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Navigation: Code Documentation > RSCommon > RSInterfaceCollections > Classes

TIHashTable<TKey> Class

The TIHashTable class implements and manages a hash table of TKey-interface associations. It stores interfaces (IUnknown and its descendants) indexed by a key. Hash tables provide constant time O(C) search access to any value in the table (using the key) as the table grows (unlike a TList where to search for an item is O(n). The TIHashTable object provides properties and methods to:

• Add or delete the interfaces in the table.

• Locate and access interfaces in the table.

Note
For a small numbers of items, this class may be slower than a TList because its retrieval time constant is larger. It also consumes more memory than a TList.

Namespace: RSInterfaceCollections

Type Parameters

TKey

	Name	Description
	Create(IEqualityComparer)	Overloaded. Creates and initializes the dictionary. (Inherited from RSGenerics.Collections.TRSDictionary<TKey,TValue>.)
	Create(Integer)	Overloaded. Creates and initializes the dictionary. (Inherited from RSGenerics.Collections.TRSDictionary<TKey,TValue>.)
	Create(Integer,IEqualityComparer)	Overloaded. Creates and initializes the dictionary. (Inherited from RSGenerics.Collections.TRSDictionary<TKey,TValue>.)
	Create(TEnumerable)	Overloaded. Creates and initializes the dictionary. (Inherited from RSGenerics.Collections.TRSDictionary<TKey,TValue>.)
	Create(TEnumerable,IEqualityComparer)	Overloaded. Creates and initializes the dictionary. (Inherited from RSGenerics.Collections.TRSDictionary<TKey,TValue>.)

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	Name	Description
	Count	Number of entries. Count holds the number of key-value pairs in the dictionary. The Items property holds Count entries.
	Empty	Returns true if the hash table is empty (Inherited from RSGenerics.Collections.TRSHashTable<TKey,TValue>.)
	ItemByIndex[Integer]	Returns the value at the specified index. (Inherited from RSGenerics.Collections.TRSHashTable<TKey,TValue>.)
	Items[TKey]	Indexable list of all dictionary entries. Items is an indexable list of all key-value pairs in the dictionary. The Count property holds the number of dictionary entries in Items. You can set and get values by indexing the Items property. Setting the value this way overwrites an existing value and does not raise an exception.
	Item[TKey]	Retrieve or Set item in hash table (Inherited from RSGenerics.Collections.TRSHashTable<TKey,TValue>.)
	KeyByIndex[Integer]	Returns the key at the specified index. (Inherited from RSGenerics.Collections.TRSHashTable<TKey,TValue>.)
	Keys	Indexable list of all dictionary keys. Keys is a read-only enumerable collection of all keys in the dictionary. The Count property holds the number of entries in Keys.
	OnChange	Occurs when the hash table is changed, i.e., items are added or removed. Write an OnChange event handler to respond to changes in the hash table
	OnKeyNotify	Occurs when a dictionary key pair changes. The OnKeyNotify event occurs when items are added or removed from the dictionary. Multiple events may occur for a single operation. This allows removed objects to be freed.
	OnValueNotify	Occurs when a dictionary key pair changes. The OnValueNotify event occurs when items are added or removed from the dictionary. Multiple events may occur for a single operation. This allows removed objects to be freed.
	Updating	Counts the number of BeginUpdate calls without equivalent EndUpdate calls. (Inherited from RSGenerics.Collections.TRSHashTable<TKey,TValue>.)
	Values	Indexable list of all dictionary values. Values is a read-only enumerable collection of all values in the dictionary. The Count property holds the number of entries in Values.

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	Name	Description
	Add(TKey,TValue)	Add key-value pair. Add adds a key and its corresponding value to the dictionary. Both the key and the value can be nil. If the key already exists in the dictionary, an exception is thrown. An OnKeyNotify event and an OnValueNotify event occur indicating that an entry was added to the dictionary. The Items property lists all dictionary entries. You can also set and get values by indexing directly the Items property. For instance, you can set a value this way: Delphi
Items[key] := value;

Setting the value this way overwrites the value for an existing key, but does not raise an exception.

public method

AddOrSetValue(TKey,TValue)

Add key-value pair even when key already exists.

AddOrSetValue adds a key-value pair to a dictionary even if the key already exists. The key cannot be nil, but the value can. This method checks to see if the key exists in the dictionary, and if it does, it is equivalent to Items[key] := value;. Otherwise it is equivalent to Add(key, value);.

An OnKeyNotify event and an OnValueNotify event occur indicating an entry was added to the dictionary.

public method

AfterConstruction

Represents method AfterConstruction. (Inherited from RSGenerics.Collections.TRSHashTable<TKey,TValue>.)

public method

Assign(TPersistent)

Copies the source dictionary to the current dictionary. The current dictionary is cleared first. (Inherited from RSGenerics.Collections.TRSDictionary<TKey,TValue>.)

public method

BeginUpdate

Defers change events and discards notify events until EndUpdate is called. This method allows faster processing of multiple items by deferring or discarding events.

There must be an equal number of EndUpdate method calls for every BeginUpdate method calls to reenable events.

protected method

Change

Calls the OnChange event (Inherited from RSGenerics.Collections.TRSHashTable<TKey,TValue>.)

public method

Clear

Clear all data.

Clear removes all keys and values from the dictionary. The Count property is set to 0. The capacity is also set to 0. This operation requires O(n) time, where n is Count, the number of dictionary entries.

