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A type that you can use to declare a custom delegate type for your own events. delegate supports any number of parameters, and they are not limited to Windows Runtime types.
The delegate type has no ABI (it has no interface for use across application binaries), so its use case is when you're both authoring and consuming an event within the same project. For more details of that scenario, see Parameterized delegates, simple signals, and callbacks within a project.
For more info about handling events, and code examples, see Handle events by using delegates in C++/WinRT.
Syntax
template <typename... T>
struct delegate : Windows::Foundation::IUnknown
Template parameters
typename... T
A variadic template parameter pack containing the types of the parameters that the delegate is passed when it's called.
Requirements
Minimum supported SDK: Windows SDK version 10.0.17134.0 (Windows 10, version 1803)
Namespace: winrt
Header: %WindowsSdkDir%Include<WindowsTargetPlatformVersion>\cppwinrt\winrt\base.h (included by default)
Constructors
| Constructor | Description |
|---|---|
| delegate::delegate constructor | Initializes a new instance of the delegate struct from the input data. |
Member operators
| Operator | Description |
|---|---|
| delegate::operator() (function call operator) | Invokes the delegate represented by the delegate object with the provided arguments. |
delegate::delegate constructor
Initializes a new instance of the delegate struct from the input data.
Syntax
delegate(std::nullptr_t = nullptr) noexcept; // (1)
template <typename L>
delegate(L lHandler); // (2)
template <typename F>
delegate(F* fHandler); // (3)
template <typename O, typename M>
delegate(O* object, M method); // (4)
template <typename O, typename M>
delegate(winrt::com_ptr<O>&& object, M method); // (5)
template <typename O, typename M>
delegate(winrt::weak_ref<O>&& object, M method); // (6)
template <typename O, typename M>
delegate(winrt::weak_ref<O>&& object, L lHandler); // (7)
template <typename O, typename M>
delegate(std::shared_ptr<O>&& object, M method); // (8)
template <typename O, typename M>
delegate(std::weak_ptr<O>&& object, M method); // (9)
template <typename O, typename M>
delegate(std::weak_ptr<O>&& object, L lHandler); // (10)
Template parameters
typename L
A lambda type, or more generally, any type that supports function call syntax, such as a std::function.
typename F
A free function type.
typename O
An object type.
typename M
A pointer-to-member-function type.
Parameters
lHandler
A lambda object, or more generally, an object that supports function call syntax, such as a std::function, which will handle the event.
fHandler
A pointer-to-free-function, which will handle the event.
object
An object, one of whose member functions will handle the event.
Depending on the overload, this object may be represented by a raw pointer or a smart pointer.
method
A pointer-to-member-function, which will handle the event.
Remarks
The default constructor (1) constructs an empty delegate.
Constructor (2) constructs a delegate which calls the lambda with the delegate arguments.
Constructor (3) constructs a delegate which calls the function with the delegate arguments.
Constructor (4) constructs a delegate which calls the pointed-to object's method with the delegate arguments.
Constructor (5) constructs a delegate which calls the referenced object's method with the delegate arguments.
Constructor (6) constructs a delegate which attempts to resolve the weak_ref to a strong reference.
If successful, then it calls the object's method with the delegate arguments; otherwise, it does nothing.
Constructor (7) constructs a delegate which attempts to resolve the weak_ref to a strong reference.
If successful, then it calls the lambda with the delegate arguments; otherwise, it does nothing.
Requires C++/WinRT version 2.0.240111.5.
Constructor (8) constructs a delegate which calls the shared object's method with the delegate arguments. Requires C++/WinRT version 2.0.240111.5.
Constructor (9) constructs a delegate which attempts to resolve the weak_ptr to a shared pointer.
If successful, then it calls the shared object's method with the delegate arguments; otherwise, it does nothing.
Requires C++/WinRT version 2.0.240111.5.
Constructor (10) constructs a delegate which attempts to resolve the weak_ptr to a shared pointer.
If successful, then it calls the lambda with the delegate arguments; otherwise, it does nothing.
Requires C++/WinRT version 2.0.240111.5.
delegate::operator() (function call operator)
Invokes the delegate represented by the delegate object with the provided arguments.
Syntax
void operator()(T const&... args) const