Question

Just have a quick question… any help would be greatly appreciate!

I’m writing a database. I have a class called “Mechanism” which is inherited by two other classes called “motorcycle” and “automobile.” How would i go about printing the contents of motorcycle or automobile – depending on what the user has decided to enter into the database?

this is what i have so far, it’s giving me this error: InvalidCastException was unhandled. Unable to cast object of type “ConsoleApplication1.Automobile” to type “ConsoleApplication1.Motorcycle”

foreach (Mechanism m in mechanisms)
{
    //ptr = m;
    if (flagAuto == true)
    {
        Mechanism ptr = null;
        ptr = m;
        Console.WriteLine("ptr = " + ptr);
        Console.WriteLine("ptr2 = " + ptr2); 
        ptr2 = (Automobile)ptr;
        Console.WriteLine("inside Auto");
        ofp.WriteLine("" + (ptr2.getManufacturer()));
        ofp.WriteLine("" + ptr2.getModel());
        ofp.WriteLine("" + ptr2.getModelYear());
        ofp.WriteLine("" + ptr2.getVIN());
        ofp.WriteLine("" + ptr2.getInitialPurchasePrice());
        ofp.WriteLine("" + ptr2.getPurchaseDate());
        ofp.WriteLine("" + ptr2.getSizeOfEngine());
        ofp.WriteLine("" + ptr2.getTypeOfFuel());
        ofp.WriteLine("" + ptr2.getNumberOfDoors());
        ptr2 = null;
        ptr = null; 
        Console.WriteLine("finishinge Auto");
    }
    else if (flagMotor == true)
    {
        Mechanism ptr = null;
        ptr = m;
        Console.WriteLine("ptr = " + ptr);
        Console.WriteLine("ptr2 = " + ptr1); 
        Console.WriteLine("inside Motor");
        ptr1 = (Motorcycle)ptr;
        ofp.WriteLine("" + ptr1.getManufacturer());
        ofp.WriteLine("" + ptr1.getModel());
        ofp.WriteLine("" + ptr1.getModelYear());
        ofp.WriteLine("" + ptr1.getVIN());
        ofp.WriteLine("" + ptr1.getInitialPurchasePrice());
        ofp.WriteLine("" + ptr1.getPurchaseDate());
        ofp.WriteLine("" + ptr1.getSizeOfEngine());
        ofp.WriteLine("" + ptr1.getTypeOfMotorcycle());
        ptr1 = null;
        ptr = null; 
        Console.WriteLine("finishing Motor");
    }

the flags are supposed to keep track of which type of vehicle is trying to be entered into my database – then it should write it out to a text file..

Answer 1

That means the value of the flag is wrong.

You should do this instead:

if (m is Automobile)
{
    Automobile autoMobile = m as Automobile;
    //.. work with autoMobile
}
else if (m is Motorcycle)
{
    Motorcycle motorCycle = m as Motorcycle;
    //.. work with motorCycle 
}

By the way, you’re doing the same thing in the both branch. That implies, that you could implement them in a base class (Mechanism), call those methods on m object.