How to Correct & Improve the Design of this Code?
- by DaveDev
HI Guys, I've been working on a little experiement to see if I could create a helper method to serialize any of my types to any type of HTML tag I specify.
I'm getting a NullReferenceException when _writer = _viewContext.Writer; is called in
protected virtual void Dispose(bool disposing) {/*...*/}
I think I'm at a point where it almost works (I've gotten other implementations to work) and I was wondering if somebody could point out what I'm doing wrong? Also, I'd be interested in hearing suggestions on how I could improve the design?
So basically, I have this code that will generate a Select box with a number of options:
// the idea is I can use one method to create any complete tag of any type
// and put whatever I want in the content area
<% using (Html.GenerateTag<SelectTag>(Model, new { href = Url.Action("ActionName") })) { %>
<%foreach (var fund in Model.Funds) {%>
<% using (Html.GenerateTag<OptionTag>(fund)) { %>
<%= fund.Name %>
<% } %>
<% } %>
<% } %>
This Html.GenerateTag helper is defined as:
public static MMTag GenerateTag<T>(this HtmlHelper htmlHelper, object elementData, object attributes) where T : MMTag
{
return (T)Activator.CreateInstance(typeof(T), htmlHelper.ViewContext, elementData, attributes);
}
Depending on the type of T it'll create one of the types defined below,
public class HtmlTypeBase : MMTag
{
public HtmlTypeBase()
{ }
public HtmlTypeBase(ViewContext viewContext, params object[] elementData)
{
base._viewContext = viewContext;
base.MergeDataToTag(viewContext, elementData);
}
}
public class SelectTag : HtmlTypeBase
{
public SelectTag(ViewContext viewContext, params object[] elementData)
{
base._tag = new TagBuilder("select");
//base.MergeDataToTag(viewContext, elementData);
}
}
public class OptionTag : HtmlTypeBase
{
public OptionTag(ViewContext viewContext, params object[] elementData)
{
base._tag = new TagBuilder("option");
//base.MergeDataToTag(viewContext, _elementData);
}
}
public class AnchorTag : HtmlTypeBase
{
public AnchorTag(ViewContext viewContext, params object[] elementData)
{
base._tag = new TagBuilder("a");
//base.MergeDataToTag(viewContext, elementData);
}
}
all of these types (anchor, select, option) inherit from HtmlTypeBase, which is intended to perform base.MergeDataToTag(viewContext, elementData);. This doesn't happen though. It works if I uncomment the MergeDataToTag methods in the derived classes, but I don't want to repeat that same code for every derived class I create.
This is the definition for MMTag:
public class MMTag : IDisposable
{
internal bool _disposed;
internal ViewContext _viewContext;
internal TextWriter _writer;
internal TagBuilder _tag;
internal object[] _elementData;
public MMTag() {}
public MMTag(ViewContext viewContext, params object[] elementData)
{ }
public void Dispose()
{
Dispose(true /* disposing */);
GC.SuppressFinalize(this);
}
protected virtual void Dispose(bool disposing)
{
if (!_disposed)
{
_disposed = true;
_writer = _viewContext.Writer;
_writer.Write(_tag.ToString(TagRenderMode.EndTag));
}
}
protected void MergeDataToTag(ViewContext viewContext, object[] elementData)
{
Type elementDataType = elementData[0].GetType();
foreach (PropertyInfo prop in elementDataType.GetProperties())
{
if (prop.PropertyType.IsPrimitive || prop.PropertyType == typeof(Decimal) || prop.PropertyType == typeof(String))
{
object propValue = prop.GetValue(elementData[0], null);
string stringValue = propValue != null ? propValue.ToString() : String.Empty;
_tag.Attributes.Add(prop.Name, stringValue);
}
}
var dic = new Dictionary<string, object>(StringComparer.OrdinalIgnoreCase);
var attributes = elementData[1];
if (attributes != null)
{
foreach (PropertyDescriptor descriptor in TypeDescriptor.GetProperties(attributes))
{
object value = descriptor.GetValue(attributes);
dic.Add(descriptor.Name, value);
}
}
_tag.MergeAttributes<string, object>(dic);
_viewContext = viewContext;
_viewContext.Writer.Write(_tag.ToString(TagRenderMode.StartTag));
}
}
Thanks
Dave
