DictionaryBase::IDictionary::Keys Property
Gets an ICollection object containing the keys in the DictionaryBase object.
Assembly: mscorlib (in mscorlib.dll)
private: property ICollection^ Keys { virtual ICollection^ get() sealed = IDictionary::Keys::get; }
Property Value
Type: System.Collections::ICollection^An ICollection object containing the keys in the DictionaryBase object.
Implements
IDictionary::KeysThe order of the keys in the ICollection object is unspecified, but is the same order as the associated values in the ICollection object returned by the Values property.
The returned ICollection is not a static copy; instead, the ICollection refers back to the keys in the original DictionaryBase object. Therefore, changes to the DictionaryBase continue to be reflected in the returned ICollection.
Retrieving the value of this property is an O(1) operation.
The following code example implements the DictionaryBase class and uses that implementation to create a dictionary of String keys and values that have a Length property of 5 characters or less.
using namespace System; using namespace System::Collections; public ref class ShortStringDictionary: public DictionaryBase { public: property String^ Item [String^] { String^ get( String^ key ) { return (dynamic_cast<String^>(Dictionary[ key ])); } void set( String^ value, String^ key ) { Dictionary[ key ] = value; } } property ICollection^ Keys { ICollection^ get() { return (Dictionary->Keys); } } property ICollection^ Values { ICollection^ get() { return (Dictionary->Values); } } void Add( String^ key, String^ value ) { Dictionary->Add( key, value ); } bool Contains( String^ key ) { return (Dictionary->Contains( key )); } void Remove( String^ key ) { Dictionary->Remove( key ); } protected: virtual void OnInsert( Object^ key, Object^ value ) override { if ( key->GetType() != Type::GetType( "System.String" ) ) throw gcnew ArgumentException( "key must be of type String.","key" ); else { String^ strKey = dynamic_cast<String^>(key); if ( strKey->Length > 5 ) throw gcnew ArgumentException( "key must be no more than 5 characters in length.","key" ); } if ( value->GetType() != Type::GetType( "System.String" ) ) throw gcnew ArgumentException( "value must be of type String.","value" ); else { String^ strValue = dynamic_cast<String^>(value); if ( strValue->Length > 5 ) throw gcnew ArgumentException( "value must be no more than 5 characters in length.","value" ); } } virtual void OnRemove( Object^ key, Object^ /*value*/ ) override { if ( key->GetType() != Type::GetType( "System.String" ) ) throw gcnew ArgumentException( "key must be of type String.","key" ); else { String^ strKey = dynamic_cast<String^>(key); if ( strKey->Length > 5 ) throw gcnew ArgumentException( "key must be no more than 5 characters in length.","key" ); } } virtual void OnSet( Object^ key, Object^ /*oldValue*/, Object^ newValue ) override { if ( key->GetType() != Type::GetType( "System.String" ) ) throw gcnew ArgumentException( "key must be of type String.","key" ); else { String^ strKey = dynamic_cast<String^>(key); if ( strKey->Length > 5 ) throw gcnew ArgumentException( "key must be no more than 5 characters in length.","key" ); } if ( newValue->GetType() != Type::GetType( "System.String" ) ) throw gcnew ArgumentException( "newValue must be of type String.","newValue" ); else { String^ strValue = dynamic_cast<String^>(newValue); if ( strValue->Length > 5 ) throw gcnew ArgumentException( "newValue must be no more than 5 characters in length.","newValue" ); } } virtual void OnValidate( Object^ key, Object^ value ) override { if ( key->GetType() != Type::GetType( "System.String" ) ) throw gcnew ArgumentException( "key must be of type String.","key" ); else { String^ strKey = dynamic_cast<String^>(key); if ( strKey->Length > 5 ) throw gcnew ArgumentException( "key must be no more than 5 characters in length.","key" ); } if ( value->GetType() != Type::GetType( "System.String" ) ) throw gcnew ArgumentException( "value must be of type String.","value" ); else { String^ strValue = dynamic_cast<String^>(value); if ( strValue->Length > 5 ) throw gcnew ArgumentException( "value must be no more than 5 characters in length.","value" ); } } }; void PrintKeysAndValues2( ShortStringDictionary^ myCol ); void PrintKeysAndValues3( ShortStringDictionary^ myCol ); int main() { // Creates and initializes a new DictionaryBase. ShortStringDictionary^ mySSC = gcnew ShortStringDictionary; // Adds elements to the collection. mySSC->Add( "One", "a" ); mySSC->Add( "Two", "ab" ); mySSC->Add( "Three", "abc" ); mySSC->Add( "Four", "abcd" ); mySSC->Add( "Five", "abcde" ); // Display the contents of the collection using the enumerator. Console::WriteLine( "Contents of the collection (using enumerator):" ); PrintKeysAndValues2( mySSC ); // Display the contents of the collection using the Keys property and the Item property. Console::WriteLine( "Initial contents of the collection (using Keys and Item):" ); PrintKeysAndValues3( mySSC ); // Tries to add a value that is too long. try { mySSC->Add( "Ten", "abcdefghij" ); } catch ( ArgumentException^ e ) { Console::WriteLine( e ); } // Tries to add a key that is too long. try { mySSC->Add( "Eleven", "ijk" ); } catch ( ArgumentException^ e ) { Console::WriteLine( e ); } Console::WriteLine(); // Searches the collection with Contains. Console::WriteLine( "Contains \"Three\": {0}", mySSC->Contains( "Three" ) ); Console::WriteLine( "Contains \"Twelve\": {0}", mySSC->Contains( "Twelve" ) ); Console::WriteLine(); // Removes an element from the collection. mySSC->Remove( "Two" ); // Displays the contents of the collection. Console::WriteLine( "After removing \"Two\":" ); PrintKeysAndValues2( mySSC ); } // Uses the enumerator. void PrintKeysAndValues2( ShortStringDictionary^ myCol ) { DictionaryEntry myDE; System::Collections::IEnumerator^ myEnumerator = myCol->GetEnumerator(); while ( myEnumerator->MoveNext() ) if ( myEnumerator->Current != nullptr ) { myDE = *dynamic_cast<DictionaryEntry^>(myEnumerator->Current); Console::WriteLine( " {0,-5} : {1}", myDE.Key, myDE.Value ); } Console::WriteLine(); } // Uses the Keys property and the Item property. void PrintKeysAndValues3( ShortStringDictionary^ myCol ) { ICollection^ myKeys = myCol->Keys; IEnumerator^ myEnum1 = myKeys->GetEnumerator(); while ( myEnum1->MoveNext() ) { String^ k = safe_cast<String^>(myEnum1->Current); Console::WriteLine( " {0,-5} : {1}", k, myCol->Item[ k ] ); } Console::WriteLine(); } /* This code produces the following output. Contents of the collection (using enumerator): Three : abc Five : abcde Two : ab One : a Four : abcd Initial contents of the collection (using Keys and Item): Three : abc Five : abcde Two : ab One : a Four : abcd System.ArgumentException: value must be no more than 5 characters in length. Parameter name: value at ShortStringDictionary.OnValidate(Object key, Object value) at System.Collections.DictionaryBase.System.Collections.IDictionary.Add(Object key, Object value) at SamplesDictionaryBase.Main() System.ArgumentException: key must be no more than 5 characters in length. Parameter name: key at ShortStringDictionary.OnValidate(Object key, Object value) at System.Collections.DictionaryBase.System.Collections.IDictionary.Add(Object key, Object value) at SamplesDictionaryBase.Main() Contains "Three": True Contains "Twelve": False After removing "Two": Three : abc Five : abcde One : a Four : abcd */
Available since 10
.NET Framework
Available since 1.1