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RequiredAttribute Class

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.

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

Namespace:  Microsoft.Build.Framework
Assembly:  Microsoft.Build.Framework (in Microsoft.Build.Framework.dll)

[AttributeUsageAttribute(AttributeTargets::Property, AllowMultiple = false, 
	Inherited = false)]
public ref class RequiredAttribute sealed : public Attribute

The RequiredAttribute type exposes the following members.

  NameDescription
Public methodRequiredAttributeInitializes a new instance of the RequiredAttribute class.
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  NameDescription
Public propertyTypeIdWhen implemented in a derived class, gets a unique identifier for this Attribute. (Inherited from Attribute.)
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  NameDescription
Public methodEqualsInfrastructure. Returns a value that indicates whether this instance is equal to a specified object. (Inherited from Attribute.)
Public methodGetHashCodeReturns the hash code for this instance. (Inherited from Attribute.)
Public methodGetTypeGets the Type of the current instance. (Inherited from Object.)
Public methodIsDefaultAttributeWhen overridden in a derived class, indicates whether the value of this instance is the default value for the derived class. (Inherited from Attribute.)
Public methodMatchWhen overridden in a derived class, returns a value that indicates whether this instance equals a specified object. (Inherited from Attribute.)
Public methodToStringReturns a string that represents the current object. (Inherited from Object.)
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  NameDescription
Explicit interface implemetationPrivate method_Attribute::GetIDsOfNamesMaps a set of names to a corresponding set of dispatch identifiers. (Inherited from Attribute.)
Explicit interface implemetationPrivate method_Attribute::GetTypeInfoRetrieves the type information for an object, which can be used to get the type information for an interface. (Inherited from Attribute.)
Explicit interface implemetationPrivate method_Attribute::GetTypeInfoCountRetrieves the number of type information interfaces that an object provides (either 0 or 1). (Inherited from Attribute.)
Explicit interface implemetationPrivate method_Attribute::InvokeProvides access to properties and methods exposed by an object. (Inherited from Attribute.)
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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;
		}
	}
}

To run this task use a project file like this:

<Project xmlns="http://schemas.microsoft.com/developer/msbuild/2003">
    <Target Name="MyTarget">
        <MkDir Directories="NewDir" />
    </Target>
</Project>

.NET Framework

Supported in: 4.5, 4, 3.5, 3.0, 2.0

Windows 8.1, Windows Server 2012 R2, Windows 8, Windows Server 2012, Windows 7, Windows Vista SP2, Windows Server 2008 (Server Core Role not supported), Windows Server 2008 R2 (Server Core Role supported with SP1 or later; Itanium not supported)

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

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