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RequiredAttribute Class

Note: This class is new in the .NET Framework version 2.0.

Defines the metadata attribute that task authors use to identify required task properties. Task properties with this attribute must have a set value when the task is run.

Namespace: Microsoft.Build.Framework
Assembly: Microsoft.Build.Framework (in microsoft.build.framework.dll)

[AttributeUsageAttribute(AttributeTargets.Property, AllowMultiple=false, Inherited=false)] 
public sealed class RequiredAttribute : Attribute
/** @attribute AttributeUsageAttribute(AttributeTargets.Property, AllowMultiple=false, Inherited=false) */ 
public final class RequiredAttribute extends Attribute
AttributeUsageAttribute(AttributeTargets.Property, AllowMultiple=false, Inherited=false) 
public final class RequiredAttribute extends Attribute

If a property marked with this attribute is not assigned a value when the task is invoked, the build will fail.

For more information about using attributes, see Extending Metadata Using Attributes.

The following example shows the code for a task that creates one or more directories.

using System;
using System.IO;
using System.Security;
using System.Collections;
using Microsoft.Build.Framework;
using Microsoft.Build.Utilities;

namespace Microsoft.Build.Tasks
{
	/*
	 * Class: MakeDir
	 *
	 * An MSBuild task that creates one or more directories.
	 *
	 */
	public class MakeDir : Task
	{
	    // The Required attribute indicates the following to MSBuild:
	    //	     - if the parameter is a scalar type, and it is not supplied, fail the build immediately
	    //	     - if the parameter is an array type, and it is not supplied, pass in an empty array
	    // In this case the parameter is an array type, so if a project fails to pass in a value for the 
            // Directories parameter, the task will get invoked, but this implementation will do nothing,
            // because the array will be empty.
		[Required]
            // Directories to create.
		public ITaskItem[] Directories
		{
			get
			{
				return directories;
			}

			set
			{
				directories = value;
			}
		}

		// The Output attribute indicates to MSBuild that the value of this property can be gathered after the
		// task has returned from Execute(), if the project has an <Output> tag under this task's element for 
		// this property.
		[Output]
		// A project may need the subset of the inputs that were actually created, so make that available here.
		public ITaskItem[] DirectoriesCreated
		{
			get
			{
				return directoriesCreated;
			}
		}

		private ITaskItem[] directories;
		private ITaskItem[] directoriesCreated;

		/// <summary>
		/// Execute is part of the Microsoft.Build.Framework.ITask interface.
		/// When it's called, any input parameters have already been set on the task's properties.
		/// It returns true or false to indicate success or failure.
		/// </summary>
		public override bool Execute()
		{
			ArrayList items = new ArrayList();
			foreach (ITaskItem directory in Directories)
			{
				// ItemSpec holds the filename or path of an Item
				if (directory.ItemSpec.Length > 0)
				{
					try
					{
						// Only log a message if we actually need to create the folder
						if (!Directory.Exists(directory.ItemSpec))
						{
							Log.LogMessage(MessageImportance.Normal, "Creating directory " + directory.ItemSpec);
							Directory.CreateDirectory(directory.ItemSpec);
						}

						// Add to the list of created directories
						items.Add(directory);
					}
					// If a directory fails to get created, log an error, but proceed with the remaining 
					// directories.
					catch (Exception ex)
					{
						if (ex is IOException
							|| ex is UnauthorizedAccessException
							|| ex is PathTooLongException
							|| ex is DirectoryNotFoundException
							|| ex is SecurityException)
						{
							Log.LogError("Error trying to create directory " + directory.ItemSpec + ". " + ex.Message);
						}
						else
						{
							throw;
						}
					}
				}
			}

			// Populate the "DirectoriesCreated" output items.
			directoriesCreated = (ITaskItem[])items.ToArray(typeof(ITaskItem));

			// Log.HasLoggedErrors is true if the task logged any errors -- even if they were logged 
			// from a task's constructor or property setter. As long as this task is written to always log an error
			// when it fails, we can reliably return HasLoggedErrors.
			return !Log.HasLoggedErrors;
		}
	}
}

System.Object
   System.Attribute
    Microsoft.Build.Framework.RequiredAttribute

Any public static (Shared in Visual Basic) members of this type are thread safe. Any instance members are not guaranteed to be thread safe.

Windows 98, Windows 2000 SP4, Windows Millennium Edition, Windows Server 2003, Windows XP Media Center Edition, Windows XP Professional x64 Edition, Windows XP SP2, Windows XP Starter Edition

The .NET Framework does not support all versions of every platform. For a list of the supported versions, see System Requirements.

.NET Framework

Supported in: 2.0

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