I have a UIScrollView with a custom content view that uses drawRect to display its contents.
In my drawRect method I respect the passed CGRect parameter and only draw what's needed.
However, each time the drawRect is called it is passed the entire bounds of the view, even if it is several thousand pixels, and I'm worried about performance and memory use. Is there any way to make a UIScrollView limit this, or am I worrying too much over nothing?
Also, I've tried using CATiledLayer as the layer, and while this corrects the passed rect, it feels like I'm misusing the class. Also, the view still keeps all the pixels backed as far as I can tell. (Even if it doesn't draw some of them right away)
using CATiledLayer is probably the best option. I'm familiar with CATiledLayer as a concept, but never used it myself, so I'm not going to say anything about that. What I can say, is that if you subclass the UIScrollView and implement
layoutSubviews
you should be able to redraw the subviews toll-free with good performance, as long as you implement a construction using
CGRectIntersectsRect()
In which you can see if the current visible rect, in the case of a subclass
[self bounds]
intersects with the rect of the object you want to draw. if it doesn't, you can choose to ignore the object or even (if it is already on the scrollview) remove it from superview. if it does, you can place the object on superview.
again, CATiledLayer is a way better solution, but if you feel like you are misusing it, try the approach I described.
1.content view large than scrollview is true..
2.may be you should realize UiScrollViewDelegate's
scrollViewDidScroll
caculate content view 's rect that should be redrawed ,not the entire bounds .
Related
What are the differences between adding a view as a subView VS drawing the view in that view's drawRect method?.
I use both approaches, but I was wondering apart from the obvious such as, if you do in drawRect it will be a single View, as opposed as two views, or adding as a subview is just easier. Are there any specific situations where you should definitely use one over the other?
Overriding -drawRect: can be a good way to draw complex UITableViewCells. Having all of the subviews composited and drawn as one view helps table view scrolling performance immeasurably.
Having said that, I typically stick with the highest level API available and drop down to a lower level only if performance suffers.
Adding a subview is easier as you point out, and I really see this as no contest in 90% of cases. You should generally add a subview and let the libraries handle drawing of subviews in their correct position.
I only use -drawRect: to accomplish custom drawing within my view, but not to draw subviews, it creates unnecessary complexity. If you need a lot of performance, -drawRect: can help you there. Also, in the case of simple drawing, -drawRect: is very nice as opposed to making several subviews. But in general, it pays to just add a subview.
If in the future you decide you want these subviews to receive touch events or handle things interactively, it is more difficult to refactor your -drawRect: code.
I've got a pretty big UIScrollView (contentSize 8000 x 960) with a lot of small labels.
The labels are only added if you scroll to the area where the label belongs to. So, at first, the scrooling is smooth, but as more and more labels are loaded, the performance suffers more and more.
What's the best solution to keep the scrolling smooth? Is CATiledLayer the way to go? Or should the labels off the view should be hidden or something like that?
Thanks a lot for your help!
Stefan
EDIT:
I got a huge performance boost when drawing some objects instead of using views; but now, I've got another problem; if I draw directly onto the UIScrollView, everything performs great. But if I lay a UIView on the UIScrollView and draw on that, performance goes down again (both times calling setNeedsDisplayInRect: in scrollViewDidScroll:).
So hierarchy:
UIWindow
UIView
UIScrollView <== drawing here
works fine.
But hierarchy:
UIWindow
UIView
UIScrollView (size 8000x960)
UIView (size 8000 x 960) <== drawing here
performs bad.
Any ideas why? I need the UIView above because the drawing should be ABOVE some UIViews; so I place the UIViews in the scrollView and draw in the view above...
The label reuse is one of possible solutions. Sometimes it doesn't help a lot. When a new UIView appears the drawRect method will be called and that may cause problems with animation.
Sometimes the best solution is to draw your labels (I mean text) directly using Core Graphics without creating UILabel object or something else. The CALayer will increase performance, but there is a possibility that it will not help you a lot.
But first of all you should remember that views with alpha = 0 or hidden = YES will not be drawn at all, so there is no penalty for using them. Maybe you should try to hide unused ones before using Core Graphics.
The best way would be to have just a few UILabels and reuse them. But you'll have to implement - (void)scrollViewDidScroll:(UIScrollView *)scrollView and do some reusable logic there. Depending on case it might be easier to use a UITableView and transform it 90 degrees, so it looks like a scrollview. That way you can the build-in reusable logic of the TableView.
