It is suggested that IDisposable objects should be disposed in either using statement or by calling Dispose() method. I find it is not intuitive to find out if an object is disposable in Visual Studio.
My question is: is there any way to recognize IDisposable objects in VS?
If you want to highlight disposable objects differently in VS please check out this post. I personally prefer Resharper answer as I always use R#.
If you just want to figure out if your object is an instance of some interface you can right-button-click on the variable name and Navigate -> Object Browser or Go to Declaration and then right-button-click on class name Go to Definition/Peek Definition.
You might like Peek Definition as it shows everything you need inline:
You can always check what methods object has, if it has Dispose() method then 99.9% it's a disposable object. I'll give this 0.01% for those who give methods bad names :).
I'm surprised that no-one else has mentioned this yet. If your edition of Visual Studio supports it, I'd suggest turning on Code Analysis for Build.
Once that's done, pick whatever rule sets you like so long as they ensure that, at the least, CA2000 (Dispose objects before losing scope), CA2213 (Disposable fields should be disposed) and CA2202 (Do not dispose objects multiple times) rules are covered. That way, the compiler should shout at you if you're not dealing with disposable objects correctly.
(Although note that getting the compiler to not flag some usage of disposable objects can then turn into the bigger challenge, as many StackOverflow questions can attest)
You can use Object Browser to view class inheritance hierarchy with implemented interfaces
For the sake of completeness, if you don't ask how to check it in your code but you just want to know where you can look if the type implements an interface like IDisposable, you can always look at MSDN.
For example FileStream
This type implements the
IDisposableinterface. When you have finished using the type, you should dispose of it either directly or indirectly. To dispose of the type directly, call its Dispose method in a try/catch block. To dispose of it indirectly, use a language construct such as using (in C#) or Using (in Visual Basic). For more information, see the “Using an Object that Implements IDisposable” section in the IDisposable interface topic.
or search for the Dispose method. There you can see if this class or any parent class implements IDispable. In this case it is inherited from Stream which implements that interface which is mentioned at the class syntax and in the remarks section.
public abstract class Stream : MarshalByRefObject, IDisposable
If you want to know how to find implementations of an interface in Visual Studio, here is already a question that answers that:
A way to see what interfaces a class implements, along with all of it's publicly exposed fields, properties, methods etc. is to go to that class in the code. For example:
Image image = Image.FromFile(path);
Make sure you click on the class, not the instance and press F12. This will take you to a metadata file for that class. For example: the Image.cs file has the following above class declaration:
public abstract class Image : MarshalByRefObject, ISerializable, ICloneable, IDisposable
You can then also use F12 to click through to other classes. Note that these classes are usually shown up in the Light Blue colour in Visual Studio:
You can also get to this meta data file by right clicking on the class and selecting "Go To Definition" from the drop down list.
Though not ideal you can also go to an instance of the class and put a . on the end. This should bring up the intellisense and you will be able to see Dispsose() in the list if the item implements the interface.
You could also just write myInstance.Dispose(); or using (myInstance = new MyClass()) {} and if it compiles the class implements the interface else it doesn't.
As a (silly?) alternative to shelling out for Resharper and its ilk, Visual Studio does have the concept of External Tools (in the Tools menu), which you could (ab)use to do something like:
Is Disposa&bleC:\Windows\System32\WindowsPowerShell\v1.0\powershell.exe-Command "&{$i=[Type]::GetType('System.IDisposable');[AppDomain]::CurrentDomain.GetAssemblies()|%{ $_.GetTypes()}|?{$_.FullName.EndsWith('.$(CurText)')}|%{New-Object PSObject -Property @{'Type'=$_;'IDisposable'=$i.IsAssignableFrom($_)}}|ft}"This would read whatever string you had selected in the editor, search for .NET types with that string as a name and show a True/False as to whether that string implemented IDisposable.
The Powershell command in the tool is just the quickest approach I could do to demonstrate the possibility, but it is far from perfect -- it only finds types in assemblies that Powershell loads by default. If you wanted to expand on the idea, you could build a command-line .NET app that loaded your project and scanned all the assemblies that your project loaded.
If you highlighted the word Stream in your code, for example, and ran your external tool (ALT+T,ALT+B in the example), it would return:
Type IDisposable ---- ----------- System.IO.Stream True
To break down the Powershell command:
&{ $i=[Type]::GetType('System.IDisposable'); # Get the IDisposable interface
[AppDomain]::CurrentDomain.GetAssemblies() ` # Get all loaded assemblies
| %{ $_.GetTypes() } ` # For each assembly, get all types
| ?{ $_.FullName.EndsWith('.$(CurText)') } ` # Filter types that are named $(CurText) - $(CurText) is a macro within VS External Tools
| %{ New-Object PSObject -Property @{ # For each type, return an object containing...
'Type' = $_; # ...the type name...
'IDisposable' = $i.IsAssignableFrom($_) # ...and whether the IDisposable interface is implemented
} } `
| ft } # Format all returned objects as a table
Easiest way to find out this is by using memory warning in Code Analysis.
Enable Code Analysis to "Run on build" on project properties.
Look for following warnings after build
A local object of an IDisposable type is created, but the object is not disposed before all references to the object are out of scope.
A type that implements System.IDisposable declares fields that are of types that also implement IDisposable. The Dispose method of the field is not called by the Dispose method of the declaring type.
either using or in Dispose() method Use the using construct when you can. Here's why. Using this MSDN example, here are two equivalent blocks of code. This one with using:
using (Font font1 = new Font("Arial", 10.0f))
{
byte charset = font1.GdiCharSet;
}
This one without using:
{
Font font1 = new Font("Arial", 10.0f);
try
{
byte charset = font1.GdiCharSet;
}
finally
{
if (font1 != null)
((IDisposable)font1).Dispose();
}
}
Each part of the second block is there for a reason: the curly braces, the try-finally, the null check, and the cast to IDisposable. No one should be expected to remember this. That's why the using construct exists.
Something clean that can be done in C#7
class Foo : IDisposable {
string _bar = "init";
void Fooy() { _bar = "fooy"; }
public void Dispose() {
_bar = null;
}
static void Main()
{
var v = new Foo();
Console.WriteLine(v._bar);
if(v is IDisposable id) using(id)
v.Fooy();
else
v.Fooy();
Console.WriteLine(v._bar ?? "null");;
}
}
Fooy could be some virtual or abstract function. Some base classes may implement IDisposable while others not. Try running the above code. The console will print different text depending whether or not IDisposable has been implemented
