Improve: Make the numeric parameter control keep precision when the i…

…nput value is spinning up and down. (Issue #50)

BlazingStory/Internals/Components/Inputs/NumberInput.razor

@@ -39,15 +39,33 @@
 
     private bool _InitialFocused;
 
+    private string? _PrevValue;
+
+    private int _PrevDecimalPartLen = 1;
+
     protected override void OnParametersSet()
     {
         base.OnParametersSet();
         if (this.AllowDecimalPoint)
         {
+            if (this._PrevValue == this.Value) return;
+
             var parts = this.Value?.Split('.') ?? [];
             var hasDecimalPoint = parts.Length == 2;
-            var dicimalPartLen = (hasDecimalPoint ? parts[1] : "").Length;
-            this._Step = dicimalPartLen == 0 ? (hasDecimalPoint ? "0.1" : "1") : ("0." + new String('0', dicimalPartLen - 1) + "1");
+            var decimalPartLen = (hasDecimalPoint ? parts[1] : "").Length;
+
+            if (decimalPartLen < this._PrevDecimalPartLen && decimal.TryParse(this._PrevValue, out var prevValue) && decimal.TryParse(this.Value, out var value))
+            {
+                var stepValue = decimal.Parse(this._Step);
+                if (prevValue + stepValue == value || prevValue - stepValue == value)
+                {
+                    decimalPartLen = this._PrevDecimalPartLen;
+                }
+            }
+
+            this._Step = decimalPartLen == 0 ? (hasDecimalPoint ? "0.1" : "1") : ("0." + new String('0', decimalPartLen - 1) + "1");
+            this._PrevValue = this.Value;
+            this._PrevDecimalPartLen = decimalPartLen;
         }
         else
         {

Tests/BlazingStory.Test/Internals/Components/Inputs/NumberInputTest.cs

@@ -0,0 +1,113 @@
+using BlazingStory.Internals.Services;
+using Bunit;
+using Microsoft.AspNetCore.Components;
+
+namespace BlazingStory.Test.Internals.Components.Inputs;
+
+public class NumberInputTest
+{
+    [Test]
+    public void NumberInput_Step_with_Empty_Test()
+    {
+        // Given
+        using var ctx = new Bunit.TestContext();
+
+        // When
+        var cut = ctx.RenderComponent<BlazingStory.Internals.Components.Inputs.NumberInput>(builder => builder
+            .Add(_ => _.AllowDecimalPoint, true)
+            .Add(_ => _.Value, ""));
+
+        // Then
+        cut.Find("input").GetAttribute("step").Is("1");
+    }
+
+    [Test]
+    public void NumberInput_Step_with_IntegerText_Test()
+    {
+        // Given
+        using var ctx = new Bunit.TestContext();
+
+        // When
+        var cut = ctx.RenderComponent<BlazingStory.Internals.Components.Inputs.NumberInput>(builder => builder
+            .Add(_ => _.AllowDecimalPoint, true)
+            .Add(_ => _.Value, "321"));
+
+        // Then
+        cut.Find("input").GetAttribute("step").Is("1");
+    }
+
+    [Test]
+    public void NumberInput_Step_with_DecimalText_Test()
+    {
+        // Given
+        using var ctx = new Bunit.TestContext();
+
+        // When
+        var cut = ctx.RenderComponent<BlazingStory.Internals.Components.Inputs.NumberInput>(builder => builder
+            .Add(_ => _.AllowDecimalPoint, true)
+            .Add(_ => _.Value, "1.234"));
+
+        // Then
+        cut.Find("input").GetAttribute("step").Is("0.001");
+    }
+
+    [Test]
+    public void NumberInput_Step_KeepPrecision_IncrementalSpin_Test()
+    {
+        // Given
+        using var ctx = new Bunit.TestContext();
+
+        // When: null value -> Then: the step is 1.
+        var cut = ctx.RenderComponent<BlazingStory.Internals.Components.Inputs.NumberInput>(builder => builder
+            .Add(_ => _.AllowDecimalPoint, true)
+            .Add(_ => _.Value, null));
+        cut.Find("input").GetAttribute("step").Is("1");
+
+        // When: input text "1.29" for each typing -> Then: the step changes 1, 0.1, and 0.01.
+        cut.SetParametersAndRender(builder => builder.Add(_ => _.Value, "1"));
+        cut.Find("input").GetAttribute("step").Is("1");
+        cut.SetParametersAndRender(builder => builder.Add(_ => _.Value, "1."));
+        cut.Find("input").GetAttribute("step").Is("0.1");
+        cut.SetParametersAndRender(builder => builder.Add(_ => _.Value, "1.2"));
+        cut.Find("input").GetAttribute("step").Is("0.1");
+        cut.SetParametersAndRender(builder => builder.Add(_ => _.Value, "1.29"));
+        cut.Find("input").GetAttribute("step").Is("0.01");
+
+        // When: emulate incremental spin button -> Then: keep the step even though the decimal point length is descreased.
+        cut.SetParametersAndRender(builder => builder.Add(_ => _.Value, "1.3"));
+        cut.Find("input").GetAttribute("step").Is("0.01");
+
+        // When: redrawn was happened -> Then: keep the step.
+        cut.SetParametersAndRender(builder => builder.Add(_ => _.Value, "1.3"));
+        cut.Find("input").GetAttribute("step").Is("0.01");
+
+        // When: emulate incremental spin button -> Then: keep the step.
+        cut.SetParametersAndRender(builder => builder.Add(_ => _.Value, "1.31"));
+        cut.Find("input").GetAttribute("step").Is("0.01");
+    }
+
+    [Test]
+    public void NumberInput_Step_KeepPrecision_DecrementalSpin_Test()
+    {
+        // Given
+        using var ctx = new Bunit.TestContext();
+
+        // When: input "1.21" -> Then: the step is 0.01.
+        var cut = ctx.RenderComponent<BlazingStory.Internals.Components.Inputs.NumberInput>(builder => builder
+            .Add(_ => _.AllowDecimalPoint, true)
+            .Add(_ => _.Value, "1.21"));
+        cut.Find("input").GetAttribute("step").Is("0.01");
+
+        // When: emulate decremental spin button -> Then: keep the step even though the decimal point length is descreased.
+        cut.SetParametersAndRender(builder => builder.Add(_ => _.Value, "1.2"));
+        cut.Find("input").GetAttribute("step").Is("0.01");
+
+        // When: redrawn was happened -> Then: keep the step.
+        cut.SetParametersAndRender(builder => builder.Add(_ => _.Value, "1.2"));
+        cut.Find("input").GetAttribute("step").Is("0.01");
+
+        // When: emulate decremental spin button -> Then: keep the step.
+        cut.SetParametersAndRender(builder => builder.Add(_ => _.Value, "1.19"));
+        cut.Find("input").GetAttribute("step").Is("0.01");
+    }
+}