What's a proper way to print variable with a hex pointer given (Xcode 10.3, 11 betas)

Question

Given the infamous < NSLayoutConstraint:0x1c809d970 UIView:0x11fe288b0.height == 16 (active)> & co from the autolayout engine

what's the brave new swiftly world way to print an object of UIView class by a hex pointer value?

(lldb) p *((UIView*)0x11fe288b0)

error: :3:12: error: expected ',' separator *((UIView*)0x11fe288b0) ^ ,

(lldb) po *((UIView*)0x11fe288b0)

error: :3:12: error: expected ',' separator *((UIView*)0x11fe288b0) ^ ,

(lldb) expr *((UIView*)0x11fe288b0)

error: :3:12: error: expected ',' separator *((UIView*)0x11fe288b0) ^ ,

This is in xcode 10.3 and 11 beta 3

UPD:

(lldb) p *((UIView*)0x11fe288b0)

worked at first in xcode 11 beta 5, now it ceased to work: this might have been fixed in beta 5 but possibly that fix got clobbered when I went back to xcode 10.3 that "installed additional components"

UPD2: this seems to be a duplicate of Xcode debugger (lldb) get object description from memory address

score 6 · Answer 1 · answered Jul 31 '19 at 00:34

6

You can cast from an address to a UIView (or mutatis mutandis for any other class) in Swift using unsafeBitCast like:

(lldb) po unsafeBitCast(<ADDRESS>, to: UIView.self)

You can also access properties this way:

(lldb) po unsafeBitCast(<ADDRESS>, to: UIView.self).bounds

etc...

answered Jul 31 '19 at 00:34

Jim Ingham

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(lldb) po unsafeBitCast(0x1021a8410, to: UIView.self) error: use of undeclared identifier 'to' – Anton Tropashko Jul 31 '19 at 10:16
That's odd. "to:" has been the name for the type parameter in unsafeBitCast since at least swift4.0. If you can repro this in a small example, please file a bug with http://bugs.swift.org. – Jim Ingham Jul 31 '19 at 19:34
1

Ah, I see. I get the same error you showed if I run this expression in a C frame, since that's the best the C parser can do with the expression. lldb chooses the default language for expressions from the language of the currently selected frame. If you are in a C-frame, use the expression from the previous answer. Only use this one if a swift frame is the currently selected one. – Jim Ingham Jul 31 '19 at 19:37

matt · Accepted Answer · 2019-07-30T12:52:27.627

4

If the problem is just layout constraints, the simplest solution is to give your constraint a string identifier. You can do that in code or in the storyboard. Makes debugging constraints really easy; the identifier appears in quotes first thing in the debug output:

[LayoutConstraints] Unable to simultaneously satisfy constraints.
(
    "<NSLayoutConstraint:0x600003af86e0 'getStartedBad' ... >",
    "<NSLayoutConstraint:0x600003af8730 'getStartedTop' ... >"
)

If the question is about a UIView for which you have only the address, you can send messages to it like this:

(lldb) expr -l objc -O -- [(UIView*)0x11fe288b0 layer]

(Yes, you have to talk Objective-C to it, but I don't think there's any other way.)

edited Jul 30 '19 at 12:52

answered Jul 30 '19 at 11:21

matt

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In general there is this https://stackoverflow.com/a/45464836/341994 but you already know these are constraints – matt Jul 30 '19 at 11:26
pardon my ignorance by how do you give a string identifier to a view in code? – Anton Tropashko Jul 30 '19 at 11:32
here https://stackoverflow.com/questions/57109674/how-do-i-change-names-to-tell-apart-uiviews-in-xcode-visual-debugger I've added bounty for that programmatic identifier question – Anton Tropashko Jul 30 '19 at 11:35
Oh, I see, you want to identify the view, not the layout constraint. – matt Jul 30 '19 at 11:59
But you see what I do is give the layout constraint an identifier that identifies the view it affects. It’s just a name so you pack it with information. – matt Jul 30 '19 at 12:01
Constraints identification is also useful to tell between dozens of them at a glance. – Anton Tropashko Jul 30 '19 at 12:02
I expanded my answer to be a bit more helpful. – matt Jul 30 '19 at 13:10
What I don't see is a property to set a name or identifier here https://developer.apple.com/documentation/uikit/nslayoutanchor – Anton Tropashko Jul 30 '19 at 13:19
how to you get that getStartedTop to a constraint created programmatically? – Anton Tropashko Jul 30 '19 at 13:19
By setting the constraint's `identifier` when I create the constraint programmatically. – matt Jul 30 '19 at 13:25
rg8t success. I see that prop added in ios7. Thanks a bunch! – Anton Tropashko Jul 30 '19 at 13:28
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"What I don't see is a property to set a name or identifier here" Because an anchor is not a constraint. – matt Jul 30 '19 at 13:30
right, found it, gave you the rightfully deservedbounty in another bountied question that this discussion really belongs to – Anton Tropashko Jul 30 '19 at 13:32

What's a proper way to print variable with a hex pointer given (Xcode 10.3, 11 betas)

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