## FieldStart class

Represents a start of a Word field in a document.

To learn more, visit the [Working with Fields](https://docs.aspose.com/words/net/working-with-fields/) documentation article.

```csharp
public class FieldStart : FieldChar
```

## Properties

| Name | Description |
| --- | --- |
| [CustomNodeId](../../aspose.words/node/customnodeid/) { get; set; } | Specifies custom node identifier. |
| virtual [Document](../../aspose.words/node/document/) { get; } | Gets the document to which this node belongs. |
| [FieldData](../../aspose.words.fields/fieldstart/fielddata/) { get; } | Gets custom field data which is associated with the field. |
| [FieldType](../../aspose.words.fields/fieldchar/fieldtype/) { get; } | Returns the type of the field. |
| [Font](../../aspose.words/inline/font/) { get; } | Provides access to the font formatting of this object. |
| virtual [IsComposite](../../aspose.words/node/iscomposite/) { get; } | Returns `true` if this node can contain other nodes. |
| [IsDeleteRevision](../../aspose.words/inline/isdeleterevision/) { get; } | Returns true if this object was deleted in Microsoft Word while change tracking was enabled. |
| [IsDirty](../../aspose.words.fields/fieldchar/isdirty/) { get; set; } | Gets or sets whether the current result of the field is no longer correct (stale) due to other modifications made to the document. |
| [IsFormatRevision](../../aspose.words/inline/isformatrevision/) { get; } | Returns true if formatting of the object was changed in Microsoft Word while change tracking was enabled. |
| [IsInsertRevision](../../aspose.words/inline/isinsertrevision/) { get; } | Returns true if this object was inserted in Microsoft Word while change tracking was enabled. |
| [IsLocked](../../aspose.words.fields/fieldchar/islocked/) { get; set; } | Gets or sets whether the parent field is locked (should not recalculate its result). |
| [IsMoveFromRevision](../../aspose.words/inline/ismovefromrevision/) { get; } | Returns `true` if this object was moved (deleted) in Microsoft Word while change tracking was enabled. |
| [IsMoveToRevision](../../aspose.words/inline/ismovetorevision/) { get; } | Returns `true` if this object was moved (inserted) in Microsoft Word while change tracking was enabled. |
| [NextSibling](../../aspose.words/node/nextsibling/) { get; } | Gets the node immediately following this node. |
| override [NodeType](../../aspose.words.fields/fieldstart/nodetype/) { get; } | Returns FieldStart. |
| [ParentNode](../../aspose.words/node/parentnode/) { get; } | Gets the immediate parent of this node. |
| [ParentParagraph](../../aspose.words/inline/parentparagraph/) { get; } | Retrieves the parent [`Paragraph`](../../aspose.words/paragraph/) of this node. |
| [PreviousSibling](../../aspose.words/node/previoussibling/) { get; } | Gets the node immediately preceding this node. |
| [Range](../../aspose.words/node/range/) { get; } | Returns a [`Range`](../../aspose.words/range/) object that represents the portion of a document that is contained in this node. |

## Methods

| Name | Description |
| --- | --- |
| override [Accept](../../aspose.words.fields/fieldstart/accept/)(*[DocumentVisitor](../../aspose.words/documentvisitor/)*) | Accepts a visitor. |
| [Clone](../../aspose.words/node/clone/)(*bool*) | Creates a duplicate of the node. |
| [GetAncestor](../../aspose.words/node/getancestor/)(*[NodeType](../../aspose.words/nodetype/)*) | Gets the first ancestor of the specified [`NodeType`](../../aspose.words/nodetype/). |
| [GetAncestor](../../aspose.words/node/getancestor/)(*Type*) | Gets the first ancestor of the specified object type. |
| [GetField](../../aspose.words.fields/fieldchar/getfield/)() | Returns a field for the field char. |
| override [GetText](../../aspose.words/specialchar/gettext/)() | Gets the special character that this node represents. |
| [NextPreOrder](../../aspose.words/node/nextpreorder/)(*[Node](../../aspose.words/node/)*) | Gets next node according to the pre-order tree traversal algorithm. |
| [PreviousPreOrder](../../aspose.words/node/previouspreorder/)(*[Node](../../aspose.words/node/)*) | Gets the previous node according to the pre-order tree traversal algorithm. |
| [Remove](../../aspose.words/node/remove/)() | Removes itself from the parent. |
| [ToString](../../aspose.words/node/tostring/)(*[SaveFormat](../../aspose.words/saveformat/)*) | Exports the content of the node into a string in the specified format. |
| [ToString](../../aspose.words/node/tostring/)(*[SaveOptions](../../aspose.words.saving/saveoptions/)*) | Exports the content of the node into a string using the specified save options. |

