winRT DataContractSerialized

class AppDataManager
{
    public static async Task SaveAsync<T>(T data, string fileName)
    {
        StorageFile file = await ApplicationData.Current.LocalFolder.CreateFileAsync(fileName, 
            CreationCollisionOption.ReplaceExisting);

        var stream = await file.OpenStreamForWriteAsync();
        var serializer = new DataContractSerializer(typeof(T));
        serializer.WriteObject(stream ,data);
        await stream.FlushAsync();
    }
    public static async Task<T> RestoreAsync<T>(string fileName)
    {
        try
        {
            var file = await ApplicationData.Current.LocalFolder.GetFileAsync(fileName);
            var instream = await file.OpenStreamForReadAsync();
            var serializer = new DataContractSerializer(typeof(T));
            return (T)serializer.ReadObject(instream);
        }
        catch (Exception)
        {
            return default(T);
        }
    }
}

在主页中。XAML .

    private async void SaveButton_Click_1(object sender, RoutedEventArgs e)
    {
        data = new UserData()
        {
            Name = "ibraheem",
            ID = 1,
            phoneNumber = 799,
            Course = "java"
        };
        await AppDataManager.SaveAsync<UserData>(data, fileName);
    }

当我点击保存按钮时，它给了我一个异常

DesigningElements类型"。UserData'不能被序列化。考虑用DataContractAttribute属性标记它，并标记所有您想要用DataMemberAttribute序列化的成员属性。如果类型是集合，请考虑使用CollectionDataContractAttribute。参见Microsoft .NET框架其他支持类型的文档。