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Usefull .NET 2.0 Features

~ chriseyre2000 ~ Leave a comment

I am studying C# 2.0 to get myself upto speed with .NET 2.0
I am reading “A Programmers Introduction to C# 2.0 – Apress”

There is a great new class in .NET 2:

System.Security.SecureString

 
This provides a  mutable string that is encrypted in memory.
This is ideal for passwords &c that need to be hidden for prying debuggers.

More C# Oddities

~ chriseyre2000 ~ Leave a comment

As a Delphi Developer learning C# there are a few very odd things to deal with:

  • The  final  line of a method  must be terminated  with a  ;
  • Why  does a  switch  statement require  a  break at  every stage?  There presence is enforced by the compiler – why bother?
  • Why can’t you call a class method on an instance?
  • Where are the meta classes?

Useful delphi TStream descendants

~ chriseyre2000 ~ Leave a comment

Delphi has a number of very useful stream classes.

They all derive from TStream.

The basic version is TFileStream – this writes to a filesystem.

There is also THandleStream – this writes to a windows handle – useful if you need to keep a file locked then write to it.

TStringStream is useful when dealing with delphi strings – especially when writing to another stream.

TBlobStream is used for accessing blob data from a database.

TResourceStream is used to read from embedded resources.

TMemoryStream that acts upon blocks of memory. 

There are also the adapter streams that takes another stream as a parameter.

 There is the TIStream that acts as a bridge between TStreams and the IStreams interface.

These include ZipStreams, EncryptionStreams, SocketStreams &c

These all take the approach that everything looks like a file this massively simplifys code.

 

Storing jpegs in databases

~ chriseyre2000 ~ Leave a comment

I know that storing images in a database is oftern a bad idea.
However there can come requirements that force things on you.

For the database end I have used an IMAGE datatype in SQL Server.

The delphi approach is as follows:

You need to use GraphicEx to allow display in the normal controls.
All this requires is adding the GraphicEx unit to the end of your uses clause.

procedure LoadJPEGImageFromStream(const aImage: TImage;
  const stream: TStream);
var
  aJPEG : TJpegImage;
begin
    aJPEG := TJPEGImage.Create;
    try
      aJPEG.LoadFromStream(stream);
      aImage.Picture.Assign(aJPEG);
    finally
      aJPEG.Free;
    end;
end;

 

procedure LoadFromDB(Image : TImage; aField : TBlobField)
var
  aBLOBStream : TStream;
begin
  ado.Open;
  ado.First;

  aBLOBStream := adoFAX.CreateBlobStream(aField,bmRead);
  try
    LoadJPEGImageFromStream(Image, aBLOBStream );
  finally
    aBLOBStream.free;
  end;

end;
 

procedure SaveToDB(const filename : string)
var
  FS : TFileStream;
begin
  FS := TFileStream.Create(filename, fmOpenRead);
  try
    ado.open;
    ado.Insert;
    adoIMAGE.LoadFromStream(FS);
    ado.Post;
  finally
    FS.Free;
  end;
end;
 

Just to check that this is not a Delphi-only format I wrote the following test from C#:

            sqlDataAdapter1.Fill(dataSet11, “DB”);
            // How to get an image from a database in .NET                   
            pictureBox1.Image = new Bitmap( new MemoryStream( dataSet11.DB[0].IMAGE ) );
            pictureBox1.Height = pictureBox1.Image.Height;
            pictureBox1.Width = pictureBox1.Image.Width;
 

This loads the image previously stored by a Delphi app.

This ensures that the image format used is language neutral.