Sync date filter UI with filter criteria in BandGridBase

Added logic to synchronize the date filter UI with the current
filter criteria by updating _filterFrom and _filterTo based on
the CriteriaOperator. Introduced SyncDateFilterFromContext and
ParseDateOperand helpers to extract and apply "from" and "to"
date values, ensuring UI and filter state remain consistent.

DbFirst.BlazorWebApp/Components/BandGridBase.cs

@@ -1,6 +1,7 @@
 using DbFirst.BlazorWebApp.Models.Grid;
 using DbFirst.BlazorWebApp.Services;
 using DevExpress.Blazor;
+using DevExpress.Data.Filtering;
 using Microsoft.AspNetCore.Components;
 using Microsoft.AspNetCore.Components.Forms;
 using Microsoft.AspNetCore.Components.Rendering;
@@ -24,6 +25,16 @@ public abstract class BandGridBase<TItem> : ComponentBase
     protected bool gridLayoutApplied;
     protected IGrid? gridRef;
 
+    // --- Datumsfilter-Zustand ---
+    private readonly Dictionary<string, DateTime?> _filterFrom = new(StringComparer.OrdinalIgnoreCase);
+    private readonly Dictionary<string, DateTime?> _filterTo = new(StringComparer.OrdinalIgnoreCase);
+
+    // Stabile Referenzen: werden einmal pro FieldName erstellt und wiederverwendet
+    private readonly Dictionary<string, EventCallback<DateTime?>> _fromCallbacks = new(StringComparer.OrdinalIgnoreCase);
+    private readonly Dictionary<string, EventCallback<DateTime?>> _toCallbacks = new(StringComparer.OrdinalIgnoreCase);
+    private readonly Dictionary<string, RenderFragment<GridDataColumnFilterMenuTemplateContext>> _dateFilterTemplates = new(StringComparer.OrdinalIgnoreCase);
+    private readonly Dictionary<string, GridDataColumnFilterMenuTemplateContext> _filterContexts = new(StringComparer.OrdinalIgnoreCase);
+
     // --- SizeMode ---
     protected SizeMode _sizeMode = SizeMode.Medium;
     protected static readonly List<SizeMode> _sizeModes = Enum.GetValues<SizeMode>().ToList();
@@ -224,9 +235,134 @@ public abstract class BandGridBase<TItem> : ComponentBase
             builder.AddAttribute(seq++, "DisplayFormat", column.DisplayFormat);
         if (column.ReadOnly)
             builder.AddAttribute(seq++, "ReadOnly", true);
+        if (column.FilterType == ColumnFilterType.Date)
+            builder.AddAttribute(seq++, "FilterMenuTemplate", GetOrCreateDateFilterTemplate(column.FieldName));
         builder.CloseComponent();
     }
 
