1

我可以解析数据并查看输出，但是当我调用包含 JSON 的视图时，我无法在表视图中显示它们，应用程序崩溃了

这是我的代码：

在第一行代码中，我们定义了一个宏，它为我们提供了一个后台队列——我喜欢为此设置一个 kBgQueue 快捷方式，这样我可以让我的代码更紧凑。在第二行代码中，我们创建了一个名为 kLatestKivaLoansURL 的宏，它返回一个指向该 URL http://api.kivaws.org/v1/loans/search.json?status=fundraising的 NSURL 。

#define kBgQueue dispatch_get_global_queue(
 DISPATCH_QUEUE_PRIORITY_DEFAULT, 0) //1
#define kLatestKivaLoansURL [NSURL URLWithString: 
 @"http://api.kivaws.org/v1/loans/search.json?status=fundraising"] //2
 @interface TeacherViewController ()
   @end
@implementation TeacherViewController

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

将 kBGQueue 定义为为我们提供后台队列的宏？

- (void)viewDidLoad

{
    [super viewDidLoad];

    dispatch_async(kBgQueue, ^{
        NSData* data = [NSData dataWithContentsOfURL:kLatestKivaLoansURL];
        [self performSelectorOnMainThread:@selector(fetchedData:)
                               withObject:data waitUntilDone:YES];
    });

}
@synthesize latestLoans;
@synthesize arrayOfFighterName;

将被调用并将 NSData 实例传递给它。在我们的例子中，JSON 文件相对较小，所以我们将在主线程中的 fetchedData: 中进行解析。如果您正在解析大型 JSON 提要（通常是这种情况），请务必在后台执行此操作。

- (void)fetchedData:(NSData *)responseData {
    //parse out the json data
    NSError* error;
    NSDictionary* json = [NSJSONSerialization
                          JSONObjectWithData:responseData //1
                          options:kNilOptions
                          error:&error];

     latestLoans = [json objectForKey:@"loans"]; //2
    arrayOfFighterName=[[NSMutableArray alloc] init];
//NSLog(@"loans: %@", latestLoans); //3
    for( int i = 0; i<[latestLoans count]; i++){

        // NSLog(@"%@", [matchListArray objectAtIndex:i]);
        arrayOfFighterName[i]=[[latestLoans objectAtIndex:i] objectForKey:@"name"];
       // NSLog(@"%@", [arrayOfFighterName objectAtIndex:i]);
    }



}
- (void)viewDidUnload
{

    [super viewDidUnload];
    latestLoans = nil;
}

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

#pragma mark - Table view data source

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

}

在表格视图中显示结果但不幸的是结果不显示并且应用程序崩溃了

- (NSInteger)tableView:(UITableView *)tableView numberOfRowsInSection:(NSInteger)section
{
#warning Incomplete method implementation.
    // Return the number of rows in the section.
   return [arrayOfFighterName count];
}

- (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath
{
    UITableViewCell *cell = [tableView
                           dequeueReusableCellWithIdentifier:@"TeacherCell"];
            cell.textLabel.text = [arrayOfFighterName objectAtIndex:indexPath.row];
       return cell;


   //  NSLog(@"viewDidLoad is called");
}

/*
// 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:[NSArray arrayWithObject: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;
}
*/

#pragma mark - Table view delegate

- (void)tableView:(UITableView *)tableView didSelectRowAtIndexPath:(NSIndexPath *)indexPath
{
    // Navigation logic may go here. Create and push another view controller.
    /*
     <#DetailViewController#> *detailViewController = [[<#DetailViewController#> alloc] initWithNibName:@"<#Nib name#>" bundle:nil];
     // ...
     // Pass the selected object to the new view controller.
     [self.navigationController pushViewController:detailViewController animated:YES];
     */
}

@end
4

1 回答 1

1

更改获取的数据方法，如：

- (void)fetchedData:(NSData *)responseData {
    //parse out the json data
    NSError* error;
    NSDictionary* json = [NSJSONSerialization
                          JSONObjectWithData:responseData //1
                          options:kNilOptions
                          error:&error];

     latestLoans = [json objectForKey:@"loans"]; //2
    arrayOfFighterName=[[NSMutableArray alloc] init];
//NSLog(@"loans: %@", latestLoans); //3
    for( int i = 0; i<[latestLoans count]; i++){

        // NSLog(@"%@", [matchListArray objectAtIndex:i]);
        arrayOfFighterName[i]=[[latestLoans objectAtIndex:i] objectForKey:@"name"];
       // NSLog(@"%@", [arrayOfFighterName objectAtIndex:i]);
    }


[tableView reloadData];
}

因为在第一次，tableView 是在数据添加到数组之前加载的。由于异步调用。当从服务器检索数据时，数据被解析并添加到数组中。所以你需要重新加载你的 tableView 来显示数据。

请参考本教程中的异步调用。

于 2012-11-04T10:11:53.120 回答