C# Reflection - Get field values from a simple class

Question

I have a class:

class A {
    public string a = "A-val" , b = "B-val";
}

I want to print the object members by reflection

//Object here is necessary.
Object data = new A();
FieldInfo[] fields = data.GetType().GetFields();
String str = "";
foreach(FieldInfo f in fields){
    str += f.Name + " = " + f.GetValue(data) + "\r\n";
}

Here is the desired result:

a = A-val
b = B-val

Unfortunately this did not work. Please help, thanks.

Your code (with some little modifications to make it compile) does work... what's the problem exactly? — Paolo Tedesco, Oct 04 '11 at 14:23
I haven't tried to compile this but doesn't f.GetValue(data) return an object? should this be .ToString() to put into the string — Martin Booth, Oct 04 '11 at 14:24
@Martin Booth: `GetValue` returns an object, but you can add an object to a string, so that is ok (more or less) — Paolo Tedesco, Oct 04 '11 at 14:25

score 79 · Accepted Answer · answered Oct 04 '11 at 14:19

79

Once fixed to get rid of the errors (lacking a semi-colon and a bad variable name), the code you've posted does work - I've just tried it and it showed the names and values with no problems.

My guess is that in reality, you're trying to use fields which aren't public. This code:

FieldInfo[] fields = data.GetType().GetFields();

... will only get public fields. You would normally need to specify that you also want non-public fields:

FieldInfo[] fields = data.GetType().GetFields(BindingFlags.Public | 
                                              BindingFlags.NonPublic | 
                                              BindingFlags.Instance);

(I hope you don't really have public fields, after all...)

answered Oct 04 '11 at 14:19

Jon Skeet

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1

The fields are public aren't they? – Martin Booth Oct 04 '11 at 14:22
2

@MartinBooth: Yeah, I was editing - basically it actually works okay with the code given, but I *suspect* that when it's not working, the OP has private fields. – Jon Skeet Oct 04 '11 at 14:34
1

I wasn't aware that you had to specify `BindingFlags.Instance` explicitly - I thought that would be the default. Without that flag, though, no fields were returned in my case. – Oliver Aug 20 '13 at 13:01
1

@Oliver: If you're specifying *any* flags, you need to specify it. The default it something like "public, instance, static". – Jon Skeet Aug 20 '13 at 13:16
2

@JonSkeet as of today 8/18/2015 the defaults I'm getting are: BindingFlags.Public | BindingFlags.NonPublic | BindingFlags.Instance | BindingFlags.Static | BindingFlags.DeclaredOnly; – honestduane Aug 19 '15 at 00:38

Stanislav Gibelbogov · Answer 2 · 2013-03-08T08:24:29.710

3

Remember when you write fields like :

public string VarName{ get; set;}

Then actually you have this code(this is what reflection see) :

private string _varName;
public string get_VarName(){
....
}
public void set_VarName(strig value){
....
}

edited Mar 08 '13 at 08:24

answered Mar 08 '13 at 08:16

Stanislav Gibelbogov

31
2

7

Don't want to nitpick on an old post (thread-necro on 3 yr old post), but `public string VarName { get; set; }` is **not** a field at all. It's a property. To be specific, an autoproperty that, just as you write, creates a private field at compile-time. But the property itself is just a property. Just wanted to straighten that out if anyone happens to stumble across this and get confused. – Jerri Kangasniemi Nov 23 '16 at 21:27

score 1 · Answer 3 · answered Jul 22 '15 at 19:19

As @Stanislav say, you must keep in mind the backing fields generated by the compiler for properties. If you want to exclude these fields you can use the following code:

FieldInfo[] fields = data.GetType()
    .GetFields(BindingFlags.Public | BindingFlags.NonPublic | BindingFlags.Instance)
    .Where(f => f.GetCustomAttribute<CompilerGeneratedAttribute>() == null)
    .ToArray();

C# Reflection - Get field values from a simple class

3 Answers3

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