文章主旨：分辨在SharePoint的WebApplication, Site, Web, List, Item, File级别下，用不存在的"对象名"获取"对象"时是否马上抛出异常。用形式化的方式表示如下：SPWebService.ContentService.WebApplications["webAppName"]，webApp.Sites["siteName"]，web.Webs["webName"], web.Lists["listName"] and list.Items["itemIndex"], folder.Files["SeverRelativeUrl"]
经过自己的测试发现：webApplication, site, web, (即前三个)即使对象名字不存在也不会抛异常，而是在Try{}中继续执行后面语句；List, Item, File(即后三个)如果对象名字不存在，会获得不了该对象，直接抛异常去执行Catch(){}中的语句。
第一部分：测试webApplication, site, web级别。先定义每个级别中对象的数量都为0，然后用不存在的名字去获得对象之后，让其数量加1，如果输出的数量为0，则说明直接抛异常；如果输出的数量是1，则说明没有直接抛异常。请看如下代码：
1 using System; 2 using System.Collections.Generic; 3 using System.Linq; 4 using System.Text; 5 using Microsoft.SharePoint; 6 using Microsoft.SharePoint.Administration; 7 8 namespace MyTesting2 9 { 10 class Program 11 { 12 static void Main( string [] args) 13 { 14 // --SPWebApplication, SPSite and SPWeb don't throw exception. 15 16 SPWebApplicationCollection myWebAppCol = SPWebService.ContentService.WebApplications; 17 int webAppCount = 0 ; 18 try 19 { 20 // SharePoint - 123456的名字不存在 21 SPWebApplication testWebApp = myWebAppCol[ " SharePoint - 123456 " ]; 22 webAppCount ++ ; 23 Console.WriteLine( " Program doesn't throw exception. And the count of webApp is: {0} " , webAppCount); 24 } 25 catch 26 { 27 Console.WriteLine( " Exception: The WebApplcition doesn't exist. And the count of WebApp is: {0} " , webAppCount); 28 } 29 30 31 SPWebApplication mWebApp = myWebAppCol[ " SharePoint - 12345 " ]; 32 int siteCount = 0 ; 33 try 34 { 35 // MyTeamSite100的名字不存在 36 SPSite testSite = mWebApp.Sites[ " MyTeamSite100 " ]; 37 siteCount ++ ; 38 Console.WriteLine( " Program doesn't throw exception. And the count of site is: {0} " , siteCount); 39 } 40 catch 41 { 42 Console.WriteLine( " Exception: The site doesn't exist. And the count of site is: {0} " , siteCount); 43 } 44 45 46 SPSite mySite = new SPSite( " http://mosstemplate:12345/sites/MyTeamSiteCollection1 " ); 47 SPWeb myRootWeb = mySite.RootWeb; 48 SPWeb myWeb = myRootWeb.Webs[ " MyTeamSite1 " ]; 49 50 int webCount = 0 ; 51 52 try 53 { 54 // NewNewSubWeb的名字不存在 55 SPWeb testSubWeb = myWeb.Webs[ " NewNewSubWeb " ]; 56 webCount ++ ; 57 Console.WriteLine( " Program doesn't throw exception. And the count of web is: {0} " , webCount); 58 } 59 catch 60 { 61 Console.WriteLine( " Exception: This wed doesn't exist. And the count of web is: {0} " , webCount); 62 } 63 } 64 } 65 66 } 67
经过我的测试，输出的结果如下：Program doesn't throw exception. And the count of webApp is: 1
Program doesn't throw exception. And the count of site is: 1
Program doesn't throw exception. And the count of web is: 1
可以看出，虽然用不存在的名字去获取相应的对象，程序也没有直接抛异常，而是继续执行后面的语句。
第二部分：测试List, Item, File级别。(判断方式和上面的一样)请看如下代码：
1 using System; 2 using System.Collections.Generic; 3 using System.Linq; 4 using System.Text; 5 using Microsoft.SharePoint; 6 using Microsoft.SharePoint.Administration; 7 8 9 namespace MyTesting2 10 { 11 class Program 12 { 13 static void Main( string [] args) 14 { 15 16 #region 17 // --SPList, SPItem and SPFile throw exception. 18 19 SPSite mySite = new SPSite( " http://mosstemplate:12345/sites/MyTeamSiteCollection1 " ); 20 SPWeb myRootWeb = mySite.RootWeb; 21 SPWeb myWeb = myRootWeb.Webs[ " MyTeamSite1 " ]; 22 SPList myList = myWeb.Lists[ " Tasks " ]; 23 SPList yourList = myWeb.Lists[ " NewDocLib1 " ]; 24 25 int listCount = 0 ; 26 int itemCount = 0 ; 27 int fileCount = 0 ; 28 29 #region 30 try 31 { 32 // MyNewNewDocLib名字不存在 33 SPList testList = myWeb.Lists[ " MyNewNewDocLib " ]; 34 listCount ++ ; 35 Console.WriteLine( " Program doesn't throw exception. And the count of list is: {0} " , listCount); 36 } 37 catch 38 { 39 Console.WriteLine( " Exception: This list doesn't exist. And the count of list is: {0} " , listCount); 40 } 41 #endregion 42 43 #region 44 try 45 { 46 // 下标为100的Item不存在 47 SPItem testItem = myList.Items[ 100 ]; 48 itemCount ++ ; 49 Console.WriteLine( " Program doesn't throw exception. And the count of item is: {0} " , itemCount); 50 } 51 catch 52 { 53 Console.WriteLine( " Exception: This item doesn't exist. And the count of item is: {0} " , itemCount); 54 } 55 #endregion 56 57 try 58 { 59 // myFile名字不存在（即：没有此ServerRelativeUrl） 60 SPFile mFile = yourList.RootFolder.Files[ " sites/MyTeamSiteCollection1/MyTeamSite1/NewDocLib1/myFile " ]; 61 fileCount ++ ; 62 Console.WriteLine( " Program doesn't throw exception. And the count of file is: {0} " , fileCount); 63 } 64 catch 65 { 66 Console.WriteLine( " Exception: This file doesn't exist. And the count of file is: {0} " , fileCount); 67 } 68 #endregion 69 } 70 } 71 } 72 经过我的测试，输出结果如下：Exception: This list doesn't exist. And the count of list is: 0
Exception: This item doesn't exist. And the count of item is: 0
Exception: This file doesn't exist. And the count of file is: 0
可以看出：在此三个级别中，用不存在的名字去获得对象时，程序会直接抛出异常。（Try{}中后面的语句将不会执行）。
区分在这几个级别中，用不存在的名字去获取对象时是否直接抛异常的作用是什么呢？
答案是：可以用这种方法去判断，以此为名的对象是否已经存在，如果存在，就不去在此创建此对象；如果不存在，则说明此名字唯一，那么就可以根据是否抛异常，分别在Try{}中或者Catch(){}中取创建此对象。【即：保证创建对象的唯一性，并且保证此唯一的对象一定会被创建成功】