Collections
Similar data can often be handled more efficiently when stored and manipulated as a collection. You can use the System.Array class or the classes in the System.Collections namespace to add, remove, and modify either individual elements or a range of elements in a collection.
For more info go to https://docs.microsoft.com/en-us/dotnet/standard/collections/index.
TinyCLR OS collections support ArrayLists, Hash tables, Stacks, and Queues.
ArrayLists
ArrayLists have a significant advantage over arrays in that ArrayLists are automatically resized as needed, whereas arrays are limited to a fixed number of elements. The following code sample creates an ArrayList, adds a couple of records, and then iterates through the ArrayList items and displays each record.
class Program {
private struct rmaRecord {
public System.DateTime date;
public string modelNumber;
public string fault;
}
private static void Main() {
var rmaList = new System.Collections.ArrayList();
var record = new rmaRecord();
record.date = new System.DateTime(2020, 2, 21);
record.modelNumber = "XY23";
record.fault = "No power";
rmaList.Add(record);
record.date = new System.DateTime(2020, 2, 20);
record.modelNumber = "XY42";
record.fault = "Blown fuse";
rmaList.Add(record);
PrintValues(rmaList);
}
private static void PrintValues(System.Collections.ArrayList list) {
System.Diagnostics.Debug.WriteLine("Count: " + list.Count);
System.Diagnostics.Debug.WriteLine("Capacity: " + list.Capacity);
System.Diagnostics.Debug.WriteLine(" ");
System.Diagnostics.Debug.WriteLine("Values:");
foreach (rmaRecord record in list) {
System.Diagnostics.Debug.WriteLine(" Date: " + record.date.Year +
"/" + record.date.Month + "/" + record.date.Day);
System.Diagnostics.Debug.WriteLine(" Model#: " + record.modelNumber);
System.Diagnostics.Debug.WriteLine(" Fault: " + record.fault);
System.Diagnostics.Debug.WriteLine("----------");
}
}
}
The above code outputs the following:
Count: 2
Capacity: 4
Values:
Date: 2020/2/21
Model#: XY23
Fault: No power
----------
Date: 2020/2/20
Model#: XY42
Fault: Blown fuse
----------
In the above sample, rmaList.Clear() will remove all elements from rmaList, rmaList.RemoveAt(1) will remove only the second element in the list, and rmaList.Remove(record) will remove the first element that is equal to record.
Hash tables
Hash tables are used to store information in a way that associates each data element, or value, with a key that can be used to look up that value. Hash tables make it easy to quickly retrieve information that would otherwise be difficult to organize in an efficient manner.
For example, imagine trying to look up a phone number from a given name. You could make a two dimension array of names and phone numbers and then iterate through the array looking for the correct name, but this would be slow with a large array. Hash tables solve this problem by using a hash function to convert a key, in this case a name, into an array index that points directly to the data element you are looking for. This allows you to quickly retrieve the data directly instead of searching for it.
The following code sample creates a hash table, adds elements to the hash table, and then reads back the value for each key.
//Create a hash table.
System.Collections.Hashtable processorPin = new System.Collections.Hashtable();
//Add some elements to the hash table. There can be no duplicate keys, but duplicate
// values are allowed.
// Key Value
processorPin.Add("LDR", "PE3");
processorPin.Add("APP", "PB7");
processorPin.Add("MOD", "PD7");
processorPin.Add("WKUP", "PA0");
processorPin.Add("BTN1", "PE3");
processorPin.Add("BTN2", "PB7");
processorPin.Add("BTN3", "PD7");
//If a key does not exist, setting the default Item property
//for that key adds a new key/value pair.
processorPin["BTN4"] = "PD9";
//When you use foreach to enumerate hash table elements, the elements are retrieved
// as DictionaryEntry objects.
foreach (System.Collections.DictionaryEntry de in processorPin) {
System.Diagnostics.Debug.WriteLine("Key = " + de.Key + " Value = " + de.Value);
}
The above code outputs the following:
Key = MOD Value = PD7
Key = LDR Value = PE3
Key = BTN1 Value = PE3
Key = BTN2 Value = PB7
Key = BTN3 Value = PD7
Key = BTN4 Value = PD9
Key = WKUP Value = PA0
Key = APP Value = PB7
Stacks
Stacks are first in, last out (or last in, first out) collections of objects. The Push method is used to add items to a stack, and the Pop method is used to remove items from a stack. There is also a Peek method that returns the item at the top of the stack without removing it from the stack.
var sitCoreDevices = new System.Collections.Stack();
sitCoreDevices.Push("SC20100S");
sitCoreDevices.Push("SC20260B");
sitCoreDevices.Push("SCM20260D");
sitCoreDevices.Push("SCM20260E");
sitCoreDevices.Push("SCM20260N");
PrintValues(sitCoreDevices);
System.Diagnostics.Debug.WriteLine("Popped: " + sitCoreDevices.Pop().ToString());
System.Diagnostics.Debug.WriteLine(" ");
PrintValues(sitCoreDevices);
void PrintValues(System.Collections.Stack myQueue) {
System.Diagnostics.Debug.WriteLine("Count: " + myQueue.Count);
System.Diagnostics.Debug.WriteLine("Items in queue:");
foreach (System.Object obj in myQueue)
System.Diagnostics.Debug.WriteLine(" " + obj);
System.Diagnostics.Debug.WriteLine(" ");
}
The above code outputs the following:
The thread '<No Name>' (0x2) has exited with code 0 (0x0).
Count: 5
Items in queue:
SCM20260N
SCM20260E
SCM20260D
SC20260B
SC20100S
Popped: SCM20260N
Count: 4
Items in queue:
SCM20260E
SCM20260D
SC20260B
SC20100S
Queues
Queues are first in, first out collections of objects. To add items to a queue, the enqueue method is used. To remove items, the dequeue method is used.
var sitCoreDevices = new System.Collections.Queue();
sitCoreDevices.Enqueue("SC20100S");
sitCoreDevices.Enqueue("SC20260B");
sitCoreDevices.Enqueue("SCM20260D");
sitCoreDevices.Enqueue("SCM20260E");
sitCoreDevices.Enqueue("SCM20260N");
PrintValues(sitCoreDevices);
System.Diagnostics.Debug.WriteLine("Dequeued: " +
sitCoreDevices.Dequeue().ToString());
System.Diagnostics.Debug.WriteLine(" ");
PrintValues(sitCoreDevices);
void PrintValues(System.Collections.Queue myQueue) {
System.Diagnostics.Debug.WriteLine("Count: " + myQueue.Count);
System.Diagnostics.Debug.WriteLine("Items in queue:");
foreach (System.Object obj in myQueue)
System.Diagnostics.Debug.WriteLine(" " + obj);
System.Diagnostics.Debug.WriteLine(" ");
}
The above code outputs the following:
Count: 5
Items in queue:
SC20100S
SC20260B
SCM20260D
SCM20260N
SCM20260E
Dequeued: SC20100S
Count: 4
Items in queue:
SC20260B
SCM20260D
SCM20260N
SCM20260E