WebPartTransformerAttribute Class

Transformers are used to translate data between two Web Parts controls with incompatible connection points. Connection points are incompatible when they provide or consume data through different interfaces. For example, a provider implementing a provider connection point of type IWebPartRow could not directly connect to a consumer expecting a provider connection point of type IWebPartTable. Instead, a transformer must be used to connect the two connection points. A customized transformer can be created by deriving a class from the WebPartTransformer class.

The WebPartTransformerAttribute attribute is applied to a WebPartTransformer class. It defines the type of provider connection point and the type of consumer connection point that a transformer supports. The type of consumer and provider connection points supported by the transformer must match the connection points of the consumer and provider Web Parts controls for a connection to be made between the controls. At run time, the type of connection points that a particular transformer supports can be retrieved through the GetConsumerType and GetProviderType methods.

The following code example demonstrates the use of a WebPartTransformerAttribute attribute with a customized WebPartTransformer class. The attribute indicates that the RowToStringTransformer class can transform a provider connection point of type IWebPartRow to a consumer connection point of type IString.

This code example is part of a larger example found in the WebPartTransformer class overview.

// A transformer that transforms a row to a string.
[AspNetHostingPermission(SecurityAction.Demand,
  Level = AspNetHostingPermissionLevel.Minimal)]
[AspNetHostingPermission(SecurityAction.InheritanceDemand,
  Level = AspNetHostingPermissionLevel.Minimal)]
[WebPartTransformer(typeof(IWebPartRow), typeof(IString))]
public class RowToStringTransformer : WebPartTransformer, IString
{

    private IWebPartRow _provider;
    private StringCallback _callback;

    private void GetRowData(object rowData)
    {
        PropertyDescriptorCollection props = _provider.Schema;
        if (props != null && props.Count > 0 && rowData != null)
        {
            string returnValue = String.Empty;
            foreach (PropertyDescriptor prop in props)
            {
                if (prop != props[0])
                {
                    returnValue += ", ";
                }
                returnValue += prop.DisplayName + ": " + prop.GetValue(rowData);
            }
            _callback(returnValue);
        }
        else
        {
            _callback(null);
        }
    }

    public override object Transform(object providerData)
    {
        _provider = (IWebPartRow)providerData;
        return this;
    }

    void IString.GetStringValue(StringCallback callback)
    {
        if (callback == null)
        {
            throw new ArgumentNullException("callback");
        }

        if (_provider != null)
        {
            _callback = callback;
            _provider.GetRowData(new RowCallback(GetRowData));
        }
        else
        {
            callback(null);
        }
    }
}

.NET Framework

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.

Reference