滾動TableView時應用崩潰

Question

當我滾動TableView時，我的應用程序崩潰了。 首先，在我的viewDidLoad方法中，從文件中加載字典，並為此字典列舉所有鍵。

 - (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，我用該詞典中的數據填充單元格。 無論如何，當我的應用程序啟動時，一切看起來都很好，正確繪制了前五行，但是當我開始滾動時，我的應用程序崩潰了。 我的想法是問題出在這里自動釋放的對象，我試圖保留它們，並在使用它們釋放后，但未成功。 調試器顯示我的問題很粗體

// 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

用下面的代碼更改viewDidLoad，它將起作用

- (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 2

討論的結果是， [banks objectForKey:@"Last Updated"]為您提供了NSString，而不是NSDictionary！

您可以通過執行以下操作來解決此錯誤

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

Answer 3

-[NSCFString objectForKey：]：無法識別的選擇器已發送到實例0x4bab9c0

如另一個答案中所述，不會保留您的bank和key變量，但這不是錯誤。

根據此錯誤，您的fetchedCurrency對象是NSString ，而不是NSDictionary 。 檢查currency.archive文件的格式。