How to keep widget at bottom of frame? - ruby

Question

My main window launches a top-level window with a sub-frame (to browse/select a directory) along with 'load' and 'add directory' buttons at the bottom. The 'add directory' button deletes all the directory entry subframes (but leaves the buttons), checks that there are no duplicates directories entered or empty strings, and recreates subframes for valid entries and creates another one left blank.
The problem is that when I click the 'add directory' button, the buttons end up on top. Is there a way to fix the buttons to the bottom of the window?
In Main class:
def add_directory
dir_window = TkToplevel.new(#root) {title 'Directories'}
dir_frame = Tk::Tile::Frame.new(dir_window) {padding "3 3 12 12"}.grid(:sticky => 'nsew')
DirectoryFrame.show(dir_frame)
loadDirectoriesButtonClicked = proc {load_files}
Tk::Tile::Button.new(dir_frame) {text 'Load directories'; command loadDirectoriesButtonClicked}.grid(:column=>0, :sticky=>'s')
addDirButtonClicked = proc {DirectoryFrame.show(dir_frame)}
Tk::Tile::Button.new(dir_frame) {text '+'; width 2; command addDirButtonClicked}.grid(:column=>1, :sticky=>'sw')
end
In directory frame class:
class DirectoryFrame < Tk::Tile::Frame
##directory_frames = []
##directories = []
def self.show(parent_frame)
if !(##directory_frames.nil? || ##directory_frames.empty?)
directories
remove_frames(parent_frame)
end
##directories.delete("")
if !(##directories.nil? || ##directories.empty?)
##directories.each do |dir|
dir_frame = DirectoryFrame.new(parent_frame)
dir_frame.directory = dir
##directory_frames << dir_frame
end
end
##directory_frames << DirectoryFrame.new(parent_frame)
refresh
end
def self.refresh
##directory_frames.each_with_index do |dir_frame, index|
dir_frame.grid(:row=>index, :sticky=>'ew')
end
end

Answer 1

If you don't specify which row to put a widget on when you grid it in, Tk picks the row with number one larger than the current largest used row number. This is often just fine, but is wrong for you. Instead, you should explicitly put your buttons in a row with a large number (e.g., 1000), and then have a counter of inserted rows that you use to decide which new explicit row to do the insertion on.
+--------------------+
| row 1 |
+--------------------+
| row 2 |
+--------------------+
| row 3 |
+--------------------+
| ... empty ... |
+--------------------+
| row 1000 |
+--------------------+
The other alternative is to put the buttons in a frame with another inner frame that holds the gridded space that you are adding rows into.
+----------------------+
|+--------------------+|
|| row 1 ||
|+--------------------+|
|| row 2 ||
|+--------------------+|
|| row 3 ||
|+--------------------+|
+----------------------+
| buttons |
+----------------------+
Either technique will work.