RequiredAttribute Class

Definition

Namespace:

Microsoft.Build.Framework

Assembly:

Microsoft.Build.Framework.dll

Package:

Microsoft.Build.Framework v17.11.4

Source:

RequiredAttribute.cs

This class defines the attribute that a task writer can apply to a task's property to declare the property to be a required property.

public ref class RequiredAttribute sealed : Attribute

[System.AttributeUsage(System.AttributeTargets.Property, AllowMultiple=false, Inherited=false)]
public sealed class RequiredAttribute : Attribute

[<System.AttributeUsage(System.AttributeTargets.Property, AllowMultiple=false, Inherited=false)>]
type RequiredAttribute = class
    inherit Attribute

Public NotInheritable Class RequiredAttribute
Inherits Attribute

Inheritance

Attribute

RequiredAttribute

Attributes

AttributeUsageAttribute

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

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.

Constructors

RequiredAttribute()

Default constructor.