Save ArrayList to Tree Nodes

How do I use this to remove child nodes. For example, I'm going to Find the "State" node and I want to remove all child nodes under it when they are variables. I started to try: TreeNode node = FindNode(tvFilters, "State"); node.Nodes.Remove(node); but that removes the State node. I won't know the tag of the child nodes because they are created dynamically in another piece of my code - so how do I say, anything under state, remove? Thanks for all your help on this!!

Well - I guess I figured out what was happening. At least I have it working now. I had created all the initial nodes in the formload event, so when I was again referencing the form, it didn't re-instantiate the nodecollection. I now have it in the constructor and its working fine again. Sorry for the trouble!! Thanks for looking at it and responding!!!

I would need to see the code. If I had to guess, I would say that your tv variable is not set to an actual instance of a TreeView control. Your SaveState function passes tv to FindNode, but I don't see where it is being set. Is this a global variable? I don't see why it would work without the user control. Unless in addition to creating the user control you are also initializing the tv variable. Try changing it to this.tv and see if the problem goes away.

One more thing... I figured out the only other difference between when it works and now when it doesn't. I have added a user control to the form. When I took it off, the FindNode worked again; however as soon as I added it back on, it no longer works. I am not using any sort of a treeview with the usercontrol so I don't understand how that would impact it. Any ideas?

I've had these methods working for almost a month and haven't touched them except I did add more nodes to my tree. For some reason now, on the FindNode method, I am receiveing an error that Object reference not set to an instance of an object. When I step through the code I see that its because in the FindNode method, its not recognizing the collection of nodes, therefore, it is not looping through all the nodes in the treeview. When it gets to the foreach statement, it does not see the collection of nodes so it returns a null value. Here is part of my code: private void Form_Load(object sender, System.EventArgs e) { tv.Tag = "Selected Filters"; TreeNode state = new TreeNode(); state.Text = "State"; state.Tag = "State"; this.tv.Nodes.Add(state); TreeNode city = new TreeNode(); city.Text = "City"; city.Tag = "City"; this.tv.Nodes.Add(city); TreeNode zip = new TreeNode(); zip.Text = "Zip"; zip.Tag = "Zip"; this.tv.Nodes.Add(zip); TreeNode number = new TreeNode(); number.Text = "Number"; number.Tag = "Number"; this.tv.Nodes.Add(number); } private void SaveState() { TreeNode node = FindNode(tv, "State");//THIS is where it returns error TreeNode selectedState = new TreeNode(); node.Nodes.Add(selectedState); selectedState.Text = stLbx01; selectedState.Tag = stLbx01; selectedState.ForeColor = Color.DarkMagenta; } private TreeNode FindNode(TreeView tv, string strText) { foreach (TreeNode node in tv.Nodes) //THIS IS the actual point its erroring { if (node.Tag.ToString() == strText) { return node; } else { TreeNode nodeChild = FindChildNode (node, strText); if (nodeChild != null) return nodeChild; } } return (TreeNode)null; }//end of FindNode method Thanks for looking at this!

I have finally got it all fixed to where it is functioning as I had hoped. Your detailed explanation really helped me to understand what I was doing wrong - I was way off - I was only calling the method and not doing anything with the return node, but couldn't figure out what was wrong - I'm sure you were thinking I was an idiot! (I had declared my variables, just at global level, which is why it was partly working when I revised a few things.) I am now using your code exactly as you have outlined. Thank you so much for your patience, detailed explanation and direction. I have even gained a better understand of C# due to your instructions! Thanks Steven!!!!!!!!

In your btnSaveRegion_Click function, you call FindNode but don't do anything with the returned value. If it finds the node, you don't do anything with it. FindNode(tv,"Region"); should be TreeNode node = FindNode(tv,"Region"); You later try to add a Child TreeNode with node.Nodes.Add(state); , but node has not been set to an object. In fact, node has not even been declared. How does this line not generate an error? Another question I have is inside my functions you set node = n; then return node, why did you change that? You need only return n; Again you have not declared node as a TreeNode. But I think the ultimate answer to you problem is: node.Nodes.Add(temp); you went to all the trouble of creating a TreeNode named selectedState, then threw it away and added a new node with only the string temp. Try using: node.Nodes.Add(selectedState); instead. Same problem as you had before. You are adding a node as a string, and it has no .Tag property. You should really declare you variables.

I appreciate you sticking with me.......here's a sample of my code: private void btnSaveRegion_Click(object sender, System.EventArgs e) { FindNode(tv,"Region"); TreeNode state = new TreeNode(); state.Text = "State"; //adds a node to Region named State state.Tag = "State"; node.Nodes.Add(state); FindNode(tv,"State"); temp = (cbxStates.SelectedValue.ToString()); TreeNode selectedState = new TreeNode(); selectedState .Text = temp; //adds selection to "State" node added above selectedState .Tag = temp; node.Nodes.Add(temp); foreach(DataRowView drv in lbxZip.SelectedItems) { node.Nodes.Add(zipDRV["Zip"].ToString()); //adds Zip code } } private void btnType_Click(object sender, System.EventArgs e) { FindNode(tv, "Type"); foreach(DataRowView drv in lbxType.SelectedItems) { node.Nodes.Add(drv["TypeName"].ToString()); //adds the TypeName //the user selected to the Node named "Type" } } private TreeNode FindNode(TreeView tv, string strText) { foreach (TreeNode n in tv.Nodes) { if (n.Tag.ToString() == strText) { node = n; return node; } else { TreeNode nodeChild = FindChildNode (n, strText); if (nodeChild != null) return nodeChild; } } return (TreeNode)null; } private TreeNode FindChildNode(TreeNode nodeStart, string strText) { foreach (TreeNode n in nodeStart.Nodes) { if (n.Tag.ToString() == strText) //this is when it errors when I have //already added State, selectedState, Zip and then trying to add a //TypeName under the "Type" node (added on page load). // "n" will read as the selected State, but I still receive the //error that I didn't instantiate it????? { node = n; return node; } else { TreeNode nodeChild = FindChildNode (n, strText); if (nodeChild != null) return nodeChild; } } return (TreeNode)null; } Hopefully this is clear. Thanks again for your continued help!!

My guess is that the problem is where you add the grandchild. It would help if you could post that code. Everything between where you Find the parent and the where the new child goes out of scope. What are you setting the .Tag property to? Is it a string, or an object that does not have a .ToString() method. That would probably do it to.

Thanks for spending your time working on this Saturday. I have changed and used the updated code and the foreach loop works now! I am not sure why referencing the treeview fixed the foreach, but it works. The recursive method is really helpful - I hadn't even thought of that and I had just added another method - but this is great! Anyway, now I have a new problem that I'm hoping you can help me with if I'm not wearing you out. My error occurs after I dynamically add a node, say a grandchild node (I did add the node.Tag too), then I am calling the FindNode method to add a child node under a completely different root node. It does fine, looping through until it gets to the grandchild node that I added during runtime, specifically, the error is in the FindChildNode method: if (node.Tag.ToString() == strText) - the error is "Object reference not set to an instance of an object.". When I step through the code and mouse over, the value displayed for node.Tag.ToString(), is what it should be and it doesn't yet equal the strText, but this is where I receive the error - before it even goes on. I hope this makes sense - my code where I call FindNode is extensive, but I'll send it if that helps to clarify. Thanks again. This is really helping me a lot - just a few bugs is all. Thanks.

I updated my functions for you so they will be more generic. The FindNode funciton now take a TreeView control as a parameter so you can call the function on any TreeView, not just the Treeview1 like before. The second function is now recursive so it looks in children, grandchildren, greatgrandchildren.. All the way back to Lucy if you want. So if you want to find a node ANYWHERE in the tree, you call FindNode. If you want to look only wthin a certain Branch, you can call FindChildNode directly. Keep in mind that since the new FindChildNode is recursive, you will automatically find grandchildren, so if you want to limit your seach to only direct children, you can use the old version. private TreeNode FindNode(TreeView tv, string strText) { foreach (TreeNode node in tv.Nodes) { if (node.Tag.ToString() == strText) return node; else { TreeNode nodeChild = FindChildNode (node, strText); if (nodeChild != null) return nodeChild; } } return (TreeNode)null; } private TreeNode FindChildNode(TreeNode nodeStart, string strText) { foreach (TreeNode node in nodeStart.Nodes) { if (node.Tag.ToString() == strText) return node; else { TreeNode nodeChild = FindChildNode (node, strText); if (nodeChild != null) return nodeChild; } } return (TreeNode)null; }

Post your code and I will have a look.

I have just now had a chance to work on the subsequent root tree nodes and have encountered a problem with the FindNode methods. It works just fine on the 1st root tree node. However, if I'm trying to find the 2nd root tree node, it goes through FindNode & Get ChildNode just fine (searching through the first node to find a tag match), however, when it completes the GetChildNode method and returns to the FindNode method, even though it hasn't found a match to the tag, it just exits the method without looping through the foreach statement (it should loop through 3 times for my 3 root nodes). Then I get a runtime error " Object reference not set to an instance of an object.", since it didn't find a tag match. Does anyone (stevenmjones?) know why it isn't looping through the code on the foreach loops: foreach(TreeNode node in treeView1.Nodes) ? Thanks for your help.

WOW!!! Thank you so much. This works exactly like I was trying to make it work...thanks to your help!!! My only issue now is if I select mulitple items in the listbox, its adding the first item selected to the node multiple times (if I select Kansas, New York, Wyoming, under the STATE node, it's added Kansas, Kansas, Kansas). But, I'm making headway.....THANK YOU SO MUCH!!

Yes. Even if you have no intention of ever looking for the node in question, make sure you give it some value. That way when your code just reads right past it, it will not give you an error. My guess is that every node is important and you will want to give it's Tag a meaningful value.

duh - I should have known to add the new node to the node I found - that was a stupid oversight. Thanks for your patience with me!! I am fairly new to development, so I need more direction on setting the node's tag property. I don't know what you mean by "make sure that every node in your tree has a Tag of some sort". Do you mean setting it up like: stateNode.Tag = "State"; Sorry - I hope this isn't too basic for me to be asking. Thanks again!!

This code is searching the Root Nodes for a node with Tag of "STATE". Once you find it, you are then adding the new node as another Root though. You need to add the new node to the Nodes collection of the state node you found. In your code here you would use: node.Nodes.Add(...) because node is the one you found. As for the error, make sure that every node in your tree has a Tag of some sort. Also note that the Tag property is a reference to an Object, not just a string. You typically will have your Tag reference a String object so this fact is easy to overlook. You can set Tag to any object which has a .ToString() method and use my code here. But if you don't set a node's Tag property to something, you should get this error.

Okay - this has been a great help to understand conceptually how this process should work. I have been working on this a few days - actually what I have decided to do is hard code the Category titles and then have the child nodes filled by the user's selections. So, what I have done is, if based on the button clicked on the form, I will know which parent node has been referenced, so then I only need to loop through the TreeView to find that node, then add the child nodes selected from the listbox. This is my code: private void btnSTATE_Click(object sender, System.EventArgs e) { foreach(TreeNode node in treeView1.Nodes) { if(node.Tag.ToString() == "STATE") { treeView1.Nodes.Add((string)(listBox1.SelectedValue)); } } } (I thought I would need an array, but I didn't add that since it looks like the treeview will act as the collection of items.) However, when I run this I receive the following error: "Object reference not set to an instance of an object.", on line if(node.Tag.ToString() == "STATE") I assume I don't have something instantiated, but I'm not sure what because treeView1 has been set at a global level. Thanks for your continued help!!

If you are populating the tree all at once, it is easy. When you add a node, you just start adding its children to its Nodes collection. And their children to their Nodes collection. If you are adding the children later, it is a bit more complicated. In the old days, you could find a node by simply using a key. You can't do that anymore. Now you need to find the parent node yourself. You need to have either a Text or Tag value that you can find. Then you start at the Root nodes, the Treeview's Nodes collection, and start looking. This has to be a recursive search because you can't access ALL of the nodes at once from the Treeview. If you don't find what you are looking for in a node, you then search it's nodes, and so on. If you don't have a single value to look for, you need to do this is steps. Find "STATE", then in its Nodes, find "Ohio", then in its nodes find "CITIES", then "Columbus", then "ZIPS". Now you can add a zip code node to that. You can make this easier by creating a unique string to store in the node's Tag property to search for. You could set it to "OH|COLUMBUS|ZIPS". Then your recursive function to find it won't need to stop at each branch. Here is some code that will get you going if you choose to use the Tag property: private TreeNode FindNode(string strText) { foreach (TreeNode node in this.treeView1.Nodes) { if (node.Tag.ToString() == strText) return node; else { TreeNode nodeChild = GetChildNode(node, strText); if nodeChild != null return nodeChild; } } return (TreeNode)null; } private TreeNode GetChildNode(TreeNode nodeStart, string strText) { foreach (TreeNode node in nodeStart.Nodes) { if (node.Tag.ToString() == strText) return node; } return (TreeNode)null; }

Thanks, this is a great start, but I don't know how to find the child node. All I can figure out how to do is add to the very top root node. How do I drill down to the child nodes? Thanks for your time and help!

You can't do it this way. You have to actually add the child nodes to the parent's Nodes collection. This means that in order to add a Zip, you first need to find the STATE node, then find the proper State child, then the ZIPs child. You then add your Zip child to that node's Nodes collection. I was easier in the past when you could just insert a node by building it's FullPath. The tree took care of finding the correct location.