像Android API一样的AnglePicker

Question

I want to create an "Angle Picker" like the Android TimerPicker in Alarm Clock since API Level 19 KitKat.

I only want to pick an angle between 0 and 360 degrees. Anybody know how to create something like this?

Android TimePicker in Clock App

Answer 1

Create your own component:

public class AnglePicker extends View { ... }

Override the onDraw(Canvas canvas) method. You should draw a circle, a few texts (0º, 90º, º180 and 270º for example)...
You only need a few calls to canvas.drawCircle() and canvas.drawText() . The most "difficult" part would probably be calculating the text positions. But it's not a big problem, just a little bit of sin and cos .

Then override onTouchEvent(MotionEvent event) too, so you can listen to touch events and repaint the component depending on your needs (drawing a line between center and the selected number, highlighting the closest number with an additional drawCircle ...).
Basically when the user touches your view, calculate the (x,y) position:

Point pt = new Point( (int)event.getX(), (int)event.getY() );

And get the angle with double theta = Math.atan2(pt.x-center.x, center.y-pt.y); . Translate it into degrees or whatever you need, cause theta is expressed in radians.

Finally, add a public double getAngle() so other components can read the selected angle.
Seems complicated, but it's not. You can search for "android custom view" if you want some code to start with.