Add undetermined state to wxCheckBoxXmlHandler

3-state checkboxes can have their initial value set to checked
or undetermined -- this adds support for the undetermined
state to the handler (only allowed if the style includes wxCHK_3STATE).

Closes #22468.

docs/doxygen/overviews/xrc_format.h

@@ -946,8 +946,10 @@ No additional properties.
 @hdr3col{property, type, description}
 @row3col{label, @ref overview_xrcformat_type_text,
      Label to use for the checkbox (default: empty).}
-@row3col{checked, @ref overview_xrcformat_type_bool,
-     Should the checkbox be checked initially (default: 0)?}
+@row3col{checked, integer,
+    Sets the initial state of the checkbox. 0 is unchecked (default),
+    1 is checked, and since wxWidgets 3.1.7, 2 sets the undetermined
+    state of a 3-state checkbox.}
 @endTable
 
 

misc/schema/xrc_schema.rnc

@@ -765,7 +765,7 @@ wxCheckBox =
         stdObjectNodeAttributes &
         stdWindowProperties &
         [xrc:p="important"] element label {_, t_text }* &
-        [xrc:p="o"] element checked {_, t_bool }*
+        [xrc:p="o"] element checked       {_, t_integer }*
     }
 
 

src/xrc/xh_chckb.cpp

@@ -43,7 +43,38 @@ wxObject *wxCheckBoxXmlHandler::DoCreateResource()
                     wxDefaultValidator,
                     GetName());
 
-    control->SetValue(GetBool( wxT("checked")));
+    switch (GetLong("checked", wxCHK_UNCHECKED))
+    {
+        case wxCHK_UNCHECKED:
+            // Nothing to do here, we could call SetValue() but the default state
+            // is unchecked anyhow.
+            break;
+
+        case wxCHK_CHECKED:
+            control->SetValue(true);
+            break;
+
+        case wxCHK_UNDETERMINED:
+            // While just trying to set it would generate an assert if wxCHK_3STATE
+            // is not set, prefer to give an error here as we have more information
+            // about the problem.
+            if ( !control->HasFlag(wxCHK_3STATE) )
+            {
+                ReportParamError("checked",
+                    "A checkbox must have wxCHK_3STATE style to use wxCHK_UNDETERMINED");
+                break;
+            }
+
+            control->Set3StateValue(wxCHK_UNDETERMINED);
+            break;
+
+        default:
+            ReportParamError("checked",
+                             wxString::Format("Unknown checkbox state: \"%s\"",
+                                              GetParamValue("checked")));
+            break;
+    }
+
     SetupWindow(control);
 
     return control;