Tag: .NET

Posted on

SupressFinalize in IDisposable interface

  • informs GC that object does not need to be added to finalizer queue
  • finalizer execution is not deterministic and objects can live for long time in queue – this is optimization technique
  • to make sure that object disposes of any unamanaged resources even if Dispose will be not called we need to implement finalizer

Basically finalizer execution time is not deterministic. We cannot predict when this will be called and till that time – object is existing and still taking memory space. Since we are controlling creation and disposal of those resources we can say to GC: ‘Do not worry about that! It already had been taken care of!’. So this way object will be destroyed sooner, leaving this space to be used by something else possibly.

The Dispose() method must call Dispose(true) and should suppress finalization for performance.

MSDN


Further read:

https://learn.microsoft.com/en-us/dotnet/api/system.idisposable?view=net-6.0

Posted on

IDisposable interface pattern

Example implementation of IDisposable

public class MyResource : IDisposable
{
    public MyResource(IntPtr handle)
    {
        this.handle = handle;
    }

    public void Dispose()
    {
        Dispose(disposing: true);
        GC.SuppressFinalize(this);
    }

    protected virtual void Dispose(bool disposing)
    {
        if(!this.disposed)
        {
            if(disposing)
            {
                component.Dispose();
            }
           
            CloseHandle(handle);
            handle = IntPtr.Zero;
            disposed = true;
        }
    }

    ~MyResource()
    {
        Dispose(disposing: false);
    }
}

MyResource object have pointer which is unmanaged. This is why this class should implement IDisposable interface. Implementation should be correct according to recommended pattern (see below for documentation).

There a re few points to highlight here:

  • IDisposable is meant to be used with using keyword.
  • using is calling IDisposable.Dispose method in the background
  • This method should be public then
  • protected Dispose(bool) method is meant to be called from finalizer via GC
  • SuppressFinalize disables this object from finalization mechanism in GC to prevent finalization code to be executed second time (see here)
  • Finalization is called from GC *only* if whoever is using this object will forget to use using or otherwise fail to call Dispose manually
  • Dispose must be save to call multiple times (if(!this.disposed))
  • Dispose(true) is meant to dispose also any other managed resources this implementation relies on
  • Dispose(false) is meant to be called from GC finalization mechanism. All managed resource are most likely already disposed so we cannot dispose them again

Further read:

https://learn.microsoft.com/en-us/dotnet/api/system.idisposable?view=net-6.0

Posted on

Automatic scrolling to edited text box in Xamarin Android.

Important note: this should work well with newer version of Xamarin (2.3.3). If you cannot update for some reason this article will explain workaround.

Introduction

In previous article I explained how to detect show and hide events of software keyboard in Xamarin Android. I did it in my project because of the fact that some of text boxes was hidden by software keyboard that suppose to edit contents of those text boxes. In this article I will explain how to work around this issue in some older versions of Xamarin. Continue reading “Automatic scrolling to edited text box in Xamarin Android.”