有关更新Winforms标签文本的问题

Question

I have a windows forms application I have a public class inside my form code behind with the following structure :

 public partial class Home : Form
 {
     public class AsynchronousSocketListener
     {
         public void ReadCallback(IAsyncResult ar)
         {
           //Here I want to Update a labels text this waw :
           //label1.Text = currantRFID;
         }
     }
 }

I can not access lablel1 control inside the ReadCallback() function and update It's text . when I try to do that I get the following error :

Error 3 Cannot access a non-static member of outer type 'SFTWindowApplications.Home' via nested type 'SFTWindowApplications.Home.AsynchronousSocketListener'

how can I access It and what is the best way to update It's text ? I mean is It better to update It Asynchronously or not ?

thx in advance .

Answer 1

A nested class (ie AsynchronousSocketListener ) does not automagically have access to the non-static members of its outer type (ie Home ).

Restarting your IDE will not change this. IntelliSense is doing what it should - not listing a member of an outer type that is not in scope.

If you wish for the async listener to affect the form's label, an instance of AsynchronousSocketListener will need a reference to label1 ...

// Really this is just an example of how it could avoid the error you encountered -
// reality checked only by my cerebral compiler. :)
public partial class Home : Form
{
    // instance of the async socket listener to use
    private AsynchronousSocketListener asyncSocketListener; 

    public Home()
    {
        // Initialize the async socket listener, and provide to it a reference to
        // the label it should update.
        asyncSocketListener = new AsynchronousSocketListener(label1);
    }

    public class AsynchronousSocketListener
    {
        private Label targetLabel;

        public AsynchronousSocketListener(Label targetLabel)
        {
            this.targetLabel = targetLabel;
        }

        public void ReadCallback(IAsyncResult ar)
        {
            // // assuming currantRFID is part of the async result ar
            this.targetLabel.Text = ar.currantRFID;
        }
    }
}

..., or you need to take an event-driven approach.

Ideally the relationship between the classes and what happens following a response would be less concrete & rigid (eg not specific to just a label, not requiring the classes to know so much about each other). An event-driven approach (ie the async listener raises an event to which this particular form subscribes and handles by updating its label) would achieve these goals. But I am admittedly just trying to give you a sense how it could work with respect to the non-static member access that is at the center of the question you asked.

Answer 2

It's a different class, so you need to pass the label instance or pass the Home class instance to the method and make the label public (imo it's protected by default).

UPDATE : New code with BackGroundWorker Note: I didn't test this code, but it should give you an idea.

public partial class Home : Form
{
 public class AsynchronousSocketListener : IDisposable
 {
   private BackgroundWorker worker = new System.ComponentModel.BackgroundWorker();

   private Label myLabel;
   public AsynchronousSocketListener(Label lbl)
   {
       myLabel = lbl;
       worker.RunWorkerCompleted += WorkerCompleted;
       worker.DoWork += DoWork;
       worker.RunWorkerAsync();
   }
   public void Dispose()
    {
        worker.RunWorkerCompleted -= WorkerCompleted;
        worker.CancelAsync();
        worker.Dispose();
    }

   private void DoWork(object sender, System.ComponentModel.DoWorkEventArgs e)
   {
     // Perform your work on the other Thread
     e.Result = currantRFID;
   }

   public void WorkerCompleted(object sender, RunWorkerCompletedEventArgs args)
   {
      //Here I want to Update a labels text this waw :
      myLabel.Text = args.Result;
   }
         }
}




/*

    public partial class Home : Form
     {
         public class AsynchronousSocketListener
         {
             private Label myLabel;
             public AsynchronousSocketListener(Label lbl)
             {
                myLabel = lbl;
             }
             public void ReadCallback(IAsyncResult ar)
             {
               //Here I want to Update a labels text this waw :
               myLabel.Text = currantRFID;
             }
         }
     }

*/

Answer 3

尝试重新启动IDE，如果无济于事，请显示设计者代码。

Answer 4

You can't access member of one class inside other class without having any reference to parent class. You need to access label1 inside ReadCallback through your Home class.

See this example

Answer 5

You need to provide your Home-Class to the classes where you want to use the controls, eg

[...] new AsynchronousSocketListener(this)

and pass it until you are in the depth where you need it.