blocks|key|2337140|text|您找到PT的索引并添加1吗？(但请记住要检查索引%2B1<列表的长度)|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|2337141|//+Find+the+index+of+PT
int+ix+=+TagList.FindIndex(x+=>+x.FieldTag+==+"PT");

//+index+found
if+(ix+!=+-1)
{
++++//+Check+that+index+%2B+1+<+the+length+of+the+List
++++if+(ix+%2B+1+<+TagList.Count)
++++{
++++++++var+position+=+TagList[ix+%2B+1];+//+Add+1
++++}
}|code-block|syntax|javascript|2337142|entityMap^0|3|2|0|0^^$0|@$1|2|3|4|5|6|7|M|8|@$9|N|A|O|B|C]]|D|@]|E|$]]|$1|F|3|G|5|H|7|P|8|@]|D|@]|E|$I|J]]|$1|K|3|-4|5|6|7|Q|8|@]|D|@]|E|$]]]|L|$]]

You find the index of <code>PT</code> and add 1? (but remember to check that the index + 1 &lt; the length of the List)

<pre><code>// Find the index of PT
int ix = TagList.FindIndex(x =&gt; x.FieldTag == "PT");

// index found
if (ix != -1)
{
 // Check that index + 1 &lt; the length of the List
 if (ix + 1 &lt; TagList.Count)
 {
 var position = TagList[ix + 1]; // Add 1
 }
}
</code></pre>

blocks|key|2337172|text|如果希望在每个项目之后使用LINQ+PT获得下一个元素的Position，那么可以用LINQ在一两行中解决它：|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|2337173|var+resultTag+=+TagList.SkipWhile(x+=>+x.FieldTag+!=+"PT").Skip(1).FirstOrDefault();
var+resultPosition+=+resultTag+==+null+?++0+:+resultTag.Position;|code-block|syntax|javascript|2337174|附加信息：|BOLD|2337175|如果您想将其转换为int，那么只需显式地转换它即可。|2337176|var+resultTag+=+TagList.SkipWhile(x+=>+x.FieldTag+!=+"PT").Skip(1).FirstOrDefault();
int+resultPosition+=+resultTag+==+null+?++0+:+(int)resultTag.Position;|2337177|entityMap^0|S|8|0|0|0|5|0|9|3|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|@$9|Y|A|Z|B|M]]|D|@]|E|$]]|$1|N|3|O|5|6|7|10|8|@$9|11|A|12|B|C]]|D|@]|E|$]]|$1|P|3|Q|5|H|7|13|8|@]|D|@]|E|$I|J]]|$1|R|3|-4|5|6|7|14|8|@]|D|@]|E|$]]]|S|$]]

If you want to get next element's <code>Position</code> after each item with <code>FieldTag</code> PT, then you can solve it in one or two lines with LINQ:

<pre><code>var resultTag = TagList.SkipWhile(x =&gt; x.FieldTag != "PT").Skip(1).FirstOrDefault();
var resultPosition = resultTag == null ? 0 : resultTag.Position;
</code></pre>

Additional: 
If you want to cast it to <code>int</code> then just cast it explicitly.

<pre><code>var resultTag = TagList.SkipWhile(x =&gt; x.FieldTag != "PT").Skip(1).FirstOrDefault();
int resultPosition = resultTag == null ? 0 : (int)resultTag.Position;
</code></pre>

blocks|key|2337201|text|不幸的是，每次执行搜索时，您都必须遍历列表，找到要查找的字段标记，然后转到下一个元素并获取位置值。e..：用于查找解决方案的O(n)：|type|unstyled|depth|inlineStyleRanges|offset|length|style|BOLD|entityRanges|data|2337202|++++private+static+object+SearchPosition(List<TagType<object>>+tagList,+string+fieldTag)
++++{
++++++++var+i+=+tagList.FindIndex(x+=>+x.FieldTag+==+"PT");

++++++++if+(i+>=+0+&&+i+<+tagList.Count)
++++++++{
++++++++++++return+tagList[i+%2B+1].Position;
++++++++}
++++}|code-block|syntax|javascript|2337203|和测试：|2337204|++++[Test]
++++public+void+FieldTagTest()
++++{
++++++++var+res+=+SearchPosition(_tagList,+"PT");

++++++++res.ToString().Should().Be("ID2");
++++}|2337205|如果列表不经常更改，则应该生成一个Dictionary<string,int>，其中FieldTag作为Key，列表索引位置为value。当然，每次修改列表时，都需要再次构建此索引。|CODE|2337206|O(1)解决方案是：|2337207|++++private+static+object+SearchPositionUsingIndex(List<TagType<object>>+tagList,+string+fieldTag)
++++{
++++++++//+You+would+save+this+index,+and+build+it+only+once,+
++++++++//+or+rebuild+it+whenver+something+changes.
++++++++//+you+could+implement+custom+index+modifications.
++++++++var+index+=+BuildIndex(tagList);

