I have a custom view in my application, which is layer-backed and embedded in an NSScrollView. I allow the user to zoom in (which is accomplished by increasing the size of my custom view). I'm having trouble zooming in on an arbitrary point, though, since the NSScrollView keeps getting in the way and causing the view to jump around (typically to the view's origin) before I point it to the new scroll point. I would really like to use a CAScrollLayer, since I know I could definitely get the zooming right with it and have it move smoothly, but then I lose all built-in scrolling facilities.
Is there any way to leverage CAScrollLayer within an NSScrollView, possibly backing the NSClipView? If not, what purpose does CAScrollLayer actually serve? Is it possible, with a different approach, to change my view's size and the scroll point atomically and have that animate?
In short, is CAScrollLayer completely useless, or mostly useless?
Update
I've gotten my inner view to jump around less by making a CALayer subclass to display my view's contents. Rather than sizing with layout constraints, I have it sizing in an override of -resizeWithOldSuperlayerSize:. I still can't change the frame size and origin of my view simultaneously and get a smooth animation, though. To get a sense of what I'm looking for, open an image in Preview and zoom in and out. It zooms about the center of the image in a smooth manner.
In the limit, you can use an NSScroller instead; that way you would be able to use CAScrollLayer, if that’s your preferred implementation.
Note that on some (older) versions of Mac OS X, NSScroller has a bug that causes it to invoke an Apple private method on its containing view. You’ll know if this happens because you’ll get an exception about your custom view not responding to a method starting with an ‘_’.
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I have a custom NSView subclass, and I put it in a NSScrollView, and the basics are working fine. It always takes up the full width of its available space, so its constraints take up the whole width of the scroll view. How much vertical space it takes up depends on how much data it has to display, so it can scroll vertically, only. That's all great.
The catch is that if my custom view needs less space than the NSScrollView that it's in, it doesn't expand to fill the visible area. In cases where there's less data than fits in the visible area, I want it to expand downwards -- so that space is available as a drag-and-drop target, among other things.
I've tried changing its "hugging priority". I've tried adding a constraint to keep the bottom below the NSClipView's bottom. I can't come up with any constraint-based solution to fix this (though I haven't ruled out the possibility, either).
I've tried catching the notifications when the NSScrollView changes size, and adjusting the custom view's frame if it's too small, but (presumably because I can only change its current frame, while the layout system does all layout later) I can't seem to make this work, either.
Is there a trick for adding a view to an NSScrollView such that it expands to the bottom of the visible area, whenever it would otherwise be too short? It seems like it should be so simple, and I've done it before in cases where I just call -setFrame on everything manually, but once you move to the autolayout world, that approach stops working.
Without knowing what your constraints and content hugging and content compression actually look like...
Content hugging with at least one edge having >= constraint to superview might do it but you might need to adjust priorities.
You might also need to make sure you've implemented intrinsicContentSize in your custom view class this tells the content hugging and compression what they need to knowfirst.
I'm having all kinds of trouble understanding how NSWindows can have larger documents than the window bounds in them.
Unfortunately, layout and contents prevents me from simply shrinking the document (and I wouldn't want to make the layout cramped for those with larger screens).
A school needs to run this app on their new 13", non-retina MacBook Pros. Scrolling is acceptable to them, but I'm unsure as to the approach, and I'd like your advice on the best way to handle this to avoid forced scrolling on larger screens.
I've tried setting the NSWindow min and max size and embedding the document in a Scroll View. But even though you can see part of the document view sticking out, no scroll bars appear (I have set them to Always in sys prefs).
If this is the way to go I would appreciate a link to a tutorial on this exact subject, because I'm a bit lost with all the measurements and options.
If not I'd like a pointer where to start and what to read. I'm experienced with Cocoa Touch but a relative newcomer to Mac development.
Without more information it sounds like you have embedded a NSScrollView but didn't set up the springs and struts properly to allow the scroll view to resize when its parent view (assuming it's the window) resizes.
