Dictionary<TKey,TValue>.ContainsKey(TKey) Metode

Definisi

Ruang nama:

System.Collections.Generic

Rakitan:

System.Collections.dll

Sumber:

Dictionary.cs

Menentukan apakah Dictionary<TKey,TValue> berisi kunci yang ditentukan.

public:
 virtual bool ContainsKey(TKey key);

public bool ContainsKey (TKey key);

abstract member ContainsKey : 'Key -> bool
override this.ContainsKey : 'Key -> bool

Public Function ContainsKey (key As TKey) As Boolean

Parameter

key

TKey

Kunci untuk menemukan di Dictionary<TKey,TValue>.

Mengembalikan

Boolean

trueDictionary<TKey,TValue> jika berisi elemen dengan kunci yang ditentukan; jika tidak, false.

Penerapan

ContainsKey(TKey) ContainsKey(TKey)

Pengecualian

ArgumentNullException

keyadalah null.

Contoh

Contoh kode berikut menunjukkan cara menggunakan ContainsKey metode untuk menguji apakah kunci ada sebelum memanggil Add metode . Ini juga menunjukkan cara menggunakan TryGetValue metode untuk mengambil nilai, yang merupakan cara efisien untuk mengambil nilai ketika program sering mencoba kunci yang tidak ada dalam kamus. Akhirnya, ini menunjukkan cara yang paling tidak efisien untuk menguji apakah kunci ada, dengan menggunakan Item[] properti (pengindeks di C#).

Contoh kode ini adalah bagian dari contoh yang lebih besar yang disediakan untuk Dictionary<TKey,TValue> kelas (openWith adalah nama Kamus yang digunakan dalam contoh ini).

// ContainsKey can be used to test keys before inserting
// them.
if (!openWith->ContainsKey("ht"))
{
    openWith->Add("ht", "hypertrm.exe");
    Console::WriteLine("Value added for key = \"ht\": {0}",
        openWith["ht"]);
}

// ContainsKey can be used to test keys before inserting
// them.
if (!openWith.ContainsKey("ht"))
{
    openWith.Add("ht", "hypertrm.exe");
    Console.WriteLine("Value added for key = \"ht\": {0}",
        openWith["ht"]);
}

' ContainsKey can be used to test keys before inserting 
' them.
If Not openWith.ContainsKey("ht") Then
    openWith.Add("ht", "hypertrm.exe")
    Console.WriteLine("Value added for key = ""ht"": {0}", _
        openWith("ht"))
End If

// When a program often has to try keys that turn out not to
// be in the dictionary, TryGetValue can be a more efficient
// way to retrieve values.
String^ value = "";
if (openWith->TryGetValue("tif", value))
{
    Console::WriteLine("For key = \"tif\", value = {0}.", value);
}
else
{
    Console::WriteLine("Key = \"tif\" is not found.");
}

// When a program often has to try keys that turn out not to
// be in the dictionary, TryGetValue can be a more efficient
// way to retrieve values.
string value = "";
if (openWith.TryGetValue("tif", out value))
{
    Console.WriteLine("For key = \"tif\", value = {0}.", value);
}
else
{
    Console.WriteLine("Key = \"tif\" is not found.");
}

' When a program often has to try keys that turn out not to
' be in the dictionary, TryGetValue can be a more efficient 
' way to retrieve values.
Dim value As String = ""
If openWith.TryGetValue("tif", value) Then
    Console.WriteLine("For key = ""tif"", value = {0}.", value)
Else
    Console.WriteLine("Key = ""tif"" is not found.")
End If

// The indexer throws an exception if the requested key is
// not in the dictionary.
try
{
    Console::WriteLine("For key = \"tif\", value = {0}.",
        openWith["tif"]);
}
catch (KeyNotFoundException^)
{
    Console::WriteLine("Key = \"tif\" is not found.");
}

// The indexer throws an exception if the requested key is
// not in the dictionary.
try
{
    Console.WriteLine("For key = \"tif\", value = {0}.",
        openWith["tif"]);
}
catch (KeyNotFoundException)
{
    Console.WriteLine("Key = \"tif\" is not found.");
}

' The default Item property throws an exception if the requested
' key is not in the dictionary.
Try
    Console.WriteLine("For key = ""tif"", value = {0}.", _
        openWith("tif"))
Catch 
    Console.WriteLine("Key = ""tif"" is not found.")
End Try

Keterangan

Metode ini mendekati operasi O(1).

Lihat juga

• ContainsValue(TValue)