C#: How to get the assigned value from an action?

Question

Hello,

I use the following code to Invoke and access properties on my from from a different thread.

    public static void PFA(Action<frmain> action)
    {
        var form = Form.ActiveForm as frmain;
        if (form != null)
        {
            form.PerformAction(action);
        }
    }

    public void PerformAction(Action<frmain> action)
    {
        if (InvokeRequired)
            Invoke(action, this);
        else
            action(this);
    }

My Question:

If I call PFA(form => form.Richbox1.Text = "Test") - I want PFA() to check if the action is (Richbox1.Text) and if so then Add "\n" to the text("Test").

The Idea is to call

PFA(form => form.Richbox1.Text = "Test");

instead of

PFA(form => form.Richbox1.Text = "Test\n");

In other words I want to add a new line automaticly if the action is "Richbox1.Text ="

How I do that? I never worked with actions before.

Answer 1

You can add an extension method to do the trick. Try the following.

public static void AddNewLineIfMatch(this RichTextBox rtb, string toMatch) {
  if ( rtb.Text == toMatch ) {
    rtb.AppendText("\n");
  }
}

PFDA(() => form.Richbox1.AddNewLineIfMatch("Test"));

EDIT Used the AppendText method instead of Text+=

Answer 2

You can't do this the way you want. PFA function can not check what's is inside your delegate. Think how you can solve your task another way.

[offtopic]
PS. Also, your naming convention is not very good. "PFA" doesn't explain what the function does and as for "frmain" - usually class names start with capital letter.
[/offtopic]

UPDATE: I would do it a little bit better, than Josh offered:

PFA(form => SetControlText(form.Richbox1, "Test"));

public void SetControlText(Control control, string text)
{ 
  control.Text = text;  
  // choose control type for which you want to add new line
  if(control is RichTextbox || control is TextBox || control is ... )
    control.Text += Environment.NewLine;
}

Answer 3

What if you did:

PFA(form => UpdateTextBox(form.Richbox1,"Test"));


public void UpdateTextBox(RichTextBox box,string text)
{

   if (box.Name=="Richbox1")
   {
       text+="\n";
   }

   box.AppendText(text);
}

Your not going to be able to look inside the action and determine it's using a specific cotnrol from outside of the action. So either you need to add the \n before you call PFA, or have PFA call a function which will do what you want, or have PFA implement the logic.

Answer 4

You could accomplish this by moving from Action to Expression>. Then you can look at what's happening in the method like so

public static void PFA(Expression<Action<frmain>> expression) {
    // this will give you form.RichTextBox1
    var targetFormProperty = (MemberAccessExpression)expression.Body;
    // this only works for your example given. this gives you RichTextBox1.Text
    var textProperty = (MemberAccessExpression)targetFormProperty.Expression;

    // this is how you would run your action like normal
    var action = expression.Compile();
    action(); // invoke action (you would want to wrap this in the invoke check)
}

This gives you the info you need to figure out the property, but not how to append the \n. I'll leave this up to you to find out. I think this is overkill here, but who knows, maybe this could help you or someone else, or even inspire a nice solution.

A nice solution i could possibly think of where you could reuse this functionality is like a rule engine where you might compare what the property being accessed is and run an action right after it, etc.