dropdownlist控件设置默认值_DropDownList如何选择默认值

最新推荐文章于 2021-01-26 22:15:57 发布

weixin_39633500

最新推荐文章于 2021-01-26 22:15:57 发布

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文章标签： dropdownlist控件设置默认值

本文链接：https://blog.youkuaiyun.com/weixin_39633500/article/details/111532974

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本文介绍了在ASP.NET MVC中遇到的DropdownList控件设置默认值的问题。当在一个页面上有多个DropdownList并且它们使用相同的Items集合时，如何确保每个DropdownList显示对应的SmallViewModel中的默认ItemId。解决方案是利用EditorTemplate，创建一个`SmallViewModel.cshtml`模板文件，将SelectList作为额外视图数据传递，从而实现正确绑定并显示默认值。

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I have many DropDownLists on page

class BigViewModel

{

public List SmallVM {get;set;}

public List Items {get;set;}

//some other properties

}

class SmallViewModel

{

public string ItemId {get;set;}

//some other properties

}

@for( var i = 0;i

{

@Html.DropdownListFor(m=> m.SmallVM.ItemId, Model.Items)

}

//display other properties

in controller

bigViewModel.Items = List

{

new SelectListItem{Value = "1", Text = "aaa"},

new SelectListItem{Value = "2", Text = "bbb"},

new SelectListItem{Value = "3", Text = "ccc"},

}

bigViewModel.SmallVM = new List

{

new SmallViewModel{ItemId = 3},

new SmallViewModel{ItemId = 2},

}

In controller I set diffrent ItemId for every SmallVM and each DropDownList uses the same Items collection. I want to set default Value from SmallViewModel for each DropDownList. For example in this case there are two DropDownLists first should display default text "ccc" and second "bbb".

Should I put diffrent List for every SmallViewModel and set them Selected property or there is other way?

解决方案

This behavior has been reported as a bug on CodePlex but not yet fixed. Using DropDownListFor() in a for loop does not bind correctly and the first option is always selected despite the value of the property. In order for DropDownListFor() to work correctly when using a collection, you need to use an EditorTemplate for the model.

In /Views/Shared/EditorTemplates/SmallViewModel.cshtml

@model SmallViewModel

@Html.DropdownListFor(m => m.ItemId, (SelectList)ViewData["Items"])

Then in the main view

@model BigViewModel

@using(Html.BeginForm())

{

// Pass the select list to the EditorTemplate as addtionalViewData

@Html.EditorFor(m => m.SmallVM, new { Items = Model.Items })

}

You should now have 2 controls displaying "ccc" and "bbb" respectively.