+    private RenderFragment<GridDataColumnFilterMenuTemplateContext> GetOrCreateDateFilterTemplate(string fieldName)
+    {
+        if (!_dateFilterTemplates.TryGetValue(fieldName, out var template))
+        {
+            // EventCallbacks einmalig erstellen – stabile Referenzen über alle Renders
+            _fromCallbacks[fieldName] = EventCallback.Factory.Create<DateTime?>(this, (DateTime? v) => OnFilterFromChanged(fieldName, v));
+            _toCallbacks[fieldName] = EventCallback.Factory.Create<DateTime?>(this, (DateTime? v) => OnFilterToChanged(fieldName, v));
+            template = BuildDateFilterTemplate(fieldName);
+            _dateFilterTemplates[fieldName] = template;
+        }
+        return template;
+    }
+
+    private RenderFragment<GridDataColumnFilterMenuTemplateContext> BuildDateFilterTemplate(string fieldName) =>
+        ctx => b =>
+        {
+            _filterContexts[fieldName] = ctx;
+            SyncDateFilterFromContext(fieldName, ctx.FilterCriteria);
+            int s = 0;
+            b.OpenElement(s++, "div");
+            b.AddAttribute(s++, "class", "date-filter-menu p-2");
+
+            // Ab Datum
+            b.OpenElement(s++, "div");
+            b.AddAttribute(s++, "class", "mb-2");
+            b.OpenElement(s++, "label");
+            b.AddAttribute(s++, "class", "form-label small fw-semibold");
+            b.AddContent(s++, "Ab Datum");
+            b.CloseElement();
+            b.OpenComponent<DxDateEdit<DateTime?>>(s++);
+            b.AddAttribute(s++, "Date", _filterFrom.GetValueOrDefault(fieldName));
+            b.AddAttribute(s++, "DateChanged", _fromCallbacks[fieldName]);
+            b.AddAttribute(s++, "ClearButtonDisplayMode", DataEditorClearButtonDisplayMode.Auto);
+            b.AddAttribute(s++, "NullText", "Kein Startdatum");
+            b.AddAttribute(s++, "Width", "100%");
+            b.CloseComponent();
+            b.CloseElement();
+
+            // Bis Datum
+            b.OpenElement(s++, "div");
+            b.AddAttribute(s++, "class", "mb-0");
+            b.OpenElement(s++, "label");
+            b.AddAttribute(s++, "class", "form-label small fw-semibold");
+            b.AddContent(s++, "Bis Datum");
+            b.CloseElement();
+            b.OpenComponent<DxDateEdit<DateTime?>>(s++);
+            b.AddAttribute(s++, "Date", _filterTo.GetValueOrDefault(fieldName));
+            b.AddAttribute(s++, "DateChanged", _toCallbacks[fieldName]);
+            b.AddAttribute(s++, "ClearButtonDisplayMode", DataEditorClearButtonDisplayMode.Auto);
+            b.AddAttribute(s++, "NullText", "Kein Enddatum");
+            b.AddAttribute(s++, "Width", "100%");
+            b.CloseComponent();
+            b.CloseElement();
+
+            b.CloseElement();
+        };
+
+    private void SyncDateFilterFromContext(string fieldName, CriteriaOperator? criteria)
+    {
+        if (criteria == null)
+        {
+            _filterFrom[fieldName] = null;
+            _filterTo[fieldName] = null;
+            return;
+        }
+
+        DateTime? from = null;
+        DateTime? to = null;
+
+        if (criteria is GroupOperator group)
+        {
+            foreach (var op in group.Operands.OfType<BinaryOperator>())
+                ParseDateOperand(op, ref from, ref to);
+        }
+        else if (criteria is BinaryOperator binary)
+        {
+            ParseDateOperand(binary, ref from, ref to);
+        }
+
+        _filterFrom[fieldName] = from;
+        _filterTo[fieldName] = to;
+    }
+
+    private static void ParseDateOperand(BinaryOperator op, ref DateTime? from, ref DateTime? to)
+    {
+        if (op.RightOperand is not OperandValue val || val.Value is not DateTime dt) return;
+        if (op.OperatorType == BinaryOperatorType.GreaterOrEqual) from = dt;
+        else if (op.OperatorType == BinaryOperatorType.Less) to = dt.AddDays(-1);
+    }
+
+    private void OnFilterFromChanged(string fieldName, DateTime? value)
+    {
+        _filterFrom[fieldName] = value;
+        ApplyDateFilter(fieldName);
+    }
+
+    private void OnFilterToChanged(string fieldName, DateTime? value)
+    {
+        _filterTo[fieldName] = value;
+        ApplyDateFilter(fieldName);
+    }
+
+    private void ApplyDateFilter(string fieldName)
+    {
+        var ops = new List<CriteriaOperator>();
+        if (_filterFrom.TryGetValue(fieldName, out var from) && from.HasValue)
+            ops.Add(new BinaryOperator(fieldName, from.Value.Date, BinaryOperatorType.GreaterOrEqual));
+        if (_filterTo.TryGetValue(fieldName, out var to) && to.HasValue)
+            ops.Add(new BinaryOperator(fieldName, to.Value.Date.AddDays(1), BinaryOperatorType.Less));
+
+        CriteriaOperator? criteria = ops.Count switch
+        {
+            0 => null,
+            1 => ops[0],
+            _ => new GroupOperator(GroupOperatorType.And, ops)
+        };
+
+        gridRef?.SetFieldFilterCriteria(fieldName, criteria);
+        if (_filterContexts.TryGetValue(fieldName, out var ctx))
+            ctx.FilterCriteria = criteria;
+        _ = InvokeAsync(StateHasChanged);
+    }
+
     protected void SetEditContext(EditContext context)
     {
         if (editContext == context) return;