precedingquery.cs source code in C# .NET

                        Code:
                         / DotNET / DotNET / 8.0 / untmp / whidbey / REDBITS / ndp / fx / src / Xml / System / Xml / XPath / Internal / precedingquery.cs / 1 / precedingquery.cs
                        
                        
                            //------------------------------------------------------------------------------ 
// 
//     Copyright (c) Microsoft Corporation.  All rights reserved.
// 
// [....] 
//-----------------------------------------------------------------------------
 
namespace MS.Internal.Xml.XPath { 
    using System;
    using System.Xml; 
    using System.Xml.XPath;
    using System.Diagnostics;
    using System.Collections.Generic;
    using StackNav = ClonableStack; 

    // Algorithm: 
    // Input assumption: qyInput is in DocOrder. 
    // Preceding of a sequence of nodes will be preceding of last node in DocOrder in that sequence.
    // Because qyInput is in DO last input is last node in DO. -- "last" 
    // If last node is attribute or namespace move last to it element.
    // Push this last node and all its ancestors into the ancestorStk. The root node will be the top-most element on the stack.
    // Create descendent iterator from the root. -- "workIterator"
    // Advancing workIterator we meet all nodes from the ancestorStk in stack order. Nodes in ancestorStk do no belong to the 
    // the 'preceding' axis and must be ignored.
    // Last node in ancestorStk is a centinel node; when we pop it from ancestorStk, we should stop iterations. 
 
    internal sealed class PrecedingQuery : BaseAxisQuery {
        private XPathNodeIterator workIterator; 
        private StackNav ancestorStk;

        public PrecedingQuery(Query qyInput, string name, string prefix, XPathNodeType typeTest) : base(qyInput, name, prefix, typeTest) {
            ancestorStk = new StackNav(); 
        }
        private PrecedingQuery(PrecedingQuery other) : base(other) { 
            this.workIterator = Clone(other.workIterator); 
            this.ancestorStk = other.ancestorStk.Clone();
        } 

        public override void Reset() {
            workIterator = null;
            ancestorStk.Clear(); 
            base.Reset();
        } 
 
        public override XPathNavigator Advance() {
            if (workIterator == null) { 
                XPathNavigator last; {
                    XPathNavigator input = qyInput.Advance();
                    if (input == null) {
                        return null; 
                    }
                    last = input.Clone(); 
                    do { 
                        last.MoveTo(input);
                    } while ((input = qyInput.Advance()) != null); 

                    if (last.NodeType == XPathNodeType.Attribute || last.NodeType == XPathNodeType.Namespace) {
                        last.MoveToParent();
                    } 
                }
                // Fill ancestorStk : 
                do { 
                    ancestorStk.Push(last.Clone());
                } while (last.MoveToParent()); 
                // Create workIterator :
                // last.MoveToRoot(); We are on root already
                workIterator = last.SelectDescendants(XPathNodeType.All, true);
            } 

            while (workIterator.MoveNext()) { 
                currentNode = workIterator.Current; 
                if (currentNode.IsSamePosition(ancestorStk.Peek())) {
                    ancestorStk.Pop(); 
                    if (ancestorStk.Count == 0) {
                        currentNode = null;
                        workIterator = null;
                        Debug.Assert(qyInput.Advance() == null, "we read all qyInput.Advance() already"); 
                        return null;
                    } 
                    continue; 
                }
                if (matches(currentNode)) { 
                    position++;
                    return currentNode;
                }
            } 
            Debug.Fail("Algorithm error: we missed the centinel node");
            return null; 
        } 

        public override XPathNodeIterator Clone() { return new PrecedingQuery(this); } 
        public override QueryProps Properties { get { return base.Properties | QueryProps.Reverse; } }
    }
}
 

// File provided for Reference Use Only by Microsoft Corporation (c) 2007.
// Copyright (c) Microsoft Corporation. All rights reserved.
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precedingquery.cs source code in C# .NET

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