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        通过创建这个实例并添加到MapView中后，会在地图上出现一个随着缩放等级变换的比例尺控件。

        通过其方法可进行位置、单位等等参数设置。

Modifier and Type	Method	Description
void	setMinZoom(double zoom)	Sets the minimum zoom level for the scale bar to be drawn.
ScaleBarOverlay.UnitsOfMeasure	getUnitsOfMeasure()	Gets the units of measure to be shown in the scale bar
void	setUnitsOfMeasure(ScaleBarOverlay.UnitsOfMeasure unitsOfMeasure)	Sets the units of measure to be shown in the scale bar
void	setAlignBottom(boolean alignBottom)
void	setAlignRight(boolean alignRight)
Paint	getBarPaint()	Return's the paint used to draw the bar
void	setBarPaint(Paint pBarPaint)	Sets the paint for drawing the bar
Paint	getTextPaint()	Returns the paint used to draw the text
void	setTextPaint(Paint pTextPaint)	Sets the paint for drawing the text
void	setCentred(boolean centred)	Flag to draw the bar centered around the set offset coordinates or to the right/bottom of thecoordinates (default)
void	setMaxLength(float pMaxLengthInCm)	Sets the maximum bar length.
void	setScaleBarOffset(int x, int y)	Sets the scale bar screen offset for the bar.
void	setLineWidth(float width)	Sets the bar's line width.
void	setTextSize(float size)	Sets the text size.
void	drawLatitudeScale(boolean latitude)	Latitudinal / horizontal scale bar flag
void	drawLongitudeScale(boolean longitude)	Longitudinal / vertical scale bar flag
void	setBackgroundPaint(Paint pBgPaint)	Sets the background paint.
void	setEnableAdjustLength(boolean adjustLength)	If enabled, the bar will automatically adjust the length to reflect a round number (startingwith 1, 2 or 5).
void	draw(Canvas c, Projection projection)
void	disableScaleBar()
void	enableScaleBar()
void	onDetach(MapView mapView)	Override to perform clean up of resources before shutdown.
static String	getScaleString(Context pContext, String pValue, GeoConstants.UnitOfMeasure pUnitOfMeasure)