## Remarks

`FieldStart` is an inline-level node and represented by the [`FieldStartChar`](../../aspose.words/controlchar/fieldstartchar/) control character in the document.

`FieldStart` can only be a child of [`Paragraph`](../../aspose.words/paragraph/).

A complete field in a Microsoft Word document is a complex structure consisting of a field start character, field code, field separator character, field result and field end character. Some fields only have field start, field code and field end.

To easily insert a new field into a document, use the [`InsertField`](../../aspose.words/documentbuilder/insertfield/) method.

## Examples

Shows how to work with a collection of fields.

```csharp
Document doc = new Document();
DocumentBuilder builder = new DocumentBuilder(doc);

builder.InsertField(" DATE \\@ \"dddd, d MMMM yyyy\" ");
builder.InsertField(" TIME ");
builder.InsertField(" REVNUM ");
builder.InsertField(" AUTHOR  \"John Doe\" ");
builder.InsertField(" SUBJECT \"My Subject\" ");
builder.InsertField(" QUOTE \"Hello world!\" ");
doc.UpdateFields();

FieldCollection fields = doc.Range.Fields;

Assert.That(fields.Count, Is.EqualTo(6));

// Iterate over the field collection, and print contents and type
// of every field using a custom visitor implementation.
FieldVisitor fieldVisitor = new FieldVisitor();

using (IEnumerator<Field> fieldEnumerator = fields.GetEnumerator())
{
    while (fieldEnumerator.MoveNext())
    {
        if (fieldEnumerator.Current != null)
        {
            fieldEnumerator.Current.Start.Accept(fieldVisitor);
            FieldSeparator separator = fieldEnumerator.Current.Separator;
            if (separator != null)
                separator.Accept(fieldVisitor);
            fieldEnumerator.Current.End.Accept(fieldVisitor);
        }
        else
        {
            Console.WriteLine("There are no fields in the document.");
        }
    }
}

Console.WriteLine(fieldVisitor.GetText());
```

Shows how to work with a collection of fields (FieldVisitor).

```csharp
/// <summary>
/// Document visitor implementation that prints field info.
/// </summary>
public class FieldVisitor : DocumentVisitor
{
    public FieldVisitor()
    {
        mBuilder = new StringBuilder();
    }

    /// <summary>
    /// Gets the plain text of the document that was accumulated by the visitor.
    /// </summary>
    public string GetText()
    {
        return mBuilder.ToString();
    }

    /// <summary>
    /// Called when a FieldStart node is encountered in the document.
    /// </summary>
    public override VisitorAction VisitFieldStart(FieldStart fieldStart)
    {
        mBuilder.AppendLine("Found field: " + fieldStart.FieldType);
        mBuilder.AppendLine("\tField code: " + fieldStart.GetField().GetFieldCode());
        mBuilder.AppendLine("\tDisplayed as: " + fieldStart.GetField().Result);

        return VisitorAction.Continue;
    }

    /// <summary>
    /// Called when a FieldSeparator node is encountered in the document.
    /// </summary>
    public override VisitorAction VisitFieldSeparator(FieldSeparator fieldSeparator)
    {
        mBuilder.AppendLine("\tFound separator: " + fieldSeparator.GetText());

        return VisitorAction.Continue;
    }

    /// <summary>
    /// Called when a FieldEnd node is encountered in the document.
    /// </summary>
    public override VisitorAction VisitFieldEnd(FieldEnd fieldEnd)
    {
        mBuilder.AppendLine("End of field: " + fieldEnd.FieldType);

        return VisitorAction.Continue;
    }

    private readonly StringBuilder mBuilder;
}
```

