Only update console, when content changes

Sharp7.Monitor/CustomStyles.cs

@@ -1,5 +1,7 @@
 using Spectre.Console;
 
+namespace Sharp7.Monitor;
+
 public static class CustomStyles
 {
     public static Style Error { get; } = new Style(foreground: Color.Red);

Sharp7.Monitor/ReadPlcCommand.cs

@@ -1,15 +1,15 @@
-using System.Collections;
+using System.ComponentModel;
-using System.ComponentModel;
 using System.Reactive.Linq;
 using System.Reactive.Threading.Tasks;
 using JetBrains.Annotations;
-using Sharp7.Read;
 using Sharp7.Rx;
 using Sharp7.Rx.Enums;
 using Spectre.Console;
 using Spectre.Console.Cli;
 using Spectre.Console.Rendering;
 
+namespace Sharp7.Monitor;
+
 internal sealed class ReadPlcCommand : AsyncCommand<ReadPlcCommand.Settings>
 {
     public override async Task<int> ExecuteAsync(CommandContext context, Settings settings)
@@ -27,9 +27,9 @@ internal sealed class ReadPlcCommand : AsyncCommand<ReadPlcCommand.Settings>
         return 0;
     }
 
-    private static IRenderable FormatCellData(VariableRecord record)
+    private static IRenderable FormatCellData(object value)
     {
-        return record.Value switch
+        return value switch
         {
             IRenderable renderable => renderable,
             Exception ex => new Text(ex.Message, CustomStyles.Error),
@@ -42,10 +42,10 @@ internal sealed class ReadPlcCommand : AsyncCommand<ReadPlcCommand.Settings>
             long => FormatNo(),
             ulong => FormatNo(),
 
-            _ => new Text(record.Value.ToString() ?? "")
+            _ => new Text(value.ToString() ?? "")
         };
 
-        Markup FormatNo() => new($"[blue]0x{record.Value:X2}[/]  {record.Value}");
+        Markup FormatNo() => new($"[blue]0x{value:X2}[/]  {value}");
     }
 
     private static async Task RunProgram(Settings settings, CancellationToken token)
@@ -99,9 +99,10 @@ internal sealed class ReadPlcCommand : AsyncCommand<ReadPlcCommand.Settings>
                 while (!token.IsCancellationRequested)
                 {
                     foreach (var record in variableContainer.VariableRecords)
+                        if (record.HasUpdate(out var value))
                             table.Rows.Update(
                                 record.RowIdx, 1,
-                        FormatCellData(record)
+                                FormatCellData(value)
                             );
 
                     ctx.Refresh();

Sharp7.Monitor/StringHelper.cs

@@ -1,4 +1,4 @@
-namespace Sharp7.Read;
+namespace Sharp7.Monitor;
 
 public static class StringHelper
 {

Sharp7.Monitor/VariableContainer.cs

@@ -3,6 +3,8 @@ using Sharp7.Rx.Enums;
 using Sharp7.Rx.Interfaces;
 using Spectre.Console;
 
+namespace Sharp7.Monitor;
+
 public class VariableContainer : IDisposable
 {
     private readonly IDisposable subscriptions;

Sharp7.Monitor/VariableRecord.cs

@@ -1,6 +1,55 @@
-public class VariableRecord
+using System.Diagnostics.CodeAnalysis;
+
+namespace Sharp7.Monitor;
+
+public class VariableRecord
 {
+    private object value = new();
+    private int valueUpdated;
     public required string Address { get; init; }
     public required int RowIdx { get; init; }
-    public object Value { get; set; }
+
+    public object Value
+    {
+        get => value;
+        set
+        {
+            if (!IsEquivalent(this.value, value))
+            {
+                this.value = value;
+                valueUpdated = 1;
+            }
+        }
+    }
+
+    private bool IsEquivalent(object oldValue, object newValue)
+    {
+        // Special treatmant for byte arrays
+        if (oldValue is byte[] oldArray && newValue is byte[] newArray)
+        {
+            if (oldArray.Length != newArray.Length) return false;
+
+            for (var i = 0; i < oldArray.Length; i++)
+                if (oldArray[i] != newArray[i]) return false;
+
+            return true;
+        }
+
+        // all other types read from PLC have value compare semantics. 
+        return oldValue == newValue;
+    }
+
+    public bool HasUpdate([NotNullWhen(true)] out object? newValue)
+    {
+        if (Interlocked.Exchange(ref valueUpdated, 0) == 1)
+        {
+            newValue = value;
+            return true;
+        }
+        else
+        {
+            newValue = null;
+            return false;
+        }
+    }
 }