IMoniker::ComposeWith method (objidl.h)

Article
10/13/2021

Creates a new composite moniker by combining the current moniker with the specified moniker.

Syntax

HRESULT ComposeWith(
  [in]  IMoniker *pmkRight,
  [in]  BOOL     fOnlyIfNotGeneric,
  [out] IMoniker **ppmkComposite
);

Parameters

[in] pmkRight

A pointer to the IMoniker interface on the moniker to compose onto the end of this moniker.

[in] fOnlyIfNotGeneric

If TRUE, the caller requires a nongeneric composition, so the operation should proceed only if pmkRight is a moniker class that this moniker can compose with in some way other than forming a generic composite. If FALSE, the method can create a generic composite if necessary. Most callers should set this parameter to FALSE.

[out] ppmkComposite

A pointer to an IMoniker pointer variable that receives the composite moniker pointer. When successful, the implementation must call AddRef on the resulting moniker; it is the caller's responsibility to call Release. If an error occurs or if the monikers compose to nothing (for example, composing an anti-moniker with an item moniker or a file moniker), *ppmkComposite should be set to NULL.

Return value

This method can return the standard return values E_OUTOFMEMORY and E_UNEXPECTED, as well as the following values.

Return code	Description
S_OK	The monikers were successfully combined.
MK_E_NEEDGENERIC	Indicates that fOnlyIfNotGeneric was TRUE, but the monikers could not be composed together without creating a generic composite moniker.

Remarks

Joining two monikers together is called composition. Sometimes two monikers of the same class can be combined in what is called nongeneric composition. For example, a file moniker representing an incomplete path and another file moniker representing a relative path can be combined to form a single file moniker representing the complete path. Nongeneric composition for a given moniker class can be handled only in the implementation of ComposeWith for that moniker class.

Combining two monikers of any class is called generic composition, which can be accomplished through a call to the CreateGenericComposite function.

Composition of monikers is an associative operation. That is, if A, B, and C are monikers, then, where Comp() represents the composition operation, Comp( Comp( A, B ), C )

is always equal to Comp( A, Comp( B, C ) ).

Notes to Callers

To combine two monikers, you should call ComposeWith rather than calling the CreateGenericComposite function to give the first moniker a chance to perform a nongeneric composition.

An object that provides item monikers to identify its objects would call ComposeWith to provide a moniker that completely identifies the location of the object. This would apply, for example, to a server that supports linking to portions of a document, or to a container that supports linking to embedded objects within its documents. In such a situation, you would do the following:

Create an item moniker that identifies the object.
Get a moniker that identifies the object's container.
Call ComposeWith on the moniker identifying the container, passing the item moniker as the pmkRight parameter.

Notes to Implementers

You can use either nongeneric or generic composition to compose the current moniker with the moniker that pmkRight points to. If the class of the moniker indicated by pmkRight is the same as that of the current moniker, it is possible to use the contents of pmkRight to perform a more intelligent nongeneric composition.

In writing a new moniker class, you must decide if there are any kinds of monikers, whether of your own class or another class, to which you want to give special treatment. If so, implement ComposeWith to check whether pmkRight is a moniker of the type that should have this treatment. To do this, you can call the moniker's IPersist::GetClassID method, or if you have defined a moniker object that supports a custom interface, you can call QueryInterface on the moniker for that interface. An example of special treatment would be the nongeneric composition of an absolute file moniker with a relative file moniker. The most common case of a special moniker is the inverse for your moniker class (whatever you return from your implementation of IMoniker::Inverse).

If pmkRight completely negates the receiver so that the resulting composite is empty, you should pass back NULL in ppmkComposite and return the status code S_OK.

If the pmkRight parameter is not of a class to which you give special treatment, examine fOnlyIfNotGeneric to determine what to do next. If fOnlyIfNotGeneric is TRUE, pass back NULL through ppmkComposite and return the status code MK_E_NEEDGENERIC. If fOnlyIfNotGeneric is FALSE, call the CreateGenericComposite function to perform the composition generically.

Implementation-specific Notes

Implementation	Notes
Anti-moniker	If fOnlyIfNotGeneric is TRUE, this method sets ppmkComposite to NULL moniker and returns MK_E_NEEDGENERIC; otherwise, the method returns the result of combining the two monikers into a generic composite. Note that composing a file, item, or pointer moniker to the right of an anti-moniker produces a generic composite rather than composing to nothing, as would be the case if the order of composition were reversed.
Class moniker	Follows the contract and behaves like an item moniker in that it can return E_INVALIDARG and MK_E_NEEDGENERIC, and so forth.
File moniker	If pmkRight is an anti-moniker, the returned moniker is NULL. If pmkRight is a composite whose leftmost component is an anti-moniker, the returned moniker is the composite with the leftmost anti-moniker removed. If pmkRight is a file moniker, this method collapses the two monikers into a single file moniker, if possible. If not possible (for example, if both file monikers represent absolute paths, as in d:\work and e:\reports), the returned moniker is NULL and the return value is MK_E_SYNTAX. If pmkRight is neither an anti-moniker nor a file moniker, the method checks the fOnlyIfNotGeneric parameter; if it is FALSE, the method combines the two monikers into a generic composite; if it is TRUE, the method sets *ppmkComposite to NULL and returns MK_E_NEEDGENERIC.
Generic composite moniker	If fOnlyIfNotGeneric is TRUE, this method sets *pmkComposite to NULL and returns MK_E_NEEDGENERIC; otherwise, the method returns the result of combining the two monikers by calling the CreateGenericComposite function.
Item moniker	If pmkRight is an anti-moniker, the returned moniker is NULL. If pmkRight is a composite whose leftmost component is an anti-moniker, the returned moniker is the composite after the leftmost anti-moniker is removed. If pmkRight is not an anti-moniker, the method combines the two monikers into a generic composite if fOnlyIfNotGeneric is FALSE; if fOnlyIfNotGeneric is TRUE, the method returns a NULL moniker and a return value of MK_E_NEEDGENERIC.
OBJREF moniker	If pmkRight is an anti-moniker, the returned moniker is NULL. If pmkRight is a composite whose leftmost component is an anti-moniker, the returned moniker is the composite with the leftmost anti-moniker removed. If pmkRight is neither an anti-moniker nor a composite moniker whose leftmost component is an anti-moniker, the method checks the fOnlyIfNotGeneric parameter. If it is FALSE, the method combines the two monikers into a generic composite; if it is TRUE, the method sets *ppmkComposite to NULL and returns MK_E_NEEDGENERIC.
Pointer moniker	If pmkRight is an anti-moniker, the returned moniker is NULL. If pmkRight is a composite whose leftmost component is an anti-moniker, the returned moniker is the composite after the leftmost anti-moniker is removed. If fOnlyIfNotGeneric is FALSE, the returned moniker is a generic composite of the two monikers; otherwise, the method sets *ppmkComposite to NULL and returns MK_E_NEEDGENERIC.
URL moniker	URL monikers support composition of two URLs: a base URL composed with a relative URL. This composition is done according to the RFC on relative URLs. If fOnlyIfNotGeneric is TRUE, the method returns MK_E_NEEDGENERIC. Otherwise, this method simply returns CreateGenericComposite(this, pmkRight, ppmkComposite).

Requirements

Requirement	Value
Minimum supported client	Windows 2000 Professional [desktop apps only]
Minimum supported server	Windows 2000 Server [desktop apps only]
Target Platform	Windows
Header	objidl.h

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