4.2 event

using System;

public delegate void DownloadStartHandler(object sender, DownloadStartEventArgs e);  //声明委托
public delegate void DownloadEndHandler(object sender, DownloadEndEventArgs e);
public delegate void DownloadingHandler(object sender, DownloadingEventArgs e);  

public class DownloadStartEventArgs
{
    public string Url{ get{ return _url;} set{ _url=value;} }
    private string _url;

    public DownloadStartEventArgs( string url ){ this._url = url; }
}

public class DownloadEndEventArgs
{
    public string Url{ get{ return _url;} set{ _url=value;} }
    private string _url;

    public long ByteCount { get { return _byteCount; } set{ _byteCount=value;} }
    private long _byteCount;

    public DownloadEndEventArgs( string url, long size  ){ this._url = url; this._byteCount=size; }
}

public class DownloadingEventArgs
{
    public string Url{ get{ return _url;} set{ _url=value;} }
    private string _url;

    public double Percent { get { return _percent; } set{ _percent=value;} }
    private double _percent;

    public DownloadingEventArgs( string url, double percent  ){ this._url = url; this._percent=percent; }
}

public class Crawler
{

    public event DownloadStartHandler DownloadStart;  // 声明事件
    public event DownloadEndHandler DownloadEnd;  // 声明事件
    public event DownloadingHandler Downloading;  // 声明事件

    public string Name { get{return name;} set{ name=value;} }
    private string name;
    private string site;

    public Crawler( string name, string site )
    {
        this.name = name;
        this.site = site;
    }

    public void Craw()
    {
        while( true )
        {
            string url = GetNextUrl();
            if( url == null ) break;
            long size = GetSizeOfUrl( url );

            if( DownloadStart != null ) //下载开始的事件发生
            {
                DownloadStart( this, new DownloadStartEventArgs(url));
            }

            for( long i=; i<size+; i+= )
            {
                //下载数据。。。
                System.Threading.Thread.Sleep(  );
                double percent = (int)(i*100.0/size);
                if( percent>) percent=;

                if( Downloading != null ) //下载数据的事件发生
                {
                    Downloading( this, new DownloadingEventArgs(url, percent));
                }
            }

            if( DownloadEnd != null ) //下载结束的事件发生
            {
                DownloadEnd( this, new DownloadEndEventArgs(url, size));
            }
        }

    }
    private string GetNextUrl()
    {
        int a = rnd.Next();
        if( a ==  ) return null;
        return site + "/Page" + a + ".htm";
    }
    private long GetSizeOfUrl( string url)
    {
        return rnd.Next( * url.Length);
    }
    private Random rnd = new Random();
}

class Test
{
    static void Main()
    {
        Crawler crawler = new Crawler("Crawer101", "http://www.pku.edu.cn");

        crawler.DownloadStart += new DownloadStartHandler( ShowStart ); //注册事件
        crawler.DownloadEnd += new DownloadEndHandler( ShowEnd );
        crawler.Downloading += new DownloadingHandler( ShowPercent );

        crawler.Craw();
    }

    static void ShowStart(object sender, DownloadStartEventArgs e){
        Console.WriteLine( (sender as Crawler).Name + "开始下载" + e.Url );
    }
    static void ShowEnd(object sender, DownloadEndEventArgs e){
        Console.WriteLine( "\n\r下载" + e.Url + "结束,其下载" + e.ByteCount + "字节" );
    }
    static void ShowPercent(object sender, DownloadingEventArgs e){
        Console.Write( "\r下载" + e.Url + "......." + e.Percent + "%" );

    }

}