CODEWITHSUNDEEP
c#stringvariablesproperties
Jan Matousek
Jan Matousek

Reputation: 1006

C# get and set property by variable name

Is there any way to do this? I try to test if a property of an object exists and if it does, I want to set a value to it. (Maybe the complete idea is bad, if true - why?)

class Info
{
    public string X1{ set; get; }
    public string X2{ set; get; }
    public string X3{ set; get; }
}

Dictionary<string, string> values = new Dictionary<string, string>();
values.Add("X1","blah1");
values.Add("X2","blah2");
values.Add("NotThere","blah3");

Info info = new Info();

foreach (var item in values)
{
  string propertyName = item.Key;
  string value = item.Value;
  if (info.GetType().GetProperty(propertyName) != null)  //this probably works
  {
        info.propertyName = value; //this doesn't, how to set it?
  }
}

Upvotes: 15

Views: 29623

Answers (4)

Konstantin Chernov
Konstantin Chernov

Reputation: 1936

I think using reflection each time is a bit slow, so, if you do that initialization more than once you can use Expression Tree. But each time your dictionary should have same order of properties to init.

Possible code

class Info
{
    public string X1 { set; get; }
    public string X2 { set; get; }
    public int X3 { set; get; }
    private Action<Info, List<object>> initAction;

    public void Init(Dictionary<string, object> initDict)
    {
        //on first usage we deal with reflection and build expression tree to init properties
        if (initAction==null)
        {
            ParameterExpression targetInstanceExpression = Expression.Parameter(this.GetType());
            ParameterExpression valuesExpression = Expression.Parameter(typeof(List<object>));
            ParameterExpression value = Expression.Variable(typeof(object));
            ParameterExpression enumerator = Expression.Variable(typeof(IEnumerator));

            var expList = new List<Expression>();
            expList.Add(Expression.Assign(enumerator, Expression.TypeAs(Expression.Call(valuesExpression, "GetEnumerator", null),typeof(IEnumerator))));
            foreach (var initRecord in initDict)
            {
                Expression moveNextExp = Expression.Call(enumerator, "MoveNext", null);
                expList.Add(moveNextExp);
                Type type = initRecord.Value.GetType();
                expList.Add(Expression.Assign(value, Expression.PropertyOrField(enumerator, "Current")));
                Expression assignExp = GetPropAssigner(initRecord.Key, type, targetInstanceExpression, value);
                expList.Add(assignExp);
            }
            Expression block = Expression.Block
            (
                 new[] { value, enumerator },
                 expList
            );
            //compile epression tree and get init action 
            initAction = Expression.Lambda<Action<Info, List<object>>>(block, targetInstanceExpression, valuesExpression).Compile();
        }
        initAction(this, initDict.Values.ToList());
    }
    //little method to create property assigner
    public static Expression GetPropAssigner(string propName, Type type,
         ParameterExpression targetInstanceExp, ParameterExpression valueExp)
    {
        MemberExpression fieldExp = Expression.PropertyOrField(targetInstanceExp, propName);
        BinaryExpression assignExp = Expression.Assign(fieldExp, type.IsValueType ? Expression.Unbox(valueExp, type) : Expression.TypeAs(valueExp, type));
        return assignExp;
    }
}

Usage:

var values = new Dictionary<string, object>();
            values.Add("X1", "blah1");
            values.Add("X2", "blah2");
            values.Add("X3", 8);


Info info = new Info();
info.Init(values);

Upvotes: 1

Matten
Matten

Reputation: 17603

You need to invoke the SetValue method on the property:

var property = info.GetType().GetProperty(propertyName);
if (property != null)
{
    property.SetValue(info, value, null); 
}

Upvotes: 5

Amiram Korach
Amiram Korach

Reputation: 13296

var propertyInfo = info.GetType().GetProperty(propertyName);
if (propertyInfo != null)  //this probably works. Yes it is
  {
        propertyInfo.SetValue(info, value, null);
  }

Upvotes: 10

James
James

Reputation: 82136

Yes, your looking for the PropertyInfo.SetValue method e.g.

var propInfo = info.GetType().GetProperty(propertyName);
if (propInfo != null)
{
    propInfo.SetValue(info, value, null);
}

Upvotes: 35

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