IDictionaryEnumerator 介面

定義

命名空間:

System.Collections

組件:

netstandard.dll, System.Runtime.dll

列舉非泛型字典的專案。

C#

public interface IDictionaryEnumerator : System.Collections.IEnumerator

衍生

System.Collections.Generic.Dictionary<TKey,TValue>.Enumerator

System.Collections.Generic.OrderedDictionary<TKey,TValue>.Enumerator

System.Collections.Generic.SortedDictionary<TKey,TValue>.Enumerator

System.Windows.Markup.Localizer.BamlLocalizationDictionaryEnumerator

實作

IEnumerator

範例

此程式代碼範例示範如何定義實作 IDictionaryEnumerator 介面的字典列舉值。

C#

using System;
using System.Collections;

// This class implements a simple dictionary using an array of DictionaryEntry objects (key/value pairs).
public class SimpleDictionary : IDictionary
{
    // The array of items
    private DictionaryEntry[] items;
    private Int32 ItemsInUse = 0;

    // Construct the SimpleDictionary with the desired number of items.
    // The number of items cannot change for the life time of this SimpleDictionary.
    public SimpleDictionary(Int32 numItems)
    {
        items = new DictionaryEntry[numItems];
    }

    #region IDictionary Members
    public bool IsReadOnly { get { return false; } }
    public bool Contains(object key)
    {
       Int32 index;
       return TryGetIndexOfKey(key, out index);
    }
    public bool IsFixedSize { get { return false; } }
    public void Remove(object key)
    {
        if (key == null) throw new ArgumentNullException("key");
        // Try to find the key in the DictionaryEntry array
        Int32 index;
        if (TryGetIndexOfKey(key, out index))
        {
            // If the key is found, slide all the items up.
            Array.Copy(items, index + 1, items, index, ItemsInUse - index - 1);
            ItemsInUse--;
        }
        else
        {
            // If the key is not in the dictionary, just return.
        }
    }
    public void Clear() { ItemsInUse = 0; }
    public void Add(object key, object value)
    {
        // Add the new key/value pair even if this key already exists in the dictionary.
        if (ItemsInUse == items.Length)
            throw new InvalidOperationException("The dictionary cannot hold any more items.");
        items[ItemsInUse++] = new DictionaryEntry(key, value);
    }
    public ICollection Keys
    {
        get
        {
            // Return an array where each item is a key.
            Object[] keys = new Object[ItemsInUse];
            for (Int32 n = 0; n < ItemsInUse; n++)
                keys[n] = items[n].Key;
            return keys;
        }
    }
    public ICollection Values
    {
        get
        {
            // Return an array where each item is a value.
            Object[] values = new Object[ItemsInUse];
            for (Int32 n = 0; n < ItemsInUse; n++)
                values[n] = items[n].Value;
            return values;
        }
    }
    public object this[object key]
    {
        get
        {
            // If this key is in the dictionary, return its value.
            Int32 index;
            if (TryGetIndexOfKey(key, out index))
            {
                // The key was found; return its value.
                return items[index].Value;
            }
            else
            {
                // The key was not found; return null.
                return null;
            }
        }

        set
        {
            // If this key is in the dictionary, change its value.
            Int32 index;
            if (TryGetIndexOfKey(key, out index))
            {
                // The key was found; change its value.
                items[index].Value = value;
            }
            else
            {
                // This key is not in the dictionary; add this key/value pair.
                Add(key, value);
            }
        }
    }
    private Boolean TryGetIndexOfKey(Object key, out Int32 index)
    {
        for (index = 0; index < ItemsInUse; index++)
        {
            // If the key is found, return true (the index is also returned).
            if (items[index].Key.Equals(key)) return true;
        }

        // Key not found, return false (index should be ignored by the caller).
        return false;
    }
    private class SimpleDictionaryEnumerator : IDictionaryEnumerator
    {
        // A copy of the SimpleDictionary object's key/value pairs.
        DictionaryEntry[] items;
        Int32 index = -1;

        public SimpleDictionaryEnumerator(SimpleDictionary sd)
        {
            // Make a copy of the dictionary entries currently in the SimpleDictionary object.
            items = new DictionaryEntry[sd.Count];
            Array.Copy(sd.items, 0, items, 0, sd.Count);
        }

        // Return the current item.
        public Object Current { get { ValidateIndex(); return items[index]; } }

        // Return the current dictionary entry.
        public DictionaryEntry Entry
        {
            get { return (DictionaryEntry) Current; }
        }

        // Return the key of the current item.
        public Object Key { get { ValidateIndex();  return items[index].Key; } }

        // Return the value of the current item.
        public Object Value { get { ValidateIndex();  return items[index].Value; } }

        // Advance to the next item.
        public Boolean MoveNext()
        {
            if (index < items.Length - 1) { index++; return true; }
            return false;
        }

