Fixing the signature of the ComboBoxAssist.Get* attached property methods.
Fixing the signature of the ComboBoxAssist.Get* attached property methods.

ButchersBoy/MaterialDesignInXamlToolkit,DingpingZhang/MaterialDesignInXamlToolkit,tipunch74/MaterialDesignInXamlToolkit,tipunch74/MaterialDesignInXamlToolkit,ButchersBoy/MaterialDesignInXamlToolkit,tipunch74/MaterialDesignInXamlToolkit,ButchersBoy/MaterialDesignInXamlToolkit