Hi, I've made a "flick" command for a game once. Doesn't know if this is what your are looking for.
But basically it works like this, I have a variable InitialY and a variable FinalY, every time the player touches the screen the position of his touch goes to InitialY, while the player is touching the screen the position he is touching goes to FinalY. So when the player lifts his finger of the screen I triggered a event to compare Initial and Final Y so I could know if the player have flicked up or down.
However for this game I've made possible only Up and Down flicks, you want vertical and diagonal too, so you will need two more variables for Initial and Final X, and depending on what you want to do a little bit more complex algorithm. But it is a idea, you should give it a try ^^