execute drawRect on every frame?

Question

I'm trying to implement a custom view which visualizes a value which is changing in real time (like for example the volume of the audio output), and to achieve this I would like to have drawRect execute every animation frame to render the correct view state for the value.

The only solution I can think of is to set a timer to execute 60 times per second, and call view.setNeedsDisplay() but I'm sure this is not the best way to get this behavior and guarantee smooth performance.

edit to give a slightly more concrete example

So the situation I have is basically this:

//There is a variable which is changing continuously
var dynamicFoo : Double!

//I want to create a view class which renders foo in real-time
class fooVisualizerView : UIView {

   //I have drawing code which renders foo at any given value
   override func drawRect(rect: CGRect) {
       valueDependantDrawFunction(dynamicFoo)
   }

}

Ideally I would like fooVisualizerView to redraw on every animation frame.

Answer 1

A CADisplayLink sounds like what you want - this is effectively a timer that is called every time the screen is updated. You can call setNeedsDisplay from the display link method.

Note though that your code needs to complete in 1/60 of a second for this method or it will look terrible.