MFnExpression Class Reference

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Detailed Description

Expression function set.

This class is used to create, edit, and query expression nodes.

#include <MFnExpression.h>

Inheritance diagram for MFnExpression:

List of all members.

Public Types
enum	UnitConversion { kAll, kNone, kAngularOnly }
	Unit conversion modes. More...
Public Member Functions
virtual MFn::Type	type () const
	Function set type.
virtual	~MFnExpression ()
	Destructor.
	MFnExpression ()
	Default constructor.
	MFnExpression (MObject &object, MStatus *ReturnStatus=NULL)
	Constructor.
MObject	create (const MString &expression, MObject &object=MObject::kNullObj, MStatus *ReturnStatus=NULL)
	This method creates and returns a dependency node for a given expression.
MString	expression (MStatus *ReturnStatus=NULL)
	Gets the expression string for this expression node.
MStatus	setExpression (const MString &expression)
	Sets the expression string for this expression node.
MStatus	getDefaultObject (MObject &object)
	Gets the "default" object for the expression.
MStatus	setDefaultObject (MObject &object)
	Sets the "default" object for the expression.
bool	isAnimated (MStatus *ReturnStatus=NULL)
	If this is true, then the expression will be evaluated whenever time changes, regardless of whether the other inputs have changed.
MStatus	setAnimated (bool value=false)
	Sets the way in which the expression is evaluated.
MStatus	evaluate (MDoubleArray &result)
	Evaluate this expression and return the result.
UnitConversion	unitConversion (MStatus *ReturnStatus=NULL) const
	Get the unit conversion status for the expression node.
MStatus	setUnitConversion (UnitConversion conversion)
	Set the unit conversion options for the expression node.
	MFnExpression (const MObject &object, MStatus *ReturnStatus=NULL)
	Constructor.
MStatus	getExpression (MString &expression)
	NO SCRIPT SUPPORT.
Protected Member Functions
virtual const char *	className () const
	Class name.

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Member Enumeration Documentation

enum UnitConversion

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Unit conversion modes.

Enumerator:

kAll	Convert all units. Search for all occurrences
kNone	Do not do any unit conversion. Search for all occurrences
kAngularOnly	Only convert angular units. Search for all occurrences

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Constructor & Destructor Documentation

MFnExpression	(	MObject &	object,
		MStatus *	ReturnStatus = NULL
	)

Constructor.

Class constructor that initializes the function set to the given MObject.

Parameters:

[in]	object	The MObject to attach the function set to
[out]	ReturnStatus	the return status

Status Codes:

• MS::kSuccess if the function set is successfully attached
• MS::kInvalidParameter if the MObject does not represent a valid Maya object or if the function set is not allowed to attach to this MObject

MFnExpression	(	const MObject &	object,
		MStatus *	ReturnStatus = NULL
	)

Constructor.

Class constructor that initializes the function set to the given MObject.

Parameters:

[in]	object	The MObject to attach the function set to
[out]	ReturnStatus	the return status

Status Codes:

• MS::kSuccess if the function set is successfully attached
• MS::kInvalidParameter if the MObject does not represent a valid Maya object or if the function set is not allowed to attach to this MObject

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Member Function Documentation

MFn::Type type

(

)

const [virtual]

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Function set type.

Return the class type : MFn::kExpression.

Reimplemented from MFnDependencyNode.

const char * className

(

)

const [protected, virtual]

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Class name.

Return the class name : "MFnExpression".

Reimplemented from MFnDependencyNode.

MObject create	(	const MString &	expression,
		MObject &	object = MObject::kNullObj,
		MStatus *	ReturnStatus = NULL
	)

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This method creates and returns a dependency node for a given expression.

A default object can be specified, but if it is not specified in the expression string then the expression string values will be used.

If the expression string is of the form "objectName.attribute = ... " then the default object parameter is not needed. If you supply a default object in this case, then it will be ignored.

