DropDownList的SelectedValue对SelectedItem.Value [英] SelectedValue vs SelectedItem.Value of DropDownList

问题描述

我正在编写一个旧的项目，多年来被几个人打补丁。在某些地方，他们使用SelectedValue属性和其他使用SelectedItem.Value的地方。

问题：是 SelectedValue 只是 SelectedItem.Value 或 SelectedValue 的语法糖引擎盖下不同？哪一个表现更好？

编辑： SelectedItem.Text已被SelectedItem.Value替换

解决方案

SelectedValue 返回与 SelectedItem.Value 相同的值。 / p>

SelectedItem.Value 和 SelectedItem.Text 可能有不同价值观和表现不是一个因素，只有这些属性的含义很重要。

 < asp：DropDownList runat =服务器ID =ddlUserTypes> 
< asp：ListItem Text =AdminsValue =1Selected =true/> 
< asp：ListItem Text =UsersValue =2/> 
< / asp：DropDownList> 
  

这里， ddlUserTypes.SelectedItem.Value == ddlUserTypes.SelectedValue 并且都将返回值1。

ddlUserTypes.SelectedItem.Text 将返回管理员，这不同于 ddlUserTypes.SelectedValue

编辑

在引擎盖下，SelectedValue看起来像这样

  public virtual string SelectedValue 
 {
 get 
 {
 int selectedIndex = this.SelectedIndex; 
 if（selectedIndex> = 0）
 {
 return this.Items [selectedIndex] .Value; 
} 
 return string.Empty; 
} 
} 
  

和SelectedItem如下所示：

  public virtual ListItem SelectedItem 
 {
 get 
 {
 int selectedIndex = this.SelectedIndex; 
 if（selectedIndex> = 0）
 {
 return this.Items [selectedIndex]; 
} 
返回null; 
} 
} 
  

这两个属性之间的一个主要区别是， code> SelectedValue 还有一个 setter ，因为 SelectedItem 没有。编写代码时， SelectedValue 的 getter 更快，执行性能的问题没有真正的理由被讨论。 SelectedValue的一大优点是使用Binding表达式时。

编辑数据绑定场景（您不能使用SelectedItem.Value） p>

 < asp：Repeater runat =server> 
< ItemTemplate> 
< asp：DropDownList ID =ddlCategoriesrunat =server
 SelectedValue ='<％＃Eval（CategoryId）'> 
< / asp：DropDownList> 
< / ItemTemplate> 
< / asp：Repeater> 
  

I'm working on an old project written and then patched by several people over the years. At some places they have used SelectedValue property and other places they used SelectedItem.Value.

Question: Is SelectedValue just a syntactic sugar for SelectedItem.Value or SelectedValue works differently under the hood? Which one performs better?

Edit: SelectedItem.Text was replaced with SelectedItem.Value

解决方案

SelectedValue returns the same value as SelectedItem.Value.

SelectedItem.Value and SelectedItem.Text might have different values and the performance is not a factor here, only the meanings of these properties matters.

<asp:DropDownList runat="server" ID="ddlUserTypes">
    <asp:ListItem Text="Admins" Value="1" Selected="true" />
    <asp:ListItem Text="Users" Value="2"/>
</asp:DropDownList>

Here, ddlUserTypes.SelectedItem.Value == ddlUserTypes.SelectedValue and both would return the value "1".

ddlUserTypes.SelectedItem.Text would return "Admins", which is different from ddlUserTypes.SelectedValue

edit

under the hood, SelectedValue looks like this

public virtual string SelectedValue
{
    get
    {
        int selectedIndex = this.SelectedIndex;
        if (selectedIndex >= 0)
        {
            return this.Items[selectedIndex].Value;
        }
        return string.Empty;
    }
}

and SelectedItem looks like this:

public virtual ListItem SelectedItem
{
    get
    {
        int selectedIndex = this.SelectedIndex;
        if (selectedIndex >= 0)
        {
            return this.Items[selectedIndex];
        }
        return null;
    }
}

One major difference between these two properties is that the SelectedValue has a setter also, since SelectedItem doesn't. The getter of SelectedValue is faster when writing code, and the problem of execution performance has no real reason to be discussed. Also a big advantage of SelectedValue is when using Binding expressions.

edit data binding scenario (you can't use SelectedItem.Value)

<asp:Repeater runat="server">
 <ItemTemplate>
     <asp:DropDownList ID="ddlCategories" runat="server" 
                       SelectedValue='<%# Eval("CategoryId")'>
     </asp:DropDownList>
 </ItemTemplate>
</asp:Repeater>

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