psuedo deferred base constructor call from a derived class (C# .NET)

wigunara — Tue, 02 Jan 2007 21:05:00 GMT

I was building an exception class derived from the Exception class when I stumbled upon a problem - I wanted to perform some processing on the constructor parameters of my derived class before passing the results onto the base constructor for the exception - in the case of Exception, a string parameter for a message.

It appears the base constructor must be called before any derived constructor, which precludes performing any complex work before passing any parameters to the base class constructor.

public class DerivedClass : Exception

{
public DerivedClass(string rawData) : base(rawData) {

// this is executed after the base constructor

}

However, you can work around this by performing any processing work in a static method which you can call within the call to the base constructor

public class DerivedClass : Exception

{

public DerivedClass(string rawData) : base(DerivedClass.ProcessData(rawData)) {

// this is executed after the base constructor

}

private static string ProcessData(string rawData)

{

// this will be executed before the base constructor is called

// do stuff with the rawData and return processed data

return(processedData);

}

Obviously you're working with a static method rather than an instance method so you cannot access instance data, but if you can live with this limitation then it's quite a useful technique.

TechEd follow up...

wigunara — Wed, 08 Nov 2006 20:16:00 GMT

Thanks to all those who attended my sessions at TechEd. As promised in my SQL Mobile session here is the source for a very simpler timer class to help you monitor performance.

using System;

using System.Collections.Generic;

using System.Windows.Forms;

using System.Runtime.InteropServices;

namespace Timer

{

public class TestTimer

{

[DllImport("CoreDll.dll")]

public static extern int QueryPerformanceFrequency

(

ref Int64 lpFrequency

);

[DllImport("CoreDll.dll")]

public static extern int QueryPerformanceCounter

(

ref Int64 lpPerformanceCount

);

System.Int64 freq = 0;

public TestTimer()

{

QueryPerformanceFrequency(ref freq);

}

public delegate void timerResult(string msg,System.Int64 time);

public event timerResult OnTimerResult;

private System.Int64 _startTime = 0 ;

private System.Int64 _lastReading = 0;

public bool TimerSupported

{

get

{

bool result = true;

if (QueryPerformanceFrequency(ref freq) == 0)

result = false;

System.Int64 testCounter = 0;

if (QueryPerformanceCounter(ref testCounter) == 0)

result = false;

return (result);

}

public void Start()

{

QueryPerformanceCounter(ref _startTime);

_lastReading = _startTime;

}

public void TakeReading(string msg)

{

System.Int64 _takeReading = 0;

QueryPerformanceCounter(ref _takeReading);

System.Int64 time_ms = (_takeReading - _lastReading) * 1000 / freq;

_lastReading = _takeReading;

if (OnTimerResult!=null)

OnTimerResult(msg,time_ms);

}

public void TotalTime(string msg)

{

_lastReading = _startTime;

TakeReading(msg);

}

William Gunaratne's Blog : Sample Code

psuedo deferred base constructor call from a derived class (C# .NET)

TechEd follow up...