For unknown reason, a button click closes my window. How can I fix this? - monodevelop

Question

I am trying to replicate a simple addition of 2 entries with a button in Monodevelop (shown how to make it step-by-step) but somehow the window closes 2 seconds after pressing the button without actually changing anything.
The code for the button:
using Gtk;
using Frontend.ChatService;
public partial class MainWindow : Gtk.Window
{
public MainWindow() : base(Gtk.WindowType.Toplevel)
{
Build();
}
protected void OnDeleteEvent(object sender, DeleteEventArgs a)
{
Application.Quit();
a.RetVal = true;
}
protected void OnButton1Clicked(object sender, EventArgs e)
{
ChatService client = new ChatService();
int x = Int32.Parse(entry1.Text);
int y = Int32.Parse(entry2.Text);
int sum = client.Add(x, y);
entry1.Text = sum.ToString();
}
}
And the sum (which I tested and think works):
using System;
using System.Web;
using System.Web.Services;
namespace Backend
{
public class ChatService : System.Web.Services.WebService
{
[WebMethod]
public int Add(int x, int y)
{
return x + y;
}
}
}
I left the main file program.cs as generated and is:
using System;
using Gtk;
namespace Frontend
{
class MainClass
{
public static void Main(string[] args)
{
Application.Init();
MainWindow win = new MainWindow();
win.Show();
Application.Run();
}
}
}
The window does pop up as it should and shows no problem until the button is pressed.
Edit:
I forgot to run the backend / server part, which is why the function was not found... (beginners mistake I guess)
Works now

Answer 1

The problem is probably that your code throws an exception you are not aware of. The problem is in the code that handles the button being clicked.
protected void OnButton1Clicked(object sender, EventArgs e)
{
ChatService client = new ChatService();
int x = Int32.Parse(entry1.Text);
int y = Int32.Parse(entry2.Text);
int sum = client.Add(x, y);
entry1.Text = sum.ToString();
}
Let's go line by line:
ChatService client = new ChatService();
Here you are creating a new instance of what it seems to be a system service or maybe a web services. This could throw if the service is not known (in the former case), or if the connection is interrupted or does not reach a destination, etc., in the latter case.
These lines are also delicate:
int x = Int32.Parse(entry1.Text);
int y = Int32.Parse(entry2.Text);
They will throw in case the field entry1 or entry2 are empty, or contain a letter...
In order to manage these cases you need to add try... catch blocks in the appropriate places. Alternately, you can use Int32.TryParse.
For example, assuming the service is in the web:
protected void OnButton1Clicked(object sender, EventArgs e)
{
ChatService client;
int x;
int y;
try {
client = new ChatService();
} catch(HttpRequestException exc) {
client = null;
var dlg = new Gtk.MessageDialog(
this,
Gtk.DialogFlags.Modal,
Gtk.MessageType.Error,
Gtk.ButtonsType.Ok,
"Connection error"
);
dlg.Text = exc.Message;
dlg.Run();
dlg.Destroy();
}
if ( client != null ) {
if ( !int.TryParse( entry1.Text, out x) {
entry1.Text = "0";
x = 0;
}
if ( !int.TryParse( entry2.Text, out y) {
entry2.Text = "0";
y = 0;
}
int sum = client.Add(x, y);
entry1.Text = sum.ToString();
}
}
Getting code which correctly handles errors is always harder, of course.
Hope this helps.