/// <summary>
/// Renders the code for the given <paramref name="chunk"/>.
/// </summary>
/// <param name="chunk">A <see cref="TagHelperChunk"/> to render.</param>
public void RenderTagHelper(TagHelperChunk chunk)
{
// Remove any duplicate TagHelperDescriptors that reference the same type name. Duplicates can occur when
// multiple HtmlTargetElement attributes are on a TagHelper type and matches overlap for an HTML element.
// Having more than one descriptor with the same TagHelper type results in generated code that runs
// the same TagHelper X many times (instead of once) over a single HTML element.
var tagHelperDescriptors = chunk.Descriptors.Distinct(TypeBasedTagHelperDescriptorComparer.Default);
RenderBeginTagHelperScope(chunk.TagName, chunk.TagMode, chunk.Children);
RenderTagHelpersCreation(chunk, tagHelperDescriptors);
RenderAttributes(chunk.Attributes, tagHelperDescriptors);
// No need to run anything in design time mode.
if (!_designTimeMode)
{
RenderRunTagHelpers();
RenderWriteTagHelperMethodCall(chunk);
RenderEndTagHelpersScope();
}
}
private void RenderTagHelpersCreation(
TagHelperChunk chunk,
IEnumerable<TagHelperDescriptor> tagHelperDescriptors)
{
// This is to maintain value accessors for attributes when creating the TagHelpers.
// Ultimately it enables us to do scenarios like this:
// myTagHelper1.Foo = DateTime.Now;
// myTagHelper2.Foo = myTagHelper1.Foo;
var htmlAttributeValues = new Dictionary<string, string>(StringComparer.OrdinalIgnoreCase);
foreach (var tagHelperDescriptor in tagHelperDescriptors)
{
var tagHelperVariableName = GetVariableName(tagHelperDescriptor);
// Create the tag helper
_writer.WriteStartAssignment(tagHelperVariableName)
.WriteStartMethodInvocation(_tagHelperContext.CreateTagHelperMethodName,
tagHelperDescriptor.TypeName)
.WriteEndMethodInvocation();
// Execution contexts and throwing errors for null dictionary properties are a runtime feature.
if (_designTimeMode)
{
continue;
}
_writer.WriteInstanceMethodInvocation(
ExecutionContextVariableName,
_tagHelperContext.ExecutionContextAddMethodName,
tagHelperVariableName);
// Track dictionary properties we have confirmed are non-null.
var confirmedDictionaries = new HashSet<string>(StringComparer.Ordinal);
// Ensure that all created TagHelpers have initialized dictionary bound properties which are used
// via TagHelper indexers.
foreach (var chunkAttribute in chunk.Attributes)
{
var associatedAttributeDescriptor = tagHelperDescriptor.Attributes.FirstOrDefault(
attributeDescriptor => attributeDescriptor.IsNameMatch(chunkAttribute.Key));
if (associatedAttributeDescriptor != null &&
associatedAttributeDescriptor.IsIndexer &&
confirmedDictionaries.Add(associatedAttributeDescriptor.PropertyName))
{
// Throw a reasonable Exception at runtime if the dictionary property is null.
_writer
.Write("if (")
.Write(tagHelperVariableName)
.Write(".")
.Write(associatedAttributeDescriptor.PropertyName)
.WriteLine(" == null)");
using (_writer.BuildScope())
{
// System is in Host.NamespaceImports for all MVC scenarios. No need to generate FullName
// of InvalidOperationException type.
_writer
.Write("throw ")
.WriteStartNewObject(nameof(InvalidOperationException))
.WriteStartMethodInvocation(_tagHelperContext.FormatInvalidIndexerAssignmentMethodName)
.WriteStringLiteral(chunkAttribute.Key)
.WriteParameterSeparator()
.WriteStringLiteral(tagHelperDescriptor.TypeName)
.WriteParameterSeparator()
.WriteStringLiteral(associatedAttributeDescriptor.PropertyName)
.WriteEndMethodInvocation(endLine: false) // End of method call
.WriteEndMethodInvocation(endLine: true); // End of new expression / throw statement
}
}
}
}
}
private void RenderWriteTagHelperMethodCall(TagHelperChunk chunk)
{
_writer
.WriteStartInstrumentationContext(_context, chunk.Association, isLiteral: false)
.Write("await ");
if (!string.IsNullOrEmpty(_context.TargetWriterName))
{
_writer
.WriteStartMethodInvocation(_tagHelperContext.WriteTagHelperToAsyncMethodName)
.Write(_context.TargetWriterName)
.WriteParameterSeparator();
}
else
{
_writer.WriteStartMethodInvocation(_tagHelperContext.WriteTagHelperAsyncMethodName);
}
_writer
.Write(ExecutionContextVariableName)
.WriteEndMethodInvocation()
.WriteEndInstrumentationContext(_context);
}
private void RenderTagHelperOutput(TagHelperChunk chunk)
{
var tagHelperOutputAccessor =
$"{ExecutionContextVariableName}.{_tagHelperContext.ExecutionContextOutputPropertyName}";
if (ContainsChildContent(chunk.Children))
{
_writer
.Write("if (!")
.Write(tagHelperOutputAccessor)
.Write(".")
.Write(_tagHelperContext.TagHelperOutputIsContentModifiedPropertyName)
.WriteLine(")");
using (_writer.BuildScope())
{
_writer
.Write(tagHelperOutputAccessor)
.Write(".")
.WriteStartAssignment(_tagHelperContext.TagHelperOutputContentPropertyName)
.Write("await ")
.WriteInstanceMethodInvocation(
tagHelperOutputAccessor,
_tagHelperContext.TagHelperOutputGetChildContentAsyncMethodName);
}
}
_writer
.WriteStartInstrumentationContext(_context, chunk.Association, isLiteral: false);
if (!string.IsNullOrEmpty(_context.TargetWriterName))
{
_writer
.WriteStartMethodInvocation(_context.Host.GeneratedClassContext.WriteToMethodName)
.Write(_context.TargetWriterName)
.WriteParameterSeparator();
}
else
{
_writer.WriteStartMethodInvocation(_context.Host.GeneratedClassContext.WriteMethodName);
}
_writer
.Write(tagHelperOutputAccessor)
.WriteEndMethodInvocation()
.WriteEndInstrumentationContext(_context);
}