Question

我有这个功能：

- (NSString*) getId:(id)id_field withColumn:(int)test_column withTable:(NSString *) tableName  //renvoyer le label
{
    NSError *error = nil;
    NSFetchRequest *fetchRequest = [[NSFetchRequest alloc] init];
    NSEntityDescription *entity = [NSEntityDescription entityForName:tableName
                                              inManagedObjectContext:managedObjectContext];
    [fetchRequest setEntity:entity];
    NSArray *fetchedObjects = [managedObjectContext executeFetchRequest:fetchRequest error:&error];
    for (<tableName of class> *info in fetchedObjects)
    {
        if (test_column == LBL2_CLMN)
        {
            NSLog(@"info.id :%@", info.id);
            if ([info.id compare:id_field] == NSOrderedSame)
                NSLog(@"info.id :%@", info.label1);
            return info.label1;
        }
        else if (test_column == LBL1_CLMN)
        {
            if ([info.id compare:id_field] == NSOrderedSame)
                return info.label2;
        }
    }
    return @"";
}

如何使用变量tableName更改instanciate * info类的名称？

有可能吗？

Answer 1

不是直接的，但是因为if - else返回NSArray *fetchedObjects = [managedObjectContext executeFetchRequest:fetchRequest error:&error]; for (NSManagedObject *object in fetchedObjects) { if (test_column == LBL2_CLMN) { ClassA *info = (ClassA *)object; NSLog(@"info.id :%@", info.id); if ([info.id compare:id_field] == NSOrderedSame) { NSLog(@"info.id :%@", info.label1); return info.label1; } } else if (test_column == LBL1_CLMN) { ClassB *info = (ClassB *)object; if ([info.id compare:id_field] == NSOrderedSame) return info.label2; } } return @"";，所以在重复循环中使用它并将对象强制转换为if范围中的预期类。

我猜第二个m子句中缺少一对括号。

Answer 2

您必须使用NSClassFromString方法，然后使用id关键字来获取对象：

    getPageTopLeft(el) {
    const rect = el.getBoundingClientRect();
    const docEl = document.documentElement;
    return {
        left: rect.left + (window.pageXOffset || docEl.scrollLeft || 0),
        top: rect.top + (window.pageYOffset || docEl.scrollTop || 0)
    };
}

是否可以使用变量动态更改代码中类的名称？

2 个答案: