How can I get the value of a string property via R

问题:

public class Foo
{
   public string Bar {get; set;}
}

How do I get the value of Bar, a string property, via reflection? The following code will throw an exception if the PropertyInfo type is a System.String

Foo f = new Foo();
f.Bar = "Jon Skeet is god.";

foreach(var property in f.GetType().GetProperties())
{
 object o = property.GetValue(f,null); //throws exception TargetParameterCountException for String type
}

It seems that my problem is that the property is an indexer type, with a System.String.

Also, how do I tell if the property is an indexer?

回答1:

You can just get the property by name:

Foo f = new Foo();
f.Bar = "Jon Skeet is god.";

var barProperty = f.GetType().GetProperty("Bar");
string s = barProperty.GetValue(f,null) as string;

Regarding the follow up question: Indexers will always be named Item and have arguments on the getter. So

Foo f = new Foo();
f.Bar = "Jon Skeet is god.";

var barProperty = f.GetType().GetProperty("Item");
if (barProperty.GetGetMethod().GetParameters().Length>0)
{
    object value = barProperty.GetValue(f,new []{1/* indexer value(s)*/});
}

回答2:

I couldn't reproduce the issue. Are you sure you're not trying to do this on some object with indexer properties? In that case the error you're experiencing would be thrown while processing the Item property. Also, you could do this:

public static T GetPropertyValue<T>(object o, string propertyName)
{
      return (T)o.GetType().GetProperty(propertyName).GetValue(o, null);
}

...somewhere else in your code...
GetPropertyValue<string>(f, "Bar");

回答3:

Foo f = new Foo();
f.Bar = "x";

string value = (string)f.GetType().GetProperty("Bar").GetValue(f, null);

回答4:

var val = f.GetType().GetProperty("Bar").GetValue(f, null);

回答5:

Foo f = new Foo();
f.Bar = "Jon Skeet is god.";

foreach(var property in f.GetType().GetProperties())
{
    if(property.Name != "Bar")
    {
         continue;
    }
    object o = property.GetValue(f,null); //throws exception TargetParameterCountException for String type
}

And here is for the followup:

class Test
{
    public class Foo
    {
        Dictionary<string, int> data =new Dictionary<string,int>();
        public int this[string index]
        {
            get { return data[index]; }
            set { data[index] = value; }
        }

        public Foo()
        {
            data["a"] = 1;
            data["b"] = 2;
        }
    }

    public Test()
    {
        var foo = new Foo();
        var property = foo.GetType().GetProperty("Item");
        var value = (int)property.GetValue(foo, new object[] { "a" });
        int i = 0;
    }
}

回答6:

PropertyInfo propInfo = f.GetType().GetProperty("Bar");
object[] obRetVal = new Object[0];
string bar = propInfo.GetValue(f,obRetVal) as string;

回答7:

Its easy to get property value of any object by use Extension method like:

public static class Helper
    {
        public static object GetPropertyValue(this object T, string PropName)
        {
            return T.GetType().GetProperty(PropName) == null ? null : T.GetType().GetProperty(PropName).GetValue(T, null);
        }
    }

Usage is:

Foo f = new Foo();
f.Bar = "x";
var balbal = f.GetPropertyValue("Bar");

回答8:

the getvalue with object and null worked great for me. Thanks for the posts.

Context: Looping through all properties in an MVC model for New Hires and determining their form posted values:

newHire => the Model, with many properties, whose posted form values I want to write individually to a set of database records

foreach(var propertyValue in newHire.GetProperties())
{
string propName = propertyValue.Name;

string postedValue = newHire.GetType().GetProperty(propName).GetValue(newHire, null).ToString();

}