I have a simple WPF single window application contains Textboxes and Buttons. And I also use NotifyIcon and DateTimePicker of Windows Forms in WPF window. How can I effectively dispose all the controls?
Hardly anything in WPF has a Dispose method. The vast majority of classes encapsulate purely managed information. You can attach an object into the tree (e.g. via a Children.Add method) and you can remove it again - that's how the state management works. It exactly doesn't fit into the IDisposable pattern, because once you've removed a control you can add it again, whereas Dispose means forever (although you could use Dispose to manage it in addition to Add/Remove methods).
A discussion about it on the Microsoft forums.
There are a few things that ought to be IDisposable but aren't, like DispatcherTimer, and there's nothing to stop you from implementing IDisposable on your own classes. It's up to you when to call Dispose; basically when you know you aren't going to be using the object any more.
For a Window you just call Close to close it, and WPF takes care of everything else.
I would say that the same rule applies in WPF applications as in any other .NET applications: if an object implements IDisposable, you should call Dispose when you are done using it. If you dynamically load and unload controls, and they do not implement IDisposable, just setting any references to null (and detaching any event handlers) should be enough for the garbage collector to do its job.
Adhere to CA1001: Let the owning type implement IDisposable.
Renounce the old Windows Forms truth that all controls are IDisposable. Implement and call Dispose yourselves.
sealed partial class MainWindow : IDisposable {
readonly IDisposable disposable;
public MainWindow() {
disposable = ...
}
public void Dispose() {
disposable.Dispose();
}
protected override void OnClosed(EventArgs e) {
Dispose();
base.OnClosed(e);
}
}
If that control is a part of some IContainer (that's the common model in .NET) than your controls just needs implementation of IDisposable. Thus Dispose() will be called automatically when it is appropriate time.
Related
Hey so I have a base class coming from a 3rd party dll, which is dependent on a disposable. Context: IDisposable
public class BaseValidator
{
public BaseValidator(Context context) {}
}
We're trying to move away from tying our classes to these dependencies. So we started relying on providers instead
public interface IContextProvider
{
Context Create();
}
I have a new validator that I'm writing which inherits from the BaseValidator, but I would like it to be dependent on the IContextProvider instead. So I'd like to create the context in the inherited constructor, but I would like to dispose of it in the destructor to prevent memory leaks, However I'm not sure if this is possible.
public class EntityValidator: BaseValidator
{
public EntityValidator(IContextProvider provider) : base(provider.Create())
{
}
~EntityValidator()
{
//I'm not how I can dispose the entity I've passed into it.
}
}
My question is, is there a trick I can use to Capture the variable passed into the base?
Note: I know I can make a work around with an external helper class, but I'm interested if anyone knows how to do this in a more savvy way.
If the BaseValidator class does not expose Context in a public manner, your current design would require you use reflection and knowledge of the internal implementation of BaseValidator to dispose of it, which is of course fragile.
I would instead capture the context using an intermediate constructor:
Context _context;
private EntityValidator(Context context) : base(context)
{
_context = context;
}
public EntityValidator(IContextProvider provider) : this(provider.Create())
{
}
Note, disposing via a finalizer (a.k.a. destructor) is not ideal due to constraints it places on the garbage collector. I'd instead have EntityValidator implement IDisposable
Before, in other language like C++, developpers used to rely on destructors to do a lot of cleaning. It was guaranteed by compiler so it was a strong behavior.
Smart pointer was a good pattern that used this behavior (to implement something like very basic but automatic garbage collection system).
Code was elegant but people used it for a lot of other need. With time a lot of code used to happen in destructor making the debug and readability hard.
IDisposable has been made to force developpers to write explicitely the call to Dispose... This is also useful when you want to Dispose internal resource without your object being destructed. For example in some "Close" method of Stream, where the stream is definitively closed but you can still have reference on steam... and use IsOpen property...
So for me you should not try to hide it. If you depends on code that needs to be Disposed, embrace this dependency... or chose another third party library.
You can simply make the class that need to manipulate Disposable object (BaseValidator) IDisposable too and delegate the need to call to the user.
Usually people that write class implementing IDisposable, in open source project, also write destructor (just in case someone forgot to call Dispose) This is true for a lot of class of .Net framework too (for example Pen() { where nobody thinks to call Dispose on it in some Control drawing events...)
So I would recommend :
Go get the information about if they did it with their classes, if yes they are strong probability they will keep this behavior/code forever. So you can just make your class to inherit IDisposable too, call context.Dispose in your own Dispose implement and that's enough... no need to worry because if your user forgot to call Dispose, the third party do the cleaning. Add a destructor/finalizer on your class only if you have other unmanaged resource to clean too...