++++++++int+i;
++++++++if+(!index.TryGetValue(fieldTag,+out+i))+return+null;
++++++++if+(i+%2B+1+>=+tagList.Count)+return+null;
++++++++return+tagList[i+%2B+1].Position;
++++}

++++private+static+Dictionary<string,+int>+BuildIndex(List<TagType<object>>+tagList)
++++{
++++++++var+index+=+new+Dictionary<string,+int>();

++++++++for+(int+i+=+0;+i+<+tagList.Count;+i%2B%2B)
++++++++{
++++++++++++var+tag+=+tagList[i];
++++++++++++if+(!index.ContainsKey(tag.FieldTag))+index.Add(tag.FieldTag,+i);
++++++++}
++++++++return+index;
++++}|2337208|2337209|++++[Test]
++++public+void+FieldTagTestUsingIndex()
++++{
++++++++var+res+=+SearchPositionUsingIndex(_tagList,+"PT");

++++++++res.ToString().Should().Be("ID2");
++++}|2337210|或者您可以使用1行LINQ方法，也就是O(n)|2337211|++++[Test]
++++public+void+FieldTagTestLinq()
++++{
++++++++var+res+=+SearchUsingLinq();

++++++++res.ToString().Should().Be("ID2");
++++}

++++private+object+SearchUsingLinq()
++++{
++++++++var+p+=+_tagList.SkipWhile(x+=>+x.FieldTag+!=+"PT").Skip(1).FirstOrDefault();
++++++++return+p+!=+null+?+p.Position+:+null;
++++}|2337212|TestSetup|2337213|public+class+SO29047477
{
++++private+List<TagType<object>>+_tagList;

++++[SetUp]
++++public+void+TestSetup()
++++{
++++++++_tagList+=+new+List<TagType<dynamic>>();

++++++++_tagList.Add(new+TagType<dynamic>()+{+FieldTag+=+"ID",+Position+=+"ID1"});
++++++++_tagList.Add(new+TagType<dynamic>()+{+FieldTag+=+"PT",+Position+=+"PT1"+});
++++++++_tagList.Add(new+TagType<dynamic>()+{+FieldTag+=+"ID",+Position+=+"ID2"+});
++++++++_tagList.Add(new+TagType<dynamic>()+{+FieldTag+=+"EC",+Position+=+"EC1"+});

++++}
}|2337214|entityMap^0|1Q|4|0|0|0|0|H|M|16|8|1G|3|1R|5|0|0|4|0|0|0|0|J|4|0|0|0|9|0|0^^$0|@$1|2|3|4|5|6|7|18|8|@$9|19|A|1A|B|C]]|D|@]|E|$]]|$1|F|3|G|5|H|7|1B|8|@]|D|@]|E|$I|J]]|$1|K|3|L|5|6|7|1C|8|@]|D|@]|E|$]]|$1|M|3|N|5|H|7|1D|8|@]|D|@]|E|$I|J]]|$1|O|3|P|5|6|7|1E|8|@$9|1F|A|1G|B|Q]|$9|1H|A|1I|B|Q]|$9|1J|A|1K|B|Q]|$9|1L|A|1M|B|Q]]|D|@]|E|$]]|$1|R|3|S|5|6|7|1N|8|@$9|1O|A|1P|B|C]]|D|@]|E|$]]|$1|T|3|U|5|H|7|1Q|8|@]|D|@]|E|$I|J]]|$1|V|3|L|5|6|7|1R|8|@]|D|@]|E|$]]|$1|W|3|X|5|H|7|1S|8|@]|D|@]|E|$I|J]]|$1|Y|3|Z|5|6|7|1T|8|@$9|1U|A|1V|B|C]]|D|@]|E|$]]|$1|10|3|11|5|H|7|1W|8|@]|D|@]|E|$I|J]]|$1|12|3|13|5|6|7|1X|8|@$9|1Y|A|1Z|B|C]]|D|@]|E|$]]|$1|14|3|15|5|H|7|20|8|@]|D|@]|E|$I|J]]|$1|16|3|-4|5|6|7|21|8|@]|D|@]|E|$]]]|17|$]]

Unfortunately each time you do a search you will have to iterate over the list, find the field tag you are looking for, then go to the next element and get the position value. e..: An O(n) for lookup solution:

<pre><code> private static object SearchPosition(List&lt;TagType&lt;object&gt;&gt; tagList, string fieldTag)
 {
 var i = tagList.FindIndex(x =&gt; x.FieldTag == "PT");

 if (i &gt;= 0 &amp;&amp; i &lt; tagList.Count)
 {
 return tagList[i + 1].Position;
 }
 }
</code></pre>

And test:

<pre><code> [Test]
 public void FieldTagTest()
 {
 var res = SearchPosition(_tagList, "PT");

 res.ToString().Should().Be("ID2");
 }
</code></pre>

If your list does not change often, you should build a <code>Dictionary&lt;string,int&gt;</code> with the <code>FieldTag</code> as <code>Key</code>and the list index position as <code>value</code>. Ofcourse each time you modify the list you would need to build this index again.

