如何为Windows Phone 8消息传递应用程序绑定ViewModel

Question

 My model:

 public class MyMessageModel
  {
    public string DisplaySender { get; set; }
   //how does the below observable collection needs to be changed ,
   //if I want to add another field to itemssource template.
   //e.g. public DateTime Timestamp { get; set; }
    public ObservableCollection<string> MessagesExchanged { get; set; }
    public string NewMessage { get; set; }
  }

Chat.xaml:

<TextBlock  Name="lblFromUserName" Text="{Binding DisplaySender ,Mode=TwoWay}" Height="65" Style="{StaticResource PhoneTextNormalStyle}" FontSize="35"/>

<ItemsControl ItemsSource="{Binding Path=MessagesExchanged}">
   <ItemsControl.ItemTemplate>
    <DataTemplate>

           <TextBlock Text="{Binding ????,Mode=TwoWay}" />
           <TextBlock Text="{Binding Path=Timestamp}" HorizontalAlignment="Right" VerticalAlignment="Bottom"   Grid.Row="1"/>
        </DataTemplate>
    </ItemsControl.ItemTemplate>
<ItemsControl
<StackPanel Orientation="Horizontal" Grid.Row="1">
            <TextBox Grid.Column="0" Name="txtNewMessage" Text="{Binding NewMessage,Mode=TwoWay}" Margin="0,0,0,0" Width="350"/>
            <Button  Grid.Column="1" Command="{Binding SendClickCommand,Mode=TwoWay}"        Name="btnSend" Content="Send"  Width="100" />

</StackPanel>

Chat.xaml.cs如下所示：

 public class Chat: PhoneApplicationPage
{


    private MyMessageViewModel _MyMessageViewModel;

    public Conversation()
    {
        InitializeComponent();
        _MyMessageViewModel = new MyMessageViewModel();
        this.DataContext = _MyMessageViewModel;
    }

}

我的ViewModel MyMessageViewModel如下所示：

public System.Windows.Input.ICommand SendClickCommand
    {
        get
        {
            return new DelegateCommand((o) =>
            {

                Task.Factory.StartNew(() =>
                {
                    //loop through the selected items and clear everything
                    Deployment.Current.Dispatcher.BeginInvoke(() =>
                       {
                           try
                           {
                              //DO YOUR WORK HERE: TAKE THE NEW MESSAGE AND APPEND IT TO THE MESSAGES EXCHANGED
                           }
                           catch (Exception)
                           {

                               throw;
                           }



                       });
                });
            });
        }
    }

现在，当用户在上面称为Chat.xaml的视图中时（用户将从主页访问此页面），我想在其顶部加载DisplaySender值，该值将在整个对话过程中固定。作为主页的导航参数。

而且，每次用户单击“发送”按钮时，SendClickCommand中的添加仅通过从txtNewMessage字段添加新消息来更新MessagesExchanged集合，然后再清除此字段。

我在这里有两个问题：

当用户首次访问Chat.xaml时，如何绑定三个字段的数据，例如DisplaySender（非空值将作为导航参数传递），MessagesExchanged（最初启动新对话时为空，否则它将具有导航参数中的一个非空值）和NewMessage（最初，该值始终为空）。

其次，在SendClickCommand通知的属性中，我如何从txtNewMessage中获取文本并更新ObservableCollection MessagesExchanged，最后清除txtNewMessage的值。以及如何将MessagesExchanged的值绑定到datatemplate textblock字段？

Answer 1

我猜您正在尝试从HomePage导航到ChatPage时传递MyMessageModel类的对象。

所以定义一个属性

private MyMessageModel currentMessageModel;

public MyMessageModel CurrentMessageModel
{
    get { return currentMessageModel; }
    set { currentMessageModel = value; }
}

并在ChatPage的OnNavigatedTo方法中设置

  CurrentMessageModel=PassedObjectOfMessageModel

XAML：

<TextBlock  Name="lblFromUserName" Text="{Binding CurrentMessageModel.DisplaySender ,Mode=TwoWay}" Height="65" Style="{StaticResource PhoneTextNormalStyle}" FontSize="35"/>
<ItemsControl ItemsSource="{Binding Path=CurrentMessageModel.MessagesExchanged}">
   //No need for data template as collection only contains string
<ItemsControl
<StackPanel Orientation="Horizontal" Grid.Row="1">
        <TextBox Grid.Column="0" Name="txtNewMessage" Text="{Binding NewMessage,Mode=TwoWay}" Margin="0,0,0,0" Width="350"/>
        <Button  Grid.Column="1" Command="{Binding SendClickCommand,Mode=TwoWay}"        Name="btnSend" Content="Send"  Width="100" />
</StackPanel>

//C＃

CurrentMessageModel.MessagesExchanged.Add(txtNewMessage.Text);

并且您不需要任何文本块来显示ObservableCollection，因为您的集合仅包含字符串，因此只需将ItemsSource设置为集合即可显示数据。