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document how the on-demand treeview entries work

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Put the expand related methods beside eachother and give a hint how
to avoid placeholder inconsistencies

Change-Id: I798e5e69d5a7a1c5e30e5b77b9bcfbfe731a0536
Reviewed-on: https://gerrit.libreoffice.org/c/core/+/115951
Tested-by: Jenkins
Reviewed-by: Caolán McNamara <caolanm@redhat.com>
This commit is contained in:
Caolán McNamara 2021-05-21 17:23:12 +01:00
parent 1a0ff24766
commit 77b505b0b9
1 changed files with 37 additions and 7 deletions
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44
include/vcl/weld.hxx
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@ -933,6 +933,7 @@ public:
m_aQueryTooltipHdl = rLink;
}
// see 'expanding on-demand node details' for bChildrenOnDemand of true
virtual void insert(const TreeIter* pParent, int pos, const OUString* pStr, const OUString* pId,
const OUString* pIconName, VirtualDevice* pImageSurface,
bool bChildrenOnDemand, TreeIter* pRet)
@ -1105,13 +1106,8 @@ public:
//Don't select when frozen, select after thaw. Note selection doesn't survive a freeze.
virtual void select(const TreeIter& rIter) = 0;
virtual void unselect(const TreeIter& rIter) = 0;
virtual bool get_row_expanded(const TreeIter& rIter) const = 0;
virtual bool get_children_on_demand(const TreeIter& rIter) const = 0;
virtual void set_children_on_demand(const TreeIter& rIter, bool bChildrenOnDemand) = 0;
//visually indent this row as if it was at get_iter_depth() + nIndentLevel
virtual void set_extra_row_indent(const TreeIter& rIter, int nIndentLevel) = 0;
virtual void expand_row(const TreeIter& rIter) = 0;
virtual void collapse_row(const TreeIter& rIter) = 0;
// col index -1 sets the first text column
virtual void set_text(const TreeIter& rIter, const OUString& rStr, int col = -1) = 0;
// col index -1 sets the first text column
@ -1167,6 +1163,42 @@ public:
const std::vector<int>* pFixedWidths = nullptr)
= 0;
/* expanding on-demand node details
When a node is added with children-on-demand (typically via 'insert' with
bChildrenOnDemand of true), then initially in reality the
children-on-demand node is given a 'placeholder' child entry to indicate
the load-on-demand state.
The 'placeholder' needs to be there for the expander indicator to be
drawn/shown even when there are no "real" entries yet. This child doesn't
exist for the purposes of any of the iterator methods, e.g. iter_has_child
on an on-demand node which hasn't been expanded yet is false. Likewise the
rest of the iterator methods skip over or otherwise ignore that node.
Normal usage is the user clicks on the expander, the expansion mechanism
removes the 'placeholder' entry (set_children_on_demand(false)) and calls
any installed expanding-callback (installable via connect_expanding) which
has the opportunity to populate the node with children.
If you decide to directly populate the children of an on-demand node
outside of the expanding-callback then you also need to explicitly remove
the 'placeholder' with set_children_on_demand(false) otherwise the treeview
is in an inconsistent state. */
virtual bool get_row_expanded(const TreeIter& rIter) const = 0;
// expand row will first trigger the callback set via connect_expanding before expanding
virtual void expand_row(const TreeIter& rIter) = 0;
// collapse row will first trigger the callback set via connect_collapsing before collapsing
virtual void collapse_row(const TreeIter& rIter) = 0;
// set the empty node to appear as if it has children, true is equivalent
// to 'insert' with a bChildrenOnDemand of true. See notes above.
virtual void set_children_on_demand(const TreeIter& rIter, bool bChildrenOnDemand) = 0;
// return if the node is configured to be populated on-demand
virtual bool get_children_on_demand(const TreeIter& rIter) const = 0;
// set if the expanders are shown or not
virtual void set_show_expanders(bool bShow) = 0;
void connect_expanding(const Link<const TreeIter&, bool>& rLink) { m_aExpandingHdl = rLink; }
void connect_collapsing(const Link<const TreeIter&, bool>& rLink) { m_aCollapsingHdl = rLink; }
@ -1251,8 +1283,6 @@ public:
OUString const& get_saved_value() const { return m_sSavedValue; }
bool get_value_changed_from_saved() const { return m_sSavedValue != get_selected_text(); }
virtual void set_show_expanders(bool bShow) = 0;
// for custom rendering a cell
void connect_custom_get_size(const Link<get_size_args, Size>& rLink) { m_aGetSizeHdl = rLink; }
void connect_custom_render(const Link<render_args, void>& rLink) { m_aRenderHdl = rLink; }