How to LINQ a List<T>

prashantpatole

I am new to .Net 3x, and trying out few things in LINQ, I was trying to implement 'Command' pattern in .Net 3 for the said purpose. But i am stuck with how to use LINQ to search through List (a List of interfaceed object) Here is the code

//main control pannel class
class RemoteControl
{
List <iCommand> cmds = new List<iCommand>(); //I know this can be simple if i use simple [] array but only to chekout LINQ feature with collections.....

    Fan f = new Fan("main fan");
    Fan ef = new Fan("exaust fan");
    Light l = new Light("Hall");
    Light lD = new Light("Disco");
    MusicSystem ms = new MusicSystem("Disk");


    public RemoteControl()
    {
        cmds.Add(new FanOnCommand(f,1));
        cmds.Add(new FanOffCommand(f,2));
        //cmds.Add(new FanIncreeseCommand(f,3));
        //cmds.Add(new FanDeccreeseCommand(f,4));
        for (int i = 2; i <= 10; i++)
        {
            cmds.Add(new NoCommand(new NoDevice(),i+1));
        }
    }

    public string PressKey(int KeyNum)
    {
        if (1 < KeyNum && KeyNum < 11)
        {

            return (
                from cmd in cmds
                where cmd.KeyNum = KeyNum  ///PROBLEM AREA
                select cmd
                ).execute();
            
        }
        else
        {
            return "invalid button";
        }

    }

}

//commands code

public interface iCommand 
{
    int getKeyNum();
    string execute();
}



#region "Light Commands"
class  LightOnCommand 
    : iCommand
   {
    Light \_light;
    public int \_keyNum;

    public LightOnCommand(Light light, int keyNumber)
    {
        \_keyNum = keyNumber;
        \_light = light;
    }

     public string execute()
    {
        return \_light.LightOn();
    }

    public int getKeyNum()
    {
        return \_keyNum;
    }
}

class LightOffCommand : iCommand
{

    Light \_light;
    public int \_keyNum;

    public LightOffCommand(Light light, int keyNumber)
    {
        \_keyNum = keyNumber;
        \_light = light;
    }

      public string execute()
    {
        return \_light.LightOff();
    }
    public int getKeyNum()

Dan Mos

Hy, You need to expose it as a Property => the KeyNum. I see that you have a Java background or something cause you are not using properties but functions. Insted of

public int getKeyNum()
{
return _keyNum;
}

//use

public int KeyNum{
get{return _keyNum;} //or something like that
}

That is a general ideea/remark not just for this one. also I noticed :

where cmd.KeyNum = KeyNum //PROBLEM AREA
//sould be
where cmd.KeyNum == KeyNum//but this could just as well be a typo

Just some random remarks cause your question is not very clear at least for me. :)

Just an irritated, ranting son of ... an IT guy. At your trolling services

prashantpatole

oops.. i guess it must be "==" The problem area is indicated, only to help people get started from a point. thanks a lot buddy, i ll try that out u sure if it is possible to access tht property even if the "cmd" object is an instance of an interface "iCommand"?.

Dan Mos

Yes. It will work. As long as you have it in the interface too. That is make the interface expose the property instead of the method/function.

Just an irritated, ranting son of ... an IT guy. At your trolling services

prashantpatole

thanks a lot for your suggesstion dear.. i really helped but as i was scared same thing happened. i think some TYpe Casting is needed here i got this error at very next line on "}.execute()" Error 1 'System.Collections.Generic.IEnumerable<MyFirstWPF.Model.iCommand>' does not contain a definition for 'execute' and no extension method 'execute' accepting a first argument of type 'System.Collections.Generic.IEnumerable<MyFirstWPF.Model.iCommand>' could be found (are you missing a using directive or an assembly reference?) C:\Users\Shubee--V\Documents\Visual Studio 2008\Projects\MyFirstWPF\MyFirstWPF\Model\RemoteControl.cs 41 22 MyFirstWPF

return (
from cmd in cmds
where cmd.KeyNum = KeyNum
select cmd
).execute();

J4amieC

return (
from cmd in cmds
where cmd.KeyNum = KeyNum
select cmd
).First().execute();

prashantpatole

yaa... got it but some other way

return (
from cmd in cmds
where cmd.KeyNum = KeyNum
select cmd.execute()
).ToString();