如何使用MVVM-Light和WCF RIA服务创建可混合项目

Question

我想使用MVVM模式构建我的业务应用程序。我选择MVVM-Light是因为它适合我的需求。在我见过的所有关于MVVM-Light的例子中，都没有人使用WCF RIA。经典的MIX10示例使用同一项目中的服务，而WCF在Web项目中创建服务。问题是:构建WCF Ria创建的整个DomainContex的接口看起来非常困难(对我来说肯定很难！)但是如果没有接口，我怎么能构建一个假的DomainContex来在Blend和测试中使用呢？我是不是遗漏了什么？谢谢。

Answer 1

实际上，我使用的解决方案是可混合的，并且使混合过程更加简单。

下面是我如何使用这个框架来实现这一点的示例：

 public class FolderViewModel : VMBase
{
    private string _subject = string.Empty;
    private string _folderName = string.Empty;
    private string _service = string.Empty;
    private string _dept = string.Empty;
    private string _efolderid = string.Empty;
    private string _timingName = string.Empty;
    private WorkplanBase _planBase = null;
    private IEnumerable<PSCustomList> _timingOptions = null;
    private decimal _totalvalue = 0;


    public FolderViewModel()
    {
        registerForMessages();

        if (IsInDesignMode)
        {
            // Code runs in Blend --> create design time data.
            EFOLDERID = "0123456790123456790123456791";
            Subject = "9999-00 - This is a test nVision Subject";
            Service = "AUDCOMP";
            Department = "AUDIT";
            FolderName = "NVSN003000";


            List<PSCustomList> listItems = new List<PSCustomList>();
            listItems.Add(new PSCustomList()
            {
                ID = "1234",
                ParameterValue = "Busy Season"
            });
            listItems.Add(new PSCustomList()
            {
                ID = "1134",
                ParameterValue = "Another Season"
            });

            _timingOptions = listItems.ToArray();
            _totalvalue = 12000;

            PlanBase = new WorkplanBase()
            {
                ClientFee = 15000,
                Timing = "1234"
            };
        }
    }
}

然后，在绑定在ViewModelLocator类中的Acutal View模型的构造器中定义所有样本数据。当您在blend中时，VMBase负责不尝试实例化DataContext。

Answer 2

我发现对我来说效果很好的是以下内容(我从MVVM light和RIA业务模板中提取了部分内容)。

我构建了一个新的ViewModelBase类，继承自MVVM Light的ViewModelBase类，在这个类中我实现了一个DomainContext、可能挂起的操作列表、当前操作、IsBusy属性、一个SaveCommand和一个protected方法来记录由ViewModels创建的、从这个类继承的任何操作。

下面是一个示例：

public class VMBase : ViewModelBase
{
    protected DomainContext _context;
    protected IList<OperationBase> operations = new List<OperationBase>();
    protected OperationBase currentOperation;

    public VMBase()
    {
        if (IsInDesignMode == false)
        {
            _context = new BudgetContext();
            _context.PropertyChanged += new System.ComponentModel.PropertyChangedEventHandler(_context_PropertyChanged);
        }
        SaveChangesCommand = new RelayCommand(
                () =>
                {
                    currentOperation = _context.SubmitChanges((so) =>
                    {
                        DispatcherHelper.CheckBeginInvokeOnUI(() =>
                        {
                            OnSaveComplete();
                            SaveChangesCommand.RaiseCanExecuteChanged();
                            CancelChangesCommand.RaiseCanExecuteChanged();
                        });
                    },
                        null);
                    logCurrentOperation();
                },
                () =>
                {
                    return _context != null && _context.HasChanges;
                });
        CancelChangesCommand = new RelayCommand(
                () =>
                {
                    _context.RejectChanges();
                    SaveChangesCommand.RaiseCanExecuteChanged();
                    CancelChangesCommand.RaiseCanExecuteChanged();
                },
                () =>
                {
                    return _context != null && _context.HasChanges;
                });
    }

