flicker a screen of iphone ipad in given frequency

I want my app 开发者_如何学Pythonto blink/flicker in the screen hopefully showing a video or photos, in a given exact frequency, like from 2 Hz to 70 Hz, could go black, of with a heavy dark filter?

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Create a scheduled timer with interval of 1/70.

[NSTimer scheduledTimerWithTimeInterval:1.0/70.0 target:self selector:@selector(flicker) userInfo:nil repeats:YES];

Then, in your flicker method, change the alpha property of your view.

Alex