how to show necessary forms in c# in treeview control

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hello,
in below code it is placed in the afterselect event of a treeview control.
how is it possible to NOT repeat the frm.Show() events please?
thanks

C#

{

            string s = e.Node.Text.ToLower();


            Form frm;


            if (s == "form1")

            {

                frm = new Form1();

                frm.Show();

            }

            else if (s == "form2")

            {

                frm = new Form2();

                frm.Show();

            }             

            else if (s == "form3")

            {

                frm = new Form3();                

                frm.Show();

            }

        }

Posted 1-Apr-15 0:52am

arkiboys

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CHill60 · Answer 1 · 2015-04-01T01:40:00

Well the easiest changes for you to make are to remove all those show statements and have a single one at the end (after checking that frm is not null). I.e.

C#

if (s == "form1")
    frm = new Form1();

if (s == "form2")
    frm = new Form2();

if (s == "form3")
    frm = new Form3();

if (frm != null)
    frm.Show();

However, the switch[^] statement was designed for these scenarios E.g.

C#

switch (s)
{
    case "form1":
        frm = new Form1();
        break;
    case "form2":
        frm = new Form2();
        break;
    case "form3":
        frm = new Form3();
        break;
}

if (frm != null)
    frm.Show();

If it was me I'd do it this way

C#

Form frm = null;

//Next line not required if nodes contain real form names
s = s.Substring(0, 1).ToUpper() + s.Substring(1, s.Length - 1);

var t = Type.GetType(frm.GetType().Namespace + "." + s);
if (t != null)
{
    frm = (Form)Activator.CreateInstance(t);
    frm.Show();
}

But make sure you understand what is happening before trying to use that last bit in any assignments.

BillWoodruff · Answer 2 · 2015-04-01T06:10:00

Simply don't re-create the Form if it is already created; don't re-show the Form if it is already visible:

In Form scope:

C#

// assume the TreeView, 'treeView1 is on a MainForm which has been shown
Form1 f1 = new Form1();
Form2 f2 = new Form2();
Form3 f3 = new Form3();

private void treeView1_AfterSelect(object sender, TreeViewEventArgs e)
{
    switch(e.Node.Text)
    { 
        case "Node1":
            if(! f1.Visible) f1.Show();
        break;
        case "Node2":
            if(! f2.Visible) f2.Show();
        break;
        case "Node3":
            if(! f3.Visible) f3.Show();
        break;
    }
}

Note this code assumes the user cannot close the instances of the secondary Forms. Here's how you might handle that:

C#

private void treeView1_AfterSelect(object sender, TreeViewEventArgs e)
{
    switch(e.Node.Text)
    { 
        case "Node1":
            if(f1.IsDisposed) f1 = new Form1();
            if(! f1.Visible) f1.Show();
        break;
        case "Node2":
            if(f2.IsDisposed) f2 = new Form2();
            if(! f2.Visible) f2.Show();
        break;
        case "Node3":
            if(f3.IsDisposed) f3 = new Form1();
            if(! f3.Visible) f3.Show();
        break;
    }
}

There might be good reasons to not allow the user to close (permanently) a secondary Form: it's costly to re-instantiate Forms; you might lose data entered on the Forms (if you haven't preserved it).

If you want the user to have an easy way to "hide" a secondary Form without really "closing" it then try this:

C#

private void Form1_Load(object sender, EventArgs e)
{
    foreach(Form frm in new List<Form> {f1, f2, f3})
    {
        frm.FormClosing += frm_FormClosing;
        frm.Show();
    }
}

// do not set this EventHandler "as is" to be the FormClosing for the Main Form !

private void frm_FormClosing(object sender, FormClosingEventArgs e)
{
   (sender as Form).Hide();
   e.Cancel = true;
}

And now I'd like to tell you there's a better to handle this in general: use two "symmetric" Dictionaries of Types <TreeNode, Form> and <Form, TreeNode> to synchronize selection between the Forms and the TreeView Nodes. If you want to know how to do that: ask here.

how to show necessary forms in c# in treeview control

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