Question

I am making a windows forms project in C#, in which I made a class LabelX which inherits System.Windows.Forms.Label, then added a property Mass of float type

Now, my question is how can I handle, when value of Mass is changed.

e.g.:
When user enter value zero or less than zero
I want to fire a message that “Mass can’t be zero or negative”

Answer 1

If I am interpreting this correctly, there are two parts to this. First, you need to detect invalid values and throw exceptions. Second, you need to raise an event when the property changes. This can be achieved as follows.

private float mass;
public float Mass
{
    get
    {
        return this.mass;
    }

    set
    {
        if (value <= 0.0F)
        {
            throw new ArgumentOutOfRangeException("Mass cannot be zero or negative.");
        }

        if (this.mass != value)
        {
            this.mass = value;
            OnMassChanged(EventArgs.Empty);
        }
    }
}

public event EventHandler MassChanged;

protected virtual void OnMassChanged(EventArgs args)
{
    var handler = this.MassChanged;
    if (handler != null)
    {
        handler(this, args);
    }
}

To show a message if an invalid entry is made, you should put a try \ catch block around the call to set Mass and catch the ArgumentOutOfRangeException.