CODEWITHSUNDEEP
iosobjective-cdrawrectlagsetneedsdisplay
David Goncalves
David Goncalves

Reputation: 81

setNeedsDisplay no refresh the screen

Iim displaying a huge amount of images each time I call drawRect with setNeedsDisplay. The problem is that cause lags cause each time I call dracRect, I redraw every images (thousands).

Is there a way to not redraw all the images. I mean, keep all images and draw the one I want to draw?

thanks,

Upvotes: 0

Views: 753

Answers (3)

Sergey Kalinichenko
Sergey Kalinichenko

Reputation: 726539

One way to avoid redrawing everything is to call setNeedsDisplayInRect: instead of setNeedsDisplay:, and passing only a rectangle containing the image that needs to be redrawn. Of course this means that your drawRect can no longer ignore the rectangle passed in: go through the images, and check if an image overlaps with the rectangle being redrawn. If there is no overlap, skip the image and save some CPU time on a redraw.

Note that this is a very "manual" way of maintaining a view. Consider using some of the components that iOS provides for you, such as UICollectionView, which lets you display lots of stuff on the screen with very little code.

Upvotes: 1

Sulthan
Sulthan

Reputation: 130102

Split the view into different views (or layers), that will enable the system to cache their contents and redraw faster.

I don't know your use case but with hundreds of images, I would consider using OpenGL.

Upvotes: 0

Mike Weller
Mike Weller

Reputation: 45598

You will have to split your content into multiple views or layers (CALayer). Then only redraw the view or layer whose content actually needs to change.

Upvotes: 0

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