Custom Sitecore Index Crawler

CustomCrawler.cs

public class CustomCrawler : SitecoreItemCrawler
{
    protected override bool IsExcludedFromIndex(SitecoreIndexableItem indexable, bool checkLocation = false)
    {
        IDocumentBuilderOptions documentOptions = this.DocumentOptions;
        Assert.IsNotNull(documentOptions, "DocumentOptions");
        Item item = indexable.Item;
        Assert.ArgumentNotNull(item, "item");

        if (item == null)
        {
            return base.IsExcludedFromIndex(indexable, checkLocation);
        }

        bool isExclude = this.IsExcluded(item, this.Language);

        if (isExclude)
        {
            this.Index.Locator.GetInstance<IEvent>().RaiseEvent("indexing:excludedfromindex", this.index.Name, item.Uri);
            return true;
        }

        if (documentOptions.HasIncludedTemplates)
        {
            if (documentOptions.HasExcludedTemplates)
            {
                CrawlingLog.Log.Warn("You have specified both IncludeTemplates and ExcludeTemplates. This logic is not supported. Exclude templates will be ignored.");
            }

            var baseTemplates = item.Template.BaseTemplates;

            if (baseTemplates.Any(baseTemplate => documentOptions.IncludedTemplates.Contains(baseTemplate.ID.ToString())))
            {
                return false;
            }

            this.Index.Locator.GetInstance<IEvent>().RaiseEvent("indexing:excludedfromindex", this.index.Name, item.Uri);
            return true;
        }

        return base.IsExcludedFromIndex(indexable, checkLocation);
    }

    private bool IsExclude(Item item)
    {
        var field = item.Fields["Include In Sitecore Index"];

        return field != null && field.Value != "1";
    }
}