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I'm trying to hack a graphing library (https://github.com/KirillM/BarChart) that unfortunately does not offer a clearChart method. So instead, I'm thinking about turning everything to white pixels if that's possible.

I know that you can set a flag for the view to be reloaded with:

[self.myView setNeedsDisplay];

This is almost there but I'd ideally not want to dig into the library: Clear UIView of drawing?

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tarabyte
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  • You could try removing all the subviews: `[[yourView subviews] makeObjectsPerformSelector:@selector(removeFromSuperview)];`. Excerpt taken from question: http://stackoverflow.com/questions/2156015/remove-all-subviews – Milo Feb 06 '14 at 23:07

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A view is "cleared" each time it's drawn -- the view is essentially erased before -drawRect: is called, and the -drawRect: method draws whatever the view represents. If you want the chart to draw something other than what's there, you'll probably need to change the data that you give it.

It'd help if you'd say what library you're using, but one would expect some sort of method to set the data that the chart draws. Try calling that method with the null version of whatever the chart expects -- maybe it's an empty array, nil, or something along those lines.

Caleb
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  • good ideas for sure. i've tried the nil strategy without success. i'm using https://github.com/KirillM/BarChart – tarabyte Feb 06 '14 at 23:18
  • *cough* only if nobody has set `clearsContextBeforeDrawing` to `NO`; if set then the context contents will be undefined upon `drawRect:` given that `UIView`s may dump contents during low memory warnings, etc. – Tommy Feb 06 '14 at 23:38
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I found removing all the subviews from within the bar chart module did the trick: Remove all subviews?

  [[plotView subviews] makeObjectsPerformSelector:@selector(removeFromSuperview)];
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