You might want to check out Specifying a View’s Behavior as Its Container Resizes in the Interface Builder Help documentation.
Although I know of a solution to this problem, I am interested if someone can explain this solution to me. I also wanted to get this out there because I could not find any mention of this problem online, and it took me several hours over several days to track down. I have an NSTableView behaving strangely regarding redraws and its selection. The problem looks like this:
Table contents fades in, instead of appearing instantly upon it's appearance on screen. When scrolling through the contents, the newly appearing rows also fade in. When you make a selection (single or multiple), and scroll it off screen, then make another selection (that should replace, not add-to first selection), the first selection does not get cleared properly. If you scroll back to it, it is still there, in addition to your new selection. This is a display-update problem, not selection problem - i.e. your new selection is valid, it is just displayed wrong.
I tracked this through the NSArrayController I was binding to, the underlying Array, sorting, all the connections, and settings, etc., but all that has nothing to do with it.
What solved the problem was:
In the View Effects (right-most) Inspector, uncheck "Core Animation Layer" for the Window's main view.
Can anyone explain what is happening here, and perhaps improve upon the solution ?
It looks like Core Animation and NSTableView aren't getting along so well. The "fading" effect is a by-product of the way core animation works. When you have core animation in one view, it is also enabled in all of that view's subviews.
I don't recommend using core animation on the Mac unless absolutely necessary, because some interface elements (NSTextView and NSTableView, for example) aren't compatible with it. iOS has much better support for table views and such using core animation, mainly because it was designed with core animation in mind.
I know that some more simple UI elements are compatible (NSTextField and NSButton, for example).
If you absolutely need core animation in the rest of the window, put all the other views in a subview of the content view, while leaving the table view directly in the content view. You can then enable Core Animation in the other view.
Commenters, feel free to add to the list of what is and isn't compatible.
You see this in iPhone apps like Gilt. The user scrolls a view, and a subview apparently "sticks" to one edges as the rest of the scrollView slides underneath. That is, there is a text box (or whatever) in the scrollView, that as the scrollView hits the top of the view, then "sticks" there as the rest of the view continues to slide.
So, there are several issues. First, one can determine via "scrollViewDidScroll:" (during normal scrolling) when the view of interest is passing (or re-appearing). There is a fair amount of granularity here - the differences between delegate calls can be a hundred of points or more. That said, when you see the view approach the top of the scrollView, you turn on a second copy of the view statically displayed under the scrollView top. I have not coded this, but it seems like it will lack a real "stick" look - the view will first disappear then reappear.
Second, if one does a setContentOffset:animated, one does not get the delegate messages (Gilt does not do this). So, how do you get the callbacks in this case? Do you use KVO on "scroll.layer.presentationLayer.bounds" ?
Well, I found one way to do this. When the user scrolls by flicking and dragging, the UIScrollView gives its delegate a "scrollViewDidScroll:" message. You can look then to see if the scroller has moved the content to where you need to take some action.
When "sticking" the view, remove it from the scrollView, and then add it to the scrollView's superview (with an origin of 0,0). When unsticking, do the converse.
If you use the UIScrollView setContentOffset:animated:, it gets trickier. What I did was to subclass UIScrollView, use a flag to specify it was setContentOffset moving the offset, then start a fast running timer to monitor contentOffset.
I put the method that handles the math and sticking/unsticking the child view into this subclass. It looks pretty good.
Gilt uses a table view to accomplish this. Specifically, in the table view's delegate, these two methods:
– tableView:viewForHeaderInSection:
and – tableView:heightForHeaderInSection:
I want an NSView that can be resized by dragging its the bottom right corner around, just like an NSWindow. I want to be able to embed this NSView into a parent NSView. Is there a component like this in Cocoa or any of its extensions?
If you get more specific with your question, I can get a little more specific with the answer. :-)
There is nothing like this available that I know of, but it's not terribly difficult to create. The decision to make is "who handles drawing the resize grips and resizing / dragging logic?"
