ios - 如何在 prepareForSegue 方法中访问对象数组中选定对象的不同属性或特性

Question

首先，我的问题很严重，不适用于那些只愿意提供负面反馈或只是为了编辑和获得奖励目的的人。

我的问题很难传达，但我正在尽力传达完整的问题。实际上我在后端有两个 TableView 和两个 Json 文件，以及一个 AVPlayerViewController。首先，firstTableViewController 显示第一个 json 文件，其中包含以下 Json 数据

    [{
    "id": "0",
    "name": "Religion"
}, {
    "id": "1",
    "name": "News"
}, {
    "id": "2",
    "name": "Sport"
}, {
    "id": "3",
    "name": "Doc"
}, {
    "id": "4",
    "name": "Kids"
}, {
    "id": "5",
    "name": "Music"
}, {
    "id": "6",
    "name": "Movie"
}, {
    "id": "7",
    "name": "Entr"
}, {
    "id": "8",
    "name": "Cooking"
}, {
    "id": "9",
    "name": "All"
}]

在 SecondViewController 中，提取包含不同链接的 second Json file 以及上面第一个 json 文件中提到的类别。在我的应用程序中成功检索了两个 Json 文件的数据。

当我单击 FirstTableViewController 的任何单元格(包含特定类别)时，它会将我带到第二个TableViewController，其中包含包含该特定类别(名为 category_name)的所有对象的 title 属性> 在第二个 json 文件中)选择的类别。到目前为止，一切都非常酷。但是当我过去单击任何标题时出现的问题应该将我带到 AVPlayerViewController 并播放相关的直播链接。但它给了我以下错误，

* Terminating app due to uncaught exception 'NSRangeException', reason: '* -[NSArrayM objectAtIndex:]: index 2097174 beyond bounds [0 .. 32]' *** First throw call stack: ( 0 CoreFoundation 0x0000000104b0234b __exceptionPreprocess + 171 1 libobjc.A.dylib
0x000000010456321e objc_exception_throw + 48 2 CoreFoundation
0x0000000104a33f1b -[__NSArrayM objectAtIndex:] + 203 3 AlbTVRadio 0x00000001022bcae1 -[Second prepareForSegue:sender:] + 321 4 UIKit 0x0000000102bbef5f -[UIStoryboardSegueTemplate _performWithDestinationViewController:sender:] + 353 5 UIKit 0x0000000102bbedcd -[UIStoryboardSegueTemplate _perform:] + 82 6
UIKit 0x0000000102bbf08f -[UIStoryboardSegueTemplate perform:] + 156 7 UIKit 0x000000010253b52a -[UITableView _selectRowAtIndexPath:animated:scrollPosition:notifyDelegate:] + 1769 8 UIKit 0x000000010253b78d -[UITableView _userSelectRowAtPendingSelectionIndexPath:] + 330 9 UIKit 0x00000001023f12eb _runAfterCACommitDeferredBlocks + 320 10 UIKit 0x00000001023ddf6f _cleanUpAfterCAFlushAndRunDeferredBlocks + 566 11 UIKit 0x000000010240f3da _afterCACommitHandler + 176 12 CoreFoundation 0x0000000104aa6e17 __CFRUNLOOP_IS_CALLING_OUT_TO_AN_OBSERVER_CALLBACK_FUNCTION + 23 13 CoreFoundation 0x0000000104aa6d87 __CFRunLoopDoObservers + 391 14 CoreFoundation 0x0000000104a8bb9e __CFRunLoopRun + 1198 15 CoreFoundation
0x0000000104a8b494 CFRunLoopRunSpecific + 420 16 GraphicsServices
0x0000000106784a6f GSEventRunModal + 161 17 UIKit
0x00000001023e4964 UIApplicationMain + 159 18 AlbTVRadio
0x00000001022cd65f main + 111 19 libdyld.dylib
0x000000010a00968d start + 1 20 ???
0x0000000000000001 0x0 + 1 ) libc++abi.dylib: terminating with uncaught exception of type NSException

我认为问题出在 segue 代码中，即没有选择准确的 ChannelObject 或 Object.livestream

这是我的第二个 viewController 的代码。其中包含第二个 json 文件。所以请尽可能更正此代码。

#import "Second.h"
#import "Channel.h"
#import "UIImageView+AFNetworking.h"
#import "Type.h"
#define getDataUrl @"https://creativestudy.000webhostapp.com/webservices/test.json"

@interface Second ()

@end

@implementation Second
@synthesize tvArray,currentObject;

- (void)viewDidLoad {
    [super viewDidLoad];

    [self retrieveData];



    // Uncomment the following line to preserve selection between presentations.
    // self.clearsSelectionOnViewWillAppear = NO;

    // Uncomment the following line to display an Edit button in the navigation bar for this view controller.
    // self.navigationItem.rightBarButtonItem = self.editButtonItem;
}

