WriteLine中的System.FormatException

Question

I'm having a trouble in my code with this exception:

System.FormatException

Additional information: Input string was not in a correct format.

I have two files in my visual studio C# solution:

1. Program.cs:

    using System; using System.Collections.Generic; using System.Linq; using System.Text; using System.Threading.Tasks; namespace EventPubSub { class Program { static void Main(string[] args) { Rectangle rect = new Rectangle(); // Subscribe to the Changed event rect.Changed += new EventHandler(Rectangle_Changed); rect.Length = 10; } static void Rectangle_Changed(object sender, EventArgs e) { Rectangle rect = (Rectangle)sender; Console.WriteLine("Value Changed: Length = { 0}", rect.Length); } } } 

2. file Rectangle.cs :

    using System; using System.Collections.Generic; using System.Linq; using System.Text; using System.Threading.Tasks; namespace EventPubSub { class Rectangle { //Declare an event named Changed of //delegate type EventHandler public event EventHandler Changed; private double length = 5; public double Length { get { return length; } set { length = value; //Publish the Changed event Changed(this, EventArgs.Empty); } } } } 

The exception arise when I execute the line: rect.Length = 10;

Answer 1

Please change the event handler like this, all will work fine

static void Rectangle_Changed(object sender, EventArgs e)
{
    Rectangle rect = (Rectangle)sender;
    Console.WriteLine(string.Format("Value Changed: Length = {0}", rect.Length));
}

I have made 2 changes here -

1. Added a string.Format (which is not the problem)

2. removed the space between { & 0 . it was { 0} now I made it {0} (which is the actual problem)

Answer 2

处理程序中{和0之间有一个空格，这导致异常

Answer 3

Try first adding try catch to catch the error it is throwing. So you could identify and fix it. This is just to help you fix your own problem next time. :)

static void Main(string[] args)
  {
     Rectangle rect = new Rectangle();
     string errorMessage = String.empty;
     try
     {
          // Subscribe to the Changed event
          rect.Changed += new EventHandler(Rectangle_Changed);
          rect.Length = 10;
      }
      catch(Exception ex)
      {
           errorMessage = ex.Message;
      }
  }