I'm a rank newbie, so please excuse me.
I'm working with a barcode reader sample program from zbar. I wanted to add a sqlite3 daabase for looking up barcodes scanned. The but when I try to instance the sql control from the ViewController I get the following error.
MySQL *MS =[[MySQL alloc ] init];
[ MS viewDidLoad];
^^ MySQL may not respond to viewDidLoad
Any ideas? Thanks
PS The program crashes once it hits the offending line.
"May not respond to" means that your object may not implement the method you want to call. Your program crashes because it's essentially calling a method that does not exist.
I'm not quite sure what you're trying to do, but I don't think an object "MySQL" would have a viewDidLoad method.
There are two possible causes of “may not respond to”. Either:
You forgot to inclue a header file import for the appropriate class.
The method doesn't exist on the class you're calling it on.
Number 2 looks far more likely in your case.
Related
I have a method on one of my ViewController's that is called by one of its view's and delivered some value. It then sends out a message to a manager object with some information about the VC's state.
- (void)elementXChangedWithValue:(float)value {
ParameterManager * pMan = [ParameterManager sharedInstance];
[pMan updateParameter:self.elementX.parameter value:value];
}
In debugging, it was important for me to inspect what the .SomeElement.parameter state was so I could know what was getting lost in translation by the time I get to my ParameterManager.
Unfortunately, although Self is definitely non-nil and accessible the debugger shows scant information about the class making quick and practical glancing of the value difficult. (i will sometimes invoke "po" command in the debugger command line, however).
Not sure if it helps but this project is running heavy with the Objective-C/Swift interoperability although the ViewController is a fully Objective-C class.
Here is an image of what I am getting in the debugger. The drop-down arrow shows nothing but empty.
The debugger isn't perfect and sometimes you just cant see what is in certain areas, such as self. What does always work is NSLog's placed in code though, so if all else fails, add one of those in at the right place to print out the object you wish to know about.
The debugger may show more info after you make it execute these commands:
expr #import UIKit;
expr #import Foundation;
This loads the whole UIKit and Foundation symbols in the debugger at runtime, you only need to execute it once per debug session.
You can automate this with a user-defined breakpoint that'll be triggered every time your application starts in the debugger.
Source : http://furbo.org/2015/05/11/an-import-ant-change-in-xcode/
I want to create a breakpoint in xCode which uses LLDB and checks the current object class in condition section.
The problem is LLDB doesn't allow to use self to get a class. How to solve this problem? Maybe through other commands? For example, bt command output contains correct classname but it seems it is not allowed in LLDB too.
I presume this is related to:
Using of symbolic breakpoints for child classes in Xcode?
The problem comes if your breakpoint is in code with no debug information (like in system libraries.) The debugger knows nothing about self in this context, and you have to give it more help. In the case of self, you know that it was passed into a method call as the first argument, so you can use $arg1 to get at the value.
I'm writing a pretty straightforward ObjC app. (The only minor complexity is that it uses an external library called Chilkat for some basic networking, but I don't think that that's relevant.)
Occasionally, my project spontaneously pops up this warning message:
May 14 01:24:01 Neovenator-2.local Project[22645] : void
CGSUpdateManager::log() const: conn 0x4b29b: spurious update.
And I have no idea how to handle or even interpret it. There's nothing in my project called CGSUpdateManager, and my project doesn't call a log() function anywhere. I can't even reliably reproduce it, but it's popped up often enough to raise my interest level.
Searches at both Google and here for the term "spurious update" reveals a lightly scattered set of conversation, but nothing relevant to my project. Meanwhile, a Google search for "CGSUpdateManager" reveals it's something to do with Swift, which I'm not using at all.
Can anyone help me understand what this means? Or should I just disregard it?
Make sure to call super in viewDidLoad, viewWillAppear and viewWillDisappear.
Sorry, my code with correct Highlight/indentation:
- (void)setNeedsDisplay
{
//#if 1 //TEST (suppose we are only called by us)
if(wvImageRep_DoRebuild)
//#endif
[super setNeedsDisplay]; // "spurious update" ?
