feat: add temp template.

src/Ursa/Controls/Form/Form.cs

@@ -1,25 +1,32 @@
 using Avalonia;
-using Avalonia.Collections;
 using Avalonia.Controls;
-using Avalonia.Markup.Xaml.Templates;
-using Avalonia.Metadata;
 
 namespace Ursa.Controls;
 
 public class Form: ItemsControl
 {
-
-    public static readonly StyledProperty<AvaloniaList<FormItem>> ItemsProperty = AvaloniaProperty.Register<Form, AvaloniaList<FormItem>>(
-        "Items");
+    public static readonly AttachedProperty<string> LabelProperty =
+        AvaloniaProperty.RegisterAttached<Form, Control, string>("Label");
+    public static void SetLabel(Control obj, string value) => obj.SetValue(LabelProperty, value);
+    public static string GetLabel(Control obj) => obj.GetValue(LabelProperty);
     
-    public AvaloniaList<FormItem> Items
-    {
-        get => GetValue(ItemsProperty);
-        set => SetValue(ItemsProperty, value);
-    }
 
-    public void AddChild(object child)
+    public static readonly AttachedProperty<bool> IsRequiredProperty =
+        AvaloniaProperty.RegisterAttached<Form, Control, bool>("IsRequired");
+    public static void SetIsRequired(Control obj, bool value) => obj.SetValue(IsRequiredProperty, value);
+    public static bool GetIsRequired(Control obj) => obj.GetValue(IsRequiredProperty);
+
+    protected override bool NeedsContainerOverride(object? item, int index, out object? recycleKey)
     {
-        throw new NotImplementedException();
+        recycleKey = null;
+        return item is FormItem or FormGroup;
+    }
+    
+    protected override Control CreateContainerForItemOverride(object? item, int index, object? recycleKey)
+    {
+        if (item is not Control control) return new FormItem();
+        string label = GetLabel(control);
+        bool isRequired = GetIsRequired(control);
+        return new FormItem() { Label = label, IsRequired = isRequired, Content = control };
     }
 }