从另一个类运行SaveFileDialog

Question

I'm trying to write a software that transfers a file from the server to a client... This is how my software works.. On the client-side it gets an IP and a port then spawns a new object from the Client class to a new Thread and passes the ip and the port to the constructor and the client handles the connection and transfers the file to a byte[] variable.. Now I want to prompt the user with a saveFileDialog to save the file...But I don't have access to the parent class which is my Form. so I can't do something like savefiledialog.ShowDialog()... What is the solution to this problem?

Answer 1

Use events

http://msdn.microsoft.com/en-us/library/awbftdfh.aspx

Use background worker instead of your own thread:

http://msdn.microsoft.com/en-us/library/system.componentmodel.backgroundworker(v=vs.100).aspx

Answer 2

An event as @syned suggested is a good solution. It is kind of an observer , but in this example you need to interact with the observable class (the client).

You can declare an event in your client class, so when a file is to be received this event can be used. A normal approach is to have a special "context class" which you fill with the values you need.

public class Client {
    public event EventHandler<ReceivedFileEventArgs> ReceivedFile;

    private ReceivedFileEventArgs onReceivedFile() {
        EventHandler<ReceivedFileEventArgs> handler = ReceivedFile;
        ReceivedFileEventArgs args = new ReceivedFileEventArgs();
        if (handler != null) { handler(this, args); }
        return args;
    }

    private void receiveFileCode() {
        // this is where you download the file
        ReceivedFileEventArgs args = onReceivedFile();
        if (args.Cancel) { return; }
        string filename = args.FileName;
        // write to filename
    }
}

public class ReceivedFileEventArgs {
    public string FileName { get; set; }
    public bool Cancel { get; set; }
}

Now, in your GUI class you can "listen" to this event, and set the filename to what you want.

public class MyForm : Form {
   public MyForm() { Initialize(); }

   protected void buttonClick(object sender, EventArgs e) {
       // Suppose we initialize a client on a click of a button
       Client client = new Client();
       // note: don't use () on the function here
       client.ReceivedFile += onReceivedFile;
       client.Connect();
   }

   private void onReceivedFile(object sender, ReceivedFileEventArgs args) {
       if (InvokeRequired) {
           // we need to make sure we are on the GUI thread
           Invoke(new Action<object, args>(onReceivedFile), sender, args);
           return;
       }
       // we are in the GUI thread, so we can show the SaveFileDialog
       using (SaveFileDialog dialog = new SaveFileDialog()) {
           args.FileName = dialog.FileName;
       }
   }
}

So, what is an event? In simple terms it's a function pointer (but please read up on it for more details). So, you tell your client class to call the function when something happens, when a file is to be received for instance. You use events pretty much all the time when using Windows Forms, such as when you assign a button click to a function in your code behind file.

Now, using this pattern, you can have more events, such as a FileDownloadCompleted for instance.

Also note the += syntax. You don't assign an event to a function, you tell the event to call the function when something happens. You can even have two functions on the same event if you want.