Creating a custom Panel class C#

Hey guys, I'm trying to set up a custom Panel called FormPanel from Panel

class FormPanel : Panel
    {
        bool previous;
        FormPanel l;

        public FormPanel()
        {
            previous = false;
            l.Parent = this;
            l.Dock = DockStyle.Fill;

        }
    }

This is pretty much where I am right now. I want the FormPanel to have a bool var and want to set it's default properties of Parent and Dock. How does 开发者_开发技巧this work? How can I set those?

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In case you want your panel to have DockStyle.Fill as default for the Dock property, do this:

public class FormPanel : Panel
{
    public FormPanel()
    {
        this.Dock = DockStyle.Fill;
    }

    [System.ComponentModel.DefaultValue(typeof(DockStyle), "Fill")]
    public override DockStyle Dock
    {
        get { return base.Dock; }
        set { base.Dock = value; }
    }
}

This makes the Dock property default to Fill within the property window.

---

You shouldn't use an internal variable of your type, instead set the properties (that you inherit from the baseclass) directly:

class FormPanel : Panel
{
    bool previous;

    public FormPanel()
    {
        previous = false;
        base.Parent = this;
        base.Dock = DockStyle.Fill;

    }
}

although I don't think that "base.Parent=this" will work ...

---

You need to add more info about what you're trying to achieve.

As it stands your FormPanel has a private field (l) which is itself a FormPanel:

  FormPanel l;

You never instantiate this field, so it will always be null, and the assignments to properties in the constructor will fail with a NullReferenceException:

l.Parent = this;              
l.Dock = DockStyle.Fill;

If you did instantiate this private field, you would have recursion, since your FormPanel contains a private FormPanel, which itself contains a private FormPanel, ...

l = new FormPanel();
l.Parent = this;              
l.Dock = DockStyle.Fill;

You say you want to set a default Parent, but I don't see how a FormPanel can know what it's parent is in the constructor, unless you pass the parent as a parameter to the constructor, e.g. maybe you're looking for something like:

public FormPanel() : this(null)
{
}

public FormPanel(Control parent)
{
    if (parent != null)
    {
        this.Parent = parent;
    }
    this.Dock = DockStyle.Fill;
    ...
}