Delegates and events in C #

from:http://blog.csdn.net/xuwei_xuwei/article/details/18008013

Quan

For invokerequired, the video can be used to determine if it is required, and if there is a possibility for multiple threads to access it, then it is not necessary to do so if only the thread is accessible.

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The following narrative is personal understanding:

Definition understanding

Delegate: Using formal and class methods similar, essentially a class, compiler compile time, it will be compiled into the corresponding class, parameters can be the method name,

Event: is a response to a user action, the average user has an action, triggered an event, of course, in C # we can customize their own events, and then we need to program the trigger,

Relationship of delegates and events

An event requires a delegate to sign, and one of the purposes of the delegate is to sign the event,

Use

Delegate: There are three main purposes for signing events and invoking synchronous methods across threads using controls and asynchronously

cross-thread invocation example

Declaring a delegate

Private delegate void Appendtextdel (textbox textbox, string content);

public void AppendText (textbox textbox, string content)

{

if (textbox.invokerequired)//Determine whether a textBox is called across threads
{
Appendtextdel append = new Appendtextdel (appendtext);
Textbox.invoke (Append, TextBox, content);
}
Else
{
TextBox.Text = content + "\ r \ n" + textbox.text;//append text and line wrap
}

}

When you need to assign a value to a control of the textbox type, the call can

AppendText (TextBox1, "Hello World")

Example of an event signature

public delegate void Eventdel ();//Declaration Delegate

Public event Eventdel customevent;//declares a custom event, with a Eventdel delegate signature (in other words, this can only be called and Eventdel Delegate matching method)

Defines a method that a Eventdel can invoke

public void Methonda () {

Console.WriteLine ("Methonda");

}

Defines a method that a Eventdel can invoke

public void Methondb () {

Console.WriteLine ("Methondb");

}

Test

public void Testmethond () {

This. Customevent + = new Eventdel (Methonda);

This. Customevent + = new Eventdel (methondb);

Customevent ();//Contact Custom Event

}

Example of asynchronous method calling synchronous methods

(specifically the invocation of the delegate's BeginInvoke and EndInvoke to implement, see Code)

delegate void Messagedel ();

public void Custommessage () {

Console.WriteLine ("Synchronous method called asynchronously");

}

To invoke asynchronously, the following

Messagedel del = new Messagedel (custommessage);

Del. BeginInvoke (Asynvcallback delegate object, user-defined object type);

Or

Messagedel del = new Messagedel (custommessage);

IAsyncResult result = Del. BeginInvoke ();

...//By using result for subsequent processing, both methods of invocation are OK

Delegates and events in C #