Question

如果试图解决这个错误，我决定伸手去拿几个小时救命。我继续得到同样的错误：

＆＃34;由于未被捕获而终止应用例外＆＃39; NSInvalidArgumentException＆＃39;，原因：＆＃39; *** - [__ NSCFConstantString stringByAppendingString：]：nil参数＆＃39;＆＃34;

#import <UIKit/UIKit.h>

@interface BrowseTableViewController : UITableViewController

@property (strong) NSMutableArray *emp;     //An array to store all the information of clicked entries

@end

#import <CoreData/CoreData.h>
#import "BrowseClickViewController.h"
#import "ItemTableViewCell.h"


@interface BrowseTableViewController ()<UITableViewDelegate, UITableViewDataSource>

@end

@implementation BrowseTableViewController

- (void)viewDidLoad {
    [super viewDidLoad];

    self.navigationItem.rightBarButtonItem = self.editButtonItem;
     [self.tableView registerNib:[UINib nibWithNibName:@"ItemTableViewCell" bundle:[NSBundle mainBundle]] forCellReuseIdentifier:@"Cell1"];

}

- (BOOL)tableView:(UITableView *)tableView canEditRowAtIndexPath:(NSIndexPath *)indexPath {
    // Return YES if you want the specified item to be editable.
    return YES;
}


- (void)tableView:(UITableView *)tableView commitEditingStyle:(UITableViewCellEditingStyle)editingStyle forRowAtIndexPath:(NSIndexPath *)indexPath {
    if (editingStyle == UITableViewCellEditingStyleDelete) {
        //add code here for when you hit delete
        [_emp removeObjectAtIndex:indexPath.row];
        [tableView deleteRowsAtIndexPaths:@[indexPath] withRowAnimation:UITableViewRowAnimationAutomatic];

        [tableView reloadData];
    }
}


- (void)didReceiveMemoryWarning {
    [super didReceiveMemoryWarning];
}

- (NSManagedObjectContext *)managedObjectContext
{
    NSManagedObjectContext *context = nil;
    id delegate = [[UIApplication sharedApplication] delegate];
    if ([delegate performSelector:@selector(managedObjectContext)]) {
        context = [delegate managedObjectContext];
    }
    return context;
}
- (void)viewDidAppear:(BOOL)animated
{
    [super viewDidAppear:animated];
    NSManagedObjectContext *managedObjectContext = [self managedObjectContext];
    NSFetchRequest *fetchRequest = [[NSFetchRequest alloc] initWithEntityName:@"Employee"];
    self.emp = [[managedObjectContext executeFetchRequest:fetchRequest error:nil] mutableCopy];                 // Obtaining all the entries of persistance store to show in Table view

    [self.tableView reloadData];
}
- (NSInteger)numberOfSectionsInTableView:(UITableView *)tableView
{
    return 1;
}

- (NSInteger)tableView:(UITableView *)tableView numberOfRowsInSection:(NSInteger)section
{
    return self.emp.count;
}

- (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath
{

   static NSString *CellIdentifier = @"Cell1";
    ItemTableViewCell *cell = [self.tableView dequeueReusableCellWithIdentifier:CellIdentifier forIndexPath:indexPath];


    NSManagedObject *empp = [self.emp objectAtIndex:indexPath.row]; //obtaining the informatio of selected row in empp object

    [cell.itemName setText:[NSString stringWithFormat:@"%@", [empp valueForKey:@"name"]]];
    [cell.quantityLabel setText:[NSString stringWithFormat:@"%@", [empp valueForKey:@"quantity"]]];
    [cell.shopLabel setText:[NSString stringWithFormat:@"%@", [empp valueForKey:@"store"]]];
    return cell;
}

- (void)tableView:(UITableView *)tableView didSelectRowAtIndexPath:(NSIndexPath *)indexPath
{
    UIStoryboard *storyBoard = [UIStoryboard storyboardWithName:@"Main" bundle:nil];
    BrowseClickViewController *initViewController = [storyBoard instantiateViewControllerWithIdentifier:@"Click"];
    [self.navigationController presentViewController:initViewController animated:YES completion:nil];
}

- (void)prepareForSegue:(UIStoryboardSegue *)segue sender:(id)sender
{                           //Segue which is called when user selects any row, and this segue modifies the value of emp object of BrowseClickViewController with the clicked row details.
    if ([segue.identifier isEqualToString:@"recordClicked"]){
        NSManagedObject *selectedEmp = [self.emp objectAtIndex:[[self.tableView indexPathForSelectedRow] row]];
        BrowseClickViewController *destViewController = segue.destinationViewController;
        destViewController.emp = selectedEmp;
    }
}
@end