    /// <summary>
    /// This is called after Save is Completed
    /// </summary>
    protected virtual void OnSaveComplete() { }

    void _context_PropertyChanged(object sender, System.ComponentModel.PropertyChangedEventArgs e)
    {
        if (e.PropertyName == "HasChanges")
        {
            DispatcherHelper.CheckBeginInvokeOnUI(() =>
            {
                SaveChangesCommand.RaiseCanExecuteChanged();
                CancelChangesCommand.RaiseCanExecuteChanged();
            });
        }
    }

    /// <summary>
    /// Bind to Busy Indicator to show when async server
    /// call is being made to submit or load data via the
    /// DomainContext/
    /// </summary>
    public bool IsWorking
    {
        get
        {
            if (currentOperation != null)
                return !currentOperation.IsComplete;
            else
            {
                return operations.Any(o => o.IsComplete == false);
            }
        }
    }

    /// <summary>
    /// Call this command to save all changes
    /// </summary>
    public RelayCommand SaveChangesCommand { get; private set; }
    /// <summary>
    /// Revert all changes not submitted
    /// </summary>
    public RelayCommand CancelChangesCommand { get; private set; }

    /// <summary>
    /// Occurs after each operation is completed, which was registered with logCurrentOperation()
    /// </summary>
    /// <param name="sender"></param>
    /// <param name="e"></param>
    protected void currentOperation_Completed(object sender, EventArgs e)
    {
        currentOperation = null;
        operations.Remove((OperationBase)sender);
        DispatcherHelper.CheckBeginInvokeOnUI(() =>
        {
            RaisePropertyChanged("IsWorking");
        });
    }

    /// <summary>
    /// Logs and notifies IsBusy of the Current Operation
    /// </summary>
    protected void logCurrentOperation()
    {
        currentOperation.Completed += new EventHandler(currentOperation_Completed);
        operations.Add(currentOperation);
        RaisePropertyChanged("IsWorking");
    }

    /// <summary>
    /// Just make sure any async calls are done
    /// </summary>
    public override void Cleanup()
    {
        // Clean own resources if needed
        foreach (OperationBase op in operations)
        {
            if (op.IsComplete == false)
            {
                if (op.CanCancel)
                    op.Cancel();
            }
        }

        base.Cleanup();
    }
}

然后，在实际的视图模型中，您可以专注于视图模型的属性和命令-所有的域上下文都已经为您连接好了。只需使用_context属性-例如：

void loadFolderInfo()
    {
        if (_context != null)
        {
            EntityQuery<eFolder> query = _context.GetEFoldersByFolderQuery(_efolderid);
            currentOperation =
                _context.Load<eFolder>(query,
                new Action<LoadOperation<eFolder>>((lo) =>
                    {
                        if (lo.HasError)
                        {
                            Messenger.Default.Send<DialogMessage>(
                                new DialogMessage(lo.Error.Message, (mbr) =>
                                    {}));
                        }
                        DispatcherHelper.CheckBeginInvokeOnUI(
                            () =>
                            {
                                eFolder myFolder = lo.Entities.First();
                                Subject = myFolder.eSubject;
                                FolderName = myFolder.eFolderName;


                            });

                    }), null);
            logCurrentOperation();
        }
    }

属性可能如下所示：

public string EFOLDERID
    {
        get
        {
            return _efolderid;
        }

        set
        {
            if (_efolderid == value)
            {
                return;
            }

            var oldValue = _efolderid;
            _efolderid = value;

            // Update bindings and broadcast change using GalaSoft.MvvmLight.Messenging
            RaisePropertyChanged("EFOLDERID", oldValue, value, true);
            loadFolderInfo();
        }
    }

关键部分是VMBase类处理DomainContext的所有连接和管理。要做到这一点，在你的ViewModel实现中，确保将任何_context.BaseOperationCall(..)的返回值赋给currrentOperation，然后立即调用logCurrentOperation。之后，它就不用插手了。然后，你可以将BusyIndicator绑定到你的IsWorking属性上，这样你就有了一个简化的RIA实现。

希望这篇文章能帮助你入门。