Question

正如您可以通过我的问题告诉我，我是Objective C的新手。我可以访问静态属性，例如NSString，但似乎我无法访问数组甚至其他属性，必须做错了。基本上，我有一个模型文件，包含我的主要属性。

这是我的名为ListingManager.h的模型文件

#import <Foundation/Foundation.h>

@interface ListingManager : NSObject
@property (nonatomic, strong) NSString *listingTitle;
@property (nonatomic, strong) NSString *listingDescription;
@property (nonatomic, strong) NSString *listingPrice;
@property (nonatomic, readonly) NSString *datePosted;
@property (nonatomic, retain) NSMutableArray *lists;
@property (nonatomic) BOOL *viewed;
@end

ListingManager.m

#import "ListingManager.h"
@implementation ListingManager

@synthesize lists;
@synthesize listingPrice;
@synthesize listingDescription;
@synthesize listingTitle;
@synthesize datePosted;

@end

这是我正在使用它的另一个视图控制器ListingTableViewController.m

#import "ListingTableViewController.h"


@interface ListingTableViewController ()
@property (nonatomic, strong) ListingManager *manageListings;
@end

@implementation ListingTableViewController

@synthesize manageListings;


- (void) loadInitialData {

    ListingManager *listing1 = [[ListingManager alloc] init];
    listing1.listingTitle = @"Title here";
    listing1.listingDescription = @"another description..Whatever it is";
    listing1.listingPrice = @"100";
    [self.manageListings.lists addObject:listing1];
    NSLog(@"%@", listing1); //for debugging purposes

    ListingManager *listing2 = [[ListingManager alloc] init];
    listing2.listingTitle = @"Title here";
    listing2.listingDescription = @"a long description here";
    listing2.listingPrice = @"50";
    [self.manageListings.lists addObject:listing2];

    ListingManager *listing3 = [[ListingManager alloc] init];
    listing3.listingTitle = @"Cool stuff";
    listing3.listingDescription = @"Another descitpion righ there";
    listing3.listingPrice = @"90";
    [self.manageListings.lists addObject:listing3];

}

- (instancetype)initWithStyle:(UITableViewStyle)style
{
    self = [super initWithStyle:style];
    if (self) {
        // Custom initialization
    }
    return self;
}

- (void)viewDidLoad
{
    [super viewDidLoad];
    //self.listings= [[NSMutableArray alloc] init];
    self.manageListings = [[ListingManager alloc] init];

    [self.backdropTableView reloadData]; //reload table view

    [self loadInitialData]; //load inital static data


}
/*
- (void)viewWillAppear:(BOOL)animated
{
    [self.backdropTableView reloadData];
}
*/
- (void)didReceiveMemoryWarning
{
    [super didReceiveMemoryWarning];
    // Dispose of any resources that can be recreated.
}

#pragma mark - Table view data source

- (NSInteger)numberOfSectionsInTableView:(UITableView *)tableView
{
//#warning Potentially incomplete method implementation.
    // Return the number of sections.
    return 1;
}

- (NSInteger)tableView:(UITableView *)tableView numberOfRowsInSection:(NSInteger)section
{
//#warning Incomplete method implementation.
    // Return the number of rows in the section.
    return [self.manageListings.lists count]; //this here is not returning anything
}


- (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath
{
    static NSString *custom = @"WXCustomCell";

    WXTableCell *cell = (WXTableCell *)[tableView dequeueReusableCellWithIdentifier:custom];
    if (cell == nil)
    {
        NSArray *nib = [[NSBundle mainBundle] loadNibNamed:@"WXCell" owner:self options:nil];
        cell = [nib objectAtIndex:0];
    }

    ListingManager *listingManager = [self.manageListings.lists objectAtIndex:indexPath.row];
    cell.titleLabel.text = listingManager.listingTitle;
    cell.descriptionlabel.text = listingManager.listingDescription;
    cell.thumbnail.image = [UIImage imageNamed:@"nothumb.gif"];
    cell.price.text = @"$50";
    cell.dateLabel.text = @"N/A";
    NSLog(@"%@", cell.titleLabel.text);

    //use for later
    /*
    NSDateFormatter *DateFormatter=[[NSDateFormatter alloc] init];
    [DateFormatter setDateFormat:@"MM/dd/yyy HH:mm:ss"];
    NSLog(@"%@",[DateFormatter stringFromDate:[NSDate date]]);
    */
    return cell;
}

//Call segue
- (void)tableView:(UITableView *)tableView didSelectRowAtIndexPath:(NSIndexPath *)indexPath {

    [self performSegueWithIdentifier:@"showDetail" sender:nil];


}

// In a storyboard-based application, you will often want to do a little preparation before navigation
- (void)prepareForSegue:(UIStoryboardSegue *)segue sender:(id)sender
{
    if ([segue.identifier isEqualToString:@"showDetail"]) {
    // Get the new view controller using [segue destinationViewController].
    NSIndexPath *indexPath = [self.backdropTableView indexPathForSelectedRow];
    DetailsViewController *vc = segue.destinationViewController;
    // Pass the selected object to the new view controller.
        ListingManager *listingManager = [self.manageListings.lists objectAtIndex:indexPath.row];
        vc.titleName = listingManager.listingTitle;
        vc.descriptionDetail = listingManager.listingDescription;


    }
}


@end

例如，当我返回＆＃39; [self.manageListings.lists count]＆＃39;时，它不会返回任何内容，如果我将其硬编码为3，我会得到3个初始项目，标题，描述和标题为空。连接我的模型和VC时，一定有什么错误。

Answer 1

在Objective-C中，您已手动为对象分配内存。声明像@property (nonatomic, retain) NSMutableArray *lists;这样的iVar（属性）时，所有运行时和编译器都会为该属性创建指针内存并将内存值设置为0x00。因此，尚未分配阵列存储器。你应该像这样实例化内存

self.manageListings = [[ListingManager alloc] init];
self.manageListings.lists = [[NSMutableArray alloc] init];
[self.manageListings.lists addObject:listing1];

向nil对象发送消息只会返回，因此您不会发现任何崩溃。

Answer 2

可能是因为您在viewDidLoad

中的初始化数据之前重新加载了表

[self.backdropTableView reloadData]; //reload table view

[self loadInitialData]; //load inital static data

对此进行了尝试

[self loadInitialData]; //load inital static data

[self.backdropTableView reloadData]; //reload table view

Answer 3

正如iRavi指出的，你sholud分配内存。但是在内部对象init方法中分配是更好的做法。以这种方式覆盖它：

- (id) init {

   if (self = [super init]) // not ==
   {
      _lists = [NSMutableArray new];
   }
   return self;
}

_lists - 自动生成的iVar，如果省略@synthesize

如何正确访问Model类中的属性 - Objective C

3 个答案: