I am creating an iOS app which reads in a text file and displays the contents in a UIText field.
For the 1st three consecutive runs of thee app (Restarting a new session without exiting),
the data is read in fine. However on the fourth attempt, the data returned from the file is all nulls.
I've verified the file integrity. The issue exists when using stringWithContentsOfFile or initWithContentsOfFile.
After many hours of troubleshooting, I believe the issue is somehow related to a buffer being cleared within the above mentioned methods.
Any insight regarding this issue is greatly appreciated. I've tried many things with no luck.
Here's the code I use to read in the file:
TheString = [NSString stringWithContentsOfFile:[[NSBundle mainBundle]
pathForResource:#"My_TextFile" ofType:#"txt"] encoding:NSUTF8StringEncoding error:NULL];
Here's the code I use to display certain contents of the file (The contents are placed in an array of type NSArray):
NSArray *My_Array;
My_Array= [TheString componentsSeparatedByString:#"\n"];
/* Obtain specific data to display */
DisplayedData = [My_Array objectAtIndex:M[l]-1];
:
:
/* Display the data in the view */
MyUITextView.text = DisplayedData;
/* Log the data */
NSLog(#"%#", MyUITextView.text);
On the 4th invocation of the code above, the data returned is blank and NSLOG is returning nulls
Thanks so much for any help!
Maybe I'm a little bit late with answer, but, anyway, maybe somebody will find it useful.
OK, I have also spent a day trying to figure out why my custom class for scrollable view is working 3 times and refuse at the 4-th time... I found that the problem has quite the same attributes as yours: nested NSString objects unexpectedly disappear. Though pointers point to the same address in memory, memory is already filled with quite arbitrary objects instead my NSStrings.
And I paid attention that I created these NSStrings using the following class method:
+ (id)stringWithContentsOfFile:(NSString *)path encoding:(NSStringEncoding)enc error:(NSError **)error
So, I'm not the owner of these NSStrings.
And I assumed that to be the owner can be a solution, so I created my NSStrings through alloc and
- (id)initWithContentsOfFile:(NSString *)path encoding:(NSStringEncoding)enc error:(NSError **)error
instance method.
App was repaired!
Related
Let me start by saying I'm not proficient in objective c, nor am I an iOS developer. I'm working on a react-native app and find that I'm having to dig into the native code. So, I appreciate your patience with me and would also very much appreciate if you made zero assumptions about what I might, or might not know. Thx!
I'm trying to use react-native-mail but it fails to attach the photo I've selected to the email.
In troubleshooting, I jumped into Xcode's debugger for the first time. Stepping through the code, it appears as though the attachmentPath which is something like file:///var/mobile/... is being assigned to the variable fileData as type NSData. But then, taking one step further into the code it becomes nil.
I'm not sure why this would happen nor how to go about troubleshooting this. Here's an image of the debugger session with 3 screenshots stitched together side-by-side.
Here's the code: RNMail.m
All pointers, tips, guidance, and advice welcome
In your first screenshot, the debugger is still on the line that declares and assigns the fileData variable. This means that that line hasn't actually been executed yet. -dataWithContentsOfFile: hasn't yet been called, and thus the value that appears to be in fileData is not meaningful; what you're seeing is just garbage data prior to the variable actually being assigned. In your second screenshot, the -dataWithContentsOfFile: method has finished running, and it has returned nil. What you need to do is to figure out why you're getting nil from -dataWithContentsOfFile:. Perhaps the path to the file is incorrect, or perhaps you don't have permission to read it, or perhaps you have a sandboxing issue.
I would suggest using -dataWithContentsOfURL:options:error: instead of -dataWithContentsOfFile:. This will return an error by reference (create an NSError variable ahead of time, assign it to nil, pass a pointer to the error as the third parameter to -dataWithContentsOfURL:options:error:, and then check the error if the method returns nil). More likely than not, the contents of the error will explain what went wrong when trying to read the file.
EDIT: Looking at your screenshot again, the problem is clear; from the description of the contents of attachmentPath, we can see that it isn't a path at all, but instead it contains a URL string (with scheme file:). So you cannot pass it to the APIs that use paths. This is okay, since the URL-based mechanisms are what Apple recommends using anyway. So, just turn it into a URL by passing the string to -[NSURL URLWithString:] (or, even better, -[[NSURLComponents componentsWithString:] URL], since it conforms to a newer RFC). So, something like:
// Get the URL string, which is *not* a path
NSString *attachmentURLString = [RCTConvert NSString:options[#"attachment"][#"path"]];
// Create a URL from the string
NSURL *attachmentURL = [[NSURLComponents componentsWithString:attachmentURLString] URL];
...
// Initialize a nil NSError
NSError *error = nil;
// Pass a pointer to the error
NSData *fileData = [NSData dataWithContentsOfURL:attachmentURL options:0 error:&error];
if (fileData == nil) {
// 'error' should now contain a non-nil value.
// Use this information to handle the error somehow
}
I have a program that retrieves data from a link and i write it out to the Log like this.
NSURL *getURL=[NSURL URLWithString:#"link.php"];
NSError *error=nil;
NSString *str=[NSString stringWithContentsofURL:getURL encoding:NSUTF8StringEncoding error:&error];
NSLog(#"%",str);
This prints to the log the three values from my php as expected.
However I am having a little difficulty saving this in an array which then displays it those values in a UISplitviewController (the leftcontroller side).
which is written like this
showArray=[[NSMutableArray alloc]initWithContentofURL:getURL];
then in cellForRowAtIndexPath: method is
cell.textLabel.text=[showArray object atIndex:indexPath.row];
A second thing i have tried is write myURL to an array and tried to initlize showArray with ContentsofArray like this
NSArray *retults=[NSArray arraywithContentsOFURL:getURL];
showArray=[[NSArray alloc]initWithArray:retults];
but THAT dont work
BUT if i say
showArray=[[NSMutableArray alloc]initWithObjects:#"One",#"Two",nil];
One and two shows in my leftview controller....
Would love is someone could help me with this...Thank you
Are you trying to add the contents of the URL or the URL itself ?
If you are trying to just add the URL, then use :
showArray = [#[getURL] mutableCopy];
However, if you are trying to add the contents of the URL, then the doc clearly states that the URL must represent a string representation of an array.
Furthermore :
Returns nil if the location can’t be opened or if the contents of the location can’t be parsed into an array.
EDIT :
I saw your comment on your post and your data looks like JSON data.
You should take a look at the NSJSONSerialisation class which is pretty straightforward to use (you'll find lots of example here on SO).
U have done web services perfectly, now wat u have to do is parse it to an array
First download the SBJSON files in this link
https://github.com/stig/json-framework/
Then, copy them to your workspace.
Then, in the viewController add this
#import "SBJson.h"
Your JSON data contains values in the form of dictionary
SO, to parse them
SBJsonParser * parser=[SBJsonParser new];
NSDictionary * jsonData=(NSDictionary *)[parser objectWithString:outputData];
NSArray * arr=(NSArray *)[NSDictionary objectForKey:#"animal"];
I think this will help
I am keeping my data in a property called practiceRecords (an NSArray of dictionaries).
I check to see if the data already exists in the documents folder.
If yes, I load the data into self.practiceRecords.
If not, I build the array of dictionaries (using literal syntax), keeping this data in the self.practiceRecords property, and then write the data out to the documents folder.
(I am NOT reloading the data after writing it out)
As far as I am able to tell, there are no problems occurring during this process.
Then I have a step where I modify my data as follows ...
-(void)incNumberOfTriesFor:(NSString *)stringOfIndex {
if (self.practiceRecords)
{
int index = [stringOfIndex intValue];
int numberOfTries = [(NSNumber *)(self.practiceRecords[index][#"tries"]) intValue] + 1;
//CRASHING on this next line.
self.practiceRecords[index][#"tries"] = #(numberOfTries);
//message to helper method
[self writePracticeRecords];
}
}
So the first time through (when the array is built and written out) I get a crash at the indicated line.
The error is:
-[__NSDictionaryI setObject:forKeyedSubscript:]: unrecognized selector sent to instance
I quit the app, check the documents folder and see the data file written out with no issues.
