<image>As shown in the figure, given the linear function $$y=kx-4$$ which intersects the $$x$$-axis and the $$y$$-axis at points $$A$$ and $$B$$ respectively, and intersects the graph of the inverse variation function $$y= \dfrac {8}{x}$$ in the first quadrant at point $$C$$, with $$A$$ being the midpoint of $$BC$$, then $$k=$$ ______ . 
