Injecting Commands into ViewModels - silverlight

I'm trying to figure out what is the right way to inject an ICommand into my ViewModel.
Given that my ViewModel looks like this.
public class ViewModel : IViewModel
{
ICommand LoadCommand { get; }
ICommand SaveCommand { get; }
}
I currently do this in my constructor
public ViewModel(IRepository repository, IErrorLog errorLog, IValidator validator)
{
LoadCommand = new LoadCommandImpl(repository, errorLog);
SaveCommand = new SaveCommandImpl(repository, errorLog, validator);
}
Note that the parameters are not used by the ViewModel at all, aside from constructing the commands.
While I try to contain as much of the logic as possible in the injected interfaces, there is still logic in the commands.
It would seem more appropriate to do this
public ViewModel(ICommand loadCommand, ICommand saveCommand)
{
LoadCommand = loadCommand;
SaveCommand = saveCommand;
LoadCommand.SetViewModel(this);
SaveCommand.SetViewModel(this);
}
However to do this, I would need to make my Unity registrations like this. Which isn't the end of the world, but it seems like a pain.
container.RegisterType<ICommand, LoadCommandImpl>("loadCommand");
container.RegisterType<ICommand, SaveCommandImpl>("saveCommand");
container.RegisterType<IViewModel, ViewModel>(
new InjectionConstructor(
new ResolvedParameter<ICommand>("loadCommand"),
new ResolvedParameter<ICommand>("SaveCommand")));
Alternatively, I could make ILoadCommand and ISaveCommand interfaces, but these interfaces would be empty or might implement ICommand.
I'm not a huge fan of any of these solutions. What is the recommended approach here?
Edit in response to blindmeis
Let's pretend this is something other than commands for a moment.
public ViewModel(IFoo foo)
{
Bar = new Bar(foo);
}
In my opinion, it would be more appropriate to just inject IBar
public ViewModel(IBar bar)
{
Bar = bar;
}
But now I have Bar1 and Bar2. So I can either do
public ViewModel(IFoo foo)
{
Bar1 = new Bar1(foo);
Bar2 = new Bar2(foo);
}
or
public ViewModel(IBar bar1, IBar bar2)
{
Bar1 = bar1;
Bar2 = bar2;
}

This behavior is not included in Unity but its not hard to retrofit.
var container = new UnityContainer();
container.AddNewExtension<MapParameterNamesToRegistrationNamesExtension>();
container.RegisterType<ICommand, LoadCommand>("loadCommand");
container.RegisterType<ICommand, SaveCommand>("saveCommand");
container.RegisterType<ViewModel>(new MapParameterNameToRegistrationName());
var vm = container.Resolve<ViewModel>();
Assert.IsType(typeof(LoadCommand), vm.LoadCommand);
Assert.IsType(typeof(SaveCommand), vm.SaveCommand);
public class MapParameterNamesToRegistrationNamesExtension : UnityContainerExtension
{
protected override void Initialize()
{
var strategy = new MapParameterNamesToRegistrationNamesStrategy();
this.Context.Strategies.Add(strategy, UnityBuildStage.PreCreation);
}
}
public class MapParameterNamesToRegistrationNamesStrategy : BuilderStrategy
{
public override void PreBuildUp(IBuilderContext context)
{
if (context.Policies.Get<IMapParameterNameToRegistrationNamePolicy>(context.BuildKey) == null)
{
return;
}
IPolicyList resolverPolicyDestination;
IConstructorSelectorPolicy selector = context.Policies.Get<IConstructorSelectorPolicy>(context.BuildKey, out resolverPolicyDestination);
var selectedConstructor = selector.SelectConstructor(context, resolverPolicyDestination);
if (selectedConstructor == null)
{
return;
}
var parameters = selectedConstructor.Constructor.GetParameters();
var parameterKeys = selectedConstructor.GetParameterKeys();
for (int i = 0; i < parameters.Length; i++)
{
Type parameterType = parameters[i].ParameterType;
if (parameterType.IsAbstract || parameterType.IsInterface)
{
IDependencyResolverPolicy resolverPolicy = new NamedTypeDependencyResolverPolicy(parameterType, parameters[i].Name);
context.Policies.Set<IDependencyResolverPolicy>(resolverPolicy, parameterKeys[i]);
}
}
resolverPolicyDestination.Set<IConstructorSelectorPolicy>(new SelectedConstructorCache(selectedConstructor), context.BuildKey);
}
}
public class MapParameterNameToRegistrationName : InjectionMember
{
public override void AddPolicies(Type serviceType, Type implementationType, string name, IPolicyList policies)
{
policies.Set<IMapParameterNameToRegistrationNamePolicy>(new MapParameterNameToRegistrationNamePolicy(), new NamedTypeBuildKey(implementationType, name));
}
}
public interface IMapParameterNameToRegistrationNamePolicy : IBuilderPolicy
{
}
public class MapParameterNameToRegistrationNamePolicy : IMapParameterNameToRegistrationNamePolicy
{
}
The code and test can be found in the source code of the TecX project on CodePlex. Project TecX.Unity (folder Injection).