}
It's an example (#see my full response), it helped me
I defined a class called "FilterCriteria" which has a bunch of function .m files (getAMask, getBMask, etc.) associated with it. When I create the FilterCriteria object and call the functions using it, I don't have any problems. However, recently I added another function (which, on a side note, is almost identical to another function that still works), and Matlab returns the error, "No appropriate method, property, or field getHMask for class FilterCriteria."
I've searched online for this problem, but I can't find anything. The file getHMask.m is definitely in the correct folder, so I don't understand why Matlab seems to have such a problem finding it.
Here's getHMask.m's header:
function mask = getHMask(object, quadrant, channel)
Any help would be greatly appreciated. Thanks in advance.
1) A mistake I make sometimes is not saving the file with the correct name. Make sure capital letters are in the right places etc!
2) Another layer of error checking here... You can call methods('object here') (see here) and make sure it lists the method (function) that you are trying to add to it. If it doesn't show up here you should check into the implementation of the method and make sure it's correctly being added to the class you're using for your object.
I had the same problem that's kind of suggested by Ben's bullet #2 and it was driving me crazy. Turns out MatLab wasn't loading the latest version of my class's m-file. I vaguely remembered it gave me a warning earlier about that, because there were old instances of the class in the workspace and to keep from invalidating them it said it wouldn't update the class until I cleared the workspace...
So if that's the problem, restarting MatLab will work, or you can just enter >> clear
I have written this trivial action method associated to a textfield.
Every time I enter text into a textfield a search in a PDF is performed and PDFView automatically scroll to selection:
- (IBAction) search:(id)id
{
NSString *query = [self.searchView stringValue]; // get from textfield
selection = [document findString: query fromSelection:NULL withOptions:NSCaseInsensitiveSearch];
if (selection != nil)
{
[self.pdfView setCurrentSelection:selection];
[self.pdfView scrollSelectionToVisible:self.searchView];
}
}
Problem is that after 3 or 4 searches I get EXC_BAD_ACCESS on row (i).
If I debug I see that query contains an NSCFString and not an NSString.
I think it is a memory management problem..but where?
I replicated the same issue inside a trivial testcase:
#interface PDFRef_protoTests : SenTestCase {
#private
PDFDocument *document;
}
........
- (void)setUp
{
[super setUp];
document = [[PDFDocument alloc] initWithURL: #"a local url ..."];
}
- (void)test_exc_bad_access_in_pdfdocument
{
for (int i =0 ;i<100; i++)
{
NSString *temp;
if (i % 2 == 0) temp = #"home";
else if (i % 3 ==0) temp = #"cocoa";
else temp=#"apple";
PDFSelection *selection = [document findString: temp
fromSelection:nil
withOptions:NSCaseInsensitiveSearch];
NSLog(#"Find=%#, iteration=%d", selection, i);
}
}
Update:
1) It seems that it happens also if I use asynchronous search (method beginFindString: withOptions) every time I perform second search.
2) I found a similar problem to mine in MacRuby Issue Tracking: http://www.macruby.org/trac/ticket/1029
3) It seems that if I disable temporarily garbage collection it works but memory goes up.
I wrote something like:
[[NSGarbageCollector defaultCollector] disable];
[[NSGarbageCollector defaultCollector] enable];
surrounding search code
Another Update
Very weird thing is that sometimes all works. Than I clean and Rebuild and problem arises again. From a certain point of view is is not 100% reproducible. I suspect a bug in PDFKit or some compiler setting I have to do
Update Again
Dears it seems very crazy. I'd concentrate on testcase which is very trivial and which replicates easily the problem. What's wrong with it? This testcase works only if I disable (by code or by project setting) GC
Another Update
Boys it seems a bug but I downloaded an example called PDFLinker from Apple website (http://developer.apple.com/library/mac/#samplecode/PDFKitLinker2/Introduction/Intro.html#//apple_ref/doc/uid/DTS10003594). This example implements a PDFViewer. Code of my app and this example are quite similars. For the same search action on same PDF, my memory rises at 300/400 MB while PDFLinker rises at 190MB. Clearly there is something wrong in my code. But I am comparing it bit by bit and I don't think I am inserting memory leaks (and Instrument doesn't give me any evidence). Maybe is there some project-wide setting ?
