C Sharp事件处理程序

Question

private void button1_Click(object sender, EventArgs e)
{
    Button source = (Button)sender;
    MessageBox.Show("The message inside the button is " + source.Text);
}

I am following a tutorial on C sharp's Event Handler , I was a Python user,

public static void Main()
{
    Message myMessage = new Message();
    myMessage.ShowMessage += new MessageHandler(myMessage.DisplayMessage);
}

I kind of know the basic syntax of creating new instances of a class now, but I don't get why there is a bracket for the Button in the first line.What are the differences between these two codes ?

Answer 1

In c# every class is inherited from object class. as Object is a parent class it can be used to instantiate any child class. so here when we receive an object class instance we expect it to be a Button so we parse it into a Button object

private void button1_Click(object sender, EventArgs e)

here sender is specified as an object type variable.

Button source = (Button)sender;

Here that object variable sender is parsed into a Button object and save in a Button Type variable

Answer 2

Here (Button) is used to cast object sender to button type because you want the type in button. and in second example as you have mentioned its creating instance of Message class.

For more information go through this

http://msdn.microsoft.com/en-IN/library/ms173105.aspx

Typecasting in C#

Answer 3

sender is an object . In order you get the Text property of the button, whose click handler is button1_Click , you have to cast the sender to an object of type Button , in order later get source.Text .

Actually, the sender is the control that the action is for. Because all the types in .NET inherit the base type System.Object , in order you get a specific property of the button, you have to cast the sender to an object of type Button .