        // Validate the enumeration index and throw an exception if the index is out of range.
        private void ValidateIndex()
        {
            if (index < 0 || index >= items.Length)
            throw new InvalidOperationException("Enumerator is before or after the collection.");
        }

        // Reset the index to restart the enumeration.
        public void Reset()
        {
            index = -1;
        }
    }
    public IDictionaryEnumerator GetEnumerator()
    {
        // Construct and return an enumerator.
        return new SimpleDictionaryEnumerator(this);
    }
    #endregion

    #region ICollection Members
    public bool IsSynchronized { get { return false; } }
    public object SyncRoot { get { throw new NotImplementedException(); } }
    public int Count { get { return ItemsInUse; } }
    public void CopyTo(Array array, int index) { throw new NotImplementedException(); }
    #endregion

    #region IEnumerable Members
    IEnumerator IEnumerable.GetEnumerator()
    {
        // Construct and return an enumerator.
        return ((IDictionary)this).GetEnumerator();
    }
    #endregion
}

public sealed class App
{
    static void Main()
    {
        // Create a dictionary that contains no more than three entries.
        IDictionary d = new SimpleDictionary(3);

        // Add three people and their ages to the dictionary.
        d.Add("Jeff", 40);
        d.Add("Kristin", 34);
        d.Add("Aidan", 1);

        Console.WriteLine("Number of elements in dictionary = {0}", d.Count);

        Console.WriteLine("Does dictionary contain 'Jeff'? {0}", d.Contains("Jeff"));
        Console.WriteLine("Jeff's age is {0}", d["Jeff"]);

        // Display every entry's key and value.
        foreach (DictionaryEntry de in d)
        {
            Console.WriteLine("{0} is {1} years old.", de.Key, de.Value);
        }

        // Remove an entry that exists.
        d.Remove("Jeff");

        // Remove an entry that does not exist, but do not throw an exception.
        d.Remove("Max");

        // Show the names (keys) of the people in the dictionary.
        foreach (String s in d.Keys)
            Console.WriteLine(s);

        // Show the ages (values) of the people in the dictionary.
        foreach (Int32 age in d.Values)
            Console.WriteLine(age);
    }
}

// This code produces the following output.
//
// Number of elements in dictionary = 3
// Does dictionary contain 'Jeff'? True
// Jeff's age is 40
// Jeff is 40 years old.
// Kristin is 34 years old.
// Aidan is 1 years old.
// Kristin
// Aidan
// 34
// 1

備註

C# 語言的 foreach 語句（在 Visual Basic 中for each）會隱藏列舉值的複雜性。 因此，建議使用 foreach，而不是直接操作列舉值。

列舉值可用來讀取集合中的數據，但無法用來修改基礎集合。

一開始，列舉值會放在集合中的第一個專案之前。 Reset 方法也會讓列舉值回到這個位置。 在這個位置上，Current 未定義。 因此，您必須先呼叫 MoveNext 方法，將列舉值前移至集合的第一個專案，再讀取 Current的值。

Current 會傳回相同的物件，直到呼叫 MoveNext 或 Reset 為止。 MoveNext 會將 Current 設定為下一個專案。

如果 MoveNext 傳遞集合結尾，則列舉值位於集合的最後一個項目之後，MoveNext 傳回 false。 當列舉值位於這個位置時，後續呼叫 MoveNext 也會傳回 false。 如果最後一次呼叫傳回 MoveNextfalse，則 Current 未定義。 若要再次將 Current 設定為集合的第一個專案，您可以呼叫 Reset，後面接著 MoveNext。

只要集合維持不變，列舉值會維持有效狀態。 如果對集合進行變更，例如新增、修改或刪除專案，列舉值會無法復原地失效，且下一次呼叫 MoveNext 或 Reset 會擲回 InvalidOperationException。

列舉值沒有集合的獨佔存取權;因此，透過集合列舉本質上不是安全線程的程式。 即使集合同步處理，其他線程仍然可以修改集合，這會導致列舉值擲回例外狀況。 若要保證列舉期間的線程安全性，您可以在整個列舉期間鎖定集合，或攔截其他線程所做的變更所產生的例外狀況。

給實施者的注意事項

繼承自 IEnumerator 的 Current 屬性會傳回 boxed DictionaryEntryObject。 與 Entry 屬性類似，不同之處在於 Entry 會傳回 DictionaryEntry，而不是 Object。

屬性

Current	取得集合中位於列舉值目前位置的專案。 (繼承來源 IEnumerator)
Entry	取得目前字典專案的索引鍵和值。
Key	取得目前字典專案的索引鍵。
Value	取得目前字典專案的值。

方法

MoveNext()	將列舉值前進至集合的下一個專案。 (繼承來源 IEnumerator)
Reset()	將列舉值設定為其初始位置，也就是集合中第一個專案之前。 (繼承來源 IEnumerator)

適用於

另請參閱

• IDictionary
• IEnumerator
• IEnumerator<T>