Shows how to find all hyperlinks in a Word document, and then change their URLs and display names.

```csharp
using System;
using System.Linq;
using System.Text;
using System.Text.RegularExpressions;
using Aspose.Words;
using Aspose.Words.Fields;
using NUnit.Framework;

namespace ApiExamples
{
    public class ExReplaceHyperlinks : ApiExampleBase
    {
        [Test]
        public void Fields()
        {
            Document doc = new Document(MyDir + "Hyperlinks.docx");

            // Hyperlinks in a Word documents are fields. To begin looking for hyperlinks, we must first find all the fields.
            // Use the "SelectNodes" method to find all the fields in the document via an XPath.
            NodeList fieldStarts = doc.SelectNodes("//FieldStart");

            foreach (FieldStart fieldStart in fieldStarts.OfType<FieldStart>())
            {
                if (fieldStart.FieldType == FieldType.FieldHyperlink)
                {
                    Hyperlink hyperlink = new Hyperlink(fieldStart);

                    // Hyperlinks that link to bookmarks do not have URLs.
                    if (hyperlink.IsLocal)
                        continue;

                    // Give each URL hyperlink a new URL and name.
                    hyperlink.Target = NewUrl;
                    hyperlink.Name = NewName;
                }
            }

            doc.Save(ArtifactsDir + "ReplaceHyperlinks.Fields.docx");
        }

        private const string NewUrl = @"http://www.aspose.com";
        private const string NewName = "Aspose - The .NET & Java Component Publisher";
    }

    /// <summary>
    /// HYPERLINK fields contain and display hyperlinks in the document body. A field in Aspose.Words 
    /// consists of several nodes, and it might be difficult to work with all those nodes directly. 
    /// This implementation will work only if the hyperlink code and name each consist of only one Run node.
    ///
    /// The node structure for fields is as follows:
    /// 
    /// [FieldStart][Run - field code][FieldSeparator][Run - field result][FieldEnd]
    /// 
    /// Below are two example field codes of HYPERLINK fields:
    /// HYPERLINK "url"
    /// HYPERLINK \l "bookmark name"
    /// 
    /// A field's "Result" property contains text that the field displays in the document body to the user.
    /// </summary>
    internal class Hyperlink
    {
        internal Hyperlink(FieldStart fieldStart)
        {
            if (fieldStart == null)
                throw new ArgumentNullException("fieldStart");
            if (fieldStart.FieldType != FieldType.FieldHyperlink)
                throw new ArgumentException("Field start type must be FieldHyperlink.");

            mFieldStart = fieldStart;

            // Find the field separator node.
            mFieldSeparator = FindNextSibling(mFieldStart, NodeType.FieldSeparator);
            if (mFieldSeparator == null)
                throw new InvalidOperationException("Cannot find field separator.");

            // Normally, we can always find the field's end node, but the example document 
            // contains a paragraph break inside a hyperlink, which puts the field end 
            // in the next paragraph. It will be much more complicated to handle fields which span several 
            // paragraphs correctly. In this case allowing field end to be null is enough.
            mFieldEnd = FindNextSibling(mFieldSeparator, NodeType.FieldEnd);

            // Field code looks something like "HYPERLINK "http:\\www.myurl.com"", but it can consist of several runs.
            string fieldCode = GetTextSameParent(mFieldStart.NextSibling, mFieldSeparator);
            Match match = gRegex.Match(fieldCode.Trim());

            // The hyperlink is local if \l is present in the field code.
            mIsLocal = match.Groups[1].Length > 0; 
            mTarget = match.Groups[2].Value;
        }

        /// <summary>
        /// Gets or sets the display name of the hyperlink.
        /// </summary>
        internal string Name
        {
            get
            {
                return GetTextSameParent(mFieldSeparator, mFieldEnd);
            }
            set
            {
                // Hyperlink display name is stored in the field result, which is a Run 