Now if they did not, you can just wrap third party "Context" class in your own Context class. Your Context class will have to implement destructor that call Dispose on the instance of third party Context class. And that's it. You can even make your Context class sealed. Your Context class is here to make the behavior of your app as close as if 1) was true and implemented by third party. So this class will be easy to remove later because third party will probably implement finalizer one day (if they are serious). Doing just a sealed wrapper around just one class will avoid some complexity/issue related to how destructors (finallizers) works in .Net : They are all called in any order. Because of this underterministic behavior it makes your code hard to maintain later. For example if third party Context class's finalizer is called before your wrapping class => exception can occured and at a bad time (when gc is doing its stuff) which can make your app crash. Because of all these problems, you better go back to 1)
in my WPF application code i got the following Warnings:
CA1001 Types that own disposable fields should be disposable Implement
IDisposable on 'MainWindow' because it creates members of the
following IDisposable types: 'BackgroundWorker', 'DataTable'. If
'MainWindow' has previously shipped, adding new members that implement
IDisposable to this type is considered a breaking change to existing
consumers. yesMonitor MainWindow.xaml.cs 38
for code of main window:
public partial class MainWindow : Window
{
// Some code..
}
what should be the reason for these warning?
It is safe to ignore this warning.
Both Backgroundworker and DataTable implement IDisposable for formal reasons, they don't really need it.
Besides, your MainWindow has (defines) the lifetime of the application so there is no resource leakage anyway.
If you want to be formally correct and stick to all the rules, then just add IDisposable to your MainWindow class. There is a snippet for that.
This is not a as simple a question as it looks, due to MainWindow being a class that has special meaning in a WPF application.
I think you are confusing yourself here. MainWindow is just another class. It just so happens that it gets opened when the application starts. However this is default behavior, it can be changed.
Look in the App.xaml file, and you'll see the StartupUri property set to MainWindow, you can change this if you want.
There isn't anything special about MainWindow, it isn't some kind of super-important built-in holy messiah that WPF needs, heck, you can even delete it if you want. As it's just another class, it should follow the same principles as any other class. In your case, you are creating instances of classes which implement IDisposable, therefore, it is good practice to implement IDisposable in your class to dispose your instances too. Otherwise, the garbage collector might ignore them and you may find you will have memory leaks. See the message below:
Types that own disposable fields should be disposable Implement IDisposable on 'MainWindow' because it creates members of the following IDisposable types...
I am no expert in IDisposable principles and architecture, but you should implement this where it's needed.
See the documentation on guidance of how to implement IDisposable properly.
You need to implement IDisposable on MainWindow. Actually you have some resources in MainWindow class which needs to be closed. They are not closed when MainWindow will be destroyed. To achieve this, we implement IDisposable and in the implementation we dispose these objects.
https://msdn.microsoft.com/library/ms182172.aspx
In your case,
public partial class MainWindow : Window, IDisposable
{
public void Dispose()
{
Dispose(true);
GC.SuppressFinalize(this);
}
protected virtual void Dispose(bool disposing)
{
if (disposing)
{
// dispose managed resources
if (BackgroundWorker != null)
{
BackgroundWorker.Dispose(); or BackgroundWorker.Close();
BackgroundWorker = null;
}
// Dispose remaining objects,
}
}
}
As has already been read by others, in real life this is not likely to be an issue, as:
Most likely the application is just about to exit once MainWindow is not in use.
The two given classes don’t really need Dispose() calling on them, if they have a USEFULL lifetime that is the same as the application.
If MainWindow is not being used with the default wpf behaviour, it should be renamed to make it clear that it is not. Then lifetime issues can be considered depending on how it is used.
Doing unneeded cleaning while an application is existing is not helpful to the user, as it slows down the exit and may needlessly page in many pages of memory.
As MainWindow is a subclass of System.Windows.Window a case could be made for doing the cleanup in the Closed event/method instead of Dispose(), but that will most likely not stop the warning unless you called Dispose() from OnClosed().
Just making MainWindow implement IDisposable would make the warning go away, but you then need to ask how will Dispose() get called on the MainWindow?
However if you wish to make the code analytics a part of your day to day development, you must stop false positives, as otherwise you will not notice the important warning. If so the path of lease resistance is to implement IDisposable on MainWindow.
I am refactoring a program right now. Trying to prevent memory leaks I was looking for objects to enclose in using blocks when I found a TaskDefinition object (class found in Microsoft.Win32.TaskScheduler) that Dispose was not called on. When I tried to enclose it VisualStudio told me that this class does not implement IDisosable. Looking at the class this is certainly true:
namespace Microsoft.Win32.TaskScheduler
{
// Summary:
// Defines all the components of a task, such as the task settings, triggers,
// actions, and registration information.
public sealed class TaskDefinition
{
...
