ConditionalWeakTable<TKey, TValue>::GetValue Method (TKey, ConditionalWeakTable<TKey, TValue>::CreateValueCallback^)
Atomically searches for a specified key in the table and returns the corresponding value. If the key does not exist in the table, the method invokes a callback method to create a value that is bound to the specified key.
Assembly: mscorlib (in mscorlib.dll)
public:
TValue GetValue(
TKey key,
ConditionalWeakTable<TKey, TValue>::CreateValueCallback^ createValueCallback
)
Parameters
- key
-
Type:
TKey
The key to search for. key represents the object to which the property is attached.
- createValueCallback
-
Type:
System.Runtime.CompilerServices::ConditionalWeakTable<TKey, TValue>::CreateValueCallback^
A delegate to a method that can create a value for the given key. It has a single parameter of type TKey, and returns a value of type TValue.
Return Value
Type: TValueThe value attached to key, if key already exists in the table; otherwise, the new value returned by the createValueCallback delegate.
| Exception | Condition |
|---|---|
| ArgumentNullException | key or createValueCallback is null. |
If key does not exist in the table, GetValue invokes the method that is defined by the createValueCallback parameter and passes it the key. A new value is bound to the key in the table and returned as a result.
Use this method only when the class that represents the table's value does not define a default constructor. If it does define a default constructor, use the GetOrCreateValue method instead. To retrieve the value of an existing key without adding the key/value pair if the key is not found in the table, call the TryGetValue method.
If multiple threads try to create the same key, createValueCallback may be invoked multiple times with the same key. Only one of these calls will succeed, and its returned value will be added to the table. Which thread succeeds in creating the value is indeterminate. This rule permits the table to invoke createValueCallback outside the internal table lock to prevent deadlocks.
The following example defines a MainClass class and a MainInfo class, which provides information about the MainClass instance. It also defines a static (Shared in Visual Basic) CreateAttachedValue method that can be assigned to the ConditionalWeakTable<TKey, TValue>::CreateValueCallback delegate and passed to the GetValue method. The example calls the GetValue method to add a MainClass object and its attached MainInfo object to a ConditionalWeakTable<TKey, TValue> table. The example also illustrates calls to the Add and GetOrCreateValue methods to add key/value pairs to the table, and to the TryGetValue method to retrieve the value of an existing key.
requires full trust for the immediate caller. This member cannot be used by partially trusted or transparent code.
Available since 8
.NET Framework
Available since 4.0
Portable Class Library
Supported in: portable .NET platforms
Silverlight
Available since 4.0
Windows Phone Silverlight
Available since 8.0
Windows Phone
Available since 8.1