I re-run the app, and then get no crash and the data file still looks great.
This is repeatable.
If the data file exists, no crash.
If the data first needs to be created, then a crash.
(In all cases, I manually look inside the resulting data file and see exactly what I expect to see - no issues there)
I'm not sure where to even begin squashing this bug, and would really like to understand the details of why this is happening.
Thanks very much for any help!
Just to recap the correct comments above:
-[__NSDictionaryI setObject:forKeyedSubscript:]: unrecognized selector sent to instance
NSDictionary does not implement any of the set... methods because it is immutable. You state that you're creating with literals syntax when the data is not found on disk. The literal syntax creates immutable containers
Instead, try...
// try to initialize from disk, but if not
// we can still use literal (immutable) syntax, but in a mutable container
self.practiceRecords = [NSMutableDictionary
dictionaryWithDictionary:#{ #"key" : #"value" }];
I have been attempting to debug a issue with my code, and just came upon an odd phenomenon. Found this in the debug area when a breakpoint was triggered:
Am I correct in observing that there are multiple values for this key: #"6898173"??
What are possible causes of this? I do not set those key-value pairs using the string literal, but by getting a substring of a string retrieved and decoded from a GKSession transmission.
I still have this up in the debug area in xcode, incase theres anything else there that might help.
EDIT:
By request, here is the code that would have created one of the two strings (another was created at an earlier time):
[carForPeerID setObject:[[MultiScreenRacerCarView alloc] initWithImage:[UIImage imageNamed:#"simple-travel-car-top_view"] trackNumber:[[[NSString stringWithUTF8String:data.bytes] substringWithRange:range] intValue]] forKey:[[NSString stringWithUTF8String:[data bytes]] substringFromIndex:9]];
The string in data might look something like this:
car00.0146898173
EDIT:
Code that sends the data:
[self.currentSession sendData:[[NSString stringWithFormat:#"car%i%#%#", [(MultiScreenRacerCarView *)[carForPeerID objectForKey:peerID] trackNumber], speed, [(MultiScreenRacerCarView *)[carForPeerID objectForKey:peerID] owner]] dataUsingEncoding:NSUTF8StringEncoding] toPeers:#[(NSString *)[peersInOrder objectAtIndex:(self.myOrderNumber + 1)]] withDataMode:GKSendDataReliable error:nil];
Sorry its hard to read. Its only one line.
What you're seeing is a debugger "feechure". When you have a mutable dictionary and modify it, the debugger may not show you the correct view of the object.
To reliably display the contents of an NSMutableArray or NSMutableDictionary, switch to the console and type po carForPeerID.
So I have read this question, which seems to be exactly the kind of problem I am having, but the answer in that post does not solve my problem. I am attempting to write a data serialization subclass of NSMutableData. The problematic function header looks like this:
-(void)readString:(__autoreleasing NSString **)str
I do some data manipulation in the function to get the particular bytes the correspond to the next string in the data stream, and then I call this line:
*str = [[NSString alloc] initWithData:strData encoding:NSUTF8StringEncoding];
No errors in this code. But when I try to call the function like so:
+(id) deserialize:(SerializableData *)data
{
Program *newProgram = [[Program alloc] init];
[data readString:&(newProgram->programName)];
On the line where I actually call the function, I get the following error:
Passing address of non-local object to __autoreleasing parameter for write-back
I have tried placing the __autoreleasing in front of the NSString declaration, in front of the first *, and between the two *'s, but all configurations generate the error.
Did I just miss something when reading the other question, or has something in the ARC compiler changed since the time of that post?
EDIT:
It seems that the problem is coming from the way I am trying to access the string. I can work around it by doing something like this:
NSString* temp;
[data readString&(temp)];
newProgram.programName = temp;
but I would rather have direct access to the ivar
You can't. You might gain insight from LLVM's document Automatic Reference Counting, specifically section 4.3.4. "Passing to an out parameter by writeback". However, there really isn't that much extra detail other than you can't do that (specifically, this isn't listed in the "legal forms"), which you've already figured out. Though maybe you'll find the rationale interesting.