mcs/class/referencesource/System.Xml/System/Xml/XPath/XPathNodeIterator.cs

   1 //------------------------------------------------------------------------------
   2 // <copyright file="XPathNodeIterator.cs" company="Microsoft">
   3 //     Copyright (c) Microsoft Corporation.  All rights reserved.
   4 // </copyright>
   5 // <owner current="true" primary="true">Microsoft</owner>
   6 //------------------------------------------------------------------------------
   7
   8 using System.Collections;
   9 using System.Diagnostics;
  10 using System.Text;
  11
  12 namespace System.Xml.XPath {
  13
  14     [DebuggerDisplay("Position={CurrentPosition}, Current={debuggerDisplayProxy}")]
  15     public abstract class XPathNodeIterator : ICloneable, IEnumerable {
  16         internal int count = -1;
  17
  18         object ICloneable.Clone() { return this.Clone(); }
  19
  20         public abstract XPathNodeIterator Clone();
  21         public abstract bool MoveNext();
  22         public abstract XPathNavigator Current { get; }
  23         public abstract int CurrentPosition { get; }
  24         public virtual int Count {
  25             get {
  26                 if (count == -1) {
  27                     XPathNodeIterator clone = this.Clone();
  28                     while(clone.MoveNext()) ;
  29                     count = clone.CurrentPosition;
  30                 }
  31                 return count;
  32             }
  33         }
  34         public virtual IEnumerator GetEnumerator() {
  35             return new Enumerator(this);
  36         }
  37
  38         private object debuggerDisplayProxy { get { return Current == null ? null : (object)new XPathNavigator.DebuggerDisplayProxy(Current); } }
  39
  40         /// <summary>
  41         /// Implementation of a resetable enumerator that is linked to the XPathNodeIterator used to create it.
  42         /// </summary>
  43         private class Enumerator : IEnumerator {
  44             private XPathNodeIterator original;     // Keep original XPathNodeIterator in case Reset() is called
  45             private XPathNodeIterator current;
  46             private bool iterationStarted;
  47
  48             public Enumerator(XPathNodeIterator original) {
  49                 this.original = original.Clone();
  50             }
  51
  52             public virtual object Current {
  53                 get {
  54                     // 1. Do not reuse the XPathNavigator, as we do in XPathNodeIterator
  55                     // 2. Throw exception if current position is before first node or after the last node
  56                     if (this.iterationStarted) {
  57                         // Current is null if iterator is positioned after the last node
  58                         if (this.current == null)
  59                             throw new InvalidOperationException(Res.GetString(Res.Sch_EnumFinished, string.Empty));
  60
  61                         return this.current.Current.Clone();
  62                     }
  63
  64                     // User must call MoveNext before accessing Current property
  65                     throw new InvalidOperationException(Res.GetString(Res.Sch_EnumNotStarted, string.Empty));
  66                 }
  67             }
  68
  69             public virtual bool MoveNext() {
  70                 // Delegate to XPathNodeIterator
  71                 if (!this.iterationStarted) {
  72                     // Reset iteration to original position
  73                     this.current = this.original.Clone();
  74                     this.iterationStarted = true;
  75                 }
  76
  77                 if (this.current == null || !this.current.MoveNext()) {
  78                     // Iteration complete
  79                     this.current = null;
  80                     return false;
  81                 }
  82                 return true;
  83             }
  84
  85             public virtual void Reset() {
  86                 this.iterationStarted = false;
  87             }
  88         }
  89
  90         private struct DebuggerDisplayProxy {
  91             private XPathNodeIterator nodeIterator;
  92
  93             public DebuggerDisplayProxy(XPathNodeIterator nodeIterator) {
  94                 this.nodeIterator = nodeIterator;
  95             }
  96
  97             public override string ToString() {
  98                 // Position={CurrentPosition}, Current={Current == null ? null : (object) new XPathNavigator.DebuggerDisplayProxy(Current)}
  99                 StringBuilder sb = new StringBuilder();
 100                 sb.Append("Position=");
 101                 sb.Append(nodeIterator.CurrentPosition);
 102                 sb.Append(", Current=");
 103                 if (nodeIterator.Current == null) {
 104                     sb.Append("null");
 105                 } else {
 106                     sb.Append('{');
 107                     sb.Append(new XPathNavigator.DebuggerDisplayProxy(nodeIterator.Current).ToString());
 108                     sb.Append('}');
 109                 }
 110                 return sb.ToString();
 111             }
 112         }
 113     }
 114 }