Add wxControl::GetSizeFromTextSize() to size the control to its text.

This function can be used to size a, say, wxTextCtrl to be exactly of the size
needed to enter the given amount of text in it.

This patch adds wxGTK implementation for wxTextCtrl, wxChoice and wxCombobox;
changes to the samples and the documentation.

Closes #14812.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@72935 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

src/gtk/choice.cpp

@@ -348,8 +348,38 @@ wxSize wxChoice::DoGetBestSize() const
     // Get the height of the control from GTK+ itself, but use our own version
     // to compute the width large enough to show all our strings as GTK+
     // doesn't seem to take the control contents into account.
-    return wxSize(wxChoiceBase::DoGetBestSize().x + 40,
-                  wxControl::DoGetBestSize().y);
+    return GetSizeFromTextSize(wxChoiceBase::DoGetBestSize().x);
+}
+
+wxSize wxChoice::DoGetSizeFromTextSize(int xlen, int ylen) const
+{
+    wxASSERT_MSG( m_widget, wxS("GetSizeFromTextSize called before creation") );
+
+    // a GtkEntry for wxComboBox and a GtkCellView for wxChoice
+    GtkWidget* childPart = gtk_bin_get_child(GTK_BIN(m_widget));
+
+    // Set a as small as possible size for the control, so preferred sizes
+    // return "natural" sizes, not taking into account the previous ones (which
+    // seems to be GTK+3 behaviour)
+    gtk_widget_set_size_request(m_widget, 0, 0);
+
+    // We are interested in the difference of sizes between the whole contol
+    // and its child part. I.e. arrow, separators, etc.
+    GtkRequisition req;
+    gtk_widget_size_request(childPart, &req);
+    wxSize totalS = GTKGetPreferredSize(m_widget);
+
+    wxSize tsize(xlen + totalS.x - req.width, totalS.y);
+
+    // For a wxChoice, not for wxComboBox, add some margins
+    if ( !GTK_IS_ENTRY(childPart) )
+        tsize.IncBy(5, 0);
+
+    // Perhaps the user wants something different from CharHeight
+    if ( ylen > 0 )
+        tsize.IncBy(0, ylen - GetCharHeight());
+
+    return tsize;
 }
 
 void wxChoice::DoApplyWidgetStyle(GtkRcStyle *style)