提问by Hamid Reza
I want to create an empty dropdown list that has just default value.I use the following code:
我想创建一个只有默认值的空下拉列表。我使用以下代码：
@Html.DropDownList("parent","--Select Parent--")
But in running time I see this error:
但在运行时我看到这个错误：
There is no ViewData item of type 'IEnumerable' that has the key 'parent'.
没有键为“父”的“IEnumerable”类型的 ViewData 项。
How can I solve it? Thanks.
我该如何解决？谢谢。
采纳答案by Shyju
You may simply create an HTML Select option in your view.
您可以简单地在您的视图中创建一个 HTML 选择选项。
<select id="parent" name="parent">
<option value="">Select parent </option>
</select>
EDIT :As per the comment.
编辑：根据评论。
When you submit the form, You can get the selected value by either having a parameter with parentname
当您提交表单时，您可以通过具有parent名称的参数来获取所选值
[HttpPost]
public ActionResult Create(string parent,string otherParameterName)
{
//read and save and return / redirect
}
ORhave a parentproperty in your ViewModel which you are using for Model binding.
或者parent在您的 ViewModel 中有一个用于模型绑定的属性。
public class CreateProject
{
public string parent { set;get;}
public string ProjectName { set;get;}
}
and in your action method.
并在您的操作方法中。
[HttpPost]
public ActionResult Create(CreateProject model)
{
// check model.parent value.
}
回答by stenlytw
You can build an empty DropDownList like this:
您可以像这样构建一个空的 DropDownList：
@Html.DropDownList("parent", Enumerable.Empty<SelectListItem>(), "--Select Parent--")
Reference: Build an empty MVC DropdownListFor for a Cascade Sub-List
回答by Carlos Maia de Morais
Adding html attributes to the above example:
在上面的例子中添加 html 属性：
@Html.DropDownList("Idparent", Enumerable.Empty<SelectListItem>(), "Select one...", new {@class="form-control"})
回答by Syed Raffiuddin
You can do something like this in your controller to build a empty dropdown list
你可以在你的控制器中做这样的事情来建立一个空的下拉列表
ViewBag.ClassID = new SelectList(db.Classes.Where(c => c.ClassID == 0) , "ClassID", "ClassName").ToList();
