Android touch control

I made an Android egg timer app that shows how to make custom touch controlled views.

You basically turn the dial by touch and then it gradually counts down.

Touch input sequence

  • First you need to get the right touch inputs from inside the graphic.
  • Then you create a vector from coordinates based on a center in the middle of the circle graphic.
  • Use trigonometry and then pythagoras to calculate the degrees that the clock should rotate based on the movement vector.

TeggTimer Demo Screenshot

Trig code:

    //Distance to center from last touch using trig
    double lastSide = getLastTouchX()/Math.cos(Math.atan2(getLastTouchY(), getLastTouchX()));
    double oppoSide = dx/Math.cos(Math.atan2(dy, dx));
    double firstSide = latestX/Math.cos(Math.atan2(latestY, latestX));

    // Do the pythagoras for the triangles sides
    double a = lastSide;
    double b = firstSide;
    double c = oppoSide;
    double degrees = Math.toDegrees(Math.acos((Math.pow(a,2)+Math.pow(b, 2)-Math.pow(c, 2))/(2*a*b)));


You can find the rest of the code here