Update Yet
Changing from 64 bit to 32 bit memory consumption lowered. Surely there is a problem with 64bit and PDFKit. BTW still EXC_BAD_ACCESS on second search
SOLUTION
Crucial point is that PDFKit with Garbage collection is bugged.
If I disable GC all works correctly.
I had another issue that had complicated my analysis: I disabled GC on Project Setting but GC remained enabled on Target Settings. So Apple's example PDFLinked2 worked while mine not.
I agree you have found a bug in PDFKit.
I got various forms of errors (segmentation fault, selector not understood, etc) running your test case. Wrapping the code in #try/#catch doesn't prevent all errors associated with this method.
I also got errors printing the log message.
To work around the bug(s), I suggest you disable GC during your invocation of -findString:fromSelection:, as you've already discovered.
Also, be sure to make copies of the values of interest from selection before re-enabling GC. Don't just copy selection either.
If you conduct searches from multiple places in your code I also suggest you extract a separate method to perform the search. Then you can invoke that one to conduct the searches for you without duplicating the GC disable/enable nesting.
This sort of thing is usually evidence that you're hanging onto a pointer to an object that has been destroyed. Turn on zombie objects (with NSZombieEnabled) to see exactly where and when you're accessing a bad object.
Judging from your screen shot it doesn't seem like you have NSZombie turned on. Probably the reason why it doesn't help you. Here's how you turn it on:
How to enable NSZombie in Xcode?
The screenshot you provided was otherwise very useful, but you really need NSZombie to figure out this kind of errors. Well, unless it's obvious, which it isn't from the code you posted.
EDIT: I read the comment that you're using garbage collection. I'm an iOS developer, so I have very limited experience with garbage collection in Objective-C, but as far as I understand NSZombie doesn't work in a garbage collected environment.
I'm not sure it should be possible to get EXC_BAD_ACCESS in a garbage collected environment, unless you create your own pointer and try to call methods on it without having created an object and I don't see why you would do that.
I've heard that some frameworks doesn't work well with garbage collection, but I wouldn't think PDFKit was among them. Anyway, the solution might be to not use garbage collection. Perhaps you should file a bug report with Apple.
keep PDFSelection *selection as a member variable and pass it in fromSelection: instead of nil.
It is possible that PDFDocument keeps the returned PDFSelection instance to improve the performance.
Did you try retaining the searchview stringvalue object before using it?
As you say it happens when you type fast and it happens for async calls, it is possible that the object stringValue is pointing to is being released between the time your query object is pointing to it, and the time you use it int the search.
You could try something like this to see if the problem persists:
- (IBAction) search:(id)id
{
NSString *query = [[self.searchView stringValue] retain]; // get from textfield
selection = [document findString: query fromSelection:NULL withOptions:NSCaseInsensitiveSearch];
if (selection != nil)
{
[self.pdfView setCurrentSelection:selection];
[self.pdfView scrollSelectionToVisible:self.searchView];
}
[query release];
}
Of course there is also the possibility that document is relased. How do you declare it? is it a property with retain? Can it be released by the time you are searching?
EDIT:
I see that you posted the code with the second parameter as NULL, but in your screenshot, this value is nil.
The documentation says you should use NULL when you want to start the search from the beginning.
http://developer.apple.com/library/mac/#documentation/GraphicsImaging/Reference/QuartzFramework/Classes/PDFDocument_Class/Reference/Reference.html#//apple_ref/doc/uid/TP40003873-RH2-DontLinkElementID_1
And as the compiler interprets nil and NULL differently, this could be leading to some weird behavior internally.