# wx.VarScrollHelperBase¶

This class provides all common base functionality for scroll calculations shared among all variable scrolled window implementations as well as automatic scrollbar functionality, saved scroll positions, controlling target windows to be scrolled, as well as defining all required virtual functions that need to be implemented for any orientation specific work.

Documentation of this class is provided specifically for referencing use of the functions provided by this class for use with the variable scrolled windows that derive from here. You will likely want to derive your window from one of the already implemented variable scrolled windows rather than from wx.VarScrollHelperBase directly.

## Class Hierarchy¶

Inheritance diagram for class VarScrollHelperBase:

## Methods Summary¶

 __init__ Constructor taking the target window to be scrolled by this helper class. CalcScrolledPosition Translates the logical coordinate given to the current device coordinate. CalcUnscrolledPosition Translates the device coordinate given to the corresponding logical coordinate. EnablePhysicalScrolling With physical scrolling on (when this is True), the device origin is changed properly when a wx.PaintDC is prepared, children are actually moved and laid out properly, and the contents of the window (pixels) are actually moved. EstimateTotalSize When the number of scroll units change, we try to estimate the total size of all units when the full window size is needed (i.e. GetNonOrientationTargetSize This function needs to be overridden in the in the derived class to return the window size with respect to the opposing orientation. GetOrientation This function need to be overridden to return the orientation that this helper is working with, either HORIZONTAL or VERTICAL . GetOrientationTargetSize This function needs to be overridden in the in the derived class to return the window size with respect to the orientation this helper is working with. GetTargetWindow This function will return the target window this helper class is currently scrolling. GetVisibleBegin Returns the index of the first visible unit based on the scroll position. GetVisibleEnd Returns the index of the last visible unit based on the scroll position. IsVisible Returns True if the given scroll unit is currently visible (even if only partially visible) or False otherwise. OnGetUnitSize This function must be overridden in the derived class, and should return the size of the given unit in pixels. OnGetUnitsSizeHint This function doesn’t have to be overridden but it may be useful to do so if calculating the units’ sizes is a relatively expensive operation as it gives your code a chance to calculate several of them at once and cache the result if necessary. RefreshAll Recalculate all parameters and repaint all units. SetTargetWindow Normally the window will scroll itself, but in some rare occasions you might want it to scroll (part of) another window (e.g. UpdateScrollbar Update the thumb size shown by the scrollbar. VirtualHitTest Returns the virtual scroll unit under the device unit given accounting for scroll position or NOT_FOUND if none (i.e.

## Class API¶

class wx.VarScrollHelperBase(object)

Possible constructors:

VarScrollHelperBase(winToScroll)


This class provides all common base functionality for scroll calculations shared among all variable scrolled window implementations as well as automatic scrollbar functionality, saved scroll positions, controlling target windows to be scrolled, as well as defining all required virtual functions that need to be implemented for any orientation specific work.

### Methods¶

__init__(self, winToScroll)

Constructor taking the target window to be scrolled by this helper class.

This will attach scroll event handlers to the target window to catch and handle scroll events appropriately.

Parameters

winToScroll (wx.Window) –

CalcScrolledPosition(self, coord)

Translates the logical coordinate given to the current device coordinate.

For example, if the window is scrolled 10 units and each scroll unit represents 10 device units (which may not be the case since this class allows for variable scroll unit sizes), a call to this function with a coordinate of 15 will return -85.

Parameters

coord (int) –

Return type

int

CalcUnscrolledPosition(self, coord)

Translates the device coordinate given to the corresponding logical coordinate.

For example, if the window is scrolled 10 units and each scroll unit represents 10 device units (which may not be the case since this class allows for variable scroll unit sizes), a call to this function with a coordinate of 15 will return 115.

Parameters

coord (int) –

Return type

int

EnablePhysicalScrolling(self, scrolling=True)

With physical scrolling on (when this is True), the device origin is changed properly when a wx.PaintDC is prepared, children are actually moved and laid out properly, and the contents of the window (pixels) are actually moved.

When this is False, you are responsible for repainting any invalidated areas of the window yourself to account for the new scroll position.

Parameters

scrolling (bool) –

EstimateTotalSize(self)

When the number of scroll units change, we try to estimate the total size of all units when the full window size is needed (i.e.

to calculate the scrollbar thumb size). This is a rather expensive operation in terms of unit access, so if the user code may estimate the average size better or faster than we do, it should override this function to implement its own logic. This function should return the best guess for the total virtual window size.

Return type

wx.Coord

Note

Although returning a totally wrong value would still work, it risks resulting in very strange scrollbar behaviour so this function should really try to make the best guess possible.

GetNonOrientationTargetSize(self)

This function needs to be overridden in the in the derived class to return the window size with respect to the opposing orientation.

If this is a vertical scrolled window, it should return the height.

Return type

int

GetOrientation(self)

This function need to be overridden to return the orientation that this helper is working with, either HORIZONTAL or VERTICAL .

Return type

wx.Orientation

GetOrientationTargetSize(self)

This function needs to be overridden in the in the derived class to return the window size with respect to the orientation this helper is working with.

If this is a vertical scrolled window, it should return the width.

Return type

int

GetTargetWindow(self)

This function will return the target window this helper class is currently scrolling.

Return type

wx.Window

GetVisibleBegin(self)

Returns the index of the first visible unit based on the scroll position.

Return type

int

GetVisibleEnd(self)

Returns the index of the last visible unit based on the scroll position.

This includes the last unit even if it is only partially visible.

Return type

int

IsVisible(self, unit)

Returns True if the given scroll unit is currently visible (even if only partially visible) or False otherwise.

Parameters

unit (int) –

Return type

bool

OnGetUnitSize(self, unit)

This function must be overridden in the derived class, and should return the size of the given unit in pixels.

Parameters

unit (int) –

Return type

wx.Coord

OnGetUnitsSizeHint(self, unitMin, unitMax)

This function doesn’t have to be overridden but it may be useful to do so if calculating the units’ sizes is a relatively expensive operation as it gives your code a chance to calculate several of them at once and cache the result if necessary.

OnGetUnitsSizeHint is normally called just before OnGetUnitSize but you shouldn’t rely on the latter being called for all units in the interval specified here. It is also possible that OnGetUnitSize will be called for units outside of this interval, so this is really just a hint, not a promise.

Finally, note that unitMin is inclusive, while unitMax is exclusive.

Parameters
• unitMin (int) –

• unitMax (int) –

RefreshAll(self)

Recalculate all parameters and repaint all units.

SetTargetWindow(self, target)

Normally the window will scroll itself, but in some rare occasions you might want it to scroll (part of) another window (e.g.

a child of it in order to scroll only a portion the area between the scrollbars like a spreadsheet where only the cell area will move).

Parameters

target (wx.Window) –

UpdateScrollbar(self)

Update the thumb size shown by the scrollbar.

VirtualHitTest(self, coord)

Returns the virtual scroll unit under the device unit given accounting for scroll position or NOT_FOUND if none (i.e.

if it is below the last item).

Parameters

coord (int) –

Return type

int

### Properties¶

NonOrientationTargetSize

Orientation

OrientationTargetSize

TargetWindow

VisibleBegin

VisibleEnd