Views Handle Their Own
If your user-resizable view handles drawing the grips and responding to the resizing/dragging actions itself, then you have to choose whether you want the grips drawn atop the view's contents or "around the outside." If you want the grips "outside," the "usable area" decreases because your content has to be inset enough to leave room for you to draw the resizing controls, which can complicate drawing and sizing metrics. If you draw the grips "atop" the content, you can avoid this problem.
Container View Handles All Subviews
The alternative is to create a "resizable view container view" that draws the resize grips around any subviews' perimeters and handles the dragging/resizing logic by "bossing the subviews around" when it (the container) receives dragging events on one of its grip areas. Placing the logic here allows any type of subview to be draggable / resizable and gives you the added benefit of only having one instance of the slightly-heavier-weight view (versus many instances of subviews that have the more complicated logic in them).
The Basic Mechanism
Once you've decided that, it's really just a matter of creating your subview, which does the drawing, manages NSTrackingArea instances (for the grip areas), and responds to the appropriate mouse methods (down, moved, etc.). In the case of each subview handling its own, they'll manage their own tracking areas, grip drawing, and mouse moved, setting their own frame in response. In the case of a container view handling all this for its subviews, it will manage all subviews' tracking areas and draw their grips on itself, and set the targeted subview's frame (and the subview is blissfully ignorant of the whole thing).
I hope this helps give you at least a general idea of possible mechanisms. Had I not just gotten up and started my morning coffee, I'd probably be able to write this more succinctly, but there you have it. :-)
EDIT 7 YEARS LATER
Because there wasn't much detail about what the OP wanted, I gave a very generic answer, but I should make a few points:
Always prefer an NSSplitView if it can be made to work for you (ie, if the views align with each other and divide the common container view's space). A split view lets you customize grip areas, etc. and does all of this to your subview for free.
AutoLayout didn't exist when I wrote this answer and it greatly complicates rolling your own solution for the view-handling-multiple-sizable-subviews scenario.
If you really do need a UI element that can be dragged/resized within some container, try your best to get away with using CALayers inside a master view that handles all the layout/sizing logic if you can.
If you can't do the above (ie, the resizable view contains complex controls and layout, has its own NSViewController, etc.), try a hybrid approach (use layers to display cached images of non-selected views and only add a full, interactive sizable subview for the selected item (or subviews for items).
Because of the complexities of AutoLayout, I really can't recommend the real draggable subview approach at all unless it's unavoidable. If you're designing a view that contains movable, sizable things, it's best (and most efficient) to make everything inside it that view's responsibility. Example: a graphics app with lots of shapes should have a Canvas view that represents the shapes (and any GUI decorations like size/drag grips, etc.) using CALayers. This takes advantage of graphics acceleration and is far more efficient than a bunch of (very resource-heavy) NSView subviews. All the move/size/select logic is handled by the "Canvas View" and the only subviews might be overlaid controls (though if your Canvas itself needs to be enclosed in a scroll view, it's best to use NSScrollView machinery to allow stationary overlay views for this purpose).
If designing a view that draws lots of things (for which you should definitely use layers to represent those things) but allows selecting only one thing, the approach of adding a subview is manageable enough even with AutoLayout. If the "selected for editing" thing has lots of complex controls that become visible when editing, an "editor subview" with accompanying view controller makes sense and is a good tradeoff in maintainability (because view controller compartmentalizes all editing functionality/UI handling) vs. container view complexity (because one subview isn't going to break the resource bank and maintaining temporary AutoLayout constraints for keeping its position during container view resizes & editor interactions isn't overly complex).
All of this assumes macOS; if designing for iOS, definitely bend over backwards to use layers and the new (as of this writing) drag and drop machinery, of which I know precious little at present.
In summary, the answer was incomplete as well as somewhat outdated, so I feel my original advice isn't as good as it could be these days.
Instead of using views, you can use windows and set the style mask of the window to NSResizableWindowMask.
Another option is using an NSSplitView, if you have two resizable, contiguous subviews.