System.IO for saving a collection - Xtreme Visual Basic Talk

02-05-2008, 11:09 AM

XL Jedi

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System.IO for saving a collection

I'd like to create a routine that would allow me to save/load a collection to a file. I'd like it to (preferrably) not just be a text file. Is there any simple binary file IO code around?

Any suggestions would be appreciated.

02-05-2008, 12:16 PM

AtmaWeapon

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It depends on what you mean by "a collection". If it's a built-in .NET collection, check the documentation and see if it is marked with SerializableAttribute. If not, see if it implements ISerializable. If so, then binary serialization will work without any additional work. Most collection classes in the .NET Framework are marked with the attribute, but I have not verified if all of them are.

If it's a collection you created yourself, you'll have to either mark your class with SerializableAttribute or implement ISerializable (don't forget the special constructor!).

Once your collection class is serializable, look at this thread for a bare-bones example of serialization.

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02-05-2008, 12:33 PM

XL Jedi

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It's my own collection...

I have a custom class of waypoints (stored in a collection) that I need to save and then load to allow users to store and retrieve plots they've created. If it were just a matter of saving coordinates it would be simple, but the waypoints have a lot of extra properties that I don't want to have to write individually.

02-07-2008, 10:18 AM

XL Jedi

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For those who might be interested, saving a collection (or list) of a custom class turned out to be painfully easy!

Thanks to AtmaWeapon for a push in the right direction (by giving me the "Serializable" keyword to research.)

In my case I have a plotting application that saves graphic objects as custom "Unit" classes. The instances of the unit class are stored in a collection (although a list could also be used) called "units".

A simplified example of my custom class now looks like this:

Code:

<Serializable()> _
Public Class Cls_Unit

    <NonSerialized()> _
    Public MyPath As GraphicsPath
    Public Name As String = Nothing
    Public Type As String = Nothing
    Public ObjtName As String = Nothing
    Public Selected As Boolean = False

End Class

Notice above I had to configure my class for serialization by adding the Serializable attribute. Also worth noting, if you have a property in your custom class that is typed as another custom class, that child class also has to be marked as Serializable. If you fail to configure any related objects as Serializable, you'll get a SerializationException error at runtime. And it will point out to you specifically which objects are not properly marked.

In my case above I was getting an error on the GraphicsPath object. Since I generate that path with a draw method anyway, it wasn't necessary to save it, so I just marked that object "NonSerialized" and the BinaryFormatter now has no issues with it.

Now in my app, as I plot a new unit, the unit is stored in a collection called "units". The collection of units is what defines the resulting graphic plot.

To save the plot as a binary file the code is really very simple:

Code:

Imports System.Runtime.Serialization.Formatters.Binary
Imports System.IO

Sub Write_BinFile()
        Dim binFormat As BinaryFormatter = New BinaryFormatter()
        Dim fStream As Stream = New FileStream("SaveData.dat", FileMode.Create, FileAccess.Write, FileShare.None)
        binFormat.Serialize(fStream, Units)
        fStream.Close()
    End Sub

Then to re-load my Units collection from the saved bin file:

Code:

Sub Read_BinFile()
        Dim fstream As Stream = File.OpenRead("SaveData.dat")
        Dim binFormat As BinaryFormatter = New BinaryFormatter()
        Units = binFormat.Deserialize(fstream)
        fstream.Close()
    End Sub

I have to admit, I was actually a little dumbfounded to learn how simple a task this turned out to be!