Question

我正在使用mvvm概念（数据，组，模型）开发一个win phone 8应用程序，我使用这个概念完成了我的应用程序设计。现在我正在尝试将我的应用程序连接到azure DB，我还通过以下代码使用MVVM概念连接了azure DB，并且它成功运行。

var js = new JObject { { "institutionid", obj.institutionid }, { "userid", obj.userid } };
var result = await App.MobileService.InvokeApiAsync("school_365_create_dynamic_tile", js, System.Net.Http.HttpMethod.Post, null);

在创建ViewModel时，我必须使用Azure移动服务Sdk调用从Azure移动服务读取数据的服务。

Sdk apis使用async / await来完成工作，我无法在ViewModel中进行异步调用。

Model类的代码如下：

public class ModelMail : INotifyPropertyChanged
{

    //newly added
    public Group Mail { get; set; }
    public Group OutBox { get; set; }
    public Group Draft { get; set; }
    public Group SendItems { get; set; }
    public bool IsDataLoaded { get; set; }

    public event PropertyChangedEventHandler PropertyChanged;
    private void NotifyPropertyChanged(string property)
    {
        if (PropertyChanged != null)
        {
            PropertyChanged(this, new PropertyChangedEventArgs(property));
        }
    }

    public void LoadData()
    {
        //Newly created
        Mail = CreateMail();
        OutBox = CreateOutBox();
        Draft = CreateDraft();
        SendItems = CreateSendItems();
        IsDataLoaded = true;
    }


    private Group CreateDraft()
    {
        Group data = new Group();

        data.Title = "all";
        string[] gataFromDB = new string[] { "sample ", "sample", "sample", "sample" };

        data.Items.Add(new Data { Name_1 = "Nisar Mohamed VM", Subject = "Subject Inbox sample mail subject Inbox sample mail subject Inbox sample mail subject Inbox sample mail subject Inbox sample mail subject 456", Message = "Message This is a sample mail message from nisar This is a sample mail message from nisar This is a sample mail message from nisar This is a sample mail message from nisar This is a sample mail message from nisarThis is a sample mail message from nisar", time = "11:00 AM", IsChecked = false, foreground = "Black", to = "gowthamrajs@hotmail.com", mailFullDateTime = "Fri 9/12 9:25 PM", from = "kkkk@knowledgeq.com" });

        foreach (string dataa in gataFromDB)
        {

            data.Items.Add(new Data { Name_1 = "Nisar Mohamed VM", Subject = "Subject Inbox sample mail subject Inbox sample mail subject Inbox sample mail subject Inbox sample mail subject Inbox sample mail subject 456", Message = "Message This is a sample mail message from nisar This is a sample mail message from nisar This is a sample mail message from nisar This is a sample mail message from nisar This is a sample mail message from nisarThis is a sample mail message from nisar", time = "11:10 AM", IsChecked = false, foreground = "Black", to = "nisr199@hotmail.com", cc = "nisr19@gmail.com", mailFullDateTime = "Fri 9/12 9:25 PM", from = "kkkk@knowledgeq.com" });
        }


        return data;
    }

    private Group CreateOutBox()
    {
        Group data = new Group();

        data.Title = "unread";

        return data;
    }

    private Group  CreateMail()
    {
        Group data = new Group();

        data.Title = "all";

        return data;
    }

    private Group CreateSendItems()
    {
        Group data = new Group();

        data.Title = "all";

        return data;
    }

}

我怎么能

Answer 1

您可能会发现我的MSDN article on async data binding有帮助。总之，如果您是数据绑定，则需要在下载数据完成时引发PropertyChanged。 Task未实现INotifyPropertyChanged，因此需要一些帮助。我的文章中有一个类型NotifyTaskCompletion<T>，可以用作异步操作的数据绑定包装。

您将在构造函数中启动异步操作，并创建一个包含（data-bindable）结果的NotifyTaskCompletion<T>：

public class MyViewModel
{
  public MyViewModel()
  {
    Mail = new NotifyTaskCompletion<Group>(CreateMailAsync());
  }

  public NotifyTaskCompletion<Group> Mail { get; private set; }

  private async Task<Group> CreateMailAsync()
  {
    // Azure calls go here
  }
}

然后，您的数据绑定代码可以使用NotifyTaskCompletion<T>上的属性来更新UI：

<Grid>
  <!-- Busy indicator -->
  <Label Content="Loading..." Visibility="{Binding Mail.IsNotCompleted, Converter={StaticResource BooleanToVisibilityConverter}}"/>

  <!-- Results -->
  <Label Content="{Binding Mail.Result.Title}" Visibility="{Binding Mail.IsSuccessfullyCompleted, Converter={StaticResource BooleanToVisibilityConverter}}"/>

  <!-- Error details -->
  <Label Content="{Binding Mail.ErrorMessage}" Background="Red" Visibility="{Binding Mail.IsFaulted, Converter={StaticResource BooleanToVisibilityConverter}}"/>
</Grid>

请注意，您的应用程序UI中需要一些额外的状态。具体而言，操作正在进行时的“加载”状态;操作异步失败时的“错误”状态。

viewmodel中的MVVM异步调用：如何将azure DB与MVVM连接

1 个答案: