foreach(var someDisposableObject in listOfDisposableObjects)
{
//some code
someDisposableObject.Dispose(); //current code contains something like this.
}
Is there safe way, like a using clause to use in this scenario?
For my second iteration (before getting responses) I changed the code to
foreach(var someDisposableObject in listOfDisposableObjects)
{
try
{
//some code
}
finally
{
someDisposableObject.Dispose(); //current code contains something like this.
}
}
though
foreach(var someDisposableObject in listOfDisposableObjects)
{
using( someDisposableObject )
{
//some code
}
}
is much more tidy and most likely safer.
I think this may be your best bet:
try
{
foreach(var someDisposableObject in listOfDisposableObjects)
{
//some code
}
}
finally
{
foreach(var someDisposableObject in listOfDisposableObjects)
{
someDisposableObject.Dispose();
}
}
EDITED TO ADD:
If you absolutely have to dispose of every object no matter what, then you can do this:
private static void DoStuff(IEnumerable<IDisposable> listOfDisposableObjects)
{
using (var enumerator = listOfDisposableObjects.GetEnumerator())
{
if (enumerator.MoveNext())
DoStuffCore(enumerator);
}
}
private static void DoStuffCore(IEnumerator<IDisposable> enumerator)
{
using (var someDisposableObject = enumerator.Current)
{
if (enumerator.MoveNext())
DoStuffCore(enumerator);
// Do stuff with someDisposableObject
}
}
I would say your Dispose code should be outside of this foreach.
The key point you haven't addressed in your sample is how the list of disposable objects is generated. What happens if an exception is thrown while you are generating the list of disposable objects? You will want to dispose those that you have created so far.
Ideally you want a container that implements IDisposable to hold your disposable objects. If your disposable objects implement IComponent, then System.ComponentModel.Container is what you need. If not, you may have to roll your own.
Code might look something like:
using(Container container = new Container())
{
// Generate list and add each element to the container
for (...)
{
someDisposableComponent = ...;
container.Add(someDisposableComponent);
listOfDisposableObjects.Add(someDisposableComponent);
}
...
foreach(var someDisposableObject in listOfDisposableObjects)
{
... some code ...
}
}
I suggest you post code that generates the list if you need more help.
foreach(var someDisposableObject in listOfDisposableObjects)
{
using (someDisposableObject)
{
//some code
}
}
Related
I am using the BLOC pattern for my latest Flutter app and I started out using something like this for my output streams:
class MyBloc {
// Outputs
final Stream<List<Todo>> todos;
factory MyBloc(TodosInteractor interactor) {
final todosController = BehaviorSubject<List<Todo>>()
..addStream(interactor.todos);
return MyBloc._(todosController);
}
MyBloc._(this.todos);
}
but slowly I found myself doing something more like this, using a method (or getter) after awhile:
class MyBloc {
final TodosInteractor _interactor;
// Outputs
Stream<List<Todo>> todos(){
return _interactor.todos;
}
MyBloc(this._interactor) { }
}
For people who want to see... getter for todos in TodosInteractor:
Stream<List<Todo>> get todos {
return repository
.todos()
.map((entities) => entities.map(Todo.fromEntity).toList());
}
When I look at the differing code, I see that the first example uses a field versus a method to expose the stream but I couldn't figure out why I would choose one over the other. It seems to me that creating another controller just to push through the stream is a little much... Is there a benefit to this other than being immutable in my todos stream definition? Or am I just splitting hairs?
Well maybe this will not be a best answer but it is a good practice expose your output stream using get methods. Below a example of a bloc class that i have written to a project using RxDart.
class CityListWidgetBloc {
final _cityInput = PublishSubject<List<Cidade>>();
final _searchInput = new PublishSubject<String>();
final _selectedItemsInput = new PublishSubject<List<Cidade>>();
// exposing stream using get methods
Observable<List<Cidade>> get allCities => _cityInput.stream;
Observable<List<Cidade>> get selectedItems => _selectedItemsInput.stream;
List<Cidade> _searchList = new List();
List<Cidade> _selectedItems = new List();
List<Cidade> _mainDataList;
CityListWidgetBloc() {
//init search stream
_searchInput.stream.listen((searchPattern) {
if (searchPattern.isEmpty) {
_onData(_mainDataList); // resend local data list
} else {
_searchList.clear();
_mainDataList.forEach((city) {
if (city.nome.toLowerCase().contains(searchPattern.toLowerCase())) {
_searchList.add(city);
}
});
_cityInput.sink.add(_searchList);
}
});
}
//getting data from firebase
getCity( {#required String key}) {
FirebaseStateCityHelper.getCitiesFrom(key, _onData);
//_lastKey = key;
}
searchFor(String pattern) {
_searchInput.sink.add(pattern);
}
void _onData(List<Cidade> list) {
_mainDataList = list;
list.sort((a, b) => (a.nome.compareTo(b.nome)));
_cityInput.sink.add(list);
}
bool isSelected(Cidade item) {
return _selectedItems.contains(item);
}
void selectItem(Cidade item) {
_selectedItems.add(item);
_selectedItemsInput.sink.add(_selectedItems);
}
void selectItems(List<Cidade> items){
_selectedItems.addAll( items);
_selectedItemsInput.sink.add( _selectedItems );
}
void removeItem(Cidade item) {
_selectedItems.remove(item);
_selectedItemsInput.sink.add(_selectedItems);
}
dispose() {
_cityInput.close();
_searchInput.close();
_selectedItemsInput.close();
}
}
I am creating an application with MVC4 and entity framework 5. How do can I implement this?
I have looked around and found that I need to override SaveChanges .
Does anyone have any sample code on this? I am using code first approach.
As an example, the way I am saving data is as follows,
public class AuditZoneRepository : IAuditZoneRepository
{
private AISDbContext context = new AISDbContext();
public int Save(AuditZone model, ModelStateDictionary modelState)
{
if (model.Id == 0)
{
context.AuditZones.Add(model);
}
else
{
var recordToUpdate = context.AuditZones.FirstOrDefault(x => x.Id == model.Id);
if (recordToUpdate != null)
{
recordToUpdate.Description = model.Description;
recordToUpdate.Valid = model.Valid;
recordToUpdate.ModifiedDate = DateTime.Now;
}
}
try
{
context.SaveChanges();
return 1;
}
catch (Exception ex)
{
modelState.AddModelError("", "Database error has occured. Please try again later");
return -1;
}
}
}
There is no need to override SaveChanges.
You can
Trigger Context.ChangeTracker.DetectChanges(); // may be necessary depending on your Proxy approach
Then analyze the context BEFORE save.
you can then... add the Change Log to the CURRENT Unit of work.
So the log gets saved in one COMMIT transaction.
Or process it as you see fit.
But saving your change log at same time. makes sure it is ONE Transaction.
Analyzing the context sample:
I have a simple tool, to Dump context content to debug output so when in debugger I can use immediate window to check content. eg
You can use this as a starter to prepare your CHANGE Log.
Try it in debugger immediate window. I have FULL dump on my Context class.
Sample Immediate window call. UoW.Context.FullDump();
public void FullDump()
{
Debug.WriteLine("=====Begin of Context Dump=======");
var dbsetList = this.ChangeTracker.Entries();
foreach (var dbEntityEntry in dbsetList)
{
Debug.WriteLine(dbEntityEntry.Entity.GetType().Name + " => " + dbEntityEntry.State);
switch (dbEntityEntry.State)
{
case EntityState.Detached:
case EntityState.Unchanged:
case EntityState.Added:
case EntityState.Modified:
WriteCurrentValues(dbEntityEntry);
break;
case EntityState.Deleted:
WriteOriginalValues(dbEntityEntry);
break;
default:
throw new ArgumentOutOfRangeException();
}
Debug.WriteLine("==========End of Entity======");
}
Debug.WriteLine("==========End of Context======");
}
private static void WriteCurrentValues(DbEntityEntry dbEntityEntry)
{
foreach (var cv in dbEntityEntry.CurrentValues.PropertyNames)
{
Debug.WriteLine(cv + "=" + dbEntityEntry.CurrentValues[cv]);
}
}
private static void WriteOriginalValues(DbEntityEntry dbEntityEntry)
{
foreach (var cv in dbEntityEntry.OriginalValues.PropertyNames)
{
Debug.WriteLine(cv + "=" + dbEntityEntry.OriginalValues[cv]);
}
}
}
EDIT: Get the changes
I use this routine to get chnages...
public class ObjectPair {
public string Key { get; set; }
public object Original { get; set; }
public object Current { get; set; }
}
public virtual IList<ObjectPair> GetChanges(object poco) {
var changes = new List<ObjectPair>();
var thePoco = (TPoco) poco;
foreach (var propName in Entry(thePoco).CurrentValues.PropertyNames) {
var curr = Entry(thePoco).CurrentValues[propName];
var orig = Entry(thePoco).OriginalValues[propName];
if (curr != null && orig != null) {
if (curr.Equals(orig)) {
continue;
}
}
if (curr == null && orig == null) {
continue;
}
var aChangePair = new ObjectPair {Key = propName, Current = curr, Original = orig};
changes.Add(aChangePair);
}
return changes;
}
edit 2 If you must use the Internal Object tracking.
var context = ???// YOUR DBCONTEXT class
// get objectcontext from dbcontext...
var objectContext = ((IObjectContextAdapter) context).ObjectContext;
// for each tracked entry
foreach (var dbEntityEntry in context.ChangeTracker.Entries()) {
//get the state entry from the statemanager per changed object
var stateEntry = objectContext.ObjectStateManager.GetObjectStateEntry(dbEntityEntry.Entity);
var modProps = stateEntry.GetModifiedProperties();
Debug.WriteLine(modProps.ToString());
}
I decompiled EF6 . Get modified is indeed using private bit array to track fields that have
been changed.
// EF decompiled source..... _modifiedFields is a bitarray
public override IEnumerable<string> GetModifiedProperties()
{
this.ValidateState();
if (EntityState.Modified == this.State && this._modifiedFields != null)
{
for (int i = 0; i < this._modifiedFields.Length; ++i)
{
if (this._modifiedFields[i])
yield return this.GetCLayerName(i, this._cacheTypeMetadata);
}
}
}
I've tried following the steps in Joost Van Schaik's article on tombstoning but was unable to get it to work for me. I'm no doubt doing something wrong. In my ViewModel:
private string _foobar ="init";
public string testStr
{
get
{
return _foobar;
}
set
{
_foobar = value;
}
}
And in my page:
<TextBox x:Name="tBoxTest" Text="{Binding testStr, Mode=TwoWay}" />
While the application is running, changing the value in tBoxTest sets _foobar just fine, but try to serialize it and it’s as if it has forgotten the instance??? Any help would be greatly appreciated.
I was able to get tombstoning to work, along with having an object be visible to all my ViewModels, by doing the following:
In a Model class, I added:
private static Model1 _instance;
public static Model1 Instance
{
get { return _instance; }
set { _instance = value; }
}
public static void CreateNew()
{
if (_instance == null)
{
_instance = new Model1();
_instance.FirstString = "init";
}
}
Then in ApplicationExtensions.cs I added:
public static void SaveToIsolatedStorage(this Application app, Model1 model)
{
var dataFileName = GetIsFile((model.GetType()));
using (var userAppStore =
IsolatedStorageFile.GetUserStoreForApplication())
{
if (userAppStore.FileExists(dataFileName))
{
userAppStore.DeleteFile(dataFileName);
}
using (var iss = userAppStore.CreateFile(dataFileName))
{
SilverlightSerializer.Serialize(model, iss);
}
}
}
And in App.xaml.cs I changed LoadModel() to:
private void LoadModel()
{
try
{
Model1.Instance = this.RetrieveFromIsolatedStorage<Model1>();
}
catch (Exception) { }
if (Model1.Instance == null) Model1.CreateNew();
}
That all made things like this work in my ViewModel files:
public string TestStr
{
get
{
return Model1.Instance.FirstString;
}
set
{
Model1.Instance.FirstString = value;
}
}
And by that, I mean that the Model1 object is getting serialized and tombstoning is working - at least I’m getting what I think I want. I’ve tested it a lot by navigating between apps, phone settings, turning the phone off and on, locking it and calling it while in the app from another phone. Performance when deserializing is great. And I can work with the vars.
That said, Mr. Van Schaik replied to a request for assistance with: "If you are subclassing from an MVVMLight ViewModelBase it does, and then you should call RaisePropertyChanged from your setter like this:
private string _foobar ="init";
public string TestStr
{
get
{
return _foobar;
}
set
{
RaisePropertyChanged("TestStr");
_foobar = value;
}
}
RaisePropertyChanged notifies any listenings views (i.e. the TextBox you bound to it) that a property is changed and that the should update their contents. This is a crucial mechanism."
So I will work with what I was originally trying but with the addition of RaisePropertyChanged to see what that does.
UPDATE
Although I implemented RaisedPropertyChanged (using the code snippet mvvminpc) in my MainViewModel.cs file, that still had no effect (as good as it may be for other things) on serializing anything created within the ViewModel. I'm probably still doing something wrong, but it may also be because view models inherit from a protected class (answer from Laurent Bugnion). I (very reluctantly) tried changing that class from protected to public and recompiling, but it didn't help in my case and I hate to fork a referenced library like that. Anyway, I'm just forging ahead for now with creating the Model1 instance in App.xaml.cs. Seems to work. While I was at it, I modified one of Van Schaik's methods to accept any type of object:
public static void SaveToIsolatedStorage<T>(this Application app, T obj)
where T : class
{
var dataFileName = GetIsFile(typeof(T));
using (var userAppStore =
IsolatedStorageFile.GetUserStoreForApplication())
{
if (userAppStore.FileExists(dataFileName))
{
userAppStore.DeleteFile(dataFileName);
}
using (var iss = userAppStore.CreateFile(dataFileName))
{
SilverlightSerializer.Serialize(obj, iss);
}
}
}
From the code you've posted there isn't an instant answer.
My advice to debug this is:
if you've copied the code exactly from that article then add something (a messagebox?) to the empty catch handler - `catch (Exception){ }
use the debugger to put breakpoints in the LoadModel and SaveToIsolatedStorage methods
use these breakpoints to step through the Load and Save code - is the code correctly loading and saving?
To be honest, with problems like this, doing a little investigation yourself is much better than asking questions on here (IMO!)
I'm wanting to have a simple duck typing example in C# using dynamic objects. It would seem to me, that a dynamic object should have HasValue/HasProperty/HasMethod methods with a single string parameter for the name of the value, property, or method you are looking for before trying to run against it. I'm trying to avoid try/catch blocks, and deeper reflection if possible. It just seems to be a common practice for duck typing in dynamic languages (JS, Ruby, Python etc.) that is to test for a property/method before trying to use it, then falling back to a default, or throwing a controlled exception. The example below is basically what I want to accomplish.
If the methods described above don't exist, does anyone have premade extension methods for dynamic that will do this?
Example: In JavaScript I can test for a method on an object fairly easily.
//JavaScript
function quack(duck) {
if (duck && typeof duck.quack === "function") {
return duck.quack();
}
return null; //nothing to return, not a duck
}
How would I do the same in C#?
