fix(Search): DisplayText needs to be shown on first load (#6351)

* fix bug #6350

* refactor: 重构 OnSearch 参数更改为可为空

---------
Co-Authored-By: yacper <[email protected]>
Co-authored-by: Argo Zhang <[email protected]>

Author: yacper

src/BootstrapBlazor/Components/Search/Search.razor.cs

@@ -133,7 +133,7 @@ public partial class Search<TValue>
     /// Gets or sets the callback delegate when the search button is clicked.
     /// </summary>
     [Parameter]
-    public Func<string, Task<IEnumerable<TValue>>>? OnSearch { get; set; }
+    public Func<string?, Task<IEnumerable<TValue>>>? OnSearch { get; set; }
 
     /// <summary>
     /// Gets or sets the callback method to get display text. Default is null, using ToString() method.
@@ -200,13 +200,16 @@ protected override void OnParametersSet()
         NoDataTip ??= Localizer[nameof(NoDataTip)];
         _filterItems ??= [];
 
+        // 这里应该获得初始值
+        _displayText = GetDisplayText(Value);
+
         if (Debounce == 0)
         {
             Debounce = 200;
         }
     }
 
-    private string _displayText = "";
+    private string? _displayText;
     private async Task OnSearchClick()
     {
         if (OnSearch != null)
@@ -226,7 +229,7 @@ private async Task OnSearchClick()
 
     private async Task OnClearClick()
     {
-        _displayText = "";
+        _displayText = null;
         if (OnClear != null)
         {
             await OnClear();
@@ -247,7 +250,7 @@ private async Task OnClearClick()
     private async Task OnClickItem(TValue val)
     {
         CurrentValue = val;
-        _displayText = GetDisplayText(val) ?? "";
+        _displayText = GetDisplayText(val);
 
         if (OnSelectedItemChanged != null)
         {