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winrt::observable_map_base struct template (C++/WinRT))

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A base class from which you can derive to implement your own custom observable associative collection. For more info, and code examples, see Collections with C++/WinRT.

Syntax

template <typename D, typename K, typename V>
struct observable_map_base : map_base<D, K, V>

Template parameters

typename D Your derived type name.

typename K The type of the keys in the collection.

typename V The type of the values in the collection.

Requirements

Minimum supported SDK: Windows SDK version 10.0.17763.0 (Windows 10, version 1809)

Namespace: winrt

Header: %WindowsSdkDir%Include<WindowsTargetPlatformVersion>\cppwinrt\winrt\base.h (included by default)

Member functions

Function Description
observable_map_base::Clear function Removes all elements from the observable_map_base object.
observable_map_base::First function Retrieves an IIterator representing the first element in the observable_map_base object.
observable_map_base::GetView function Retrieves an immutable view of the observable_map_base object.
observable_map_base::HasKey function Determines whether the specified key belongs to an element in the observable_map_base object.
observable_map_base::Insert function Inserts or updates an element in the observable_map_base object.
observable_map_base::Lookup function Looks up the element identified by the specified key, and retrieves the corresponding value.
observable_map_base::MapChanged function Registers and revokes a delegate that handles the map-changed event of the observable_map_base object.
observable_map_base::Remove function Removes an element from the observable_map_base object.
observable_map_base::Size function Retrieves the number of elements in the observable_map_base object.

Iterators

A observable_map_base is a range, and that range is defined by internal free functions (each of which retrieves an iterator) that are compatible with standard language features. Because of this, you can enumerate the elements in a observable_map_base object with a range-based for statement.

You can also retrieve an IIterator from the observable_map_base::First function, and use that to iterate through the elements in a observable_map_base object.

...
#include <iostream>
using namespace winrt;
using namespace Windows::Foundation::Collections;
...
struct MyObservableMap :
    implements<MyObservableMap, IObservableMap<winrt::hstring, int>, IMap<winrt::hstring, int>, IMapView<winrt::hstring, int>, IIterable<IKeyValuePair<winrt::hstring, int>>>,
    winrt::observable_map_base<MyObservableMap, winrt::hstring, int>
{
    auto& get_container() const noexcept
    {
        return m_values;
    }

    auto& get_container() noexcept
    {
        return m_values;
    }

private:
    std::map<winrt::hstring, int> m_values{
        { L"AliceBlue", 0xfff0f8ff }, { L"AntiqueWhite", 0xfffaebd7 }
    };
};
...
IObservableMap<winrt::hstring, int> map{ winrt::make<MyObservableMap>() };

for (auto const& el : map)
{
    std::wcout << el.Key().c_str() << L", " << std::hex << el.Value() << std::endl;
}

IIterator<IKeyValuePair<winrt::hstring, int>> it{ map.First() };
while (it.HasCurrent())
{
    std::wcout << it.Current().Key().c_str() << L", " << std::hex << it.Current().Value() << std::endl;
    it.MoveNext();
}

observable_map_base::Clear function

Removes all elements from the observable_map_base object.

Syntax

void Clear() noexcept;

observable_map_base::First function

Retrieves an IIterator representing the first element in the observable_map_base object.

Syntax

auto First();

Return value

An IIterator representing the first element in the observable_map_base object.

observable_map_base::GetView function

Retrieves an immutable view of the observable_map_base object.

Syntax

winrt::Windows::Foundation::Collections::IMapView<K, V> GetView() const;

Return value

An IMapView containing an immutable view of the observable_map_base.

observable_map_base::HasKey function

Determines whether the specified key belongs to an element in the observable_map_base object.

Syntax

bool HasKey(K const& key) const noexcept;

Parameters

key The key to look for.

Return value

true if an element containing the key is found, otherwise false.

observable_map_base::Insert function

Inserts or updates an element in the observable_map_base object.

Syntax

bool Insert(K const& key, V const& value);

Parameters

key The key associated with the element to insert or update.

value The value to insert or replace.

Return value

true if an element with the specified key was found and updated; otherwise false.

observable_map_base::Lookup function

Looks up the element identified by the specified key, and retrieves the corresponding value.

Syntax

V Lookup(K const& key) const;

Parameters

key The key to look up.

Return value

The value corresponding to the key being looked up if found, otherwise a winrt::hresult_out_of_bounds exception is thrown.

observable_vector_base::MapChanged function

Registers and/or revokes a delegate that handles the map-changed event of the observable_map_base object.

Syntax

// Register
winrt::event_token MapChanged(winrt::Windows::Foundation::Collections::MapChangedEventHandler<K, V> const& handler);

// Revoke with event_token
void MapChanged(winrt::event_token const cookie);

// Revoke with event_revoker
MapChanged_revoker MapChanged(winrt::auto_revoke_t, winrt::Windows::Foundation::Collections::MapChangedEventHandler<K, V> const& handler) const

Return value

Either void, a winrt::event_token with which you can revoke a registered delegate, or a MapChanged_revoker (a type alias for a winrt::event_revoker<IObservableMap<K, V>>) with which you can revoke a registered delegate.

Example

winrt::event_revoker<IObservableMap<winrt::hstring, int>> m_event_revoker;
...
m_event_revoker = map.MapChanged(winrt::auto_revoke, [this](IObservableMap<winrt::hstring, int> const&, IMapChangedEventArgs<winrt::hstring> const&)
{
    ...
});

observable_map_base::Remove function

Removes an element from the observable_map_base object.

Syntax

void Remove(K const& key);

Parameters

key The key associated with the element to remove.

observable_map_base::Size function

Retrieves the number of elements in the observable_map_base object.

Syntax

uint32_t Size() const noexcept;

Return value

A value representing the number of elements in the observable_map_base object.

See also