使用LINQ递归查找通用列表C＃

Question

I have generic list of a custom class which has 2 properties. These properties store the raltionship between on form and another form. The list is structured as a hierachical list (parent / child ) relationship. What I want to be able to do is get a list of all forms based on a parent form reference which will be passed to a function. I am thinking the best way to go about this is with a LINQ query using a recursive approach. I am sure someone can point me in the right direction

This is the class used in the list

class FormStack    {

    #region Declares

    private Form _form;
    private Form _parent;

    #endregion

    #region Constructor

    static FormStack()
    {
    }

    #endregion

    public Form Form
    {
        get { return _form; }
        set { _form = value; }
    }

    public Form Parent
    {
        get { return _parent; }
        set { _parent = value; }
    }

}

So I would like to be able to Call a method and pass a form reference to the function and get all the children form related to this parent.

This is some of the code I have been stumbling with

// create a lookup list
var list = formStack.ToLookup( p => object.ReferenceEquals( p.Parent, parent ) );

// create a function
Func<IEnumerable<Form>, IEnumerable<Form>> recurse = null;
recurse = qs =>
{
    return
        qs
            .Concat(
                from q in qs
                from q2 in recurse( list[] )
                select q2 );
};

// filter the list
var children = recurse( list[parent] ).ToList();

I have a winform application which has standard CRUD functionality. Lets say there is a list of customers and each customer can have multiple address and each one of these addresses have multiple buildings, the way I have structured the forms is there is a list of customers, from this list you can open a detail form for a particular customer. This form has the details of the customer and all the addresses in a list. This list allows the user to now selected an address in the list and open the address details form which has a list of buildings and so on.... My problem is I want to close the customer detail and all the related forms for this customer. My idea was to keep of the relationship between the forms, but maybe I there is a better way???

Answer 1

Okay, it sounds to me like you have two issues. One is a syntax error ( recurse(list[]) is wrong), but the other is that your FormStack isn't really a stack. It's just two forms, with no way to create a recursive chain. I think you want this:

public class FormStack : IEnumerable<Form> // or just implement SelectMany
{    
    public Form Form { get; set; }
    public FormStack Parent { get; set; }  
    //implement IEnumerable<Form> or the SelectMany method
}

Then I think you can just do this, but it seems like an awkward thing to do:

Func<FormStack, IEnumerable<Form>> recurse = qs =>
{
    return from q in qs
           select (new[] { qs.Form }).Concat(recurse(qs.Parent));
};

var list = recurse(formStack).ToList();

That's if you're insisting on the query syntax.

If I were you, though, I'd forget all that and implement an IEnumerator<Form> to do it all for you:

public class FormStack : IEnumerable<Form> 
{    
    public Form Form { get; set; }
    public FormStack Parent { get; set; }  
    public IEnumerator IEnumerable:GetEnumerator() 
    { 
        return (IEnumerator)GetEnumerator();
    }
    public IEnumerator<Form> GetEnumerator() 
    { 
        return new FormStackEnumerator(this);
    }
}
public class FormStackEnumerator : IEnumerator<Form>
{
    private FormStack _stack;
    private FormStack _first;
    public Form Current { get { return _stack.Form; } }
    object IEnumerator.Current { get { return Current; } }

    public FormStackEnumerator(FormStack stack)
    {
        _stack = stack;
        _first = stack;
    }
    public bool MoveNext()
    {
        if (_stack.Parent == null)
        {
            return false;
        }
        _stack = _stack.Parent;
        return true;
    }
    public void Reset() { _stack = _first; }
    void IDisposable.Dispose() { }
}

Then all you'd need to do in your main code is this:

var list = new List<Form>();
foreach (var node in formStack)
{
    list.Add(node.Form);
}

---

By the way, I just looked up the Form class (I'm not a WinForms developer) and the Forms themselves have a Parent member. So you don't really need to wrap them in a node-type construct; they're already nodes! That makes everything easy:

var list = new List<Form>();

Action<Control> recurse = target =>
{
    var form = target as Form;
    if (form != null)
    {
        list.Add(form);
        recurse(target.Parent);
    }
}

Answer 2

here is what I made up:

Create a base Form for all your Forms:

 public class MyFormBase : Form { public MyFormBase() { FormRepository.RegisterForm(this); } public MyFormBase(MyFormBase parent) : this() { Parent = parent; } public MyFormBase Parent { get; set; } } 

Each Form can only have one Parent that is passed in the constuctor.

Create a Repository (or something simiar) to store your forms -> I do not want to store all children in the Form itself

//infrastructure - simulated with a static class
public static class FormRepository
{
    private static List<MyFormBase> _allForms = new List<MyFormBase>();

    public static void RegisterForm(MyFormBase form)
    {
        _allForms.Add(form);
    }

    public static void CloseFormAndChildren(MyFormBase form)
    {
        _allForms.Where(x => x.Parent.Equals(form)).ToList().ForEach(x => CloseFormAndChildren(x));
        form.Close();
    }
}

Call CloseFormAndChildren on any form you want to close (including the children). This could be called in the closing event...