How to pass properties by reference in c#?

Question

I am not sure if I have asked the question correctly. Please correct me if I am wrong.

Anyways, we would like to use a variable's value on a different phases of the page's life cycle.

So for example,

public partial class TestUserControl: UserControl{
    public TestUserControl(){
        Objects = new List<object>(){
            Property1,
            Property2,
            Property3
        };
    }

    public int Property1 { get; set; }
    public bool Property2 { get; set; }
    public string Property3 { get; set; }
    public List<object> Objects { get; set; }

    protected override OnLoad(EventArgs e){
        foreach(var item in Objects){
            Page.Controls.Add(new LiteralControl(item.ToString() + "<br/>"));
        }
    }
}

So if we say the values of Property1, Property2, Property3 are set as they were written on the tag, how could we use the properties' values just as when needed?

That on the constructor, instead of the values of the properties will be listed down on the List, only the Properties' names will be listed down so their current values will be used on OnLoad.

Thanks a lot.

---

Edit: I have adopted deerchao's and Jon's approach, but there seems to be another problem we will be facing... It's like:

public partial class TestUserControl: UserControl{
    public TestUserControl(){
        Objects = List<Func<object>>{
            () => Property1,
            () => Property2,
            () => Property3
        };
    }

    public int Property1 { get; set; }
    public bool Property2 { get; set; }
    public string Property3 { get; set; }
    public List<Func<object>> Objects { get; set; }

    protected override OnLoad(EventArgs e){
        foreach (var item in Objects) {
            //Here is the problem... can we get the variable name using this approach?
            //We have tried some other ways like reflection and expressions but to no avail. Help please =)
            string key = GetVariableName(item());

            string value = item() == null ? string.Empty : item().ToString();
            Page.Controls.Add(new LiteralControl(key + " : " + value + "<br/>"));
        }
    }
}

Answer 1

You can pass variables by reference (using ref) but not properties. Additionally, the "ref-ness" is only for the duration of the method: it aliases the argument and the parameter, but if you copy the parameter value into another variable, that other variable isn't an alias.

It's not really clear exactly what you want to do here, but you could use delegates instead:

    Objects = new List<Func<object>>(){
        () => Property1,
        () => Property2,
        () => Property3
    };

Then:

protected override OnLoad(EventArgs e){
    foreach(var itemRetriever in Objects){
        Page.Controls.Add(new Literal(itemRetriever().ToString() + "<br/>"));
    }
}

It's pretty nasty though - I'd try to find an alternative design if you can.

Answer 2

Seriously weird code, but how about:

public partial class TestUserControl: UserControl{
    public TestUserControl(){

    }

    public int Property1 { get; set; }
    public bool Property2 { get; set; }
    public string Property3 { get; set; }
    public List<object> Objects { get; set; }

    protected override OnLoad(EventArgs e){
        Objects = new List<object>(){
            Property1,
            Property2,
            Property3
        };

        foreach(var item in Objects){
            Page.Controls.Add(new Literal(item.ToString() + "<br/>"));
        }
    }
}

Answer 3

public partial class TestUserControl: UserControl{
public TestUserControl(){
    Objects = new List<Func<object>>(){
        () => Property1,
        () => Property2,
        () => Property3
    };
}

public int Property1 { get; set; }
public bool Property2 { get; set; }
public string Property3 { get; set; }
public List<Func<object>> Objects { get; set; }

protected override OnLoad(EventArgs e){
    foreach(var item in Objects){
        Page.Controls.Add(new Literal(item().ToString() + "<br/>"));
    }
}

}

Answer 4

Perhaps use PropertyDescriptor(s) in System.ComponentModel

System.ComponentModel.PropertyDescriptorCollection properties = System.ComponentModel.TypeDescriptor.GetProperties(this);

Answer 5

You need to override ToString() in your (Object) class to return the value. Or, provide a method or property to access the values directly.

FWIW, this has nothing to do with passing a variable by reference.

Answer 6

You can't do it this way, but there are a few alternatives. For example:

public partial class TestUserControl: UserControl{

public int Property1 { get; set; }
public bool Property2 { get; set; }
public string Property3 { get; set; }
public IEnumerable<object> Objects
{
    get
    {
        yield return Property1;
        yield return Property2;
        yield return Property3;
    }
}

}

It's not a list, but you can still enumerate through it. You could also write an IList wrapper, although that would be lengthier.

Answer 7

Ok, assuming I am understanding this correctly...

The values that are being displayed are "old" data. Data that gets changed during a later part of the Page Life-Cycle.

Assuming that is correct, change the OnLoad to OnRender (Or equivalent, can't remember off the top of my head)

And instead of adding Literal controls, you will just write the strings to an output stream (or a string? again, haven't done anything like this in a while...)

Does that help?

--Edit--

Ok, I finally understand what you are trying to do. I think heh.

You need to use reflection.

PropertyInfo[] props = typeof(TestUserControl).GetProperties(BindingFlags.Public);

That will get you all of the Public Properties of TestUserControl. Store that in your Objects array, then in OnLoad use:

object o =  props[0].GetValue(this, null);

to get the value.

Does that help you now? :)

Answer 8

Use the ref keyword when passing as reference

See This