- (void)didReceiveMemoryWarning {
    [super didReceiveMemoryWarning];
    // Dispose of any resources that can be recreated.
}

#pragma mark - Table view data source

- (NSInteger)numberOfSectionsInTableView:(UITableView *)tableView {

    return 1;
}

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

    return tvArray.count;
}


- (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath {
UITableViewCell *cell = [tableView dequeueReusableCellWithIdentifier:@"cells" forIndexPath:indexPath];

    Channel * ChannelObject;
    ChannelObject = [tvArray objectAtIndex:indexPath.row];

    cell.textLabel.text = ChannelObject.channelTitle;
    cell.detailTextLabel.text = ChannelObject.channelLivestream;
     cell.detailTextLabel.hidden = YES;
    cell.accessoryType = UITableViewCellAccessoryDisclosureIndicator;

    NSURL *url = [NSURL URLWithString:ChannelObject.channelImage];
    NSURLRequest *request = [NSURLRequest requestWithURL:url];
    UIImage *placeholderImage = [UIImage imageNamed:@"placeholder"];
    __weak UITableViewCell *weakCell = cell;
    [cell.imageView setImageWithURLRequest:request placeholderImage:placeholderImage success:^(NSURLRequest *request, NSHTTPURLResponse *response, UIImage *image) {
        weakCell.imageView.image = image;
        [weakCell setNeedsLayout];
    } failure:nil];



    // Configure the cell...

    return cell;
}
-(void) getType:(id)typeObject{

    currentObject = typeObject;

}

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

/*
// Override to support editing the table view.
- (void)tableView:(UITableView *)tableView commitEditingStyle:(UITableViewCellEditingStyle)editingStyle forRowAtIndexPath:(NSIndexPath *)indexPath {
    if (editingStyle == UITableViewCellEditingStyleDelete) {
        // Delete the row from the data source
        [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;
}
*/


// 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:@"playVideo"]) {

            AVPlayerViewController *playerViewController = [segue destinationViewController];

             NSIndexPath *indexPath = [self.tableView indexPathForSelectedRow];
             Channel * ChannelObject;
            ChannelObject = [self.tvArray objectAtIndex:(int)indexPath];
             NSURL *liveUrl = [NSURL URLWithString:ChannelObject.channelLivestream];
             playerViewController.player = [AVPlayer playerWithURL:liveUrl];
        [playerViewController.player play];

             }

}


-(void) retrieveData{
    NSURL * url = [NSURL URLWithString:getDataUrl];
    NSData * data = [NSData dataWithContentsOfURL:url];
    NSArray *jsonArray = [NSJSONSerialization JSONObjectWithData:data options:kNilOptions error:nil];

    tvArray = [[NSMutableArray alloc] init];

    for (int i = 0; i < jsonArray.count; i ++)
    {
        NSDictionary *aCategoryJSON = [jsonArray objectAtIndex:i];
        NSString *cId = [aCategoryJSON objectForKey:@"id"];
        NSString *cTitle = [aCategoryJSON objectForKey:@"title"];
        NSString *cCategory = [aCategoryJSON objectForKey:@"category_name"];
        NSString *cImage = [aCategoryJSON objectForKey:@"image"];
        NSString *cLivestream = [aCategoryJSON objectForKey:@"livestream"];
        NSString *cWebsite = [aCategoryJSON objectForKey:@"Website"];
        if (cCategory == currentObject.typeName){
        [tvArray addObject:[[Channel alloc] initWithChannelId:cId andChannelTitle:cTitle andChannelCategory:cCategory andChannelImage:cImage andChannelLivestream:cLivestream andChannelWebsite:cWebsite]];
        }
        else if ([currentObject.typeName isEqualToString: @"All"]){
        [tvArray addObject:[[Channel alloc] initWithChannelId:cId andChannelTitle:cTitle andChannelCategory:cCategory andChannelImage:cImage andChannelLivestream:cLivestream andChannelWebsite:cWebsite]];
        }

    }
    [self.tableView reloadData];
}

@end

Answer 1

你的问题在这里:

 ChannelObject = [self.tvArray objectAtIndex:(int)indexPath];

您已将一个对象(NSIndexPath 的实例)转换为 int，并且 Objective-C 允许您这样做，因为它基于 C，尽管这没有任何意义。

indexPath 是指向内存中对象的指针，因此当您将其转换为 int 时，您会得到一个解释为整数的内存地址，这就是为什么您会看到尝试访问数组中的元素 2097174。大概您将强制转换添加到 int 中，因为编译器告诉您不能在该函数中使用 indexPath。

您需要做的是使用 indexPath.row 从 NSIndexPath 实例获取行整数。您还可以使用更现代的数组访问语法和小写字母来启动变量(大写字母用于类):

Channel *channelObject = self.tvArray[indexPath.row];