//C# 4
dynamic Quack(dynamic duck)
{
//how do I test that the duck is not null,
//and has a quack method?
//if it doesn't quack, return null
}
If you have control over all of the object types that you will be using dynamically, another option would be to force them to inherit from a subclass of the DynamicObject class that is tailored to not fail when a method that does not exist is invoked:
A quick and dirty version would look like this:
public class DynamicAnimal : DynamicObject
{
public override bool TryInvokeMember(InvokeMemberBinder binder, object[] args, out object result)
{
bool success = base.TryInvokeMember(binder, args, out result);
// If the method didn't exist, ensure the result is null
if (!success) result = null;
// Always return true to avoid Exceptions being raised
return true;
}
}
You could then do the following:
public class Duck : DynamicAnimal
{
public string Quack()
{
return "QUACK!";
}
}
public class Cow : DynamicAnimal
{
public string Moo()
{
return "Mooooo!";
}
}
class Program
{
static void Main(string[] args)
{
var duck = new Duck();
var cow = new Cow();
Console.WriteLine("Can a duck quack?");
Console.WriteLine(DoQuack(duck));
Console.WriteLine("Can a cow quack?");
Console.WriteLine(DoQuack(cow));
Console.ReadKey();
}
public static string DoQuack(dynamic animal)
{
string result = animal.Quack();
return result ?? "... silence ...";
}
}
And your output would be:
Can a duck quack?
QUACK!
Can a cow quack?
... silence ...
Edit: I should note that this is the tip of the iceberg if you are able to use this approach and build on DynamicObject. You could write methods like bool HasMember(string memberName) if you so desired.
Try this:
using System.Linq;
using System.Reflection;
//...
public dynamic Quack(dynamic duck, int i)
{
Object obj = duck as Object;
if (duck != null)
{
//check if object has method Quack()
MethodInfo method = obj.GetType().GetMethods().
FirstOrDefault(x => x.Name == "Quack");
//if yes
if (method != null)
{
//invoke and return value
return method.Invoke((object)duck, null);
}
}
return null;
}
Or this (uses only dynamic):
public static dynamic Quack(dynamic duck)
{
try
{
//invoke and return value
return duck.Quack();
}
//thrown if method call failed
catch (RuntimeBinderException)
{
return null;
}
}
Implementation of the HasProperty method for every IDynamicMetaObjectProvider WITHOUT throwing RuntimeBinderException.
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Dynamic;
using Microsoft.CSharp.RuntimeBinder;
using System.Linq.Expressions;
using System.Runtime.CompilerServices;
namespace DynamicCheckPropertyExistence
{
class Program
{
static void Main(string[] args)
{
dynamic testDynamicObject = new ExpandoObject();
testDynamicObject.Name = "Testovaci vlastnost";
Console.WriteLine(HasProperty(testDynamicObject, "Name"));
Console.WriteLine(HasProperty(testDynamicObject, "Id"));
Console.ReadLine();
}
private static bool HasProperty(IDynamicMetaObjectProvider dynamicProvider, string name)
{
var defaultBinder = Binder.GetMember(CSharpBinderFlags.None, name, typeof(Program),
new[]
{
CSharpArgumentInfo.Create(
CSharpArgumentInfoFlags.None, null)
}) as GetMemberBinder;
var callSite = CallSite<Func<CallSite, object, object>>.Create(new NoThrowGetBinderMember(name, false, defaultBinder));
var result = callSite.Target(callSite, dynamicProvider);
if (Object.ReferenceEquals(result, NoThrowExpressionVisitor.DUMMY_RESULT))
{
return false;
}
return true;
}
}
class NoThrowGetBinderMember : GetMemberBinder
{
private GetMemberBinder m_innerBinder;
public NoThrowGetBinderMember(string name, bool ignoreCase, GetMemberBinder innerBinder) : base(name, ignoreCase)
{
m_innerBinder = innerBinder;
}
public override DynamicMetaObject FallbackGetMember(DynamicMetaObject target, DynamicMetaObject errorSuggestion)
{
