Search index events Leave feedback

This page contains information about the purpose and use of all index events.

OperationFinished event

The OperationFinished event occurs when an index operation completes. The OperationType property of the event arguments returns a value of the OperationType enumeration:

Indexing - adding documents to an index;
Updating - updating documents in an index;
Merging - merging indexes;
Optimizing - optimizing an index (merging its segments);
Deleting - deleting documents from an index by paths or by document keys.

This event can be used to receive notification of the completion of an asynchronous operation. The following example demonstrates the use of the event.

string indexFolder = @"c:\MyIndex\";
string documentsFolder = @"c:\MyDocuments\";
 
// Creating an index
Index index = new Index(indexFolder);
 
// Subscribing to the event
index.Events.OperationFinished += (sender, args) =>
{
    // Writing operation details to the console
    Console.WriteLine("Operation finished: " + args.OperationType);
    Console.WriteLine("Message: " + args.Message);
    Console.WriteLine("Index folder: " + args.IndexFolder);
    Console.WriteLine("Time: " + args.Time);
};
 
// Indexing documents from the specified folder
IndexingOptions options = new IndexingOptions();
options.IsAsync = true; // Enabling asynchronous indexing mode
index.Add(documentsFolder, options);

ErrorOccurred event

The ErrorOccurred event occurs when an error happens in an index. Errors in an index can be caused, for example, by file system errors or unsupported formats of indexed documents. The IsCritical property of the event arguments indicates a critical error after which the index gets the Failed status and has to be opened again. The CheckSegments method also reports the damage found and the repairs made through this event (see Checking index integrity). An example of receiving error notifications in the index is presented below.

string indexFolder = @"c:\MyIndex\";
string documentsFolder = @"c:\MyDocuments\";
string query = "Einstein";
 
// Creating an index
Index index = new Index(indexFolder);
 
// Subscribing to the event
index.Events.ErrorOccurred += (sender, args) =>
{
    // Writing an error message to the console
    Console.WriteLine((args.IsCritical ? "Critical error: " : "Error: ") + args.Message);
};
 
// Indexing documents from the specified folder
index.Add(documentsFolder);
 
// Searching in the index
SearchResult result = index.Search(query);

OperationProgressChanged event

The OperationProgressChanged event occurs when the progress of an indexing or updating operation changes. The event arguments (OperationProgressEventArgs) contain the total number of documents to process, the numbers of processed and skipped documents, the progress percentage, as well as the key, the path and the status of the last processed document. The example below demonstrates how to track the progress of an index operation.

string indexFolder = @"c:\MyIndex\";
string documentsFolder = @"c:\MyDocuments\";
 
// Creating an index
Index index = new Index(indexFolder);
 
// Subscribing to the event
index.Events.OperationProgressChanged += (sender, args) =>
{
    Console.WriteLine("Last processed: " + args.LastDocumentPath);
    Console.WriteLine("Result: " + args.LastDocumentStatus);
    Console.WriteLine("Processed documents: " + args.ProcessedDocuments);
    Console.WriteLine("Skipped documents: " + args.SkippedDocuments);
    Console.WriteLine("Total documents: " + args.TotalDocuments);
    Console.WriteLine("Progress percentage: " + args.ProgressPercentage);
};
 
// Indexing documents from the specified folder
index.Add(documentsFolder);

OptimizationProgressChanged event

The OptimizationProgressChanged event occurs when the progress of an index optimization operation changes. The example below demonstrates how to track the progress of the index optimization operation.

string indexFolder = @"c:\MyIndex\";

// Opening an index
Index index = new Index(indexFolder);

// Subscribing to the event
index.Events.OptimizationProgressChanged += (sender, args) =>
{
    Console.WriteLine("Processed segments: " + args.ProcessedSegments);
    Console.WriteLine("Total segments: " + args.TotalSegments);
    Console.WriteLine("Progress percentage: " + args.ProgressPercentage);
};

// Optimizing the index
index.Optimize();

PasswordRequired event

The PasswordRequired event occurs when an index requires a password to open a document. An example of processing this event is presented below.

string indexFolder = @"c:\MyIndex\";
string documentsFolder = @"c:\MyDocuments\";
 
// Creating an index
Index index = new Index(indexFolder);
 
// Subscribing to the event
index.Events.PasswordRequired += (sender, args) =>
{
    if (args.DocumentFullPath.EndsWith("ProtectedDocument.pdf", StringComparison.InvariantCultureIgnoreCase))
    {
        args.Password = "123456";
    }
};
 
// Indexing documents from the specified folder
index.Add(documentsFolder);

FileIndexing event

The FileIndexing event occurs immediately before the start of indexing a document. This event can be used for

Skipping indexing of the current document (see also Document filtering during indexing page);
Specifying the encoding of the current text document (see also Text file encoding detection page);
Specifying a custom text extractor for the current document (see also Custom text extractors page);
Setting additional arbitrary fields for the current document;
Setting the attributes of the current document (see also Document attributes page);
Specifying a custom word splitter for the current document (see also Custom text segmenter page).

