CTextLayout::TRangeChange Class Reference

#include <frmtlay.h>

class CTextLayout::TRangeChange

Public Member Enumerations
enum	TChangeType { ESet, EClear }

Public Member Functions
	TRangeChange(TInt, TInt, TChangeType)
	TRangeChange()
IMPORT_C TBool	Clip(TInt, TInt)
IMPORT_C TChangeType	Get(TInt &, TInt &)
TBool	IsJoinedTo(const TRangeChange)
void	Join(const TRangeChange)
IMPORT_C TBool	NonNull()
IMPORT_C void	OptimizeWith(TRangeChange &)
IMPORT_C void	Set(TInt, TInt, TChangeType)

Detailed Description

Specifies the range of characters involved when setting or clearing a text selection.

This class is used in the CTextLayout::Highlight() function. The following code demonstrates how it should be used to clear an existing highlight and set a new one:

	CTextLayout::TRangeChange oldHighlight(anchorPos, old_cursorPos,
	CTextLayout::TRangeChange::EClear); // existing highlight
	CTextLayout::TRangeChange newHighlight(anchorPos, new_cursorPos,
	CTextLayout::TRangeChange::ESet); // new one
	newHighlight.OptimizeWith(oldHighlight); // doesn't matter which range is
	the parameter and which is the calling object
	layout.Highlight(oldHighlight,drawRect,context); // doesn't matter in which
	order this and following line occur
	layout.Highlight(newHighlight,drawRect,context);

Member Enumeration Documentation

Enum TChangeType

Enumerates the possible change types.

Enumerator	Value	Description
ESet		The object is being used to set a range.
EClear		The object is being used to clear a range.

Constructor & Destructor Documentation

TRangeChange ( TInt, TInt, TChangeType )

IMPORT_C	TRangeChange	(	TInt	aStart,
			TInt	aEnd,
			TChangeType	aChange
		)

Constructor with a start and end position and whether the highlighting in the range should be set or cleared.

The start and end positions can be specified in any order.

Parameters
aStart	The start position.
aEnd	The end position.
aChange	Specifies whether the highlighting should be set or cleared.

TRangeChange ( )

IMPORT_C

TRangeChange

(

)

Default constructor.

The start and end positions are set to zero - Set() should be called to initialise the object.

Member Function Documentation

Clip ( TInt, TInt )

IMPORT_C TBool	Clip	(	TInt	aMin,
			TInt	aMax
		)

Clips the range so that its start and end positions are within the minimum and maximum positions specified.

Parameters
aMin	The minimum value for the start and end of the range.
aMax	The maximum value for the start and end of the range.

Return Value: ETrue if the resulting range is not of zero length, EFalse if it is of zero length.

Get ( TInt &, TInt & )

IMPORT_C TChangeType	Get	(	TInt &	aStart,
			TInt &	aEnd
		)	const

Gets the start and end of the range and whether the highlighting should be set or cleared.

Parameters
aStart	On return, the start of the range. This is always the lesser of the two positions.
aEnd	On return, the end of the range. This is always the greater of the two positions.

Return Value: Specifies whether the highlighting should be set or cleared.

IsJoinedTo ( const TRangeChange )

TBool

IsJoinedTo

(

const TRangeChange

aRange

)

Join ( const TRangeChange )

void

Join

(

const TRangeChange

aRange

)

NonNull ( )

IMPORT_C TBool

NonNull

(

)

const

Tests whether the range is not null.

Return Value: ETrue if the range is not of zero length, EFalse if the range is of zero length.

OptimizeWith ( TRangeChange & )

IMPORT_C void

OptimizeWith

(

TRangeChange &

aBuddy

)

Try to cancel out sections of the ranges that overlap Merges two ranges of characters.

Two successive calls to CTextLayout::Highlight() could cause unecessary flicker or redrawing if the arguments to each call overlap. For example, if extending a highlight involved removing the old highlight and then drawing the new one, this would cause visible flicker. This can be eliminated by calling this function to remove any overlap between the two ranges. If there is overlap, this range is set to the result of the merge, and the other range (aBuddy) is set to zero.

When calling this function, it does not matter whether or not the two ranges overlap. Also it does not matter which range is the parameter and which is the calling object. After calling OptimizeWith(), it is guaranteed that the resulting ranges will not overlap, and they will represent the same change to the highlight as the original two ranges.

See the code fragment in the class description for TRangeChange for an example of how this function is used.

Parameters
aBuddy	The range of characters to combine with this range.

Set ( TInt, TInt, TChangeType )

IMPORT_C void	Set	(	TInt	aStart,
			TInt	aEnd,
			TChangeType	aChange
		)

Sets the start and end positions and whether the highlighting should be set or cleared.

Called by the non-default constructor. The start and end positions can be specified in any order.

Parameters
aStart	The start of the range.
aEnd	The end of the range.
aChange	Whether the highlighting should be set or cleared.