examples/Layouts/SampleLayoutsApp/Layout/ForwardingLayout.cs

#region Apache License
//
// Licensed to the Apache Software Foundation (ASF) under one or more 
// contributor license agreements. See the NOTICE file distributed with
// this work for additional information regarding copyright ownership. 
// The ASF licenses this file to you under the Apache License, Version 2.0
// (the "License"); you may not use this file except in compliance with 
// the License. You may obtain a copy of the License at
//
// http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
//
#endregion

using System.IO;
using log4net.Core;
using log4net.Layout;

namespace SampleLayoutsApp.Layout;

/// <summary>
/// The ForwardingLayout forwards to a nested <see cref="ILayout"/>
/// </summary>
/// <remarks>
/// The ForwardingLayout base class is used by layouts that want
/// to decorate other <see cref="ILayout"/> objects.
/// </remarks>
public abstract class ForwardingLayout : ILayout, IOptionHandler
{
  /// <inheritdoc/>
  protected ForwardingLayout()
  {
  }

  /// <inheritdoc/>
  public ILayout? Layout { get; set; }

  #region Implementation of IOptionHandler

  /// <summary>
  /// Activate component options
  /// </summary>
  /// <remarks>
  /// <para>
  /// This is part of the <see cref="IOptionHandler"/> delayed object
  /// activation scheme. The <see cref="ActivateOptions"/> method must 
  /// be called on this object after the configuration properties have
  /// been set. Until <see cref="ActivateOptions"/> is called this
  /// object is in an undefined state and must not be used. 
  /// </para>
  /// <para>
  /// If any of the configuration properties are modified then 
  /// <see cref="ActivateOptions"/> must be called again.
  /// </para>
  /// <para>
  /// This method must be implemented by the subclass.
  /// </para>
  /// </remarks>
  public virtual void ActivateOptions()
  {
    if (Layout is IOptionHandler optionHandler)
    {
      optionHandler.ActivateOptions();
    }
  }

  #endregion

  #region Implementation of ILayout

  /// <summary>
  /// Implement this method to create your own layout format.
  /// </summary>
  /// <param name="writer">The TextWriter to write the formatted event to</param>
  /// <param name="loggingEvent">The event to format</param>
  /// <remarks>
  /// <para>
  /// This method is called by an appender to format
  /// the <paramref name="loggingEvent"/> as text.
  /// </para>
  /// </remarks>
  public virtual void Format(TextWriter writer, LoggingEvent loggingEvent)
    => Layout?.Format(writer, loggingEvent);

  /// <summary>
  /// The content type output by this layout. 
  /// </summary>
  /// <value>The content type is <c>"text/plain"</c></value>
  /// <remarks>
  /// <para>
  /// The content type output by this layout.
  /// </para>
  /// <para>
  /// This base class uses the value <c>"text/plain"</c>.
  /// To change this value a subclass must override this
  /// property.
  /// </para>
  /// </remarks>
  public virtual string ContentType => Layout?.ContentType ?? "text/plain";

  /// <summary>
  /// The header for the layout format.
  /// </summary>
  /// <value>the layout header</value>
  /// <remarks>
  /// <para>
  /// The Header text will be appended before any logging events
  /// are formatted and appended.
  /// </para>
  /// </remarks>
  public virtual string? Header => Layout?.Header;

  /// <summary>
  /// The footer for the layout format.
  /// </summary>
  /// <value>the layout footer</value>
  /// <remarks>
  /// <para>
  /// The Footer text will be appended after all the logging events
  /// have been formatted and appended.
  /// </para>
  /// </remarks>
  public virtual string? Footer => Layout?.Footer;

  /// <summary>
  /// Flag indicating if this layout handles exceptions
  /// </summary>
  /// <value><c>false</c> if this layout handles exceptions</value>
  /// <remarks>
  /// <para>
  /// If this layout handles the exception object contained within
  /// <see cref="LoggingEvent"/>, then the layout should return
  /// <c>false</c>. Otherwise, if the layout ignores the exception
  /// object, then the layout should return <c>true</c>.
  /// </para>
  /// <para>
  /// Set this value to override a this default setting. The default
  /// value is <c>true</c>, this layout does not handle the exception.
  /// </para>
  /// </remarks>
  public virtual bool IgnoresException => Layout?.IgnoresException ?? true;

  #endregion
}