在嵌套属性中使用 GetValue() 在反射中抛出 TargetException [英] TargetException thrown in Reflection using GetValue() in nested properties

问题描述

我需要获取每个对象的所有属性的 Name 和 Value.其中一些是引用类型，所以如果我得到以下对象:

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; }
}

当从 Album 对象获取属性时，我还需要获取属性 AlbumArtist.Id 和 AlbumArtist.Name 的值嵌套.

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.

到目前为止，我有以下代码，但它在尝试获取嵌套代码的值时触发了 System.Reflection.TargetException.

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());
    }
}

所以在 If 语句中，我只检查属性是否在我的引用类型的命名空间下，如果是，我应该获取所有嵌套的属性值，但这就是引发异常的地方.

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.

推荐答案

这会失败，因为您试图在 PropertyInfo 实例上获取 Artist 属性:

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());

据我所知，您需要 Artist 实例中的值，该实例嵌套在 row 对象(它是一个 Album 实例)中.

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

所以你应该改变这个:

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

为此:

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

Full(稍作改动以避免在我们不需要时调用 GetValue)

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());
    }
}

此外，您可能会遇到属性名称重复的情况，因此您的 IDictionary<,>.Add 将失败.我建议在这里使用更可靠的命名.

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.

例如:property.Name + "."+ subProperty.Name

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