在silverlight中使用downloader

     downloader对象为Silverlight 插件提供了下载功能，其通过HTTP(get)请求异步下载指定的内容.
 
     其英文定义如下：
 
      Represents the set of download functionality for a Silverlight plug-in. The downloader
can asynchronously download content that can be obtained through an HTTP GET request.


     downloader所支持的event包括：
 
     Completed：下载完成 (Downloader)
 
     DownloadFailed： 下载失败
 
     DownloadProgressChanged：下载进度变化 (Downloader)
 
 
    支持的方法包括：
 
    Abort, Equals, FindName (DependencyObject), GetHost, GetResponseText, GetValue, Open,
    Send, SetValue
 
    下面这个DEMO演示使用downloader从网上下载jpg图片以及xaml文件并完成数据加载的过程：

    

    
 
 
     其xaml代码如下所示：
 

< Canvas   Canvas.Left ="10" >
    < TextBlock  Canvas.Left ="10"  Canvas.Top ="5"  Name ="StartDownLoadImg" > 下载图片 </ TextBlock >
    < TextBlock  Canvas.Left ="150"  Canvas.Top ="5"  Name ="StartDownLoadXaml" > 下载xaml </ TextBlock >
</ Canvas >

<!--  下载进度条  -->
< Canvas  Canvas.Top ="40" >
   < Rectangle  Name ="progressRectangle"  Canvas.Left ="20"   Height ="10"  Width ="0"
    Fill ="Maroon"   />
   < Rectangle  Canvas.Top  ="-1"  Canvas.Left ="19"  Height ="12"   Width ="202"
    StrokeThickness ="1"  Stroke ="Black"   />
   < TextBlock  Name ="progressText"   Canvas.Top  ="-4"  Canvas.Left ="230"
    Text ="0%"  FontSize ="12"   />
</ Canvas >

< Image  Name ="loadimg"  Height ="400"  Width ="300"   />

< Canvas  Canvas.Top ="70"  x:Name ="loadxaml" />

     接下来就是相应的js代码（详情见注释）：
 

Silverlight_JsWeb.Downloader = function()
{
}

Silverlight_JsWeb.Downloader.prototype =
{
    handleLoad: function(plugIn, userContext, sender)
    {
        this.plugIn = plugIn;
       
        // 附加事件处理程序
        sender.findName("StartDownLoadImg").addEventListener("MouseLeftButtonDown",
                       Silverlight.createDelegate(this, this.handleMouseLeftButtonDown));
        sender.findName("StartDownLoadXaml").addEventListener("MouseLeftButtonDown",
                       Silverlight.createDelegate(this, this.handleMouseLeftButtonDown));

        progressText = sender.findName("progressText");
        progressRectangle = sender.findName("progressRectangle");
    },
   
    //开始下载
    handleMouseLeftButtonDown:function (sender, eventArgs)
    {   

        var slPlugin = sender.getHost();
        //创建downloader对象
        var downloader = slPlugin.createObject("downloader");   
        //下载进度变化事件绑定
        downloader.addEventListener("downloadProgressChanged",
                  Silverlight.createDelegate(this, this.handleDownloadProgressChanged));
        //下载结束事件绑定
        downloader.addEventListener("completed",
                  Silverlight.createDelegate(this, this.handleCompleted));
        //下载失败事件绑定
        downloader.addEventListener("downloadFailed",
                  Silverlight.createDelegate(this, this.handleDownloadFailed));
       
        //初始化下载请求
        if(sender.name == 'StartDownLoadImg') {
            downloader.open("GET", "ClientBin/tang.jpg");
        }
        else {
            downloader.open("GET", "xaml/PathScene.xaml");           
        }      
        //downloader.open("GET", "contoso.TTF");字体下载
       
        //执行下载请求
        downloader.send();
      
    },
   
    //下载进度改变
    handleDownloadProgressChanged:function (sender, eventArgs)
    {   
        var percentage = Math.floor(sender.downloadProgress * 100);   
        progressText.text = percentage + "%";
        progressRectangle.width = percentage * 2;
    },
   
    //下载完成
    handleCompleted:function (sender, eventArgs)
    {   
        var plugin = sender.getHost();

        if (sender.uri == "ClientBin/tang.jpg")
        {
            //绑定图片信息
            sender.findName("loadimg").setSource(sender,"");
           
            //清除 loadxaml 下的内容 
            sender.findName("loadxaml").children.clear();
           
            //var pathCanvas = sender.findName("pathCanvas");
            //if (pathCanvas != null)
            //{               
            //    sender.findName("loadxaml").children.remove(pathCanvas);
            //}
            //sender.findName("loadxaml").children.removeAt(0);
        }
       
        if (sender.uri == "xaml/PathScene.xaml")
        {
            // 获取下载内容.
            var xamlFragment = sender.ResponseText;
            // 创建内容.
            var xamlPath = plugin.content.createFromXaml(xamlFragment);           
            sender.findName("loadxaml").children.add(xamlPath);
           
            // 清除图片绑定              
            sender.findName("loadimg").Source = "";
        }
      
      
         // 下面为下载字体并进行加载的测试.
         // var myTextBlock = sender.findName("myTextBlock");
         //myTextBlock.setFontSource(sender);
         // 设置字体 "Contoso Font".
         //myTextBlock.fontFamily = "Contoso Font";
         //myTextBlock.text = "This is my new font!";
    },
   
    //下载失败处理事件
    handleDownloadFailed:function (sender, errorArgs)
    {
        var errorMsg = "Silverlight Error: \n\n";

        errorMsg += "Error Type:    " + errorArgs.errorType + "\n";
        errorMsg += "Error Message: " + errorArgs.errorMessage + "\n";
        errorMsg += "Error Code:    " + errorArgs.errorCode + "\n";   

        switch(errorArgs.errorType)
        {
            case "RuntimeError":          
                if (errorArgs.lineNumber != 0)
                {
                    errorMsg += "Line: " + errorArgs.lineNumber + "\n";
                    errorMsg += "Position: " +  errorArgs.charPosition + "\n";
                }
                errorMsg += "MethodName: " + errorArgs.methodName + "\n";
                break;
            case "ParserError":           
                errorMsg += "Xaml File:      " + errorArgs.xamlFile      + "\n";
                errorMsg += "Xml Element:    " + errorArgs.xmlElement    + "\n";
                errorMsg += "Xml Attribute:  " + errorArgs.xmlAttribute  + "\n";
                errorMsg += "Line:           " + errorArgs.lineNumber    + "\n";
                errorMsg += "Position:       " + errorArgs.charPosition  + "\n";
                break;
            default:
                break;
        }
        alert(errorMsg);
    } 
}

 
    好了，今天的内容就到这里了。
   
    下载源码，请点击这里:)

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