TargetException thrown in Reflection using GetValu

问题:

I need to get the Name and Value of all properties of each object. Some of them are reference type so if I get the following objects:

public class Artist {
    public int Id { get; set; }
    public string Name { get; set; }
}

public class Album {
    public string AlbumId { get; set; }
    public string Name { get; set; }
    public Artist AlbumArtist { get; set; }
}

When getting the properties from the Album object I would need also to get the values of properties AlbumArtist.Id and AlbumArtist.Name which are nested.

I have the following code so far, but it triggers the System.Reflection.TargetException when trying to get the value of the nested ones.

var valueNames = new Dictionary<string, string>();
foreach (var property in row.GetType().GetProperties())
{
    if (property.PropertyType.Namespace.Contains("ARS.Box"))
    {
        foreach (var subProperty in property.PropertyType.GetProperties())
        {
            if(subProperty.GetValue(property, null) != null)
                valueNames.Add(subProperty.Name, subProperty.GetValue(property, null).ToString());
        } 
    }
    else
    {
        var value = property.GetValue(row, null);
        valueNames.Add(property.Name, value == null ? "" : value.ToString());
    }
}

So in the If statement I just check if the property is under the namespace of my reference types, if it is I should get all the nested properties values but that's where the exception is raised.

Thanks in advance for the help..

回答1:

This fails because you are trying to get an Artist property on a PropertyInfo instance:

if(subProperty.GetValue(property, null) != null)
    valueNames.Add(subProperty.Name, subProperty.GetValue(property, null).ToString());

As I understand you need the values from the Artist instance which is nested inside the row object (which is an Album instance).

So you should change this:

if(subProperty.GetValue(property, null) != null)
    valueNames.Add(subProperty.Name, subProperty.GetValue(property, null).ToString());

to this:

var propValue = property.GetValue(row, null);
if(subProperty.GetValue(propValue, null) != null)
    valueNames.Add(subProperty.Name, subProperty.GetValue(propValue, null).ToString());

Full (with a little change to avoid calling GetValue when we don't need)

var valueNames = new Dictionary<string, string>();
foreach (var property in row.GetType().GetProperties())
{
    if (property.PropertyType.Namespace.Contains("ATG.Agilent.Entities"))
    {
        var propValue = property.GetValue(row, null);
        foreach (var subProperty in property.PropertyType.GetProperties())
        {
            if(subProperty.GetValue(propValue, null) != null)
                valueNames.Add(subProperty.Name, subProperty.GetValue(propValue, null).ToString());
        } 
    }
    else
    {
        var value = property.GetValue(row, null);
        valueNames.Add(property.Name, value == null ? "" : value.ToString());
    }
}

Also, you may run into situations when the property names are duplicated, so your IDictionary<,>.Add will fail. I suggest to use something more reliable naming here.

For example: property.Name + "." + subProperty.Name