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[Components] Create a renderer to render components into HTML (#4463)
* Adds an HtmlRenderer to Microsoft.AspNetCore.Components * It renders the component into a list of strings. * It only handles synchronous rendering.
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‎src/Components/Components.sln

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Microsoft Visual Studio Solution File, Format Version 12.00
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# Visual Studio 15
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VisualStudioVersion = 15.0.27130.2010
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# Visual Studio Version 16
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VisualStudioVersion = 16.0.28315.86
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MinimumVisualStudioVersion = 10.0.40219.1
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Project("{2150E333-8FDC-42A3-9474-1A3956D46DE8}") = "samples", "samples", "{F5FDD4E5-6A52-4A86-BE5E-5E42CB1DC8DA}"
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EndProject

‎src/Components/build/dependencies.props

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<InternalAspNetCoreSdkPackageVersion>3.0.0-alpha1-20181011.3</InternalAspNetCoreSdkPackageVersion>
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<MicrosoftAspNetCoreBenchmarkRunnerSourcesPackageVersion>2.2.0-preview1-34576</MicrosoftAspNetCoreBenchmarkRunnerSourcesPackageVersion>
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<MicrosoftAspNetCoreAppPackageVersion>3.0.0-alpha1-10605</MicrosoftAspNetCoreAppPackageVersion>
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<MicrosoftAspNetCoreHtmlAbstractionsPackageVersion>3.0.0-alpha1-10605</MicrosoftAspNetCoreHtmlAbstractionsPackageVersion>
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<MicrosoftAspNetCoreRazorDesignPackageVersion>3.0.0-alpha1-10605</MicrosoftAspNetCoreRazorDesignPackageVersion>
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<MicrosoftExtensionsDependencyInjectionPackageVersion>3.0.0-alpha1-10605</MicrosoftExtensionsDependencyInjectionPackageVersion>
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<MicrosoftNETCoreAppPackageVersion>3.0.0-preview1-26907-05</MicrosoftNETCoreAppPackageVersion>
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<SignalRPackageVersion>3.0.0-alpha1-10605</SignalRPackageVersion>
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<TemplateBlazorPackageVersion>0.8.0-preview1-20181122.3</TemplateBlazorPackageVersion>

‎src/Components/src/Microsoft.AspNetCore.Components/Rendering/ComponentState.cs

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@@ -29,6 +29,7 @@ internal class ComponentState
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public int ComponentId => _componentId;
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public IComponent Component => _component;
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public ComponentState ParentComponentState => _parentComponentState;
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public RenderTreeBuilder CurrrentRenderTree => _renderTreeBuilderCurrent;
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/// <summary>
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/// Constructs an instance of <see cref="ComponentState"/>.

