Why does the object is null if adding a child node?

Question

I m trying to add a child node but it says the object is not set.

public void Test(TreeView tree)
{
    tree.Nodes.AddRange(new TreeNode[] { new TreeNode("ok"), new TreeNode("test")});
    foreach (TreeNode node in tree.Nodes)
        tree.Nodes["test"].Nodes.Add("a child node");
}

private void Button1_Click_1(object sender, EventArgs e)
{
     Test(treeView1);
}

Edit:
I cant answer my own post because someone marked it but the problem is that I dont set the property Name in TreeNode

the worked version is that:

public void Test(TreeView tree)
{
    tree.Nodes.AddRange(new TreeNode[] { new TreeNode("ok") { Name = "ok" }, new TreeNode("test") { Name = "test" } });
    foreach (TreeNode node in tree.Nodes)
        tree.Nodes["test"].Nodes.Add(new TreeNode("a child node"));
}

thanxs to reza-aghaei

Where is the code that creates the `"test"` node? You have `tree.Nodes["test"]` but aren't creating that node anywhere that I can see. — , Sep 24 '19 at 18:09
@leylafanji Okay, then, does `tree.Nodes["test"]` evaluate to null as I suspected? — , Sep 24 '19 at 18:12
`Node.Text` is different from `Node.Text`. `new TreeNode("test")` creates a node having `Text = "test"`, but `tree["test"]` is trying to find a node having `Name = "test"`. — Reza Aghaei, Sep 24 '19 at 18:14
You can assign `Name` property of node as well. `new TreeNode("test"){Name = "test"}`. — Reza Aghaei, Sep 24 '19 at 18:18
You are using a `foreach`. Did you mean `node.Nodes.Add("a child node");`? — 001, Sep 24 '19 at 18:19
@Ondrej Tucny why you marked it as duplicate this has nothing to do with my question? — leyla fanji, Sep 24 '19 at 18:21
@leylafanji check this (https://stackoverflow.com/questions/12388249/is-there-a-method-for-searching-for-treenode-text-field-in-treeview-nodes-collec) it could be helpful — Abdullah Dibas, Sep 24 '19 at 18:22
I reopened the post as it's not a duplicate of the linked post. OP knows what is the null reference exception, but doesn't know what's wrong with tree node and why it cannot be found. — Reza Aghaei, Sep 24 '19 at 18:25

Rufus L · Accepted Answer · 2019-09-24T18:26:18.333

0

The problem here is that you're trying to access a node by it's string key (which maps to the Name property), but you're never setting the Name (only the Text).

Try this instead:

tree.Nodes.AddRange(new[]
    {
        new TreeNode("ok") {Name = "ok"},
        new TreeNode("test") {Name = "test"}
    });

edited Sep 24 '19 at 18:26

answered Sep 24 '19 at 18:24

Rufus L

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Yes, @Reza Aghaei said that too thanxs – leyla fanji Sep 24 '19 at 18:25

Why does the object is null if adding a child node?

1 Answers1