Define NativeControlComponentBase so as to eliminate direct use of RenderTreeBuilder in consumers

BlinForms.Framework/Controls/Button.cs

@@ -16,10 +16,13 @@ namespace BlinForms.Framework.Controls
 
         protected override void RenderAttributes(AttributesBuilder builder)
         {
+            base.RenderAttributes(builder);
+
             if (Text != null)
             {
                 builder.AddAttribute(nameof(Text), Text);
             }
+
             builder.AddAttribute("onclick", OnClick);
         }
 

BlinForms.Framework/Controls/FormsComponentBase.cs

@@ -1,4 +1,5 @@
-using Microsoft.AspNetCore.Components;
+using Emblazon;
+using Microsoft.AspNetCore.Components;
 using Microsoft.AspNetCore.Components.RenderTree;
 using System;
 using System.Drawing;
@@ -6,7 +7,7 @@ using System.Windows.Forms;
 
 namespace BlinForms.Framework.Controls
 {
-    public abstract class FormsComponentBase : ComponentBase
+    public abstract class FormsComponentBase : NativeControlComponentBase
     {
         [Parameter] public int? Top { get; set; }
         [Parameter] public int? Left { get; set; }
@@ -20,60 +21,40 @@ namespace BlinForms.Framework.Controls
 
         [Parameter] public AnchorStyles? Anchor { get; set; }
 
-        protected override void BuildRenderTree(RenderTreeBuilder builder)
+        protected override void RenderAttributes(AttributesBuilder builder)
         {
-            builder.OpenElement(0, GetType().FullName);
-
-            RenderAttributes(new AttributesBuilder(builder));
-
             if (Top != null)
             {
-                builder.AddAttribute(100, nameof(Top), Top.Value);
+                builder.AddAttribute(nameof(Top), Top.Value);
             }
             if (Left != null)
             {
-                builder.AddAttribute(101, nameof(Left), Left.Value);
+                builder.AddAttribute(nameof(Left), Left.Value);
             }
             if (Width != null)
             {
-                builder.AddAttribute(102, nameof(Width), Width.Value);
+                builder.AddAttribute(nameof(Width), Width.Value);
             }
             if (Height != null)
             {
-                builder.AddAttribute(103, nameof(Height), Height.Value);
+                builder.AddAttribute(nameof(Height), Height.Value);
             }
             if (Visible != null)
             {
-                builder.AddAttribute(104, nameof(Visible), Visible.Value);
+                builder.AddAttribute(nameof(Visible), Visible.Value);
             }
             if (BackColor != null)
             {
-                builder.AddAttribute(105, nameof(BackColor), BackColor.Value.ToArgb());
+                builder.AddAttribute(nameof(BackColor), BackColor.Value.ToArgb());
             }
             if (TabIndex != null)
             {
-                builder.AddAttribute(106, nameof(TabIndex), TabIndex.Value);
+                builder.AddAttribute(nameof(TabIndex), TabIndex.Value);
             }
             if (Anchor != null)
             {
-                builder.AddAttribute(107, nameof(Anchor), (int)Anchor.Value);
+                builder.AddAttribute(nameof(Anchor), (int)Anchor.Value);
             }
-
-            RenderContents(builder);
-
-            builder.CloseElement();
-        }
-
-        protected virtual void RenderAttributes(AttributesBuilder builder)
-        {
-        }
-
-        /// <summary>
-        /// Rendered contents should use sequence values 1000+.
-        /// </summary>
-        /// <param name="builder"></param>
-        protected virtual void RenderContents(RenderTreeBuilder builder)
-        {
         }
 
         public static void ApplyAttribute(Control control, ulong attributeEventHandlerId, string attributeName, object attributeValue, string attributeEventUpdatesAttributeName)

BlinForms.Framework/Controls/Label.cs

@@ -15,6 +15,8 @@ namespace BlinForms.Framework.Controls
 
         protected override void RenderAttributes(AttributesBuilder builder)
         {
+            base.RenderAttributes(builder);
+
             if (Text != null)
             {
                 builder.AddAttribute(nameof(Text), Text);

