SortedList<TKey,TValue>.TryGetValue(TKey, TValue) 方法

定义

获取与指定键关联的值。Gets the value associated with the specified key.

public:
 virtual bool TryGetValue(TKey key, [Runtime::InteropServices::Out] TValue % value);
public bool TryGetValue (TKey key, out TValue value);
abstract member TryGetValue : 'Key * 'Value -> bool
override this.TryGetValue : 'Key * 'Value -> bool
Public Function TryGetValue (key As TKey, ByRef value As TValue) As Boolean

参数

key
TKey

要获取其值的键。The key whose value to get.

value
TValue

当此方法返回时,如果找到指定键,则返回与该键相关联的值;否则,将返回 value 参数的类型的默认值。When this method returns, the value associated with the specified key, if the key is found; otherwise, the default value for the type of the value parameter. 此参数未经初始化即被传递。This parameter is passed uninitialized.

返回

如果 true 包含具有指定键的元素,则为 SortedList<TKey,TValue>;否则为 falsetrue if the SortedList<TKey,TValue> contains an element with the specified key; otherwise, false.

实现

异常

keynullkey is null.

示例

该示例演示如何使用TryGetValue方法来更有效地检索程序中的值,该方法经常尝试排序列表中没有的键。The example shows how to use the TryGetValue method as a more efficient way to retrieve values in a program that frequently tries keys that are not in the sorted list. 相反,此示例还演示了在尝试Item[TKey]检索不存在的键C#时,属性(中的索引器)如何引发异常。For contrast, the example also shows how the Item[TKey] property (the indexer in C#) throws exceptions when attempting to retrieve nonexistent keys.

此代码示例是为SortedList<TKey,TValue>类提供的更大示例的一部分。This code example is part of a larger example provided for the SortedList<TKey,TValue> class.

// When a program often has to try keys that turn out not to
// be in the list, 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 list, 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 list, 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 list.
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 list.
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 list.
Try
    Console.WriteLine("For key = ""tif"", value = {0}.", _
        openWith("tif"))
Catch 
    Console.WriteLine("Key = ""tif"" is not found.")
End Try

注解

此方法结合了ContainsKey方法Item[TKey]和属性的功能。This method combines the functionality of the ContainsKey method and the Item[TKey] property.

如果value未找到键,则参数将获取值类型TValue的适当默认值; 例如,对于整数类型, false为零(0); 对于布尔类型, null为,对于引用类型,为。If the key is not found, then the value parameter gets the appropriate default value for the value type TValue; for example, zero (0) for integer types, false for Boolean types, and null for reference types.

此方法执行二进制搜索;因此,此方法是 O (log n)操作,其中nCountThis method performs a binary search; therefore, this method is an O(log n) operation, where n is Count.

适用于

另请参阅