C# Recursion Method to create a Tree Hierarchy

Question

I've created a USB Device Scanner which allows the user to see all Devices in a Tree-Hierarchy. First i was happy that it worked, but after the joy I saw that my code quality was... not good (see code example).

For Better understanding: This is how the tree looks like and what the code is giving back.

BUS-Type              Device Description
----------            -------------------
----------
PCI      |            |USB-Controller
USB      |            |----|USB-Root Hub
USB      |            |----|-----|Generic USB Hub
USB      |            |----|-----|-----|USB Device
USB      |            |----|-----|Generic USB Hub
.                     .
.                     .
And so on.

Now a code example:

if (hierarchyDeviceZero.Children.Count != 0) {
    for (int usbHierarchyLevelOne = 0; usbHierarchyLevelOne < hierarchyDeviceZero.Children.Count; usbHierarchyLevelOne++) {
        foreach (var hierarchyDeviceOne in usbDeviceTree.USBDeviceNodes.Where(
            d1 => d1.HardwareID.Equals(hierarchyDeviceZero.Children[usbHierarchyLevelOne].HardwareID))
        ) {
            Console.WriteLine("{0}\t|\t\t|---|{1}", hierarchyDeviceOne.EnumeratorName, hierarchyDeviceOne.Description);
            if (hierarchyDeviceOne.Children.Count != 0) {
                for (int usbHierarchyLevelTwo = 0; usbHierarchyLevelTwo < hierarchyDeviceZero.Children.Count; usbHierarchyLevelTwo++) {
                    foreach (var hierarchyDeviceTwo in usbDeviceTree.USBDeviceNodes.Where(
                        d1 => d1.HardwareID.Equals(hierarchyDeviceOne.Children[usbHierarchyLevelTwo].HardwareID))
                    ) {
                        Console.WriteLine("{0}\t|\t\t    |---|{1}", hierarchyDeviceTwo.EnumeratorName, hierarchyDeviceTwo.Description);
                        if (hierarchyDeviceTwo.Children.Count != 0) {
                            for (int usbHierarchyLevelThree = 0; usbHierarchyLevelThree < hierarchyDeviceZero.Children.Count; usbHierarchyLevelThree++) {
                                foreach (var hierarchyDeviceThree in usbDeviceTree.USBDeviceNodes.Where(
                                    d1 => d1.HardwareID.Equals(hierarchyDeviceTwo.Children[usbHierarchyLevelThree].HardwareID))
                                ) {
.
.
.
.
And so on (until 10th Hierarchylevel).

My Question is, how can i put this into a Recursive Method? I tried some tutorials but i somewhat did not understand how a method can call itself 10 times without overwriting its values... I hope you guys understand what i was trying to so.

PS.: Sorry for my bad english.

refactor it to a method that can be called with a paremeter level — DrKoch
– DrKoch, Commented Feb 2, 2015 at 16:00
Variables declared in the scope of the method (and parameters) are local to the particular invocation of that method. So a recursive call uses a separate set of local variables. — Hans Keﬆing
– Hans Keﬆing, Commented Feb 2, 2015 at 16:05

Maarten · Accepted Answer · 2015-02-02 16:30:29Z

1

In your data structure I see something wierd, namely you seem to have a UsbDeviceTree with all nodes, but you also have a .Children property on an individual node.

That aside, I think you can do something like this if you can just use the .Children node.

public class Device {
    public int HardwareId { get; set; }
    public Device[] Children {get; set; }
    /* ...the rest... */
}                               

void DisplayNodes(IEnumerable<Device> currentCollection, int indentation) {
    foreach (var currentNode in currentCollection) {
        // Display current node
        Console.WriteLine(
            ...
            display the node and
            use the indentation parameter to control the --- or ---|---
            ...
        );

        if (currentNode.Children != null) {
            DisplayNode(currentNode.Children, indentation + 1);
        }
    }
}

// Data
IEnumerable<Device> allDevices = usbDeviceTree.USBDeviceNodes;
IEnumerable<Device> rootDevices = allDevices
    .Where(x => x.IsRootNode /* TODO */)
    .ToArray();

// Display
DisplayNodes(rootDevices, 1);

answered Feb 2, 2015 at 16:30

Maarten

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1 Comment

Megajin Over a year ago

Thank you very much. That helped me alot! About that structure, I am working on that too =).

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