Why dont you create a command Factory
public class CommandFactory (IUnityContainer container) : ICommandFactory
{
public ICommand CreateSaveCommand()
{
return container.Resolve("SaveCommand");
}
public ICommand CreateLoadCommand()
{
return container.Resolve("LoadCommand");
}
}
public ViewModel(ICommandFactory commandFactory)
{
LoadCommand = commandFactory.CreateLoadCommand();
SaveCommand = commandFactory.CreateSaveCommand();
}

Related

Problem loading view with MEF and ExportAttribute

I have a WPF app and I'm trying to use MEF to load viewmodels and view.
I can't successfully load Views.
The code:
public interface IContent
{
void OnNavigatedFrom( );
void OnNavigatedTo( );
}
public interface IContentMetadata
{
string ViewUri { get; }
}
[MetadataAttribute]
public class ExtensionMetadataAttribute : ExportAttribute
{
public string ViewUri { get; private set; }
public ExtensionMetadataAttribute(string uri) : base(typeof(IContentMetadata))
{
this.ViewUri = uri;
}
}
class ViewContentLoader
{
[ImportMany]
public IEnumerable<ExportFactory<IContent, IContentMetadata>> ViewExports
{
get;
set;
}
public object GetView(string uri)
{
// Get the factory for the View.
var viewMapping = ViewExports.FirstOrDefault(o =>
o.Metadata.ViewUri == uri);
if (viewMapping == null)
throw new InvalidOperationException(
String.Format("Unable to navigate to: {0}. " +
"Could not locate the View.",
uri));
var viewFactory = viewMapping.CreateExport();
var view = viewFactory.Value;
return viewFactory;
}
}
I supposed to use this code like this:
1)Decorate a User control
[Export(typeof(IContent))]
[ExtensionMetadata("CustomPause")]
[PartCreationPolicy(System.ComponentModel.Composition.CreationPolicy.NonShared)]
public partial class CustomPause : Page , IContent, IPartImportsSatisfiedNotification
{
public CustomPause()
{
InitializeComponent();
}
}
2) Compose the parts:
var cv = new CompositionContainer(aggregateCatalog);
var mef = new ViewContentLoader();
cv.ComposeParts(mef);
3) Load the view at runtime given a URI, for example:
private void CustomPause_Click(object sender, RoutedEventArgs e)
{
var vc = GlobalContainer.Instance.GetMefContainer() as ViewContentLoader;
MainWindow.MainFrame.Content = vc.GetView ("CustomPause");
}
Problem is this line in the GetView method fails:
var viewMapping = ViewExports.FirstOrDefault(o =>
o.Metadata.ViewUri == uri);
The query fails and so viewMapping is null but composition seems ok and I can see that ViewExports contains an object of type:
{System.ComponentModel.Composition.ExportFactory<EyesGuard.MEF.IContent, EyesGuard.MEF.IContentMetadata>[0]
I don't know where I'm wrong. Do you have a clue?
Gianpaolo
I had forgot this
[AttributeUsage(AttributeTargets.Class, AllowMultiple = false)]
in the MetadataAttribute