If the expression has no default object then you must supply one. For example, if the expression is of the form "attribute = ...", then you must supply a default object.

Parameters:

[in]	expression	The expression string
[in]	object	The default object (optional - see above)
[out]	ReturnStatus	Status code

Returns:

The expression node

Status Codes:

• MS::kSuccess
• MS::kLicenseFailure application not licensed for attempted operation
• MS::kFailure

MString expression

(

MStatus *

ReturnStatus = NULL

)

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Gets the expression string for this expression node.

Parameters:

[out]

ReturnStatus

Status code. See below.

Returns:

The expression string

Status Codes:

• MS::kSuccess
• MS::kFailure

MStatus setExpression

(

const MString &

expression

)

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Sets the expression string for this expression node.

Parameters:

[in]

expression

The expression string

Returns:

Status Code

Status Codes:

• MS::kSuccess
• MS::kFailure

MStatus getDefaultObject

(

MObject &

object

)

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Gets the "default" object for the expression.

Not all expressions have a default object. If there is no default object for the expression, the object will be set to MObject::kNullObject and the return status will indicate success. This is a completely legal case that the calling code should check for before blindly using the returned object.

Parameters:

[out]

object

storage for the default object

Returns:

Status Code

Status Codes:

• MS::kSuccess
• MS::kFailure

MStatus setDefaultObject

(

MObject &

object

)

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Sets the "default" object for the expression.

This allows the expression writer to not type the object name for frequently-used objects.

This method will only work for expression strings in which the object name is not specified.

Parameters:

[in]

object

the object to be set

Returns:

Status Code

Status Codes:

• MS::kSuccess
• MS::kFailure

bool isAnimated

(

MStatus *

ReturnStatus = NULL

)

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If this is true, then the expression will be evaluated whenever time changes, regardless of whether the other inputs have changed.

If it is false (the default) , then the expression will only be evaluated if one or more of the inputs change.

Note, if 'time' or 'frame' are inputs, then the expression will act as if this was set to true.

Parameters:

[out]

ReturnStatus

Status code

Returns:

• true expression will be evaluated whenever time changes
• false

Status Codes:

• MS::kSuccess
• MS::kFailure

MStatus setAnimated

(

bool

value = false

)

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Sets the way in which the expression is evaluated.

If this is true, then the expression will be evaluated whenever time changes, regardless of whether the other inputs have changed.

If it is false (the default) , then the expression will only be evaluated if one or more of the inputs change.

Note, if 'time' or 'frame' are inputs, then the expression will act as if this was set to true.

Parameters:

[in]

value

sets the objects evaluation type

Returns:

Status Code

Status Codes:

• MS::kSuccess
• MS::kFailure

MStatus evaluate

(

MDoubleArray &

result

)

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Evaluate this expression and return the result.

Parameters:

[out]

result

the value of the expression

Returns:

Status code

Status Codes:

• MS::kSuccess
• MS::kFailure

MFnExpression::UnitConversion unitConversion

(

MStatus *

ReturnStatus = NULL

)

const

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Get the unit conversion status for the expression node.

Parameters:

[out]

ReturnStatus

Status code

Returns:

The unit conversion state for this node

Status Codes:

• MS::kSuccess operation successful
• MS::kFailure function set does not have a valid object

MStatus setUnitConversion

(

UnitConversion

conversion

)

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Set the unit conversion options for the expression node.

Parameters:

[in]

conversion

unit conversion state for this node

Returns:

Status code

Status Codes:

• MS::kSuccess operation successful
• MS::kFailure function set does not have a valid object

MStatus getExpression

(

MString &

expression

)

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NO SCRIPT SUPPORT.

Gets the expression string for this expression node.

Python Notes

This method is not supported in Python. Please see the one which returns a string

Parameters:

[in]

expression

The expression string

Returns:

Status code

Status Codes:

• MS::kSuccess
• MS::kFailure