An O(1) solution is:

<pre><code> private static object SearchPositionUsingIndex(List&lt;TagType&lt;object&gt;&gt; tagList, string fieldTag)
 {
 // You would save this index, and build it only once, 
 // or rebuild it whenver something changes.
 // you could implement custom index modifications.
 var index = BuildIndex(tagList);

 int i;
 if (!index.TryGetValue(fieldTag, out i)) return null;
 if (i + 1 &gt;= tagList.Count) return null;
 return tagList[i + 1].Position;
 }

 private static Dictionary&lt;string, int&gt; BuildIndex(List&lt;TagType&lt;object&gt;&gt; tagList)
 {
 var index = new Dictionary&lt;string, int&gt;();

 for (int i = 0; i &lt; tagList.Count; i++)
 {
 var tag = tagList[i];
 if (!index.ContainsKey(tag.FieldTag)) index.Add(tag.FieldTag, i);
 }
 return index;
 }
</code></pre>

And test:

<pre><code> [Test]
 public void FieldTagTestUsingIndex()
 {
 var res = SearchPositionUsingIndex(_tagList, "PT");

 res.ToString().Should().Be("ID2");
 }
</code></pre>

Or you could use a 1 line LINQ method, which is also O(n):

<pre><code> [Test]
 public void FieldTagTestLinq()
 {
 var res = SearchUsingLinq();

 res.ToString().Should().Be("ID2");
 }

 private object SearchUsingLinq()
 {
 var p = _tagList.SkipWhile(x =&gt; x.FieldTag != "PT").Skip(1).FirstOrDefault();
 return p != null ? p.Position : null;
 }
</code></pre>

TestSetup

<pre><code>public class SO29047477
{
 private List&lt;TagType&lt;object&gt;&gt; _tagList;

 [SetUp]
 public void TestSetup()
 {
 _tagList = new List&lt;TagType&lt;dynamic&gt;&gt;();

 _tagList.Add(new TagType&lt;dynamic&gt;() { FieldTag = "ID", Position = "ID1"});
 _tagList.Add(new TagType&lt;dynamic&gt;() { FieldTag = "PT", Position = "PT1" });
 _tagList.Add(new TagType&lt;dynamic&gt;() { FieldTag = "ID", Position = "ID2" });
 _tagList.Add(new TagType&lt;dynamic&gt;() { FieldTag = "EC", Position = "EC1" });

 }
}
</code></pre>

blocks|key|5161813|text|public+Position?+GetNextPosition(string+FieldTagVal)
{
++++bool+returnNext+=+false;
++++foreach(TagType+t+in+TagList)+
++++{
+++++++if+(returnNext)+return+t.Position;
+++++++if+(t.FieldTag+==+FieldTagVal)+returnNext+=+true;
++++}
++++return+null;
}|type|code-block|depth|inlineStyleRanges|entityRanges|data|syntax|javascript|5161814|unstyled|entityMap^0|0^^$0|@$1|2|3|4|5|6|7|G|8|@]|9|@]|A|$B|C]]|$1|D|3|-4|5|E|7|H|8|@]|9|@]|A|$]]]|F|$]]

<pre><code>public Position? GetNextPosition(string FieldTagVal)
{
 bool returnNext = false;
 foreach(TagType t in TagList) 
 {
 if (returnNext) return t.Position;
 if (t.FieldTag == FieldTagVal) returnNext = true;
 }
 return null;
}
</code></pre>

This is my Generic List:

public class TagType
 {
 public string FieldTag;
 public int Position;
 }

<pre><code>List&lt;TagType&lt;dynamic&gt;&gt; TagList = new List&lt;TagType&lt;dynamic&gt;&gt;();

TagList.Add(new TagType&lt;dynamic&gt;() { FieldTag = "ID", Position = posIdStr });
TagList.Add(new TagType&lt;dynamic&gt;() { FieldTag = "PT", Position = posPtStr });
TagList.Add(new TagType&lt;dynamic&gt;() { FieldTag = "ID", Position = posIdStr });
TagList.Add(new TagType&lt;dynamic&gt;() { FieldTag = "EC", Position = posECStr });
</code></pre>

I am trying to get Position value for the FieldTag that comes after (for eg: PT).
How do I do this?

How to find the next element in a generic List?

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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这是我的通用清单：公共类TagType {公共字符串FieldTag；公共int位置；}List<TagType<dynamic>> TagList = new List<TagType<dynamic>>();TagList.Add(new TagType<dynamic>() { FieldTag = "ID", ...

问如何在泛型列表中找到下一个元素？
EN

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问如何在泛型列表中找到下一个元素？EN