feat(Select): add IsUseActiveWhenValueIsNull parameter (#6304)

* feat: 增加 IsUseActiveWhenValueIsNull 参数

* test: 增加单元测试

Author: ArgoZhang

src/BootstrapBlazor/Components/Select/Select.razor.cs

@@ -26,6 +26,12 @@ public partial class Select<TValue> : ISelect, ILookup
     [NotNull]
     private ILookupService? InjectLookupService { get; set; }
 
+    /// <summary>
+    /// Gets or sets a value indicating whether the "active" state should be used when the associated value is null.
+    /// </summary>
+    [Parameter]
+    public bool IsUseActiveWhenValueIsNull { get; set; }
+
     /// <summary>
     /// Gets or sets the display template. Default is null.
     /// </summary>
@@ -444,10 +450,18 @@ private async Task OnChange(ChangeEventArgs args)
         {
             _lastSelectedValueString = "";
             _init = false;
-            return null;
+
+            return IsUseActiveWhenValueIsNull && !IsVirtualize
+                ? SetSelectedItemState(GetItemByRows())
+                : null;
         }
 
         var item = IsVirtualize ? GetItemByVirtualized() : GetItemByRows();
+        return SetSelectedItemState(item);
+    }
+
+    private SelectedItem? SetSelectedItemState(SelectedItem? item)
+    {
         if (item != null)
         {
             if (_init && DisableItemChangedWhenFirstRender)

test/UnitTest/Components/SelectTest.cs

@@ -12,6 +12,38 @@ namespace UnitTest.Components;
 
 public class SelectTest : BootstrapBlazorTestBase
 {
+    [Fact]
+    public async Task IsUseActiveWhenValueNull_Ok()
+    {
+        var tcs = new TaskCompletionSource();
+        var selectedValue = "";
+        var cut = Context.RenderComponent<BootstrapBlazorRoot>(pb =>
+        {
+            pb.AddChildContent<Select<string>>(pb =>
+            {
+                pb.Add(a => a.ShowSearch, true);
+                pb.Add(a => a.Items, new List<SelectedItem>()
+                {
+                    new("1", "Test1"),
+                    new("2", "Test2") { Active = true }
+                });
+                pb.Add(a => a.IsUseActiveWhenValueIsNull, true);
+                pb.Add(a => a.OnSelectedItemChanged, item =>
+                {
+                    selectedValue = item.Value;
+                    tcs.SetResult();
+                    return Task.CompletedTask;
+                });
+            });
+        });
+
+        await tcs.Task;
+
+        // 组件未设置 Value 参数，应该使用 Test2 作为初始选项，并且触发 SelectedItemChanged 回调
+        Assert.Equal("2", selectedValue);
+        cut.Contains("value=\"Test2\"");
+    }
+
     [Fact]
     public async Task OnSearchTextChanged_Null()
     {