var retMetaObject = m_innerBinder.Bind(target, new DynamicMetaObject[] {});
var noThrowVisitor = new NoThrowExpressionVisitor();
var resultExpression = noThrowVisitor.Visit(retMetaObject.Expression);
var finalMetaObject = new DynamicMetaObject(resultExpression, retMetaObject.Restrictions);
return finalMetaObject;
}
}
class NoThrowExpressionVisitor : ExpressionVisitor
{
public static readonly object DUMMY_RESULT = new DummyBindingResult();
public NoThrowExpressionVisitor()
{
}
protected override Expression VisitConditional(ConditionalExpression node)
{
if (node.IfFalse.NodeType != ExpressionType.Throw)
{
return base.VisitConditional(node);
}
Expression<Func<Object>> dummyFalseResult = () => DUMMY_RESULT;
var invokeDummyFalseResult = Expression.Invoke(dummyFalseResult, null);
return Expression.Condition(node.Test, node.IfTrue, invokeDummyFalseResult);
}
private class DummyBindingResult {}
}
}
impromptu-interface seems to be a nice Interface mapper for dynamic objects... It's a bit more work than I was hoping for, but seems to be the cleanest implementation of the examples presented... Keeping Simon's answer as correct, since it is still the closest to what I wanted, but the Impromptu interface methods are really nice.
The shortest path would be to invoke it, and handle the exception if the method does not exist. I come from Python where such method is common in duck-typing, but I don't know if it is widely used in C#4...
I haven't tested myself since I don't have VC 2010 on my machine
dynamic Quack(dynamic duck)
{
try
{
return duck.Quack();
}
catch (RuntimeBinderException)
{ return null; }
}
Have not see a correct answer here, MS provides an example now with casting to a dictionary
dynamic employee = new ExpandoObject();
employee.Name = "John Smith";
employee.Age = 33;
foreach (var property in (IDictionary<String, Object>)employee)
{
Console.WriteLine(property.Key + ": " + property.Value);
}
// This code example produces the following output:
// Name: John Smith
// Age: 33
I've just been working on some tests using Moq but ran into trouble trying to test a method I wanted to call twice through a try catch block. The principle is that the first call throws an exception, then in the catch I correct the problem and call the method again.
I managed to do it with Rhino Mocks as below but being new to both frameworks I wondered if anyone could tell me if the same can be achieved using Moq.
// C.U.T
public class Mockee
{
bool theCatLives = true;
public Mockee() { }
public virtual void SetFalse()
{
theCatLives = false;
}
}
[Test]
public void TestTryCatch(){
var mr = new MockRepository();
var mock = mr.StrictMock<Mockee>();
mr.Record();
Expect.Call(mock.SetFalse).Throw(new Exception());
Expect.Call(mock.SetFalse);
mr.ReplayAll();
try
{
mock.SetFalse();
}
catch
{
mock.SetFalse();
}
mock.VerifyAllExpectations();
}
This isn't particularly easy to do with Moq, as it has no concept of ordered expectations. You can, however, use the Callback method and throw exceptions from there, like this:
var actions = new Queue<Action>(new Action[]
{
() => { throw new Exception(); },
() => { }
});
var mock = new Mock<Mockee>();
mock.Setup(m => m.SetFalse()).Callback(() => actions.Dequeue()()).Verifiable();
try
{
mock.Object.SetFalse();
}
catch
{
mock.Object.SetFalse();
}
mock.Verify();
However, one caveat is that this version only checks whether the SetFalse method was called at all.
If you want to verify that it was called twice, you can change the last statement to this:
mock.Verify(m => m.SetFalse(), Times.Exactly(2));
However, this slightly violates the DRY principle because you would be stating the same Setup twice, but you could get around that by first declaring and defining a variable of type Expression<Action<Mockee>> and use it for both the Setup and the Verify methods...