iphone - 关于单位换算的简单问题

Question

我使用以下代码在表格中显示我的数据的千克与磅。

由于某种原因，它无法正常工作，并且给了我巨大的数字。有什么想法吗？

我正在使用 DDUnitConverter (https://github.com/davedelong/DDUnitConverter )

- (void)configureCell:(UITableViewCell *)cell atIndexPath:(NSIndexPath *)indexPath
{
    NSManagedObject *managedObject = [self.fetchedResultsController objectAtIndexPath:indexPath];
    NSString *repsText = [[managedObject valueForKey:@"reps"] description];

    NSNumber *weightInPounds = [NSNumber numberWithFloat:[[managedObject valueForKey:@"weight"]floatValue]];
    NSNumber *weightInKilos = [[DDUnitConverter massUnitConverter] convertNumber:weightInPounds fromUnit:DDMassUnitUSPounds toUnit:DDMassUnitKilograms];

    NSString *weightText = nil;
    NSString *cellText = nil;
    BOOL isKgs = [[NSUserDefaults standardUserDefaults] boolForKey:@"wantsKGs"];
    if (isKgs == 1)
    {
        weightText = [[NSString alloc]initWithFormat:@"%i", weightInKilos];
        cellText = [[NSString alloc]initWithFormat:@"Set %i: %@ reps at %@ kgs",indexPath.row + 1, repsText, weightText];
    }
    else
    {
        weightText = [[NSString alloc]initWithFormat:@"%i", weightInPounds];
        cellText = [[NSString alloc]initWithFormat:@"Set %i: %@ reps at %@ lbs",indexPath.row + 1, repsText, weightText];
    }
    cell.textLabel.text = cellText;
}

Answer 1

哦，这个问题很容易解决。 weightInKilos 和 weightInPounds 是 NSNumber 实例。当您在格式中使用 %i 格式化程序时，这意味着您正在提供一个整数。您最终提供的整数是每个对象的指针值。由于您需要每个 NSNumber 的字符串值，因此请使用实例方法 -stringValue。

这是基于这些更改的代码的更新版本。

- (void) configureCell: (UITableViewCell *) cell atIndexPath: (NSIndexPath *) indexPath
{
    NSManagedObject *managedObject = [self.fetchedResultsController objectAtIndexPath: indexPath];
    NSString *repsText = [[managedObject valueForKey: @"reps"] description];

    NSNumber *weightInPounds = [NSNumber numberWithFloat: [[managedObject valueForKey: @"weight"] floatValue]];
    // Alternatively you could just use ‘[managedObject valueForKey: @"weight"]’ if the ‘weight’ attribute is a number.

    NSNumber *weightInKilos = [[DDUnitConverter massUnitConverter] convertNumber: weightInPounds
                                                                        fromUnit: DDMassUnitUSPounds
                                                                          toUnit: DDMassUnitKilograms];

    BOOL isKgs = [[NSUserDefaults standardUserDefaults] boolForKey:@"wantsKGs"];
    NSString *weightText = (isKgs ? [weightInKilos stringValue] : [weightInPounds stringValue]);

    cell.textLabel.text = [NSString stringWithFormat: @"Set %i: %@ reps at %@ lbs",indexPath.row + 1, repsText, weightText];
}

请记住，处理对象时必须遵循内存管理规则。当您使用 -init... 方法创建对象时，必须确保释放它。在您的代码中，这意味着 weightText 和 cellText。

PS:DDUnitConverter 是一个很棒的发现。如果我在未来的项目中需要它，我必须将其添加为书签。