Note
Clear does not free the items as they are removed. If you need to free them, use the OnKeyNotify event and the OnValueNotify event, which occur for every entry removed and provides the removed items.

protected method

ClearCache

Clears the index from the cache. This index is used by ItemByIndex to ensure quick iteration over the hash table. (Inherited from RSGenerics.Collections.TRSHashTable<TKey,TValue>.)

public method

ContainsItem(TValue)

Equivalent to ContainsValue. Retained for backward compatibility. (Inherited from RSGenerics.Collections.TRSHashTable<TKey,TValue>.)

public method

ContainsKey(TKey,TValue)

Overloaded. Try to get value for key.

ContainsKey returns true if the given key is in the dictionary and provides its value in FoundItem. Otherwise, it returns false and FoundItem is set to the default value type of TValue. No exception is raised if the key is not in the dictionary. This is an O(1) operation.

Note
Equivalent to TryGetValue method. Retained for backwards compatibility to TGHashTable.ContainsKey method.

public method

ContainsValue(TValue)

Check if value in dictionary.

ContainsValue returns true if the given value is in the dictionary and false otherwise. This is an O(n) operation, where n is the number of entries in the dictionary.

protected method

DefineProperties(TFiler)

Used to discard old properties from TGHashTable. LoadFactor, HashType, and Capacity are properties from TGHashTable. We define pseudo-properties with these names so that they are recognized but do nothing with them.
(Inherited from RSGenerics.Collections.TRSHashTable<TKey,TValue>.)

protected method

DiscardFloatProperty(TReader)

Reads in and discards LoadFactor property (Inherited from RSGenerics.Collections.TRSHashTable<TKey,TValue>.)

protected method

DiscardIntegerProperty(TReader)

Reads in and discards HashType and Capacity properties (Inherited from RSGenerics.Collections.TRSHashTable<TKey,TValue>.)

protected method

DiscardProperty(TWriter)

Writes out nothing for LoadFactor, HashType, and Capacity properties (Inherited from RSGenerics.Collections.TRSHashTable<TKey,TValue>.)

protected method

DoAdd(Integer,Integer,TKey,TValue)

Adds key/value pair to dictionary at the given index (Overrides RSGenerics.Collections.TRSDictionary<TKey,TValue>.DoAdd(Integer,Integer,TKey,TValue).)

protected method

DoGetEnumerator

Returns the container's enumerator.
(Overrides RSGenerics.Collections.TRSEnumerable<T>.DoGetEnumerator.)

protected method

DoRemove(TKey,Integer,TCollectionNotification)

Removes key/value pair from dictionary (Overrides RSGenerics.Collections.TRSDictionary<TKey,TValue>.DoRemove(TKey,Integer,TCollectionNotification).)

protected method

DoSetValue(Integer,TValue)

Overwrites value in dictionary at the given index (Overrides RSGenerics.Collections.TRSDictionary<TKey,TValue>.DoSetValue(Integer,TValue).)

public method

EndUpdate

Reenables change events and notify events after BeginUpdate has been called.

There must be an equal number of EndUpdate method calls for every BeginUpdate method calls to reenable events.

public method

ExtractPair(TKey)

Returns the TPair<TKey,TValue> pair with the specified Key and removes the returned pair from a dictionary.

If the dictionary does not contain the specified Key, the returned pair contains a default TValue.

public method

Get(TKey)

Retrieves the value at this key. (Inherited from RSGenerics.Collections.TRSHashTable<TKey,TValue>.)

public method

GetEnumerator

Returns an key-value pair enumerator for the dictionary.
(Inherited from RSGenerics.Collections.TRSDictionary<TKey,TValue>.)

protected method

KeyNotify(TKey,TCollectionNotification)

Triggers an OnKeyNotify event with the given parameters.

Call KeyNotify to trigger an OnKeyNotify event with the given parameters.

The meaning of the parameters is given in the following table:

Key

The key that is added, removed or extracted.

Action

The action that the key undergoes, which is of type TCollectionNotification.

(Overrides RSGenerics.Collections.TRSDictionary<TKey,TValue>.KeyNotify(TKey,TCollectionNotification).)

public method

Put(TKey,TValue)

Stores the Value defined type at the specified hash key. It returns the old value at that hash key if there was one. (Inherited from RSGenerics.Collections.TRSHashTable<TKey,TValue>.)

public method

Remove(TKey)

Remove key-value pair.

Remove removes the given key and its associated value from the dictionary. No exception is thrown if the key is not in the dictionary. This is an O(1) operation.

An OnKeyNotify event and an OnValueNotify event occur indicating an entry was removed from the dictionary.

public method

ToArray

Returns the content of the dictionary as an array.
(Overrides RSGenerics.Collections.TRSEnumerable<T>.ToArray.)

protected method

ToArrayImpl(Integer)

Converts the enumerable container's items into an equivalent TArray of items. (Inherited from RSGenerics.Collections.TRSEnumerable<T>.)

public method

TrimExcess

Reduce capacity to current number of entries.

TrimExcess changes the capacity to the number of dictionary entries, held in Count.

This method rehashes the internal hash table to save space. This is only useful after a lot of items have been deleted from the dictionary.

public method

TryGetValue(TKey,TValue)

Try to get value for key.

TryGetValue returns true if the given key is in the dictionary and provides its value in Value. Otherwise, it returns false and Value is set to the default value type of TValue. No exception is raised if the key is not in the dictionary. This is an O(1) operation.

protected method

ValueNotify(TValue,TCollectionNotification)

Triggers an OnValueNotify event with the given parameters.

Call ValueNotify to trigger an OnValueNotify event with the given parameters.

The meaning of the parameters is given in the following table:

Value

The Value that is added, removed or extracted.

Action

The action that the Value undergoes, which is of type TCollectionNotification.

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