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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.

MSBuild is now included in Visual Studio instead of the .NET Framework. You can use MSBuild 12.0 side-by-side with versions previously deployed with the .NET Framework.For more information, see What's New in MSBuild 12.0.

Inheritance Hierarchy

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

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

Syntax

'Declaration
<AttributeUsageAttribute(AttributeTargets.Property, AllowMultiple := False,  _
    Inherited := False)> _
Public NotInheritable Class RequiredAttribute _
    Inherits Attribute
[AttributeUsageAttribute(AttributeTargets.Property, AllowMultiple = false, 
    Inherited = false)]
public sealed class RequiredAttribute : Attribute
[AttributeUsageAttribute(AttributeTargets::Property, AllowMultiple = false, 
    Inherited = false)]
public ref class RequiredAttribute sealed : public Attribute
[<Sealed>]
[<AttributeUsageAttribute(AttributeTargets.Property, AllowMultiple = false, 
    Inherited = false)>]
type RequiredAttribute =  
    class 
        inherit Attribute 
    end
public final class RequiredAttribute extends Attribute

The RequiredAttribute type exposes the following members.

Constructors

  Name Description
Public method RequiredAttribute Initializes a new instance of the RequiredAttribute class.MSBuild is now included in Visual Studio instead of the .NET Framework. You can use MSBuild 12.0 side-by-side with versions previously deployed with the .NET Framework.For more information, see What's New in MSBuild 12.0.

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Properties

  Name Description
Public property TypeId (Inherited from Attribute.)

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Methods

  Name Description
Public method Equals (Inherited from Attribute.)
Public method GetHashCode (Inherited from Attribute.)
Public method GetType (Inherited from Object.)
Public method IsDefaultAttribute (Inherited from Attribute.)
Public method Match (Inherited from Attribute.)
Public method ToString (Inherited from Object.)

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Explicit Interface Implementations

  Name Description
Explicit interface implemetationPrivate method System#Runtime#InteropServices#_Attribute#GetIDsOfNames (Inherited from Attribute.)
Explicit interface implemetationPrivate method System#Runtime#InteropServices#_Attribute#GetTypeInfo (Inherited from Attribute.)
Explicit interface implemetationPrivate method System#Runtime#InteropServices#_Attribute#GetTypeInfoCount (Inherited from Attribute.)
Explicit interface implemetationPrivate method System#Runtime#InteropServices#_Attribute#Invoke (Inherited from Attribute.)

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Remarks

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.

Examples

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

Thread Safety

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

See Also

Reference

Microsoft.Build.Framework Namespace