滚动 TableView 时应用程序崩溃

Question

当我滚动 TableView 时，我的应用程序崩溃了。首先在我的 viewDidLoad 方法中，从文件加载字典，并为该字典枚举所有键。

 - (void)viewDidLoad {

     [super viewDidLoad];

     NSString *rootPath = [NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES)objectAtIndex:0];      

     path = [rootPath stringByAppendingPathComponent:[NSString stringWithFormat:@"currency.archive"]]; 

     banks = [NSKeyedUnarchiver unarchiveObjectWithFile:path];

     keys = [banks allKeys];

     // set date for last update 
     dayMonthYear.text = [banks objectForKey:@"Last Updated"];
}

在我的 cellForRowAtIndexPath 中，我使用该字典中的数据填充单元格。无论如何，当我的应用程序启动时，一切看起来都很好，前五行绘制正确，但是当我开始滚动我的应用程序时崩溃。我的想法是，问题出在自动释放的对象上，我尝试保留它们并在使用它们后释放它们，但不成功。调试器显示我的问题与粗体一致

// Customize the appearance of table view cells.
- (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath {

    NSString *CellIdentifier = [NSString stringWithFormat:@"Cell %d_%d",indexPath.section,indexPath.row];

    UITableViewCell *cell = [tableView dequeueReusableCellWithIdentifier:CellIdentifier];

    if (cell == nil) {      

        [[NSBundle mainBundle] loadNibNamed:@"CurrencyTableCell" owner:self options:nil];

        cell = currencyTableCell;

        //don't show selected cell
        cell.selectionStyle = UITableViewCellSelectionStyleNone;
        //set height
        self.cellHeight = cell.frame.size.height;
    }    

    // Fetch currency 
    NSString *currentCurrency = [keys objectAtIndex:indexPath.row];

    NSDictionary *fetchedCurrency = [banks objectForKey:currentCurrency];

    **NSString *name = [fetchedCurrency objectForKey:@"Currency Name"];**

    currencyTitle.text = name;

    NSString *charCode = [fetchedCurrency objectForKey:@"Code"];

    currencyCode.text = charCode;

    NSString* formattedNumber = [NSString stringWithFormat:@"%.02f",[[fetchedCurrency  objectForKey:@"Value"] floatValue]];

    if ([formattedNumber length] == 4) {
        formattedNumber = [NSString stringWithFormat:@"%@%@",@"0",formattedNumber];
    }

    buyPrice.text = formattedNumber;

    return cell;    
}

Answer 1

讨论的结果是，[banks objectForKey:@"Last Updated"] 为您提供了一个 NSString，而不是 NSDictionary！

您可以通过执行以下操作来解决此错误

if ([[banks objectForKey:currentCurrency] class] == [NSDictionary class]) { 
    ... rest of the code here .. 
}

Answer 2

使用下面的代码更改您的 viewDidLoad 它将起作用

- (void)viewDidLoad {
     [super viewDidLoad];

     NSString *rootPath = [NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES)objectAtIndex:0];      
     path = [rootPath stringByAppendingPathComponent:[NSString stringWithFormat:@"currency.archive"]]; 
     banks = [[NSDictionary alloc] initWithDictionary:[NSKeyedUnarchiver unarchiveObjectWithFile:path]];
     keys = [[NSArray alloc] initWithArray:[banks allKeys]];
     // set date for last update 
     dayMonthYear.text = [banks objectForKey:@"Last Updated"];
 }

Answer 3

-[NSCFString objectForKey:]：发送到实例的无法识别的选择器
0x4bab9c0

正如另一个答案中提到的，您的银行和密钥变量不会保留，但这不是错误。

根据此错误，您的 fetchedCurrency 对象是 NSString，而不是 NSDictionary。检查您的currency.archive 文件的格式。