‎src/Components/src/Microsoft.AspNetCore.Components/Rendering/HtmlRenderer.cs

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// Copyright (c) .NET Foundation. All rights reserved.
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// Licensed under the Apache License, Version 2.0. See License.txt in the project root for license information.
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using System;
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using System.Collections.Generic;
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using System.Diagnostics;
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using System.Threading.Tasks;
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using Microsoft.AspNetCore.Components.RenderTree;
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namespace Microsoft.AspNetCore.Components.Rendering
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{
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/// <summary>
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/// A <see cref="Renderer"/> that produces HTML.
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/// </summary>
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public class HtmlRenderer : Renderer
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{
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private static readonly HashSet<string> SelfClosingElements = new HashSet<string>(StringComparer.OrdinalIgnoreCase)
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{
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"area", "base", "br", "col", "embed", "hr", "img", "input", "link", "meta", "param", "source", "track", "wbr"
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};
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private readonly Func<string, string> _htmlEncoder;
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/// <summary>
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/// Initializes a new instance of <see cref="HtmlRenderer"/>.
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/// </summary>
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/// <param name="serviceProvider">The <see cref="IServiceProvider"/> to use to instantiate components.</param>
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/// <param name="htmlEncoder">A <see cref="Func{T, TResult}"/> that will HTML encode the given string.</param>
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public HtmlRenderer(IServiceProvider serviceProvider, Func<string, string> htmlEncoder) : base(serviceProvider)
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{
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_htmlEncoder = htmlEncoder;
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}
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/// <inheritdoc />
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protected override Task UpdateDisplayAsync(in RenderBatch renderBatch)
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{
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return Task.CompletedTask;
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}
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/// <summary>
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/// Renders a component into a sequence of <see cref="string"/> fragments that represent the textual representation
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/// of the HTML produced by the component.
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/// </summary>
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/// <typeparam name="T">The type of the <see cref="IComponent"/>.</typeparam>
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/// <param name="initialParameters">A <see cref="ParameterCollection"/> with the initial parameters to render the component.</param>
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/// <returns>A sequence of <see cref="string"/> fragments that represent the HTML text of the component.</returns>
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public IEnumerable<string> RenderComponent<T>(ParameterCollection initialParameters) where T : IComponent
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{
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return RenderComponent(typeof(T), initialParameters);
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}
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/// <summary>
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/// Renders a component into a sequence of <see cref="string"/> fragments that represent the textual representation
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/// of the HTML produced by the component.
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/// </summary>
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/// <param name="componentType">The type of the <see cref="IComponent"/>.</param>
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/// <param name="initialParameters">A <see cref="ParameterCollection"/> with the initial parameters to render the component.</param>
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/// <returns>A sequence of <see cref="string"/> fragments that represent the HTML text of the component.</returns>
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private IEnumerable<string> RenderComponent(Type componentType, ParameterCollection initialParameters)
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{
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var frames = CreateInitialRender(componentType, initialParameters);
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if (frames.Count == 0)
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{
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return Array.Empty<string>();
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}
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else
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{
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var result = new List<string>();
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var newPosition = RenderFrames(result, frames, 0, frames.Count);
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Debug.Assert(newPosition == frames.Count);
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return result;
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}
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}
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private int RenderFrames(List<string> result, ArrayRange<RenderTreeFrame> frames, int position, int maxElements)
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{
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var nextPosition = position;
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var endPosition = position + maxElements;
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while (position < endPosition)
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{
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nextPosition = RenderCore(result, frames, position, maxElements);
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if (position == nextPosition)
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{
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throw new InvalidOperationException("We didn't consume any input.");
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}
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position = nextPosition;
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}
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return nextPosition;
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}
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private int RenderCore(
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List<string> result,
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ArrayRange<RenderTreeFrame> frames,
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int position,
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int length)
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{
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ref var frame = ref frames.Array[position];
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switch (frame.FrameType)
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{
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case RenderTreeFrameType.Element:
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return RenderElement(result, frames, position);
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case RenderTreeFrameType.Attribute:
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return RenderAttributes(result, frames, position, 1);
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case RenderTreeFrameType.Text:
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result.Add(_htmlEncoder(frame.TextContent));
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return ++position;
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case RenderTreeFrameType.Markup:
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result.Add(frame.MarkupContent);
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return ++position;
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case RenderTreeFrameType.Component:
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return RenderChildComponent(result, frames, position);
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case RenderTreeFrameType.Region:
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return RenderFrames(result, frames, position + 1, frame.RegionSubtreeLength - 1);
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case RenderTreeFrameType.ElementReferenceCapture:
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case RenderTreeFrameType.ComponentReferenceCapture:
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return ++position;
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default:
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throw new InvalidOperationException($"Invalid element frame type '{frame.FrameType}'.");
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}
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}
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private int RenderChildComponent(
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List<string> result,
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ArrayRange<RenderTreeFrame> frames,
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int position)
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{
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ref var frame = ref frames.Array[position];
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var childFrames = GetCurrentRenderTreeFrames(frame.ComponentId);
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RenderFrames(result, childFrames, 0, childFrames.Count);
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return position + frame.ComponentSubtreeLength;
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}
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private int RenderElement(
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List<string> result,
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ArrayRange<RenderTreeFrame> frames,
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int position)
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{
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ref var frame = ref frames.Array[position];
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result.Add("<");
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result.Add(frame.ElementName);
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var afterAttributes = RenderAttributes(result, frames, position + 1, frame.ElementSubtreeLength - 1);
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var remainingElements = frame.ElementSubtreeLength + position - afterAttributes;
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if (remainingElements > 0)
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{
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result.Add(">");
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var afterElement = RenderChildren(result, frames, afterAttributes, remainingElements);
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result.Add("</");
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result.Add(frame.ElementName);
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result.Add(">");
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Debug.Assert(afterElement == position + frame.ElementSubtreeLength);
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return afterElement;
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}
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else
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{
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if (SelfClosingElements.Contains(frame.ElementName))
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{
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result.Add(" />");
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}
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else
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{
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result.Add(">");
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result.Add("</");
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result.Add(frame.ElementName);
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result.Add(">");
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}
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Debug.Assert(afterAttributes == position + frame.ElementSubtreeLength);
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return afterAttributes;
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}
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}
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private int RenderChildren(List<string> result, ArrayRange<RenderTreeFrame> frames, int position, int maxElements)
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{
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if (maxElements == 0)
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{
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return position;
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}
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return RenderFrames(result, frames, position, maxElements);
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}
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private int RenderAttributes(
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List<string> result,
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ArrayRange<RenderTreeFrame> frames, int position, int maxElements)
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{
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if (maxElements == 0)
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{
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return position;
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}
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for (var i = 0; i < maxElements; i++)
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{
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var candidateIndex = position + i;
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ref var frame = ref frames.Array[candidateIndex];
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if (frame.FrameType != RenderTreeFrameType.Attribute)
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{
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return candidateIndex;
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}
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switch (frame.AttributeValue)
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{
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case bool flag when flag:
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result.Add(" ");
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result.Add(frame.AttributeName);
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break;
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case string value:
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result.Add(" ");
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result.Add(frame.AttributeName);
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result.Add("=");
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result.Add("\"");
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result.Add(_htmlEncoder(value));
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result.Add("\"");
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break;
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default:
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break;
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}
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}
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return position + maxElements;
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}
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private ArrayRange<RenderTreeFrame> CreateInitialRender(Type componentType, ParameterCollection initialParameters)
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{
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var component = InstantiateComponent(componentType);
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var componentId = AssignRootComponentId(component);
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RenderRootComponent(componentId, initialParameters);
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return GetCurrentRenderTreeFrames(componentId);
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}
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}
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}
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‎src/Components/src/Microsoft.AspNetCore.Components/Rendering/Renderer.cs

