SPChangeToken Constructor (String)
Initializes a new instance of the SPChangeToken class, based on its serialized form.
Namespace: Microsoft.SharePoint
Assembly: Microsoft.SharePoint (in Microsoft.SharePoint.dll)
Available in Sandboxed Solutions: Yes
Available in SharePoint Online
Syntax
'Declaration
Public Sub New ( _
strChangeToken As String _
)
'Usage
Dim strChangeToken As String
Dim instance As New SPChangeToken(strChangeToken)
public SPChangeToken(
string strChangeToken
)
Parameters
strChangeToken
Type: System.StringThe serialized form of the change token.
Exceptions
| Exception | Condition |
|---|---|
| InvalidOperationException | The strChangeToken does not contain the correct tokens. -or- The version specified by the strChangeToken is not 1. |
Remarks
This overload of the constructor is useful for reconstructing a change token that has been serialized and then stored on disk. For information about serializing an SPChangeToken object, see the ToString method.
The serialized token has five fields separated by semicolons (;), in the following order:
The version number as the string representation of an int.
The scope, which is represented by the Scope property.
The scope ID, which is represented by the ScopeId property.
The date and time of the change as the string representation of a DateTime object.
The change number as the string representation of a long.
Examples
The following example is a console application that queries the change log for changes that have content database scope.
The first time the application runs, the log is queried for all changes starting from the beginning of the log. This query is performed by first setting the ChangeTokenStart property of an SPChangeQuery object to a null value, and then passing the SPQuery object to the GetChanges method. After all changes have been processed, the program serializes the last change token from the last batch of changes by calling the ToString() method and stores the result in a file on disk.
On subsequent runs, the program deserializes the stored change token and uses it to set the ChangeTokenStart property for its query against the change log. The important work is done in the GetStartingToken function, which is where the SPChangeToken constructor is called.
using System;
using System.IO;
using Microsoft.SharePoint;
using Microsoft.SharePoint.Administration;
namespace Test
{
class ConsoleApp
{
private const string DATA_FILE_PATH = "ChangeToken.dat";
static void Main(string[] args)
{
using (SPSite site = new SPSite("https://localhost"))
{
SPChangeQuery query = new SPChangeQuery(true, true);
query.ChangeTokenStart = GetStartingToken();
while (true)
{
// Get a batch of changes.
SPChangeCollection changes = site.ContentDatabase.GetChanges(query);
// Process them.
foreach (SPChange change in changes)
{
Console.WriteLine("Date: {0} Type of object: {1} Type of change: {2}",
change.Time.ToShortDateString(), change.GetType().ToString(), change.ChangeType);
}
// Starting point for next batch.
query.ChangeTokenStart = changes.LastChangeToken;
// If this is the last batch, exit.
if (changes.Count < query.FetchLimit)
break;
}
// Serialize the last token as a starting point for the next run.
SaveLastToken(query.ChangeTokenStart);
}
Console.Write("\nPress ENTER to continue...");
Console.ReadLine();
}
static SPChangeToken GetStartingToken()
{
// Passing a null token to GetChanges fetches
// changes from the start of the log.
SPChangeToken token = null;
// If we have a token from the last run, use it.
if (File.Exists(DATA_FILE_PATH))
{
using (FileStream fs = File.OpenRead(DATA_FILE_PATH))
{
BinaryReader br = new BinaryReader(fs);
try
{
string str = br.ReadString();
// Construct a change token from serialized string.
token = new SPChangeToken(str);
}
catch (EndOfStreamException e)
{
// No serialized string, so do nothing.
}
finally
{
br.Close();
}
}
}
return token;
}
static void SaveLastToken(SPChangeToken token)
{
using (FileStream fs = File.Create(DATA_FILE_PATH))
{
// Serialize the token.
BinaryWriter bw = new BinaryWriter(fs);
string s = token.ToString();
bw.Write(s);
// Flush and close.
bw.Flush();
bw.Close();
}
}
}
}
Imports System
Imports System.IO
Imports Microsoft.SharePoint
Imports Microsoft.SharePoint.Administration
Module ConsoleApp
Private Const DATA_FILE_PATH As String = "ChangeToken.dat"
Sub Main()
Using site As SPSite = New SPSite("https://localhost")
Dim query As New SPChangeQuery(True, True)
query.ChangeTokenStart = GetStartingToken()
While (True)
' Get a batch of changes.
Dim changes As SPChangeCollection = site.ContentDatabase.GetChanges(query)
' Process them.
For Each change As SPChange In changes
Console.WriteLine("Date: {0} Type of object: {1} Type of change: {2}", _
change.Time.ToShortDateString(), change.GetType().ToString(), change.ChangeType)
Next
' This is the starting point for next batch.
query.ChangeTokenStart = changes.LastChangeToken
' If this is the last batch, exit.
If changes.Count < query.FetchLimit Then
Exit While
End If
End While
' Serialize the last token as a starting point for the next run.
SaveLastToken(query.ChangeTokenStart)
End Using
Console.Write(vbCrLf + "Press ENTER to continue...")
Console.ReadLine()
End Sub
Function GetStartingToken() As SPChangeToken
' Passing a null token to GetChanges fetches
' changes from the start of the log.
Dim token As SPChangeToken = Nothing
' If we have a token from the last run, use it.
If File.Exists(DATA_FILE_PATH) Then
Using fs As FileStream = File.OpenRead(DATA_FILE_PATH)
Dim br As BinaryReader = New BinaryReader(fs)
Try
Dim str As String = br.ReadString()
' Construct a change token from serialized string.
token = New SPChangeToken(str)
Catch e As EndOfStreamException
' No serialized string, so do nothing.
Finally
br.Close()
End Try
End Using
End If
Return token
End Function
Sub SaveLastToken(ByRef token As SPChangeToken)
Using fs As FileStream = File.Create(DATA_FILE_PATH)
' Serialize the token.
Dim bw As BinaryWriter = New BinaryWriter(fs)
Dim s As String = token.ToString()
bw.Write(s)
' Flush and close.
bw.Flush()
bw.Close()
End Using
End Sub
End Module