Why does this work?

Question

 

I am new to C# and have been studying this piece of code.  It loops through an Adjacency Matrix table to populate a tree view. I have two questions about this code.

 

1. initTreeView(TreeNode N) creates a new “temp” table to hold the children for each node.  Each time the table is created it has the same name “temp”.  Why doesn’t the table just get over written each time?
2. In the foreach (DataRow r3 in temp.Rows) loop, if the temp table is empty like when Menu11 is reached the call to initTreeView(tn) is not executed but for all the parent nodes Menu1, Menu4, Menu5 and Menu6 initTreeView(tn) is executed.  There is no code to indicate that at Menu11 not to execute initTreeView(tn)  How does C# know when to execute initTreeView(tn) and when not to?

 

 

namespace DynamicTree

{

    public partial class Form1 : Form

    {

        //Declare the table that will be populated with the Adjacency Matrix data.

        DataTable tbl;

        //Declare the coumns that will be populated in the Adjacency Matrix table.

        DataColumn col;

 

        public Form1()

        {

            InitializeComponent();

            //Create the Adjacency Matrix table.

            InitTable();

            //Populate the Adjacency Matrix table.

            initTableData();

        }

 

        #region InitTable() - Create the Adjacency Matrix table.

 

        private void InitTable()

        {//Create the Adjacency Matrix table.

 

            tbl = new DataTable();

 

            col = new DataColumn("ID");

            tbl.Columns.Add(col);

            col = new DataColumn("PID");

            tbl.Columns.Add(col);

            col = new DataColumn("Info");

            tbl.Columns.Add(col);

 

            tbl.AcceptChanges();

 

        }

 

        #endregion InitTable() - Create the Adjacency Matrix table.

 

        #region initTableData() - Populate the Adjacency Matrix table.

 

        private void initTableData()

        {//Populate the Adjacency Matrix table.

            DataRow r;

 

            r = tbl.NewRow();

            r["ID"] = "0";

            r["PID"] = "-1";

            r["Info"] = "Root";

            tbl.Rows.Add(r);

 

 

            r = tbl.NewRow();

            r["ID"] = "1";

            r["PID"] = "0";

            r["Info"] = "Menu1";

            tbl.Rows.Add(r);

 

            r = tbl.NewRow();

            r["ID"] = "10";

            r["PID"] = "0";

            r["Info"] = "Menu10";

            tbl.Rows.Add(r);

 

            r = tbl.NewRow();

            r["ID"] = "2";

            r["PID"] = "0";

            r["Info"] = "Menu2";

            tbl.Rows.Add(r);

 

            r = tbl.NewRow();

            r["ID"] = "3";

            r["PID"] = "0";

            r["Info"] = "Menu3";

            tbl.Rows.Add(r);

 

            r = tbl.NewRow();

            r["ID"] = "4";

            r["PID"] = "1";

            r["Info"] = "Menu4";

            tbl.Rows.Add(r);

 

            r = tbl.NewRow();

            r["ID"] = "5";

            r["PID"] = "4";

            r["Info"] = "Menu5";

            tbl.Rows.Add(r);

 

            r = tbl.NewRow();

            r["ID"] = "6";

            r["PID"] = "5";

            r["Info"] = "Menu6";

            tbl.Rows.Add(r);

 

            r = tbl.NewRow();

            r["ID"] = "7";

            r["PID"] = "2";

            r["Info"] = "Menu7";

            tbl.Rows.Add(r);

 

            r = tbl.NewRow();

            r["ID"] = "11";

            r["PID"] = "6";

            r["Info"] = "Menu11";

            tbl.Rows.Add(r);

 

            r = tbl.NewRow();

            r["ID"] = "8";

            r["PID"] = "10";

            r["Info"] = "Menu8";

            tbl.Rows.Add(r);

 

            r = tbl.NewRow();

            r["ID"] = "9";

            r["PID"] = "3";

            r["Info"] = "Menu9";

            tbl.Rows.Add(r);

 

            r = tbl.NewRow();

            r["ID"] = "12";

            r["PID"] = "7";

            r["Info"] = "Menu12";

            tbl.Rows.Add(r);

 

            r = tbl.NewRow();

            r["ID"] = "13";

            r["PID"] = "4";

            r["Info"] = "Menu13";

            tbl.Rows.Add(r);

 

        }

 

        #endregion initTableData() - Populate the Adjacency Matrix table.

 

        #region Form1_Load() - Create the root tree node.

 

        private void Form1_Load(object sender, EventArgs e)

        {

            //Create the root tree node.

            TreeNode r = new TreeNode();

            r.Text = "Root";

            initTreeView(r);

            tree.Nodes.Add(r);

            tree.ExpandAll();

        }

 

        #endregion Form1_Load()

 

        //The first pass the root tree node created in ther form load is passed.

        private void initTreeView(TreeNode N)

        {//This is the recursive method, calling it's self from the FOR loop at 201.

         //This creates nested tables containing the children for each node.

 

            //Create a temp table to act as a buffer to hold the

            //children of the current node.

            DataTable temp = new DataTable();

            col = new DataColumn("ID");

            temp.Columns.Add(col);

            col = new DataColumn("PID");

            temp.Columns.Add(col);

            col = new DataColumn("Info");

            temp.Columns.Add(col);

            temp.AcceptChanges();

 

            //Retrieve the child ID of the current node.

            string id = getID(N);

 

           

            foreach (DataRow r1 in tbl.Rows)

            {//Step through the Adjacency Matrix table to find

             //all the children of the current node.

 

                if (r1["PID"].ToString() == id)

                {//This row represents a child of the current node.

 

                    //Add a row to the buffer table to contain this child

                    //of the of the current node.

                    DataRow r2 = temp.NewRow();

                    r2["ID"] = r1["ID"].ToString();

                    r2["PID"] = r1["PID"].ToString();

                    r2["Info"] = r1["Info"].ToString();

                    temp.Rows.Add(r2);

                    temp.AcceptChanges();

                }

            }

 

            foreach (DataRow r3 in temp.Rows)

            {//Step through the buffer table and create a node for each row. 

             //These are the children of the current node.

 

                //If temp is empty control pops ouit and goes to initTreeView()

                //calls it's self, back to 157.

 

                TreeNode tn = new TreeNode();

                tn.Text = r3["Info"].ToString();

 

                //This is where initTreeView() calls it's self, back to 157

                //To create a nested table to hold the children of this node.

                initTreeView(tn);

 

                N.Nodes.Add(tn);

            }

        }

 

        //Return the child ID of the current node.

        private string getID(TreeNode N)

        {

 

            foreach (DataRow r in tbl.Rows)

            {

                //Step through the Adjacency Matrix table to find row

                //representing the current node. Return the child ID.

                if (r["Info"].ToString() == N.Text)

                    return r["ID"].ToString();

            }

            return "";

        }

    }

}