Is it possible to make a UIView only appear inside a limited area of the screen, especially while animating? (When it reaches the boundary, it should simply cut off at the boundary point, as if it were being obscured by an object in front of it.) I need this because I have a roll-out menu comprised of UIButtons, and I don't want the menu to extend beyond the edge of the toolbar when closed. Thank you!
(Alternatively, hiding the entire UIView upon reaching the boundary would also be acceptable. I just don't know how to check for this condition without continuously querying the center property.)
You can define a clipping area for your UIVIew using the clipsToBounds property. If you are using CoreAnimation to animate your view, you may want to have a look a the maskToBounds property of CALayer objects as well (each UIVIew has a layer property of type CALayer).
From the UIView Class reference:
Normally, a subview’s visible area is
not clipped to the bounds of its
superview, but in iOS you can use the
clipsToBounds property to alter that
behavior.
Related
Is there a way to disable clipping of subviews of NSView? In UIView there is a “clip subviews checkbox” and the backing clipToBounds property, but I cant find anything similar in Cocoa.
Here is my scenario: I have this grey dot that you can drag on the screen:
When the user drags the dot I want to show up and down arrows that I have in the background. The up arrow is outside the bounds of the NSView holding the dot and arrow.
You could use the [NSView frameForAlignmentRect:] method. It defines the frame which is used for the constraints based layout. The actual frame can be much larger to allow displaying the arrows when the view is moved.
Cocoa is using this feature to compensate for shadows or other parts of views which do not "count" as actual frame of a control.
From the documentation:
The constraint-based layout system uses alignment rectangles to align views, rather than their frame. This allows custom views to be aligned based on the location of their content while still having a frame that encompasses any ornamentation they need to draw around their content, such as shadows or reflections.
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've learned that the best way to get graceful rotation is to set the auto rotation mask on the view that you want resize or move. This works fine if you're using SDK views like UILabel, but if you have your own custom view that uses the drawRect method it doesn't rotate as gracefully. In fact the only thing that happens is that it stretches whatever you drew in drawRect.
I've tried redrawing both before and after the rotation, but it doesn't give me that smooth rotation.
I looked at a UITextField auto rotating (flexible width) in slow motion and it follows the edge perfectly during the rotation. That is what I want my view to do, so how do I do that? My views jump to the right position either before or after the rotation.
The following line will make your UIView stretch the middle pixel only. If this is not your desired behavior I suggest you read the documentation for contentStretch to learn how to manipulate the values of the CGRect.
[self setContentStretch:CGRectMake(0.5, 0.5, 0.0, 0.0)];
I would guess that the UITextField you're looking at has at least three subviews, one displaying the left cap of the field's border, one displaying the right cap, and one displaying the middle, with autoresizing masks of "flexible right margin", "flexible left margin", and "flexible width", respectively. If you set up your custom view something like that, and make sure its autoresizesSubviews property is set to YES, then you should get the same smooth resize that the text field does.
The documentation says that the clipsToBounds property of UIView will clip the drawing to the bounds, or more precisely that the subView can't draw outside of the bounds of the superView.
Sounds nice, but what does that mean in practice?
If I set that to YES, then my subView will automatically only draw those parts which are not outside the bounds of the superView. so it increases the overall performance or do I still have to make sure that I don't create any views that are not visible, i.e. inside a UIScrollView ?
I think it's the opposite: turning on clipping hurts performance because it has to set up a clipping mask. I vaguely remember reading this somewhere, but I can't find it now.
The use case for clipsToBounds is more for subviews which are partially outside the main view. For example, I have a (circular) subview on the edge of its parent (rectangular) UIView. If you set clipsToBounds to YES, only half the circle/subview will be shown. If set to NO, the whole circle will show up. Just encountered this so wanted to share.
The (possible) performance hit is only deterministic if you know the view hierarchy. As mentioned above, usually the renderer will use GPU cycles to draw the view UNLESS some view within the hierarchy uses drawRect:. This does not affect OpenGL ES application because drawRect:is omitted in this type of apps.
From my understanding, determining and displaying the clipped area may take less cycles than actually calculating/drawing/blending the whole view. As of OpenGL ES 2.0 clipping can be calculated in GPU.
I have a UIScrollView that contains an image and a segmented control that allows the user to switch the image inside of the ScrollView. If I just swap the image out inside of the UIImageView, it will display the new image in the zoomed-in state. How do I reset the UIScrollView back to its un-zoomed-in state?
I have a detailed discussion of how (and why) UIScrollView zooming works at github.com/andreyvit/ScrollingMadness/.
(The link also contains a description of how to programmatically zoom UIScrollView, how to emulate Photo Library-style paging+zooming+scrolling, an example project and ZoomScrollView class that encapsulates some of the zooming magic.)
Quote:
UIScrollView does not have a notion of a “current zoom level”, because each subview it contains may have its own current zoom level. Note that there is no field in UIScrollView to keep the current zoom level. However we know that someone stores that zoom level, because if you pinch-zoom a subview, then reset its transform to CGAffineTransformIdentity, and then pinch again, you will notice that the previous zoom level of the subview has been restored.
Indeed, if you look at the disassembly, it is UIView that stores its own zoom level (inside UIGestureInfo object pointed to by the _gestureInfo field). It also has a set of nice undocumented methods like zoomScale and setZoomScale:animated:. (Mind you, it also has a bunch of rotation-related methods, maybe we're getting rotation gesture support some day soon.)
However, if we create a new UIView just for zooming and add our real zoomable view as its child, we will always start with zoom level 1.0. My implementation of programmatic zooming is based on this trick.
If you're not redrawing your view on the completion of the pinch zooming event, then the zoom factor is being set by the transform property of the view you return from the viewForZoomingInScrollView: delegate method. To reset this zoom, set the value of the view's transform property to CGAffineTransformIdentity.
Beware, though, that your next pinch-zooming operation will start where the previous pinch-zoom left off (that is, your new scale will be ignored). To work around this, you may need to implement some of what I describe here.