For others seeing this post, I was able to drastically improve performance and keep UIViews in a scroller without using a table by enabling each view's "shouldRasterize" property. This property renders the view as an image while the view is in motion, causing it to not need to be reprocess for each pixel it moves. So, if I have a UIButton called button, it gets enabled like this:
button.layer.shouldRasterize = YES;
Did u try something similar to UITableViewCell
dequeueReusableCellWithIdentifier
Using a reuseIdentifer to reuse the once allocated labels..
My question is very similar to this one Not drawing outside bounds when clipToBounds=NO which received no clear answer.
Basically I have a UIView, and I want to draw a line from the center of it, to the edge of the screen. Calculating where these points are is easy, using [self convertPoint:(CGPoint){0,0} fromView:[self superview]]; (which finds the origin with respect to my view's superview. But when I draw a line from my view's drawRect: it gets clipped at my view's bounds.
Is there a way to draw outside of my view's bounds? I've tried changing the clipsToBounds property, but it doesn't seem to have any effect.
I can't draw my lines from the superview because I need to do this with multiple views and some will be in front of others... figuring out the layer from the superview's drawRect seems like a bad idea.
Similarly, I don't think I can just resize my view's bounds to include the entire screen, because my views need to be dynamically re-sizable... the bounds would have to be HUGE (>20,000 points square) for this to work.
I wouldn't recommend ever drawing outside of a view's bounds. Either your view needs to resize automatically to include your drawing or you need to have transparent overlapping views. Or both. I can't think of a situation that either of these cases wouldn't cover, but I may lack imagination. =)
Likely what is happening currently is that when the super view gets redrawn it tells the super view that it needs redrawn, resulting in erasing the drawing you are doing outside. It's been a while, anyone more knowledgeable can (should!) correct me here if I'm wrong.
I don't know if "Quartz Debug" (from the standard apple developer tools install, /Developer/Applications/Performance Tools/Quartz Debug) works in the simulator, but it's worth a try. It has a mode that will show you when and how often redrawing takes place, with a border and optional delay on the refreshes.
You can do what you are asking, but you need to force redraw your sub-views every time you go outside the sub-view's bounds, meaning that your super-view needs to manually draw it's children inside of it's draw function. Essentially you would be throwing out apple's drawing paradigm and simply causing your sub-views to act like a drawing extension of your main view anyway.
Additionally, if your ranges are so dynamic you may want to consider drawing in percentages of the screen or super-view rather than in points, it may make more sense to code.
I'm not really sure, what am I asking...
...but if make layer composites in separate methods, and draw them to the view also outside of the drawRect: method... ...then could my app performance get raised?
I'm actually subclassed a puzzlePiece:UIView class, where the puzzlepiece gets rendered, but the redraw invoked now with setNeedsDisplay since the drawing implementation takes place in the drawRect: method. The app lags.
Can I improve performance if I get rid of the so called drawRect: method?
The thing wants to get implemented: http://gotoandplay.freeblog.hu/
I think what you want to do here is to have a very single, simple UIView that covers the entire play area. Then put each tile in a CALayer, and attach all the CALayers to the UIView and move them around and rotate them. Then there should not need to be a -drawRect: at all. You'll do all your drawing in your layers, and you should get the best performance that way. CALayer is similar to UIView in principle, but much lighter weight (faster and simpler). CALayer is basically a view that can only draw; it can't handle touches or events. It's parent view has to do that for it. But that let's CALayer be much faster.
Everytime UIView's drawRect is called, the content drawn by previous drawRect (using Core Graphics) is cleared out. How can I make it so that the paths rendered from previous drawRect calls stay until I explicitly clear it?
You basically need to clip the 'dirty' part of your rect where changes have been made, and only this part will be re-drawn.
- (void)setNeedsDisplayInRect:(CGRect)invalidRect
I'm fighting this issue myself right now. The problem is there is a property on the UIView called "clearsContextBeforeDrawing" that according to the documentation is supposed to fix this problem, however it doesn't work that way in my experience.
I think ultimately the solution to this is going to be to allocate an offscreen buffer and do all my drawing there, then blt it over to the UIView in the drawRect method.
I'm pretty certain there's no way around this; it's how UIView is designed to work. If asked to, your custom view should be able to draw any part of itself at any time. This is partly because views can do more than just appear onscreen. e.g. on the desktop they can be printed, and even on the iPhone, you might wish to capture the contents of a view to a bitmap.