Cx programmer chinese
#CX PROGRAMMER CHINESE WINDOWS#
One of the key advantages of C++/CX is that the compiler knows which types are Windows Runtime types.
#CX PROGRAMMER CHINESE CODE#
Each interface is independent, and we can only interact with an object via interfaces, so if we are using a type that implements multiple interfaces (which many types do), we are stuck having to write a lot of rather verbose type conversion code so that we can obtain the correct interface pointer to make each function call. Unlike COM, Windows Runtime does not allow an interface to derive from another Windows Runtime interface all interfaces must derive directly from IInspectable. This is an awful lot of code just to call two member functions and this example demonstrates one of the key hurdles that we have to overcome to make it easier to use Windows Runtime types. Rather, we can only refer to a Number object via an IGetValue*, an ISetValue*, or an _INumberPublicNonVirtuals*. This means that we can never have a Number* there is really no such thing. Unfortunately, we can’t do that: recall that the implementation of a reference type is opaque and that we only ever interact with an object via a pointer to one of the interfaces that it implements. This would be a lot simpler if we obtained a Number* and called SetValue and GetValue via that pointer. We use this first to get the ISetValue interface pointer to call SetValue then again to get the IGetValue interface pointer to call GetValue. The As member function template of the WRL ComPtr simply encapsulates a call to IUnknown::QueryInterface in a way that helps to prevent common programming errors. Get a pointer to the object's IGetValue interface and get the value: ComPtr getValueIf Get a pointer to the object's ISetValue interface and set the value: ComPtr setValueIf (Error checking has been omitted for brevity.) void F( ComPtr const& numberIf) This example accepts an instance of Number and calls SetValue to set the value and GetValue to get the value back. Let’s take a look at how we’d use our Number class via WRL. Because each runtime type implements the IUnknown interface and provides its own definition for QueryInterface, it can do whatever is required to get the correct interface pointer in the language and framework with which it is implemented. This member function can be considered as a language-neutral dynamic_cast: it attempts to perform a conversion to the specified interface and returns whether the conversion succeeded. To perform these conversions, we must instead use the third member function of the IUnknown interface: IUnknown::QueryInterface. Thus, we cannot rely on C++ language specific features like implicit derived-to-base conversions and casts when working directly with Windows Runtime types. A reference type implemented in C# may be laid out in memory differently from an equivalent reference type implemented in C++. These conversions do not work with Windows Runtime reference types because the implementation of a reference type is opaque and the layout of a reference type in memory is left unspecified.
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For example, if Number and the interfaces it implements were ordinary C++ types and not Windows Runtime types, conversion from Number* to IGetValue* would be implicit, and we could convert from IGetValue* to Number* using a static_cast or a dynamic_cast.
#CX PROGRAMMER CHINESE SERIES#
In C++, some type conversions involving class types are implicit others may be performed using a cast or a series of casts. If lifetime management was our only concern, there wouldn’t really be a need for the ^ at all: ComPtr is sufficient to manage object lifetime. t0 is then destroyed, which is a no-op because it is null. This calls t1->Release(), causing the reference count of the B object to drop to zero, so the B object destroys itself.
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First, t1 is destroyed (the smart pointer, not the object pointed to). At this point, all of the local variables are destroyed, in reverse order. Public ref class Number sealed : public IGetValue, ISetValue For demonstration purposes, we’ll use the following modified version of the Number class that we introduced in Part 1: public interface struct IGetValue We’ll start off by discussing how Windows Runtime objects are used via WRL, then explain how the C++/CX hat works to make things simpler. So, what exactly is a ^ type? A hat type is a smart pointer type that (1) automatically manages the lifetime of a Windows Runtime object and (2) provides automatic type conversion capabilities to simplify use of Windows Runtime objects. The hat ( ^) is one of the most prominent features of C++/CX–it’s hard not to notice it when one first sees C++/CX code. See C++/CX Part 0 of : An Introduction for an introduction to this series.