In the name of this class, “V” may stand for “variable” because it can be used for scrolling lines of variable heights; “virtual” because it is not necessary to know the heights of all lines in advance—only those which are shown on the screen need to be measured; or, even, “vertical” because this class only supports scrolling in one direction currently (this could and probably will change in the future however).
In any case, this is a generalization of the ScrolledWindow class which can be only used when all lines have the same height. It lacks some other ScrolledWindow features however, notably there is currently no support for horizontal scrolling; it can’t scroll another window nor only a rectangle of the window and not its entire client area.
To use this class, you need to derive from it and implement
on_get_line_height()() pure virtual
method. You also must call set_line_count
to let the base class know how many lines it should display but from that
moment on the scrolling is handled entirely by VScrolledWindow, you only
need to draw the visible part of contents in your OnPaint() method as
usual. You should use get_first_visible_line()()
and get_last_visible_line()() to
select the lines to display. Note that the device context origin is not shifted
so the first visible line always appears at the point $(0, 0)$ in physical as
well as logical coordinates.
VScrolledWindow.new(Window parent, Integer id = ID_ANY,
Point pos = DEFAULT_POSITION,
Size size = DEFAULT_SIZE,
Integer style = 0,
String name = PanelNameStr)This is the normal constructor, no need to call Create() after using this one.
Note that VSCROLL is always automatically added to our style, there is
no need to specify it explicitly.
NULLID_ANY by defaultBoolean create(Window parent, Integer id = ID_ANY,
Point pos = DEFAULT_POSITION,
Size size = DEFAULT_SIZE,
Integer style = 0,
String name = PanelNameStr)Same as the non default ctor but returns
status code: true if ok, false if the window couldn’t have been created.
Just as with the ctor above, VSCROLL style is always used, there is no
need to specify it explicitly.
Integer estimate_total_height()This protected function is used internally by VScrolledWindow to estimate the total height of the window when set_line_count is called. The default implementation uses the brute force approach if the number of the items in the control is small enough. Otherwise, it tries to find the average line height using some lines in the beginning, middle and the end.
If it is undesirable to access all these lines (some of which might be never shown) just for the total height calculation, you may override the function and provide your own guess better and/or faster.
Note that although returning a totally wrong value would still work, it risks to result in very strange scrollbar behaviour so this function should really try to make the best guess possible.
Integer get_first_visible_line()Returns the index of the first currently visible line.
This is same as get_visible_begin and exists only for symmetry with get_last_visible_line.
Integer get_last_visible_line()Returns the index of the last currently visible line. Note that this method
returns (Integer)-1 (i.e. a huge positive number) if the control is
empty so if this is possible you should use get_visible_end
instead.
Integer get_line_count()Get the number of lines this window contains (previously set by set_line_count()())
Integer get_visible_begin()Returns the index of the first currently visible line.
Integer get_visible_end()Returns the index of the first line after the currently visible one. If the return value is $0$ it means that no lines are currently shown (which only happens if the control is empty). Note that the index returned by this method is not always a valid index as it may be equal to get_line_count.
Integer hit_test(Integer x, Integer y)Integer hit_test(Point pt)Return the item at the specified (in physical coordinates) position or
NOT_FOUND if none, i.e. if it is below the last item.
Boolean is_visible(Integer line)Returns true if the given line is (at least partially) visible or
false otherwise.
Integer on_get_line_height(Integer n)This protected virtual function must be overridden in the derived class and it should return the height of the given line in pixels.
on_get_lines_hint(Integer lineMin, Integer lineMax)This function doesn’t have to be overridden but it may be useful to do it if calculating the lines heights is a relatively expensive operation as it gives the user code a possibility to calculate several of them at once.
OnGetLinesHint() is normally called just before
on_get_line_height()() but you
shouldn’t rely on the latter being called for all lines in the interval
specified here. It is also possible that OnGetLineHeight() will be
called for the lines outside of this interval, so this is really just a
hint, not a promise.
Finally note that lineMin is inclusive, while lineMax is exclusive, as usual.
refresh_line(Integer line)Refreshes the specified line—it will be redrawn during the next main loop iteration.
refresh_lines(Integer from, Integer to)Refreshes all lines between from and to, inclusive. from should be less than or equal to to.
refresh_all()This function completely refreshes the control, recalculating the number of items shown on screen and repainting them. It should be called when the values returned by on_get_line_height change for some reason and the window must be updated to reflect this.
Boolean scroll_lines(Integer lines)Scroll by the specified number of lines which may be positive (to scroll down) or negative (to scroll up).
Returns true if the window was scrolled, false otherwise (for
example if we’re trying to scroll down but we are already showing the last
line).
Boolean scroll_pages(Integer pages)Scroll by the specified number of pages which may be positive (to scroll down) or negative (to scroll up).
Boolean scroll_to_line(Integer line)Scroll to the specified line: it will become the first visible line in the window.
Return true if we scrolled the window, false if nothing was done.
set_line_count(Integer count)Set the number of lines the window contains: the derived class must provide the heights for all lines with indices up to the one given here in its on_get_line_height()().
[This page automatically generated from the Textile source at Thu May 01 00:50:48 +0100 2008]