Populate my ListView with item source from class

I have this Singleton that hold my ObservableCollection<MyData> as a memeber:
public sealed class Singleton
{
private static volatile Singleton instance;
private static object syncRoot = new Object();
public ObservableCollection<MyData> Files { get; private set; }
private Singleton()
{
Files = new ObservableCollection<MyData>();
}
public static Singleton Instance
{
get
{
if (instance == null)
{
lock (syncRoot)
{
if (instance == null)
instance = new Singleton();
}
}
return instance;
}
}
}
Declaration from main form class:
ObservableCollection<MyData> Files;
And here after the constructor:
Files= Singleton.Instance.Files;
XAML:
<ListView ItemsSource="{Binding Files}" />
Now when the user choose files i want to check each file:
private static void Check(IEnumerable<string> files)
{
CancellationTokenSource tokenSource = new CancellationTokenSource();
CancellationToken token = tokenSource.Token;
Task task = Task.Factory.StartNew(() =>
{
try
{
Parallel.ForEach(files,
new ParallelOptions
{
MaxDegreeOfParallelism = 1
},
file =>
{
ProcessFile(file);
});
}
catch (Exception)
{ }
}, tokenSource.Token,
TaskCreationOptions.None,
TaskScheduler.Default).ContinueWith
(t =>
{
}
, TaskScheduler.FromCurrentSynchronizationContext()
);
}
And:
private static void ProcessFile(string file)
{
// Lets assume that i want to add this file into my `ListView`
MyData data = new .....
Singleton.Instance.Files.Add(data);
}
So after this point when i am add files into my list nothing happenning.
Using your code above i was able to reproduce the issue you describe.
The problem is that WPF cannot bind to fields, see this question for more details. All you need to do is to change the ObservableCollection<MyData> in the code behind of your main form to a property instead of a field.
public partial class MainWindow : Window
{
public ObservableCollection<MyData> Files { get; private set; }

Exposing custom properties using UI Automation Framework

Given a very basic WinForms custom/user control, using System.Windows.Automation it is possible to manipulate built in properties for the custom control.
This is done like this:
public object GetPropertyValue(int propertyId)
{
if (propertyId == AutomationElementIdentifiers.NameProperty.Id)
{
return "Hello World!";
}
}
What I would like to do is expose custom properties to ui automation such as ReadyState, LastAccessed, Etc.
Is this possible?
No, you can't extend the list of properties, and this is complicated by the fact you use Winforms that has a poor UI Automation support (it uses IAccessible with bridges etc.).
What you can do though is add some fake objects to the automation tree, for example, here is a sample Winforms UserControl that does it:
public partial class UserControl1 : UserControl
{
public UserControl1()
{
InitializeComponent();
Button button = new Button();
button.Location = new Point(32, 28);
button.Size = new Size(75, 23);
button.Text = "MyButton";
Controls.Add(button);
Label label = new Label();
label.Location = new Point(49, 80);
label.Size = new Size(35, 13);
label.Text = "MyLabel";
Controls.Add(label);
MyCustomProp = "MyCustomValue";
}
public string MyCustomProp { get; set; }
protected override AccessibleObject CreateAccessibilityInstance()
{
return new UserControl1AccessibleObject(this);
}
protected class UserControl1AccessibleObject : ControlAccessibleObject
{
public UserControl1AccessibleObject(UserControl1 ownerControl)
: base(ownerControl)
{
}
public new UserControl1 Owner
{
get
{
return (UserControl1)base.Owner;
}
}
public override int GetChildCount()
{
return 1;
}
public override AccessibleObject GetChild(int index)
{
if (index == 0)
return new ValueAccessibleObject("MyCustomProp", Owner.MyCustomProp);
return base.GetChild(index);
}
}
}
public class ValueAccessibleObject : AccessibleObject
{
private string _name;
private string _value;
public ValueAccessibleObject(string name, string value)
{
_name = name;
_value = value;
}
public override AccessibleRole Role
{
get
{
return AccessibleRole.Text; // activate Value pattern
}
}
// note you need to override with member values, base value cannot always store something
public override string Value { get { return _value; } set { _value = value; } }
public override string Name { get { return _name; } }
}
And this is how it appears in the automation tree (using the inspect.exe tool):
Note this technique also supports writing back to the property because it's based on the ValuePattern.

where doese breeze fits into ntier architecture

i am Trying to fit in breezeJS with my existing architecture. I have a structure like
html/JS/Angular :: based view using hot-towel angular.
web api controllers :: whom the view calls.
Services layer :: that is being called from Web api. Any business logic goes here.
Unit of Work :: And (if) business logic requires to talk to data base for CRUDs it calls UOW.
Repository Pattern :: UOW is actually wrapping repositories. and repositores in turn talking to DbContexts.
Uptill now i was able to conver normal repositories implementation into the one using
public EFContextProvider<MyContext> DbContext { get; set; }
instead of just DbContext and i am also exposing MetaData using a string property with in UOW and IQueryables are returned using DbContext.Context.SomeEntity
Question 1 : Am i on right track ??
Question 2 : Most of the breeze examples are suggesting one SaveChanges method that give you all the entities that were changed and it will persist it at once. What if i want to trigger some business logic before Add,Update and Delete. i want to call me AddSomething service method and want to have a particular type of entity being sent to AddSomething and run some business logic before persistence. How can i put it together.
my code looksl ike
[BreezeController]//This is the controller
public class BreezeController : ApiController
{
private readonly ISomeService someService;
public BreezeController(ISomeService someService)
{
this.someService = someService;
}
// ~/breeze/todos/Metadata
[HttpGet]
public string Metadata()
{
return someService.MetaData();
}
// ~/breeze/todos/Todos
// ~/breeze/todos/Todos?$filter=IsArchived eq false&$orderby=CreatedAt
[HttpGet]
public IQueryable<Node> Nodes()
{
return nodesService.GetAllNodes().AsQueryable();
}
// ~/breeze/todos/SaveChanges
//[HttpPost]
//public SaveResult SaveChanges(JObject saveBundle)
//{
// return _contextProvider.SaveChanges(saveBundle);
//}
Below is the service
public class SomeService : BaseService, ISomeService
{
private readonly IUow Uow;
public SomeService(IUow Uow)
: base(Uow)
{
this.Uow = Uow;
}
public IEnumerable<Something> GetAllNodes()
{
return Uow.Somethings.GetAll();
}
}
every service can expose one property through base. that is actually the meta data
public class BaseService : IBaseService
{
private readonly IUow Uow;
public BaseService(IUow Uow)
{
this.Uow = Uow;
}
public string MetaData()
{
return Uow.MetaData;
}
}
and the my UOW looks like
public class VNUow : IUow, IDisposable
{
public VNUow(IRepositoryProvider repositoryProvider)
{
CreateDbContext();
repositoryProvider.DbContext = DbContext;
RepositoryProvider = repositoryProvider;
}
// Code Camper repositories
public IRepository<Something> NodeGroup { get { return GetStandardRepo<Something>(); } }
} }
public IRepository<Node> Nodes { get { return GetStandardRepo<Node>(); } }
/// <summary>
/// Save pending changes to the database
/// </summary>
public void Commit()
{
//System.Diagnostics.Debug.WriteLine("Committed");
DbContext.Context.SaveChanges();
}
public string MetaData // the Name property
{
get
{
return DbContext.Metadata();
}
}
protected void CreateDbContext()
{
// DbContext = new VNContext();
DbContext = new EFContextProvider<VNContext>();
// Load navigation properties always if it is true
DbContext.Context.Configuration.LazyLoadingEnabled = false;
// Do NOT enable proxied entities, else serialization fails
DbContext.Context.Configuration.ProxyCreationEnabled = true;
// Because Web API will perform validation, we don't need/want EF to do so
DbContext.Context.Configuration.ValidateOnSaveEnabled = false;
//DbContext.Configuration.AutoDetectChangesEnabled = false;
// We won't use this performance tweak because we don't need
// the extra performance and, when autodetect is false,
// we'd have to be careful. We're not being that careful.
}
protected IRepositoryProvider RepositoryProvider { get; set; }
private IRepository<T> GetStandardRepo<T>() where T : class
{
return RepositoryProvider.GetRepositoryForEntityType<T>();
}
private T GetRepo<T>() where T : class
{
