委托实质

1.委托是方法指针；

2.委托是一个类，当对其进行实例化的时候，要将引用方法作为它的构造方法的参数。

 

添加event关键字保护委托：在外的赋值都会报错。

 

class FileUploader
    {
        public delegate void FileUploadHandler(int progress);
        public FileUploadHandler FileUploaded;

        public void Upload()
        {
            int fileProgress = 100;
            while (fileProgress > 0)
            {
                fileProgress--;
                if(FileUploaded != null)
                {
                    FileUploaded(fileProgress);
                }
            }
        }
        public FileUploader() { }
    }

 

static void Main(string[] args)
        {
            FileUploader f1 = new FileUploader();
            f1.FileUploaded = Progress;
            //f1.FileUploaded = null;
            f1.FileUploaded += ProgressAnother;
            f1.Upload();
        }

        public static void Progress(int progress)
        {
            Console.WriteLine(progress);
        }

        public static void ProgressAnother(int progress)
        {
            Console.WriteLine(string.Format("另一个通知方法：{0}", progress));
        }

 

标准事件模型：public delegate void EventHandler(object sender, EventArgs e)

1.委托类型的名称以EventHandler结束；

2.委托原型返回值为void；

3.委托原型具有两个参数：sender表示事件触发者，e表示事件参数；

4.事件参数的名称以EventArgs结束。

实现标准的事件模型：

class FileUploader
    {
        public event EventHandler<FileUploadedEventArgs> FileUploaded;

        public void Upload()
        {
            FileUploadedEventArgs e = new FileUploadedEventArgs() { FileProgress = 100 };
            while (e.FileProgress > 0)
            {
                e.FileProgress--;
                if (FileUploaded != null)
                {
                    FileUploaded(this, e);
                }
            }
        }
        public FileUploader() { }

        public class FileUploadedEventArgs : EventArgs
        {
            public int FileProgress { get; set; }
        }
    }

static void Main(string[] args)
        {
            FileUploader f1 = new FileUploader();
            f1.FileUploaded += Progress;
            //f1.FileUploaded = null;
            f1.FileUploaded += ProgressAnother;
            f1.Upload();
        }

        public static void Progress(object sender, FileUploadedEventArgs e)
        {
            Console.WriteLine(e.FileProgress);
        }

        public static void ProgressAnother(object sender, FileUploadedEventArgs e)
        {
            Console.WriteLine(string.Format("另一个通知方法：{0}", e.FileProgress));
        }

 

委托分为：方法委托和事件委托。

方法委托在调用的时候需要传值，且没有event修饰。

事件委托多了event修饰。使用事件应该由发布者触发而不是客户端触发。