/// <summary>
/// Gets <see cref="ModelExplorer"/> for named <paramref name="expression"/> in given
/// <paramref name="viewData"/>.
/// </summary>
/// <param name="expression">Expression name, relative to <c>viewData.Model</c>.</param>
/// <param name="viewData">
/// The <see cref="ViewDataDictionary"/> that may contain the <paramref name="expression"/> value.
/// </param>
/// <param name="metadataProvider">The <see cref="IModelMetadataProvider"/>.</param>
/// <returns>
/// <see cref="ModelExplorer"/> for named <paramref name="expression"/> in given <paramref name="viewData"/>.
/// </returns>
public static ModelExplorer FromStringExpression(
string expression,
[NotNull] ViewDataDictionary viewData,
IModelMetadataProvider metadataProvider)
{
var viewDataInfo = ViewDataEvaluator.Eval(viewData, expression);
if (viewDataInfo == null)
{
// Try getting a property from ModelMetadata if we couldn't find an answer in ViewData
var propertyExplorer = viewData.ModelExplorer.GetExplorerForProperty(expression);
if (propertyExplorer != null)
{
return(propertyExplorer);
}
}
if (viewDataInfo != null)
{
if (viewDataInfo.Container == viewData &&
viewDataInfo.Value == viewData.Model &&
string.IsNullOrEmpty(expression))
{
// Nothing for empty expression in ViewData and ViewDataEvaluator just returned the model. Handle
// using FromModel() for its object special case.
return(FromModel(viewData, metadataProvider));
}
ModelExplorer containerExplorer = viewData.ModelExplorer;
if (viewDataInfo.Container != null)
{
containerExplorer = metadataProvider.GetModelExplorerForType(
viewDataInfo.Container.GetType(),
viewDataInfo.Container);
}
if (viewDataInfo.PropertyInfo != null)
{
// We've identified a property access, which provides us with accurate metadata.
var containerType = viewDataInfo.Container?.GetType() ?? viewDataInfo.PropertyInfo.DeclaringType;
var containerMetadata = metadataProvider.GetMetadataForType(viewDataInfo.Container.GetType());
var propertyMetadata = containerMetadata.Properties[viewDataInfo.PropertyInfo.Name];
Func <object, object> modelAccessor = (ignore) => viewDataInfo.Value;
return(containerExplorer.GetExplorerForExpression(propertyMetadata, modelAccessor));
}
else if (viewDataInfo.Value != null)
{
// We have a value, even though we may not know where it came from.
var valueMetadata = metadataProvider.GetMetadataForType(viewDataInfo.Value.GetType());
return(containerExplorer.GetExplorerForExpression(valueMetadata, viewDataInfo.Value));
}
}
// Treat the expression as string if we don't find anything better.
var stringMetadata = metadataProvider.GetMetadataForType(typeof(string));
return(viewData.ModelExplorer.GetExplorerForExpression(stringMetadata, modelAccessor: null));
}