Hashtable/Dictionary parameters in MSBuild Task

Question

I'm trying to send/share a Dictionary or Hashtable between MSBuildtasks.

I have the following two Custom tasks, Get that produces a Hashtable and Set that should consume it.

Get.cs

public class Get : Task
{
    [Output]
    public Hashtable Output { get; set; }

    public override bool Execute()
    {
        Output = new Hashtable();
        return true;
    }
}

Set.cs

public class Set : Task
{
    [Required]
    public Hashtable Output { get; set; }

    public override bool Execute()
    {
        var items = Output.Cast<DictionaryEntry>().ToDictionary(d => d.Key.ToString(), d => d.Value.ToString());

        foreach(var item in items)
        {
            //Do Something
        }

        return true;
    }
}

The above classes build fine into Assembly.dll

I then use that Assembly.dll in the following build target script to call the Get and Set custom tasks:

MyTarget.targets

<?xml version="1.0" encoding="utf-8"?>
<Project xmlns="http://schemas.microsoft.com/developer/msbuild/2003">
  <UsingTask TaskName="Get" AssemblyFile=".\Assembly.dll"/>
  <UsingTask TaskName="Set" AssemblyFile=".\Assembly.dll"/>

  <Target Name="Get">

    <Get>
      <Output TaskParameter="Output" ItemName="Output" />
    </Get>
    <Set Output=@(Output) />

  </Target>

</Project>

When I build the project with the above target MSBuild shows the following error:

The "System.Collections.Hashtable" type of the "Output" parameter of the "Get" task is not supported by MSBuild

How can I use an Hashtable or Dictionary in a property for a custom MSBuild task?

Answer 1

The Parameters that can go in or out a Task are limited to either ITaskItem or an array of ITaskItem's.

So your properties should change from

public Hashtable Output { get; set; }

to

public ITaskItem[] Output { get; set; }

to match that requirement.

Next you need an implementation class that implements ITaskItem. That allow you to handle your hashset or dictionary. I left that for you that add but a minimal KeyValue class could look like this:

public class KeyValue: ITaskItem
{
    string _spec = String.Empty;

    public KeyValue(string key, string value)
    {
        _spec = key;
        metadata.Add("value", value);
    }

    Dictionary<string,string> metadata = new Dictionary<string,string>();

    public string ItemSpec
    {
        get {return _spec;}
        set {}
    }
    public ICollection MetadataNames
    {
        get {return metadata.Keys;}
    }
    public int MetadataCount
    {
        get {return metadata.Keys.Count;}
    }
    public string GetMetadata(string metadataName)
    {
        return metadata[metadataName];
    }
    public void SetMetadata(string metadataName, string metadataValue) 
    {
        metadata[metadataName] = metadataValue;
    }
    public void RemoveMetadata(string metadataName)
    {
    }
    public void CopyMetadataTo(ITaskItem destinationItem)
    {
    }
    public IDictionary CloneCustomMetadata()
    {
          return metadata;
    }
}

This class will produce and Item that will look look this if it was done in plane MSBuild script:

 <Item Include="key">
    <value>some value</value>
 </Item>

Next you can adapt the Set and Get Task to use this new class KeyValue:

public class Set : Task
{

    TaskLoggingHelper log;

    public Set() {
        log = new TaskLoggingHelper(this);
    }

    [Required]
    public ITaskItem[] Output { get; set; }

    public override bool Execute()
    {
        log.LogMessage("start set");
        foreach(var item in Output)
        {
            log.LogMessage(String.Format("Set sees key {0} with value {1}.",item.ItemSpec, item.GetMetadata("value")));
        }
        log.LogMessage("end set");
        return true;
    }
}

public class Get : Task
{

    // notice this property no longer is called Output
    // as that gave me errors as the property is reserved       
    [Output]
    public ITaskItem[] Result { get; set; }

    public override bool Execute()
    {
        // convert a Dictionary or Hashset to an array of ITaskItems
        // by creating instances of the class KeyValue.
        // I use a simple list here, I leave it as an exercise to do the other colletions
        Result = new List<ITaskItem> { new KeyValue("bar", "bar-val"), new KeyValue("foo","foo val") }.ToArray();
        return true;
    }
}

The build file I used to test above code:

<Project xmlns="http://schemas.microsoft.com/developer/msbuild/2003">
  <UsingTask TaskName="Get" AssemblyFile=".\cb.dll"/>
  <UsingTask TaskName="Set" AssemblyFile=".\cb.dll"/>

  <Target Name="Get">

    <Get>
      <Output  TaskParameter="Result"  ItemName="GetResult" />
    </Get>

    <!-- lets see what we've got -->
    <Message Importance="high" Text="key: @(GetResult) :: value: %(value)" />

    <Set Output="@(GetResult)">

    </Set>

  </Target>

</Project>

When run the result will be:

Build started 24-12-2017 21:26:17.
Project "C:\Prj\bld\test.build" on node 1 (default targets).
Get:
  key: bar :: value: bar-val
  key: foo :: value: foo val
  start set
  Set sees key bar with value bar-val.
  Set sees key foo with value foo val.
  end set
Done Building Project "C:\Prj\bld\test.build" (default targets).


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