值对象不能在查询中跨方法使用
上次修改时间： 2011年5月27日
适用范围： SharePoint Foundation 2010
在使用方法或属性返回值，或返回从 ClientValueObject 类 (JavaScript: ClientValueObject) 继承的对象时，不能将该值用作同一查询中其他方法调用的参数。有关值对象的详细信息，请参阅客户端对象、值对象和标量属性。
例如，假设您要创建一个其显示名称与网站标题相同的 SharePoint 列表。如果您熟悉 SharePoint Foundation 服务器对象模型，则可能会尝试按如下所示编写代码。
错误代码
using System;
using Microsoft.SharePoint.Client;
namespace Microsoft.SDK.SharePointServices.Samples
{
class CreateList
{
static void Main()
{
ClientContext clientContext = new ClientContext("http://MyServer/sites/MySiteCollection");
Web oWebsite = clientContext.Web;
ListCreationInformation listCreationInfo = new ListCreationInformation();
listCreationInfo.TemplateType = 104;
listCreationInfo.Title = oWebsite.Title;
List oList = oWebsite.Lists.Add(listCreationInfo);
clientContext.ExecuteQuery();
}
}
}
编译该代码将会返回 PropertyOrFieldNotInitializedException，因为"属性或字段尚未初始化"。该示例返回异常的原因是：在调用 ExecuteQuery() 之前，网站对象的 Title 属性 (JavaScript: title) 不可用。尽管 SQL 允许您声明包含网站标题的本地变量，并允许您在创建列表时使用该本地变量，但是您不能在客户端对象模型中声明本地变量。因此，您必须调用两次 ExecuteQuery() 或 ExecuteQueryAsync(ClientRequestSucceededEventHandler, ClientRequestFailedEventHandler) (JavaScript: executeQueryAsync(succeededCallback, failedCallback))，第一次调用返回 Title 属性 (JavaScript: title) 的值，第二次调用创建列表，如以下修改后的示例所示。
正确代码
using System;
using Microsoft.SharePoint.Client;
namespace Microsoft.SDK.SharePointServices.Samples
{
class CreateList
{
static void Main()
{
ClientContext clientContext = new ClientContext("http://MyServer/sites/MySiteCollection");
Web oWebsite = clientContext.Web;
clientContext.Load(oWebsite,
w => w.Title);
clientContext.ExecuteQuery();
ListCreationInformation listCreationInfo = new ListCreationInformation();
listCreationInfo.TemplateType = 104;
listCreationInfo.Title = oWebsite.Title;
List oList = oWebsite.Lists.Add(listCreationInfo);
clientContext.ExecuteQuery();
}
}
}
Imports System
Imports Microsoft.SharePoint.Client
Namespace Microsoft.SDK.SharePointServices.Samples
Class CreateList
Shared Sub Main()
Dim clientContext As New ClientContext("http://MyServer/sites/MySiteCollection")
Dim oWebsite As Web = clientContext.Web
clientContext.Load(oWebsite, Function(w) w.Title)
clientContext.ExecuteQuery()
Dim listCreationInfo As New ListCreationInformation()
listCreationInfo.TemplateType = 104
listCreationInfo.Title = oWebsite.Title
Dim oList As List = oWebsite.Lists.Add(listCreationInfo)
clientContext.ExecuteQuery()
End Sub
End Class
End Namespace
function getWebSiteTitle() {
this.clientContext = new SP.ClientContext('/sites/TestWebs/TestWeb1');
this.oWebsite = clientContext.get_web();
clientContext.load(oWebsite, 'Title');
clientContext.executeQueryAsync(Function.createDelegate(this, this.createList), Function.createDelegate(this, this.onQueryFailed));
}
function createList() {
var listCreationInfo = new SP.ListCreationInformation();
listCreationInfo.set_templateType(104);
listCreationInfo.set_title(oWebsite.get_title());
var oList = oWebsite.get_lists().add(listCreationInfo);
clientContext.executeQueryAsync(Function.createDelegate(this, this.onQuerySucceeded), Function.createDelegate(this, this.onQueryFailed));
}
function onQuerySucceeded() {
alert('List created.');
}
function onQueryFailed(sender, args) {
alert('Request failed. ' + args.get_message() + '\n' + args.get_stackTrace());
}