BlinForms.Framework/Controls/Panel.cs

@@ -1,6 +1,5 @@
 using Emblazon;
 using Microsoft.AspNetCore.Components;
-using Microsoft.AspNetCore.Components.RenderTree;
 
 namespace BlinForms.Framework.Controls
 {
@@ -13,10 +12,7 @@ namespace BlinForms.Framework.Controls
 
         [Parameter] public RenderFragment ChildContent { get; set; }
 
-        protected override void RenderContents(RenderTreeBuilder builder)
-        {
-            builder.AddContent(1000, ChildContent);
-        }
+        protected override RenderFragment GetChildContent() => ChildContent;
 
         class BlazorPanel : System.Windows.Forms.Panel, IBlazorNativeControl
         {

BlinForms.Framework/Controls/SplitContainer.cs

@@ -1,6 +1,5 @@
 using Emblazon;
 using Microsoft.AspNetCore.Components;
-using Microsoft.AspNetCore.Components.RenderTree;
 using System.Windows.Forms;
 
 namespace BlinForms.Framework.Controls
@@ -17,16 +16,15 @@ namespace BlinForms.Framework.Controls
 
         protected override void RenderAttributes(AttributesBuilder builder)
         {
+            base.RenderAttributes(builder);
+
             if (Orientation != null)
             {
                 builder.AddAttribute(nameof(Orientation), (int)Orientation.Value);
             }
         }
 
-        protected override void RenderContents(RenderTreeBuilder builder)
-        {
-            builder.AddContent(1000, ChildContent);
-        }
+        protected override RenderFragment GetChildContent() => ChildContent;
 
         class BlazorSplitContainer : System.Windows.Forms.SplitContainer, IBlazorNativeControl
         {

BlinForms.Framework/Controls/SplitterPanelBase.cs

@@ -1,5 +1,4 @@
 using Microsoft.AspNetCore.Components;
-using Microsoft.AspNetCore.Components.RenderTree;
 using System;
 using System.Windows.Forms;
 
@@ -24,9 +23,6 @@ namespace BlinForms.Framework.Controls
 
         [Parameter] public RenderFragment ChildContent { get; set; }
 
-        protected override void RenderContents(RenderTreeBuilder builder)
-        {
-            builder.AddContent(1000, ChildContent);
-        }
+        protected override RenderFragment GetChildContent() => ChildContent;
     }
 }

BlinForms.Framework/Controls/TextBox.cs

@@ -20,6 +20,8 @@ namespace BlinForms.Framework.Controls
 
         protected override void RenderAttributes(AttributesBuilder builder)
         {
+            base.RenderAttributes(builder);
+
             if (Text != null)
             {
                 builder.AddAttribute(nameof(Text), Text);

Emblazon/AttributesBuilder.cs

@@ -1,6 +1,6 @@
 using Microsoft.AspNetCore.Components.RenderTree;
 
-namespace BlinForms.Framework.Controls
+namespace Emblazon
 {
     // This wraps a RenderTreeBuilder in such a way that consumers
     // can only call the desired AddAttribute method, can't supply

Emblazon/NativeControlComponentBase.cs

@@ -0,0 +1,31 @@
+using Microsoft.AspNetCore.Components;
+using Microsoft.AspNetCore.Components.RenderTree;
+
+namespace Emblazon
+{
+    public abstract class NativeControlComponentBase : ComponentBase
+    {
+        protected override void BuildRenderTree(RenderTreeBuilder builder)
+        {
+            builder.OpenElement(0, GetType().FullName);
+            RenderAttributes(new AttributesBuilder(builder));
+
+            var childContent = GetChildContent();
+            if (childContent != null)
+            {
+                builder.AddContent(2, childContent);
+            }
+
+            builder.CloseElement();
+        }
+
+        protected virtual void RenderAttributes(AttributesBuilder builder)
+        {
+        }
+
+        protected virtual RenderFragment GetChildContent()
+        {
+            return null;
+        }
+    }
+}