The following example demonstrates how to add additional fields to documents ending in “Protected.pdf” and how to skip indexing documents containing “important” text in their paths.

string indexFolder = @"c:\MyIndex\";
string documentsFolder = @"c:\MyDocuments\";
 
// Creating an index
Index index = new Index(indexFolder);
 
// Subscribing to the event
index.Events.FileIndexing += (sender, args) =>
{
    if (args.DocumentFullPath.EndsWith("Protected.pdf", StringComparison.InvariantCultureIgnoreCase))
    {
        args.AdditionalFields = new DocumentField[]
        {
            new DocumentField("Tags", "Protected")
        };
    }
    if (args.DocumentFullPath.ToLowerInvariant().Contains("important"))
    {
        args.SkipIndexing = true;
    }
};
 
// Indexing documents from the specified folder
index.Add(documentsFolder);

StatusChanged event

The StatusChanged event occurs when an index status changes. The new status is available in the Status property of the event arguments. The following example demonstrates how to use this event to notify the completion of an index operation.

string indexFolder = @"c:\MyIndex\";
string documentsFolder = @"c:\MyDocuments\";
 
// Creating an index
Index index = new Index(indexFolder);
 
// Subscribing to the event
index.Events.StatusChanged += (sender, args) =>
{
    if (args.Status == IndexStatus.Ready || args.Status == IndexStatus.Failed)
    {
        // A notification of the operation completion should be here
    }
};
 
// Setting the flag for asynchronous indexing
IndexingOptions options = new IndexingOptions();
options.IsAsync = true;
 
// Asynchronous indexing documents from the specified folder
// The method terminates before the operation completes
index.Add(documentsFolder, options);

SearchPhaseCompleted event

The SearchPhaseCompleted event occurs when a phase (or stage) of a search operation in an index completes. This event is used to study intermediate search results when tuning search queries. Information on the phases of different types of search is presented on the page Search flow. The following example demonstrates the use of this event.

string indexFolder = @"c:\MyIndex\";
string documentsFolder = @"c:\MyDocuments\";
 
// Creating an index
Index index = new Index(indexFolder);
 
// Indexing documents from the specified folder
index.Add(documentsFolder);
 
// Subscribing to the event
index.Events.SearchPhaseCompleted += (sender, args) =>
{
    Console.WriteLine("Search phase: " + args.SearchPhase);
    Console.WriteLine("Words: " + args.Words.Length);
    for (int i = 0; i < args.Words.Length; i++)
    {
        Console.WriteLine("\t" + args.Words[i]);
    }
    Console.WriteLine();
};
 
SearchOptions options = new SearchOptions();
options.UseSynonymSearch = true;
options.UseWordFormsSearch = true;
options.FuzzySearch.Enabled = true;
options.UseHomophoneSearch = true;
SearchResult result = index.Search("Einstein", options);

ImagePreparing event

The ImagePreparing event occurs immediately before adding indexed image to an index. The event can be used, for example, to save an image separately from its containing document, since it provides an image data stream. The following example demonstrates the use of this event.

string indexFolder = @"c:\MyIndex\";
string documentsFolder = @"c:\MyDocuments\";

// Creating an index
Index index = new Index(indexFolder);

// Subscribing to the event
index.Events.ImagePreparing += (sender, args) =>
{
    Console.WriteLine("Document: " + args.DocumentKey);
    Console.WriteLine("Image inner path: " + string.Join("/", args.InnerPath));
    Console.WriteLine("Image index: " + args.ImageIndex);
    Console.WriteLine("Image frames: " + args.ImageFrames.Length);
};

// Indexing files
index.Add(documentsFolder);

More resources

GitHub examples

You may easily run the code from documentation articles and see the features in action in our GitHub examples:

Free online document search App

Along with full featured .NET library we provide simple, but powerful free Apps.

You are welcome to search over your PDF, DOC, DOCX, PPT, PPTX, XLS, XLSX and more with our free online Free Online Document Search App.

We value your opinion. Your feedback will help us improve our documentation.