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protected int AssignRootComponentId(IComponent component)
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=> AttachAndInitComponent(component, -1).ComponentId;
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/// <summary>
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/// Gets the current render tree for a given component.
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/// </summary>
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/// <param name="componentId">The id for the component.</param>
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/// <returns>The <see cref="RenderTreeBuilder"/> representing the current render tree.</returns>
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private protected ArrayRange<RenderTreeFrame> GetCurrentRenderTreeFrames(int componentId) => GetRequiredComponentState(componentId).CurrrentRenderTree.GetFrames();
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/// <summary>
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/// Performs the first render for a root component. After this, the root component
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/// makes its own decisions about when to re-render, so there is no need to call
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.SetDirectParameters(ParameterCollection.Empty);
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}
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/// <summary>
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/// Performs the first render for a root component. After this, the root component
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/// makes its own decisions about when to re-render, so there is no need to call
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/// this more than once.
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/// </summary>
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/// <param name="componentId">The ID returned by <see cref="AssignRootComponentId(IComponent)"/>.</param>
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/// <param name="initialParameters">The <see cref="ParameterCollection"/>with the initial parameters to use for rendering.</param>
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protected void RenderRootComponent(int componentId, ParameterCollection initialParameters)
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{
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GetRequiredComponentState(componentId)
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.SetDirectParameters(initialParameters);
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}
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private ComponentState AttachAndInitComponent(IComponent component, int parentComponentId)
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{
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var componentId = _nextComponentId++;

‎src/Components/test/Microsoft.AspNetCore.Components.Test/Microsoft.AspNetCore.Components.Test.csproj

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<Project Sdk="Microsoft.NET.Sdk">
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<Project Sdk="Microsoft.NET.Sdk">
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<PropertyGroup>
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<TargetFramework>netcoreapp3.0</TargetFramework>
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<PackageReference Include="xunit" Version="2.3.1" />
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<PackageReference Include="xunit.runner.visualstudio" Version="2.3.1" />
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<DotNetCliToolReference Include="dotnet-xunit" Version="2.3.1" />
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<PackageReference Include="Microsoft.Extensions.DependencyInjection" Version="$(MicrosoftExtensionsDependencyInjectionPackageVersion)" />
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<PackageReference Include="Microsoft.AspNetCore.Html.Abstractions" Version="$(MicrosoftAspNetCoreHtmlAbstractionsPackageVersion)" />
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</ItemGroup>
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<ItemGroup>

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