访问NSMutableArray Count iOS时应用崩溃

Question

I landed into a weird problem where i cannot use array.count that crashes my app.

@interface LAMasterViewController ()

NSMutableArray * claimReports

@end
    -(void)  ViewDidLoad
    {
       claimReports = [[NSMutableArray alloc] init];
        [claimReports addObjectsFromArray:[[LADataModelController getSingleton] getClaimReportsOrderedByIncidentDate] ];

    }

-(NSArray *) getClaimReportsOrderedByIncidentDate
{ // it returns one record
    NSManagedObjectContext *context = [self managedObjectContext];
    NSError *error;
    NSFetchRequest *request = [[NSFetchRequest alloc] init];
    NSEntityDescription *entity = [ NSEntityDescription entityForName:@"ClaimReport" inManagedObjectContext:context];
    NSSortDescriptor *sortByIncidentDate = [[NSSortDescriptor alloc] initWithKey:@"dateOfIncident" ascending:NO];
    [request setEntity:entity];
    [request setSortDescriptors: [NSArray arrayWithObject: sortByIncidentDate]];

    NSArray *array = [context executeFetchRequest:request error:&error];
    NSLog(@"Array Count %i" ,array.count);
    return  array;
}


- (NSInteger)tableView:(UITableView *)tableView numberOfRowsInSection:(NSInteger)section
{

  return claimReports.count; //crashes here

}

error: -[LSClaimReport count]: unrecognized selector sent to instance 0xa54afc0 2014-04-01 14:56:29.022 LossAdjusting[6956:70b] * Terminating app due to uncaught exception 'NSInvalidArgumentException', reason: '-[LSClaimReport count]: unrecognized selector sent to instance 0xa54afc0'

What have i missed here. Seems a silly one. please guide. Thanks

Answer 1

Long-story-short, you are treating an instance of LSClaimReport as if it was an NSMutableArray instance.

The end.

EDIT OK, flippany aside, you are confused about instance variable and local variables and have confused the types of one of your instance variables.

In ViewDidLoad (case incorrect, so if that's copied verbatim then it won't even be called), you reference a local version of claimReports which is created and then thrown away:

-(void)ViewDidLoad
{
    NSMutableArray *claimReports = [[NSMutableArray alloc] init];
    [claimReports addObjectsFromArray:[[LADataModelController getSingleton] getClaimReportsOrderedByIncidentDate] ];
}

and later you refer to the instance variable version:

- (NSInteger)tableView:(UITableView *)tableView numberOfRowsInSection:(NSInteger)section
{
    return claimReports.count; //crashes here
}

Which is clearly a LSClaimReport instance and not a NSMutableArray .

So it looks like:

1. You have declared the wrong type in your @interface .
2. You are not initializing it correctly (you already fixed that bit).

Answer 2

please remove the local Arraydeclaration:

NSMutableArray * claimReports = [[NSMutableArray alloc] init];

instead use:

claimReports = [[NSMutableArray alloc] init];

In case this is no Class variable yet, add it to your @interface-declaration:

@interface LAMasterViewController ()
{
    NSMutableArray * claimReports
}
@end

@implementation LAMasterViewController

Answer 3

Write this in your .h file

   NSMutableArray * claimReports;

and in your .m

    -(void)viewDidLoad{
              claimReports = [[NSMutableArray alloc] init];
             [claimReports addObjectsFromArray:[[LADataModelController getSingleton] getClaimReportsOrderedByIncidentDate] ];
              }

Answer 4

You have few things wrong with your code which cleaning them up will help resolve the issue, the main issue '-[LSClaimReport count]: unrecognized selector sent to instance 0xa54afc0' is because you are calling count on an instance of LSClaimReport which clearly shouldn't be happening. Your code seems to think that claimReports is an instance of LSClaimReport and not an instance of NSMutableArray .

As for your code may I recommend changing to (Please see comments in code marked issue)

@interface LAMasterViewController ()

// Clearly you want this as a private property so why would you want to change 
// to having this in the .h file which would make it public
// But Issue 1 is here you are missing the semi-colon (`;`) of the end.
@property (nonatomic, strong) NSMutableArray *claimReports;

@end

// Issue two you are missing the `@implementation LAMasterViewController`
@implementation LAMasterViewController

// The synthesize is done automatically so getters/setters/ivar are created automatically

// Issue 3: ViewDidLoad isn't a valid selector so ViewDidLoad will never be called
// It is viewDidLoad
-(void)viewDidLoad
{
    [super viewDidLoad]; // Issue 4: you missed the call to super
    claimReports = [[NSMutableArray alloc] init];
    [claimReports addObjectsFromArray:[[LADataModelController getSingleton] getClaimReportsOrderedByIncidentDate]];

}

-(NSArray *)getClaimReportsOrderedByIncidentDate
{ // it returns one record
    NSManagedObjectContext *context = [self managedObjectContext];
    NSError *error;
    NSFetchRequest *request = [[NSFetchRequest alloc] init];
    NSEntityDescription *entity = [ NSEntityDescription entityForName:@"ClaimReport" inManagedObjectContext:context];
    NSSortDescriptor *sortByIncidentDate = [[NSSortDescriptor alloc] initWithKey:@"dateOfIncident" ascending:NO];
    [request setEntity:entity];
    [request setSortDescriptors: [NSArray arrayWithObject: sortByIncidentDate]];

    NSArray *array = [context executeFetchRequest:request error:&error];
    NSLog(@"Array Count %i" ,array.count);
    return  array;
}


- (NSInteger)tableView:(UITableView *)tableView numberOfRowsInSection:(NSInteger)section
{

    return claimReports.count;

}

@end