                // node between field separator and field end.
                Run fieldResult = (Run) mFieldSeparator.NextSibling;
                fieldResult.Text = value;

                // If the field result consists of more than one run, delete these runs.
                RemoveSameParent(fieldResult.NextSibling, mFieldEnd);
            }
        }

        /// <summary>
        /// Gets or sets the target URL or bookmark name of the hyperlink.
        /// </summary>
        internal string Target
        {
            get
            {
                return mTarget;
            }
            set
            {
                mTarget = value;
                UpdateFieldCode();
            }
        }

        /// <summary>
        /// True if the hyperlinks target is a bookmark inside the document. False if the hyperlink is a URL.
        /// </summary>
        internal bool IsLocal
        {
            get
            {
                return mIsLocal;
            }
            set
            {
                mIsLocal = value;
                UpdateFieldCode();
            }
        }

        private void UpdateFieldCode()
        {
            // A field's field code is in a Run node between the field's start node and field separator.
            Run fieldCode = (Run) mFieldStart.NextSibling;
            fieldCode.Text = string.Format("HYPERLINK {0}\"{1}\"", ((mIsLocal) ? "\\l " : ""), mTarget);

            // If the field code consists of more than one run, delete these runs.
            RemoveSameParent(fieldCode.NextSibling, mFieldSeparator);
        }

        /// <summary>
        /// Goes through siblings starting from the start node until it finds a node of the specified type or null.
        /// </summary>
        private static Node FindNextSibling(Node startNode, NodeType nodeType)
        {
            for (Node node = startNode; node != null; node = node.NextSibling)
            {
                if (node.NodeType == nodeType)
                    return node;
            }

            return null;
        }

        /// <summary>
        /// Retrieves text from start up to but not including the end node.
        /// </summary>
        private static string GetTextSameParent(Node startNode, Node endNode)
        {
            if ((endNode != null) && (startNode.ParentNode != endNode.ParentNode))
                throw new ArgumentException("Start and end nodes are expected to have the same parent.");

            StringBuilder builder = new StringBuilder();
            for (Node child = startNode; !child.Equals(endNode); child = child.NextSibling)
                builder.Append(child.GetText());

            return builder.ToString();
        }

        /// <summary>
        /// Removes nodes from start up to but not including the end node.
        /// Assumes that the start and end nodes have the same parent.
        /// </summary>
        private static void RemoveSameParent(Node startNode, Node endNode)
        {
            if (endNode != null && startNode.ParentNode != endNode.ParentNode)
                throw new ArgumentException("Start and end nodes are expected to have the same parent.");

            Node curChild = startNode;
            while ((curChild != null) && (curChild != endNode))
            {
                Node nextChild = curChild.NextSibling;
                curChild.Remove();
                curChild = nextChild;
            }
        }

        private readonly Node mFieldStart;
        private readonly Node mFieldSeparator;
        private readonly Node mFieldEnd;
        private bool mIsLocal;
        private string mTarget;

        private static readonly Regex gRegex = new Regex(
            "\\S+" + // One or more non spaces HYPERLINK or other word in other languages.
            "\\s+" + // One or more spaces.
            "(?:\"\"\\s+)?" + // Non-capturing optional "" and one or more spaces.
            "(\\\\l\\s+)?" + // Optional \l flag followed by one or more spaces.
            "\"" + // One apostrophe.    
            "([^\"]+)" + // One or more characters, excluding the apostrophe (hyperlink target).
            "\"" // One closing apostrophe.
        );
    }
}
```

### See Also

* class [FieldChar](../fieldchar/)
* namespace [Aspose.Words.Fields](../../aspose.words.fields/)
* assembly [Aspose.Words](../../)