Techie Talks

Tuesday, July 25, 2006

Mapping a business object onto a Windows Forms DataGridViewComboBoxCell

Well, after about two weeks of fighting to solve this issue, I found a solution today.

Issue: Mapping a business object onto a Windows Forms DataGridViewComboBoxCell.

The crux of the issue arises from the fact that a DataGridViewComboBoxCell doesn't have a SelectedItem property.

Solution: Got it from here.

Overview: Add a proprety to the business object that refers to itself, and map it to the DataGridViewComboBoxCell's Value property.


public class Dimension


    public Dimension Self
    { return this; }



Thursday, July 06, 2006

Using a router as a switch

In order to use a router to be used as a switch, do the following:

1) Disable DHCP in the router
2) Connect the connection to be swtiched to one of the output ports of the router.
3) Set a static IP for the router
4) Connect the devices receiving the switched connection to one of the remaining output ports

This way, the number of switced ports available would be total number of router output ports - 1.
(The WAN port of the router will be dumb, unused).

1. Make use of one of the "lying around" router as a switch.

1. Routers are costlier than switch. So, next time a router is needed, make sure you buy a switch instead and pull the router off this make-shift arrangement and use it.

Monday, July 03, 2006

Suggestion: Encapsulate-only field

How about a way of ensuring that a programmer uses only a property encapsulating a variable as opposed to directly acessing a variable?


// The property-only descriptor is the desired feature.
// The variable must be readable only in a fixed descriptor (MyInt)
// mentioned within the angle brackets.
private property-only<MyInt> int myInt;
public int MyInt
get { return myInt; } //OK to access the variable inside the descriptor
set { myInt = value; }

public int SecondAccessor
get { return myInt; } //Compiler must issue an error.

private void foo()
this.myInt = 10; //Compiler must issue an error
this.MyInt = 10; //OK

This way, it is ensured during compile time itself that no direct access to a particular variable within the code (except in the predetermined property) is allowed. This will be helpful

1) In cases in where reference variables are lazy initialized.
(eg: in get of MyRef property, if(myRef == null) myRef = new Ref(); return myRef;).

2) Moreover, ensures that the variables are initialized properly.

3) Also, it ensures access-time checking of variables - for bounds, value ranges, value legality etc.

4) Any "side-effect" code within the accessors are fired, for sure.

(Of course, for 2 and 3 the initialization/validation must be coded inside appropriate acessors. This method ensures that they are fired each time the local variable needs to be accessed, by protecting accidental access to local variable instead of the accessor.)


The current way of handling this issue is to name the private variable starting with an underscore ( _ ).

private int _myInt;
public int MyInt
get { return _myInt; }
set { _myInt = value; }

This does prevent ease of the local variable access to a great extent within the code. Yet, it doesn't warrant prevention against accidental access. However, since most of the errors would be happening while using autocomplete, I guess the underscore strategy would be good enough.

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