// Summary:
// Releases all resources used by this class.
public void Dispose();
}
}
So why would you implement a Dispose method but not implement the IDisposable interface? Are there any drawbacks from implementing the interface?
Thank you for helping me to understand this.
From the comments:
According to this page, this is a bug that's fixed in newer versions of the assembly.
An additional note, however: the documentation for IDisposable.Dispose explicitly requires implementations to support calling Dispose multiple times, so a valid reason in other cases could be that the class does not support that. In that case, pretending to implement IDisposable but not meeting its requirements would be worse than not implementing it.
I have a site which uses a C# class file, and at the top of the file, I have:
JTSEntities database = new JTSEntities(); (an ADO.NET thingy).
I have it right up the top because I don't really feel like writing the same thing over and over again.
But it raises one question... Because it's up the top there, how will it get disposed, and when - and how can I dispose of it (or do I need to) when the user closes the page?
It is bad practice to hold on to anything that wraps a database connection for longer than needed.
The best practice would be to release the database connection as soon as it is no longer needed for the current operation (such as populating initial values, etc.), e.g. something like
using (JTSEntities database = new JTSEntities())
{
// Use database
}
if it implements IDisposable.
If for some reason you must keep it alive for the duration of the page, be sure you call an appropriate method to release resources (.Close(), .Dispose(), etc.) in the page close event handler.
Ok so, based on the type of the attribute, we can say that it's an instance attribute. This means that this attribute will have the same lifecyle as the object that has it, unless its instance is passed to another object.
If it's protected, then only the owner object and its childs (that is, objects that inherit from this class) will have access to it. If you don't pass it as a reference argument, then we're ok with the first statement: it will be cleaned by the GC as soon as the object is cleaned.
If you just use this object on a regular webform page lifecycle, then you don't have to worry with disposing it. The page lifecycle will do it for you.
Regards
Implement IDisposable in this class and dispose of this object inside the Dispose() method. When using this class, make sure you call Dispose when you are done (preferably with a using block)
Beyond that, you don't need to worry about it.
public class MyClass : IDisposable
{
protected JTSEntities database = new JTSEntities();
public void Dispose()
{
database.Dispose();
}
}
// When calling this class
using(MyClass cls = new MyClass())
{
// Do Stuff
} // Dispose is automatically called here.
I am working with Active Directory using C#. Instantiating the PrincipalContext object seems to be expensive, so I'd like to store one in a class variable.
When using PrincipalContext as a local variable, I can use the convenient using syntax. When storing an IDisposable object in a static variable, how do I ensure the object is properly disposed of?
The general pattern for this is to implement the IDisposable interface on your class. Take this example:
public class YourClass : IDisposable
{
private OtherDisposableType yourResource;
public YourClass()
{
yourResource = new OtherDisposableType();
}
public void Dispose()
{
yourResource.Dispose();
}
}
This is, at a minimum, what you need to do.
EDIT
My previous version advocated following the finalizer pattern in all cases, which was (correctly) pointed out to be against the framework design guidelines. However, in the event that you're actually dealing with unmanaged resources (for example, you're making direct P/Invoke calls and obtaining a handle that needs to be explicitly freed) it's advisable that you create a finalizer and call Dispose within it to protect against people who consume your code and don't call Dispose:
public class YourClass : IDisposable
{
private OtherDisposableType yourResource;
public YourClass()
{
yourResource = new OtherDisposableType();
}
public void Dispose()
{
yourResource.Dispose();
GC.SuppressFinalize(this);
}
~YourClass()
{
Dispose();
}
}
Look at what the System.ComponentModel namespace does. Basically, the pattern I typically use is to have a collection of subcomponents, which includes everything I own that's not a 'value' - whether or not it implements IDisposable.
Then, when I Dispose() myself, I iterate over this collection and Dispose anything that implements IDisposable.
One advantage of this technique is that if an object I own starts out not being Disposable, but later adds the IDisposable interface, my class will do the right thing without ever having to change.
Also, use of a DI/IoC container can handle much of this for you.
So basically you want to cache an expensive resource. That's a good thing.
Global data (static variables in this case) is not such a good thing, IMHO. Instead, why not make it an instance variable and control the lifetime?
Write your class that handles the AD responsibilities, have it create and use the PrincipalContext, and make it IDisposable as well (using the Dispose Pattern). Extract an interface from it to decouple it and make classes that use it easier to test.
Classes that want to use AD services will take a constructor parameter of your new interface (Dependency Injection or DI). You can either create your class manually in a using block and pass it to the classes or use a DI Container Framework. You can have the framework set the lifetime of the AD object to the lifetime of the container (which may also be IDisposable). See How do you reconcile IDisposable and IoC? and your DI Container documentation for more on this.