return RepositoryProvider.GetRepository<T>();
}
private EFContextProvider<VNContext> DbContext { get; set; }
#region IDisposable
public void Dispose()
{
Dispose(true);
GC.SuppressFinalize(this);
}
protected virtual void Dispose(bool disposing)
{
if (disposing)
{
if (DbContext != null)
{
DbContext.Context.Dispose();
}
}
}
#endregion
}
in the end Repository Implementaion looks like
public class EFRepository<T> : IRepository<T> where T : class
{
public EFRepository(EFContextProvider<VNContext> dbContext)
{
if (dbContext == null)
throw new ArgumentNullException("dbContext");
DbContext = dbContext;
DbSet = DbContext.Context.Set<T>();
}
protected EFContextProvider<VNContext> DbContext { get; set; }
protected DbSet<T> DbSet { get; set; }
public virtual IQueryable<T> GetAll()
{
return DbSet;
}
public virtual IQueryable<T> GetAllEagerLoad(params Expression<Func<T, object>>[] children)
{
children.ToList().ForEach(x => DbSet.Include(x).Load());
return DbSet;
}
public virtual IQueryable<T> GetAllEagerLoadSelective(string[] children)
{
foreach (var item in children)
{
DbSet.Include(item);
}
return DbSet;
}
public virtual IQueryable<T> GetAllLazyLoad()
{
return DbSet;
}
public virtual T GetById(int id)
{
//return DbSet.FirstOrDefault(PredicateBuilder.GetByIdPredicate<T>(id));
return DbSet.Find(id);
}
public virtual T GetByIdLazyLoad(int id, params Expression<Func<T, object>>[] children)
{
children.ToList().ForEach(x => DbSet.Include(x).Load());
return DbSet.Find(id);
}
public virtual void Add(T entity)
{
DbEntityEntry dbEntityEntry = DbContext.Context.Entry(entity);
if (dbEntityEntry.State != EntityState.Detached)
{
dbEntityEntry.State = EntityState.Added;
}
else
{
DbSet.Add(entity);
}
}
public virtual void Update(T entity)
{
DbEntityEntry dbEntityEntry = DbContext.Context.Entry(entity);
if (dbEntityEntry.State == EntityState.Detached)
{
DbSet.Attach(entity);
}
dbEntityEntry.State = EntityState.Modified;
}
public virtual void Delete(T entity)
{
DbEntityEntry dbEntityEntry = DbContext.Context.Entry(entity);
if (dbEntityEntry.State != EntityState.Deleted)
{
dbEntityEntry.State = EntityState.Deleted;
}
else
{
DbSet.Attach(entity);
DbSet.Remove(entity);
}
}
public virtual void Delete(int id)
{
var entity = GetById(id);
if (entity == null) return; // not found; assume already deleted.
Delete(entity);
}
}
Much of this question is broad question and answers will be primarily opinion based... that said, here's my two cents: keep it simple. Carefully consider whether you truly need 3, 4 and 5, especially whether you need to implement UoW or the Repository Pattern yourself. The EF DbContext implements both, you could use it in your controllers directly if you wanted.
If you have custom logic that needs to execute prior to savechanges utilize one of the interceptor methods: BeforeSaveEntity or BeforeSaveEntites. Here's the documentation for those methods:
http://www.getbreezenow.com/documentation/contextprovider#BeforeSaveEntity
Breeze supports "Named saves" where you specify the name of the specific server endpoint ( i.e. your service method) on a per save basis. See:
http://www.getbreezenow.com/documentation/saving-changes
This would look something like this on your client.
var saveOptions = new SaveOptions({ resourceName: "CustomSave1" });
em.saveChanges(entitiesToSave, saveOptions).then(function (saveResult) {
// .. do something interesting.
}
and on your server
[HttpPost]
public SaveResult CustomSave1(JObject saveBundle) {
ContextProvider.BeforeSaveEntityDelegate = CustomSave1Interceptor;
return ContextProvider.SaveChanges(saveBundle);
}
private Dictionary<Type, List<EntityInfo>> CustomSave1Interceptor(Dictionary<Type, List<EntityInfo>> saveMap) {
// In this method you can
// 1) validate entities in the saveMap and optionally throw an exception
// 2) update any of the entities in the saveMap
// 3) add new entities to the saveMap
// 4) delete entities from the save map.
// For example
List<EntityInfo> fooInfos;
if (!saveMap.TryGetValue(typeof(Foo), out fooEntities)) {
// modify or delete any of the fooEntites
// or add new entityInfo instances to the fooEntities list.
}
}

