A Sample Silverlight 4 Application Using MEF, MVVM, and WCF RIA Services - Part 1

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.ComponentModel.Composition;
using System.Linq;
using System.ServiceModel.DomainServices.Client;
using System.Windows;
using GalaSoft.MvvmLight;
using GalaSoft.MvvmLight.Command;
using GalaSoft.MvvmLight.Messaging;
using IssueVision.Data.Web;
using IssueVision.Common;


namespace IssueVision.ViewModel
{
    [Export(ViewModelTypes.NewIssueViewModel, typeof(ViewModelBase))]
    [PartCreationPolicy(CreationPolicy.NonShared)]
    public class NewIssueViewModel : ViewModelBase
    {
        #region "Private Data Members"
        private IIssueVisionModel _issueVisionModel;
        #endregion "Private Data Members"

        #region "Constructor"
        [ImportingConstructor]
        public NewIssueViewModel(IIssueVisionModel issueVisionModel)
        {
            _issueVisionModel = issueVisionModel;

            // set up event handling
            _issueVisionModel.SaveChangesComplete += new EventHandler<SubmitOperationEventArgs>(_issueVisionModel_SaveChangesComplete);
            _issueVisionModel.PropertyChanged += new PropertyChangedEventHandler(_issueVisionModel_PropertyChanged);

            // initiate a new issue
            Issue newIssue = this._issueVisionModel.AddNewIssue();
            AppMessages.EditIssueMessage.Send(newIssue);
        }
        #endregion "Constructor"

        #region "ICleanup interface implementation"
        public override void Cleanup()
        {
            if (_issueVisionModel != null)
            {
                // unregister all events
                _issueVisionModel.SaveChangesComplete -= new EventHandler<SubmitOperationEventArgs>(_issueVisionModel_SaveChangesComplete);
                _issueVisionModel.PropertyChanged -= new PropertyChangedEventHandler(_issueVisionModel_PropertyChanged);
                _issueVisionModel = null;
            }
            // unregister any messages for this ViewModel
            base.Cleanup();
        }
        #endregion "ICleanup interface implementation"

        #region "Public Commands"

        private RelayCommand _submitChangeCommand = null;

        public RelayCommand SubmitChangeCommand
        {
            get
            {
                if (_submitChangeCommand == null)
                {
                    _submitChangeCommand = new RelayCommand(
                        () => this.OnSubmitChangeCommand(),
                        () => (this._issueVisionModel != null) && (this._issueVisionModel.HasChanges));
                }
                return _submitChangeCommand;
            }
        }

        private void OnSubmitChangeCommand()
        {
            try
            {
                if (!_issueVisionModel.IsBusy)
                {
                    AppMessages.SubmitChangesMessage.Send();
                }
            }
            catch (Exception ex)
            {
                // notify user if there is any error
                AppMessages.RaiseErrorMessage.Send(ex);
            }
        }

        private RelayCommand _cancelChangeCommand = null;

        public RelayCommand CancelChangeCommand
        {
            get
            {
                if (_cancelChangeCommand == null)
                {
                    _cancelChangeCommand = new RelayCommand(
                        () => this.OnCancelChangeCommand(),
                        () => (this._issueVisionModel != null) && (this._issueVisionModel.HasChanges));
                }
                return _cancelChangeCommand;
            }
        }

        private void OnCancelChangeCommand()
        {
            try
            {
                MessageBoxResult theResult = MessageBoxResult.Cancel;

                if (!_issueVisionModel.IsBusy)
                {
                    // ask to confirm canceling this new issue first
                    DialogMessage dialogMessage = new DialogMessage(
                        this,
                        CommonResources.CancelCurrentIssueMessageBoxText,
                        s => theResult = s)
                    {
                        Button = MessageBoxButton.OKCancel,
                        Caption = CommonResources.ConfirmMessageBoxCaption
                    };

                    AppMessages.PleaseConfirmMessage.Send(dialogMessage);

                    if (theResult == MessageBoxResult.OK)
                    {
                        // if confirmed, cancel this issue
                        AppMessages.CancelChangesMessage.Send();
                        // initiate a new issue again
                        Issue newIssue = this._issueVisionModel.AddNewIssue();
                        AppMessages.EditIssueMessage.Send(newIssue);
                    }
                }
            }
            catch (Exception ex)
            {
                // notify user if there is any error
                AppMessages.RaiseErrorMessage.Send(ex);
            }
        }

        #endregion "Public Commands"

        #region "Private Methods"

        private void _issueVisionModel_SaveChangesComplete(object sender, SubmitOperationEventArgs e)
        {
            if (!e.HasError)
            {
                // notify user of the new issue ID
                foreach (Entity entity in e.SubmitOp.ChangeSet.AddedEntities)
                {
                    Issue addedIssue = entity as Issue;
                    if (addedIssue != null)
                    {
                        // notify user of the new issue ID
                        DialogMessage dialogMessage = new DialogMessage(
                                    this,
                                    CommonResources.NewIssueCreatedText + addedIssue.IssueID,
                                    null)
                        {
                            Button = MessageBoxButton.OK,
                            Caption = CommonResources.NewIssueCreatedCaption
                        };

                        AppMessages.StatusUpdateMessage.Send(dialogMessage);
                    }
                }
                // save is successful, start another new issue
                Issue newIssue = this._issueVisionModel.AddNewIssue();
                AppMessages.EditIssueMessage.Send(newIssue);
            }
            else
            {
                // notify user if there is any error
                AppMessages.RaiseErrorMessage.Send(e.Error);
            }
        }

        private void _issueVisionModel_PropertyChanged(object sender, PropertyChangedEventArgs e)
        {
            if (e.PropertyName.Equals("HasChanges"))
            {
                SubmitChangeCommand.RaiseCanExecuteChanged();
                CancelChangeCommand.RaiseCanExecuteChanged();
            }
        }
        
        #endregion "Private Methods"
    }
}