NSMutableArray 和我的表的问题

Question

我正在尝试将一个对象插入到我的表中，但每当我点击添加按钮时，它就会因为未捕获的异常而崩溃。它说

Attempt to insert row 0 into section 0, but there are only 0 rows in section 0 after the update

这是我的主视图控制器，它处理我所有的表格内容...

#import "MasterViewController.h"

#import "DetailViewController.h"

#define kFileName       @"steakNames.plist"

@interface MasterViewController () {
    NSMutableArray *_objects;
}
@end

@implementation MasterViewController

@synthesize steakName;

- (NSString *)dataFilePath {
    NSArray *paths = NSSearchPathForDirectoriesInDomains(NSDocumentationDirectory, NSUserDomainMask, YES);
    NSString *documentsDirectory = [paths objectAtIndex:0];
    return [documentsDirectory stringByAppendingPathComponent:kFileName];
}

- (id)initWithNibName:(NSString *)nibNameOrNil bundle:(NSBundle *)nibBundleOrNil
{
    self = [super initWithNibName:nibNameOrNil bundle:nibBundleOrNil];
    if (self) {
        self.title = NSLocalizedString(@"Master", @"Master");
    }
    return self;
}

- (void)viewDidLoad
{
    NSString *filePath = [self dataFilePath];
    if ([[NSFileManager defaultManager] fileExistsAtPath:filePath]) {
        _objects = [[NSMutableArray alloc] initWithContentsOfFile:filePath];
    }

    UIApplication *app = [UIApplication sharedApplication];
    [[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(applicationWillResignActive:) name:UIApplicationWillResignActiveNotification object:app];

    [super viewDidLoad];
    // Do any additional setup after loading the view, typically from a nib.
    self.navigationItem.leftBarButtonItem = self.editButtonItem;

    UIBarButtonItem *addButton = [[UIBarButtonItem alloc] initWithBarButtonSystemItem:UIBarButtonSystemItemAdd target:self action:@selector(insertNewObject:)];
    self.navigationItem.rightBarButtonItem = addButton;
}

- (void)viewDidUnload
{
    [super viewDidUnload];
    // Release any retained subviews of the main view.
}

- (BOOL)shouldAutorotateToInterfaceOrientation:(UIInterfaceOrientation)interfaceOrientation
{
    return (interfaceOrientation != UIInterfaceOrientationPortraitUpsideDown);
}

- (void)insertNewObject:(id)sender
{
    if (!steakName) {
        steakName = @"No name";
    }
    [_objects insertObject:[self steakName] atIndex:0];

    NSIndexPath *indexPath = [NSIndexPath indexPathForRow:0 inSection:0];

    [self.tableView insertRowsAtIndexPaths:@[indexPath] withRowAnimation:UITableViewRowAnimationAutomatic];
}

#pragma mark - Table View

- (NSInteger)numberOfSectionsInTableView:(UITableView *)tableView
{
    return 1;
}

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

// Customize the appearance of table view cells.
- (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath
{
    static NSString *CellIdentifier = @"Cell";

    UITableViewCell *cell = [tableView dequeueReusableCellWithIdentifier:CellIdentifier];
    if (cell == nil) {
        cell = [[UITableViewCell alloc] initWithStyle:UITableViewCellStyleDefault reuseIdentifier:CellIdentifier];
        cell.accessoryType = UITableViewCellAccessoryDisclosureIndicator;
    }


    NSDate *object = [_objects objectAtIndex:indexPath.row];
    cell.textLabel.text = [object description];
    return cell;
}

- (BOOL)tableView:(UITableView *)tableView canEditRowAtIndexPath:(NSIndexPath *)indexPath
{
    // Return NO if you do not want the specified item to be editable.
    return YES;
}

- (void)tableView:(UITableView *)tableView commitEditingStyle:  (UITableViewCellEditingStyle)editingStyle forRowAtIndexPath:(NSIndexPath *)indexPath
{
    if (editingStyle == UITableViewCellEditingStyleDelete) {
        [_objects removeObjectAtIndex:indexPath.row];
        [tableView deleteRowsAtIndexPaths:@[indexPath] withRowAnimation:UITableViewRowAnimationFade];
    } else if (editingStyle == UITableViewCellEditingStyleInsert) {
        // Create a new instance of the appropriate class, insert it into the array, and add a new row to the table view.
    }
}

/*
// Override to support rearranging the table view.
- (void)tableView:(UITableView *)tableView moveRowAtIndexPath:(NSIndexPath    *)fromIndexPath toIndexPath:(NSIndexPath *)toIndexPath
{
}
*/

/*
// Override to support conditional rearranging of the table view.
- (BOOL)tableView:(UITableView *)tableView canMoveRowAtIndexPath:(NSIndexPath *)indexPath
{
    // Return NO if you do not want the item to be re-orderable.
    return YES;
}
*/

- (void)tableView:(UITableView *)tableView didSelectRowAtIndexPath:(NSIndexPath *)indexPath
{
    if (!self.detailViewController) {
        self.detailViewController = [[DetailViewController alloc] initWithNibName:@"DetailViewController" bundle:nil];
    }
    NSDate *object = [_objects objectAtIndex:indexPath.row];
    self.detailViewController.detailItem = object;
    [self.navigationController pushViewController:self.detailViewController animated:YES];
}

- (void)applicationWillResignActive:(NSNotification *)notification {
    [_objects writeToFile:[self dataFilePath] atomically:YES];
}
@end

Answer 1

错误的原因很可能是返回0：

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

    return ...;
}

我建议您首先获取一个完整的表格视图工作示例及其所有必需的方法，然后从那里开始。

一般你需要实现这些方法：

• (NSInteger)numberOfSectionsInTableView:(UITableView *)tableView

• (NSString *)tableView:(UITableView *)tableView titleForHeaderInSection:(NSInteger)section

• (NSInteger)tableView:(UITableView *)tableView numberOfRowsInSection:(NSInteger)section

• (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath

• (void)tableView:(UITableView *)tableView didSelectRowAtIndexPath:(NSIndexPath *)indexPath

到目前为止，任何 NSMutableArray 都没有问题，无论如何，如果数组还没有对象数量，则不能在索引处插入对象，例如在索引 4 处插入但数组只有 2 个对象。您可以随时将对象添加到 NSMutableArray 并增加此数组中的对象数量。