What is the right way to save and restore a disconnected entity using code first?

So that I can store the user's screen preferences, I have ScreenSettings entity that I want to retrieve when the program starts and save when the program ends.
For this reason I don't want to keep the context open.
I am wondering about the best way to do this.
I have tried the following
however I am not comfortable with the SaveSettings function because it deletes and re-adds the object.
How do I save changes to the object without actually replacing it?
namespace ClassLibrary1
{
using System.ComponentModel.DataAnnotations;
using System.Data.Entity;
//Domain Class
public class ScreenSetting
{
#region Properties
public int Id { get; set; }
[Required]
public int WindowLeft { get; set; }
[Required]
public int WindowTop { get; set; }
#endregion
}
// Context
public class Context : DbContext
{
#region Properties
public DbSet<ScreenSetting> ScreenSettings { get; set; }
#endregion
}
// UI
public class UI
{
#region Public Methods
// Get the settings object
public ScreenSetting GetSettings(int SettingsId)
{
var Db = new Context();
ScreenSetting settings = Db.ScreenSettings.Find(SettingsId);
if (settings == null)
{
settings = new ScreenSetting { Id = SettingsId, WindowTop = 100, WindowLeft = 100 };
Db.ScreenSettings.Add(settings);
}
Db.Dispose();
return settings;
}
// Save the settings object
public void SaveSettings(ScreenSetting settings)
{
var Db = new Context();
ScreenSetting oldSettings = Db.ScreenSettings.Find(settings.Id);
if (oldSettings == null)
{
Db.ScreenSettings.Add(settings);
}
else
{
Db.ScreenSettings.Remove(oldSettings);
Db.ScreenSettings.Add(settings);
}
Db.Dispose();
}
public void test()
{
ScreenSetting setting = this.GetSettings(1);
setting.WindowLeft = 500;
setting.WindowTop = 500;
this.SaveSettings(setting);
}
#endregion
#region Methods
private static void Main()
{
var o = new UI();
o.test();
}
#endregion
}
}
You ran into a common pattern, update or insert, which is so common that it's got a name: upsert. When a pattern is common, usually there also is a common solution.
In System.Data.Entity.Migrations there is an extension method AddOrUpdate that does exactly what you want:
public void SaveSettings(ScreenSetting settings)
{
using (var db = new Context())
{
db.ScreenSettings.AddOrUpdate(settings);
db.SaveChanges();
}
}

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