#import <UIKit/UIKit.h>
#import <CoreData/CoreData.h>


@interface BrowseClickViewController : UIViewController
@property (weak, nonatomic) IBOutlet UIScrollView *scroller;
@property (weak, nonatomic) IBOutlet UILabel *barcodeLabel;
@property (weak, nonatomic) IBOutlet UILabel *categoryLabel;
@property (weak, nonatomic) IBOutlet UILabel *nameLabel;
@property (weak, nonatomic) IBOutlet UILabel *priceLabel;
@property (weak, nonatomic) IBOutlet UILabel *quantityLabel;
@property (weak, nonatomic) IBOutlet UILabel *storeLabel;
@property (weak, nonatomic) IBOutlet UIImageView *imagePicture;
@property (strong) NSManagedObject *emp;
@property (weak, nonatomic) NSString *picLabel;
@end

#import "BrowseClickViewController.h"
#import "BrowseTableViewController.h"
#import <CoreData/CoreData.h>
#import "ItemTableViewCell.h"

@interface BrowseClickViewController ()

@end

@implementation BrowseClickViewController


- (NSManagedObjectContext *)managedObjectContext {
    NSManagedObjectContext *context = nil;
    id delegate = [[UIApplication sharedApplication] delegate];
    if ([delegate performSelector:@selector(managedObjectContext)]) {
        context = [delegate managedObjectContext];
    }
    return context;
}
- (void)viewDidLoad {

    [super viewDidLoad];
    _nameLabel.text=[@"Name:" stringByAppendingString:[self.emp valueForKey:@"name"]];
    _barcodeLabel.text=[@"Barcode:" stringByAppendingString:[self.emp valueForKey:@"barcode"]];
    _categoryLabel.text=[@"Category:" stringByAppendingString:[self.emp valueForKey:@"category"]];
    _priceLabel.text=[@"Price:"stringByAppendingString:[self.emp valueForKey:@"price"]];
    _quantityLabel.text=[@"Quantity:" stringByAppendingString:[self.emp valueForKey:@"quantity"]];
    _storeLabel.text=[@"Store:" stringByAppendingString:[self.emp valueForKey:@"store"]];



    _picLabel=[self.emp valueForKey:@"pic"];
    _imagePicture.image=[self loadImage:_picLabel];
}
-(UIImage *)loadImage: (NSString *)name
{
    NSArray *paths = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory,
                                                         NSUserDomainMask, YES);
    NSString *documentsDirectory = [paths objectAtIndex:0];
    NSString* path = [documentsDirectory stringByAppendingPathComponent:[NSString stringWithString:name]];
    UIImage* image = [UIImage imageWithContentsOfFile:path];
    return image;
}

- (void)didReceiveMemoryWarning {
    [super didReceiveMemoryWarning];
}
@end

#import <UIKit/UIKit.h>

@interface ItemTableViewCell : UITableViewCell

@property (nonatomic, weak) IBOutlet UILabel *itemName;
@property (nonatomic, weak) IBOutlet UILabel *quantityLabel;
@property (nonatomic, weak) IBOutlet UILabel *shopLabel;

@end


#import "ItemTableViewCell.h"
#import "BrowseClickViewController.h"


@implementation ItemTableViewCell

- (id)initWithStyle:(UITableViewCellStyle)style reuseIdentifier:(NSString *)reuseIdentifier
{
    self = [super initWithStyle:style reuseIdentifier:reuseIdentifier];
    if (self) {
        // Initialization code
    }
    return self;
}

- (void)setSelected:(BOOL)selected animated:(BOOL)animated
{
    [super setSelected:selected animated:animated];

    // Configure the view for the selected state
}

- (void)tableView:(UITableView *)tableView didSelectRowAtIndexPath:(NSIndexPath *)indexPath
{
    UIStoryboard *storyBoard = [UIStoryboard storyboardWithName:@"Main" bundle:nil];
    BrowseClickViewController *initViewController = [storyBoard instantiateInitialViewController];



    [self.window setRootViewController:initViewController];

}
@end

Answer 1

最有可能的原因是你的一些附加字符串值是nil.Do防御性编码。检查下面的代码示例并相应地更改所有代码。

if([self.emp valueForKey:@"name"])
{
   _nameLabel.text=[@"Name:" stringByAppendingString:[self.emp valueForKey:@"name"]];
}

从TableViewCell NIB到ViewController的看法 - 请看看

1 个答案: