Save ArrayList to Tree Nodes

Question

I want to use a TreeView to show items the user selects in several different categories however I can only get it to work for adding root nodes (not child). For example I want something like: STATE - 1st State - CITIES - 1st City - 2nd City - 3rd City - 2nd State - CITIES - 1st City - 2nd city - ZIPs - 1st Zip - 2nd Zip COUNTRY etc... where the capitalized entries are hard coded and the users choices dynamically fill the child nodes. This is the code I have in my method: TreeView tv = new TreeView; tv.Nodes.Add((GeoArray).ToString()); This only shows Systems.Collections.ArrayList in new root nodes for the number of items I selected in the listbox. I've looked in forums and books but there is not a lot of info on TreeViews. Any help is appreciated.

rulec444 · Answer

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!!

rulec444 · Answer

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!!!

sjones · Answer

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.

rulec444 · Answer

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?

rulec444 · Answer

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!

rulec444 · Answer

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!!!!!!!!

sjones · Answer

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(tvRegion); should be TreeNode node = FindNode(tvRegion); 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.

rulec444 · Answer

I appreciate you sticking with me.......here's a sample of my code: private void btnSaveRegion_Click(object sender System.EventArgs e) { FindNode(tvRegion); TreeNode state = new TreeNode(); state.Text = State; //adds a node to Region named State state.Tag = State; node.Nodes.Add(state); FindNode(tvState); 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!!

sjones · Answer

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.

rulec444 · Answer

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.

sjones · Answer

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; }

sjones · Answer

Post your code and I will have a look.

rulec444 · Answer

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.

rulec444 · Answer

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!!

sjones · Answer

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.

rulec444 · Answer

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!!

sjones · Answer

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.

rulec444 · Answer

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!!

sjones · Answer

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; }

rulec444 · Answer

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!

sjones · Answer

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.