blocks|key|1262849|text|如果您知道dropdownlist包含要选择的值，请使用：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1262850|ddl.SelectedValue+=+"2";|code-block|syntax|javascript|1262851|如果你不确定这个值是否存在，使用(否则你会得到一个空引用异常)：|1262852|ListItem+selectedListItem+=+ddl.Items.FindByValue("2");

if+(selectedListItem+!=+null)
{
++++selectedListItem.Selected+=+true;
}|1262853|entityMap^0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|M|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|N|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|O|8|@]|9|@]|A|$]]|$1|I|3|J|5|D|7|P|8|@]|9|@]|A|$E|F]]|$1|K|3|-4|5|6|7|Q|8|@]|9|@]|A|$]]]|L|$]]

If you know that the dropdownlist contains the value you're looking to select, use:

<pre><code>ddl.SelectedValue = "2";
</code></pre>

If you're not sure if the value exists, use (or you'll get a null reference exception):

<pre><code>ListItem selectedListItem = ddl.Items.FindByValue("2");

if (selectedListItem != null)
{
 selectedListItem.Selected = true;
}
</code></pre>

blocks|key|1262824|text|请在下面尝试：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1262825|myDropDown.SelectedIndex+=+
myDropDown.Items.IndexOf(myDropDown.Items.FindByValue("myValue"))|code-block|syntax|javascript|1262826|entityMap^0|0|0^^$0|@$1|2|3|4|5|6|7|I|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|J|8|@]|9|@]|A|$E|F]]|$1|G|3|-4|5|6|7|K|8|@]|9|@]|A|$]]]|H|$]]

Please try below:

<pre><code>myDropDown.SelectedIndex = 
myDropDown.Items.IndexOf(myDropDown.Items.FindByValue("myValue"))
</code></pre>

blocks|key|1262914|text|ddl.SetSelectedValue("2");|type|code-block|depth|inlineStyleRanges|entityRanges|data|syntax|javascript|1262915|使用一个方便的扩展：|unstyled|1262916|public+static+class+WebExtensions
{

++++///+<summary>
++++///+Selects+the+item+in+the+list+control+that+contains+the+specified+value,+if+it+exists.
++++///+</summary>
++++///+<param+name="dropDownList"></param>
++++///+<param+name="selectedValue">The+value+of+the+item+in+the+list+control+to+select</param>
++++///+<returns>Returns+true+if+the+value+exists+in+the+list+control,+false+otherwise</returns>
++++public+static+Boolean+SetSelectedValue(this+DropDownList+dropDownList,+String+selectedValue)
++++{
++++++++ListItem+selectedListItem+=+dropDownList.Items.FindByValue(selectedValue);

++++++++if+(selectedListItem+!=+null)
++++++++{
++++++++++++selectedListItem.Selected+=+true;
++++++++++++return+true;
++++++++}
++++++++else
++++++++++++return+false;
++++}
}|1262917|1262918|+Note：任何代码都会发布到公共领域。不需要属性。|blockquote|offset|length|style|BOLD|1262919|1262920|entityMap^0|0|0|0|0|1|4|0|0^^$0|@$1|2|3|4|5|6|7|T|8|@]|9|@]|A|$B|C]]|$1|D|3|E|5|F|7|U|8|@]|9|@]|A|$]]|$1|G|3|H|5|6|7|V|8|@]|9|@]|A|$B|C]]|$1|I|3|-4|5|F|7|W|8|@]|9|@]|A|$]]|$1|J|3|K|5|L|7|X|8|@$M|Y|N|Z|O|P]]|9|@]|A|$]]|$1|Q|3|-4|5|F|7|10|8|@]|9|@]|A|$]]|$1|R|3|-4|5|F|7|11|8|@]|9|@]|A|$]]]|S|$]]

<pre><code>ddl.SetSelectedValue("2");
</code></pre>

With a handy extension:

<pre><code>public static class WebExtensions
{

 /// &lt;summary&gt;
 /// Selects the item in the list control that contains the specified value, if it exists.
 /// &lt;/summary&gt;
 /// &lt;param name="dropDownList"&gt;&lt;/param&gt;
 /// &lt;param name="selectedValue"&gt;The value of the item in the list control to select&lt;/param&gt;
 /// &lt;returns&gt;Returns true if the value exists in the list control, false otherwise&lt;/returns&gt;
 public static Boolean SetSelectedValue(this DropDownList dropDownList, String selectedValue)
 {
 ListItem selectedListItem = dropDownList.Items.FindByValue(selectedValue);

 if (selectedListItem != null)
 {
 selectedListItem.Selected = true;
 return true;
 }
 else
 return false;
 }
}
</code></pre>

<blockquote>
 Note: Any code is released into the public domain. No attribution required.
</blockquote>

blocks|key|1262884|text|这是一种基于字符串val从下拉列表中选择选项的简单方法|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1262885|private+void+SetDDLs(DropDownList+d,string+val)
++++{
++++++++ListItem+li;
++++++++for+(int+i+=+0;+i+<+d.Items.Count;+i%2B%2B)
++++++++{
++++++++++++li+=+d.Items[i];
++++++++++++if+(li.Value+==+val)
++++++++++++{
++++++++++++++++d.SelectedIndex+=+i;
++++++++++++++++break;
++++++++++++}
++++++++}
++++}|code-block|syntax|javascript|1262886|entityMap^0|0|0^^$0|@$1|2|3|4|5|6|7|I|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|J|8|@]|9|@]|A|$E|F]]|$1|G|3|-4|5|6|7|K|8|@]|9|@]|A|$]]]|H|$]]

This is a simple way to select an option from a dropdownlist based on a string val

<pre><code>private void SetDDLs(DropDownList d,string val)
 {
 ListItem li;
 for (int i = 0; i &lt; d.Items.Count; i++)
 {
 li = d.Items[i];
 if (li.Value == val)
 {
 d.SelectedIndex = i;
 break;
 }
 }
 }
</code></pre>

blocks|key|4479142|text|combobox1.SelectedValue+=+x;|type|code-block|depth|inlineStyleRanges|entityRanges|data|syntax|javascript|4479143|我猜你可能想听点别的，但这就是你要的。|unstyled|4479144|entityMap^0|0|0^^$0|@$1|2|3|4|5|6|7|I|8|@]|9|@]|A|$B|C]]|$1|D|3|E|5|F|7|J|8|@]|9|@]|A|$]]|$1|G|3|-4|5|F|7|K|8|@]|9|@]|A|$]]]|H|$]]

<pre><code>combobox1.SelectedValue = x;
</code></pre>

I suspect you may want yo hear something else, but this is what you asked for.

blocks|key|1263059|text|Ian+Boyd+(上面)有一个很好的答案--将这个添加到Ian+Boyd的类"WebExtensions“中，根据文本在下拉列表中选择一项：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1263060|///+<summary>
///+Selects+the+item+in+the+list+control+that+contains+the+specified+text,+if+it+exists.
///+</summary>
///+<param+name="dropDownList"></param>
///+<param+name="selectedText">The+text+of+the+item+in+the+list+control+to+select</param>
///+<returns>Returns+true+if+the+value+exists+in+the+list+control,+false+otherwise</returns>
public+static+Boolean+SetSelectedText(this+DropDownList+dropDownList,+String+selectedText)
{
++++ListItem+selectedListItem+=+dropDownList.Items.FindByText(selectedText);
++++if+(selectedListItem+!=+null)
++++{
++++++++selectedListItem.Selected+=+true;
++++++++return+true;
++++}
++++else
++++++++return+false;
}|code-block|syntax|javascript|1263061|要调用它：|1263062|WebExtensions.SetSelectedText(MyDropDownList,+"MyValue");|1263063|entityMap^0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|M|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|N|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|O|8|@]|9|@]|A|$]]|$1|I|3|J|5|D|7|P|8|@]|9|@]|A|$E|F]]|$1|K|3|-4|5|6|7|Q|8|@]|9|@]|A|$]]]|L|$]]

Ian Boyd (above) had a great answer -- Add this to Ian Boyd's class "WebExtensions" to select an item in a dropdownlist based on text:

<pre><code>/// &lt;summary&gt;
/// Selects the item in the list control that contains the specified text, if it exists.
/// &lt;/summary&gt;
/// &lt;param name="dropDownList"&gt;&lt;/param&gt;
/// &lt;param name="selectedText"&gt;The text of the item in the list control to select&lt;/param&gt;
/// &lt;returns&gt;Returns true if the value exists in the list control, false otherwise&lt;/returns&gt;
public static Boolean SetSelectedText(this DropDownList dropDownList, String selectedText)
{
 ListItem selectedListItem = dropDownList.Items.FindByText(selectedText);
 if (selectedListItem != null)
 {
 selectedListItem.Selected = true;
 return true;
 }
 else
 return false;
}
</code></pre>

To call it:

<pre><code>WebExtensions.SetSelectedText(MyDropDownList, "MyValue");
</code></pre>

blocks|key|1494385|text|我更喜欢|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1494386|if(ddl.Items.FindByValue(string)+!=+null)
{
++++ddl.Items.FindByValue(string).Selected+=+true;
}|code-block|syntax|javascript|1494387|将ddl替换为下拉列表ID，将字符串替换为您的字符串变量名或值。|1494388|entityMap^0|0|0|0^^$0|@$1|2|3|4|5|6|7|K|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|L|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|M|8|@]|9|@]|A|$]]|$1|I|3|-4|5|6|7|N|8|@]|9|@]|A|$]]]|J|$]]

I prefer

<pre><code>if(ddl.Items.FindByValue(string) != null)
{
 ddl.Items.FindByValue(string).Selected = true;
}
</code></pre>

Replace ddl with the dropdownlist ID and string with your string variable name or value.

blocks|key|1494399|text|ddlPageSize.Items.FindByValue("25").Selected+=+true；|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1494400|entityMap^0|0^^$0|@$1|2|3|4|5|6|7|D|8|@]|9|@]|A|$]]|$1|B|3|-4|5|6|7|E|8|@]|9|@]|A|$]]]|C|$]]

ddlPageSize.Items.FindByValue("25").Selected = true;

blocks|key|1263185|text|如果其他人正在尝试这样做并面临问题，那么让我指出一个可能的问题:如果您正在使用Web应用程序，那么在Page_Load中，如果您正在从DB加载下拉列表，同时又想加载数据，那么首先加载您的下拉列表，然后使用选定的下拉条件加载您的数据。|type|unstyled|depth|inlineStyleRanges|offset|length|style|BOLD|entityRanges|data|1263186|protected+void+Page_Load(object+sender,+EventArgs+e)
{
++++if+(!this.IsPostBack)
++++{
++++++++LoadDropdown();+//drop-downs+generated+first
++++++++LoadData();+//+other+data+loading+and+drop-down+value+selection+logic+here
++++}
}|code-block|syntax|javascript|1263187|为了成功地从代码中选择下拉列表，请遵循上面批准的答案，即|1263188|ddl.SelectedValue+=+"2";。|CODE|1263189|希望它能解决这个问题|1263190|entityMap^0|1E|9|0|0|0|0|O|0|0^^$0|@$1|2|3|4|5|6|7|T|8|@$9|U|A|V|B|C]]|D|@]|E|$]]|$1|F|3|G|5|H|7|W|8|@]|D|@]|E|$I|J]]|$1|K|3|L|5|6|7|X|8|@]|D|@]|E|$]]|$1|M|3|N|5|6|7|Y|8|@$9|Z|A|10|B|O]]|D|@]|E|$]]|$1|P|3|Q|5|6|7|11|8|@]|D|@]|E|$]]|$1|R|3|-4|5|6|7|12|8|@]|D|@]|E|$]]]|S|$]]

If anyone else is trying this and facing problem then let me point one possible problem: If you are using Web Application then inside Page_Load if you are loading drop-down from DB and at the sametime you want to load data, then first load your drop-down lists and then load your data with selected drop-down conditions. 

<pre><code>protected void Page_Load(object sender, EventArgs e)
{
 if (!this.IsPostBack)
 {
 LoadDropdown(); //drop-downs generated first
 LoadData(); // other data loading and drop-down value selection logic here
 }
}
</code></pre>

And for successfully selecting drop-down from code follow the approved answer above which is 

<code>ddl.SelectedValue = "2";</code>. 

Hope it solves the problem

blocks|key|194795|text|对于那些通过搜索来这里的人(因为这个帖子已经超过3年了)：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|194796|string+entry+//+replace+with+search+value

if+(comboBox.Items.Contains(entry))
+++comboBox.SelectedIndex+=+comboBox.Items.IndexOf(entry);
else
+++comboBox.SelectedIndex+=+0;|code-block|syntax|javascript|194797|entityMap^0|0|0^^$0|@$1|2|3|4|5|6|7|I|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|J|8|@]|9|@]|A|$E|F]]|$1|G|3|-4|5|6|7|K|8|@]|9|@]|A|$]]]|H|$]]

For those who come here by search (because this thread is over 3 years old):

<pre><code>string entry // replace with search value

if (comboBox.Items.Contains(entry))
 comboBox.SelectedIndex = comboBox.Items.IndexOf(entry);
else
 comboBox.SelectedIndex = 0;
</code></pre>

How to SELECT a drop down list item by value programatically in C#.NET?

How to SELECT a dropdown list item by value programmatically

翻译质量差，导致语言生硬或混乱。

没有提供实际的解决方法或示例。

解答不清晰，无法理解或解决问题。

页面排版不美观，阅读体验差。

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如何在C#.NET中编程选择下拉列表项？

问如何以编程方式逐个选择下拉列表
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