OutputAttribute Class


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Defines the metadata attribute that task authors use to identify task properties that output data from the task.

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


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


Initializes a new instance of the OutputAttribute class.


When implemented in a derived class, gets a unique identifier for this Attribute.(Inherited from Attribute.)


This API supports the product infrastructure and is not intended to be used directly from your code. Returns a value that indicates whether this instance is equal to a specified object.(Inherited from Attribute.)


Returns the hash code for this instance.(Inherited from Attribute.)


Gets the Type of the current instance.(Inherited from Object.)


When overridden in a derived class, indicates whether the value of this instance is the default value for the derived class.(Inherited from Attribute.)


When overridden in a derived class, returns a value that indicates whether this instance equals a specified object.(Inherited from Attribute.)


Returns a string that represents the current object.(Inherited from Object.)

System_CAPS_pubinterfaceSystem_CAPS_privmethod_Attribute.GetIDsOfNames(Guid, IntPtr, UInt32, UInt32, IntPtr)

Maps a set of names to a corresponding set of dispatch identifiers.(Inherited from Attribute.)

System_CAPS_pubinterfaceSystem_CAPS_privmethod_Attribute.GetTypeInfo(UInt32, UInt32, IntPtr)

Retrieves the type information for an object, which can be used to get the type information for an interface.(Inherited from Attribute.)


Retrieves the number of type information interfaces that an object provides (either 0 or 1).(Inherited from Attribute.)

System_CAPS_pubinterfaceSystem_CAPS_privmethod_Attribute.Invoke(UInt32, Guid, UInt32, Int16, IntPtr, IntPtr, IntPtr, IntPtr)

Provides access to properties and methods exposed by an object.(Inherited from Attribute.)

The MSBuild engine will only allow task properties marked with this attribute to output data from a task. Project authors can only use properties marked with this attribute in the Output element of a project file. All other task properties are treated as inputs to a task.

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.
            // Directories to create.
		public ITaskItem[] Directories
				return directories;

				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.
		// A project may need the subset of the inputs that were actually created, so make that available here.
		public ITaskItem[] DirectoriesCreated
				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)
						// 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);

						// Add to the list of created directories
					// 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);

			// 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;

.NET Framework
Available since 2.0

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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