为 RSS 加载 XDocument 时出现 MonoDroid ObjectDisposedException

Question

我正在尝试构建一个简单的播客下载应用程序 MonoDroid（又名 Mono for Android），目前只是测试 RSS 提要内容的检索。

我的简单应用是：

• 输入 RSS 提要的 url 的编辑文本
• “下载”RSS 的按钮
• 下载操作输出的文本显示

当用户点击下载时，我获取 RSS 内容，目前使用XDocument（我也尝试使用just WebRequest / Streams etc.），这是简短版本：

void button_Click(object sender, EventArgs e)
{
    output.Text += "user input: " + rssUriInput.Text + "\n";

    try
    {
        output.Text += "### document ###";
        output.Text += XDocument.Load(rssUriInput.Text).ToString();
        output.Text += "### document ###";
    }
    catch (Exception ex)
    {
        output.Text += "OOOPS something went wrong:\n" + ex.ToString();
    }
}

我尝试了几种方法，但当我使用XDocument.Load(/*my uri here*/);时，我不断收到ObjectDisposedExceptions

我的 AssemblyInfo.cs 包括

[assembly: UsesPermission(Android.Manifest.Permission.Internet)]

现在，免责声明，在运行 hello world 之后，我有点自己跑了，所以我可能缺少一些 MonoDroid 基础知识，但是这段代码在普通的 C# 应用程序中工作（我测试过）但是
为什么我在这里做错了？我必须做一些特殊的事情才能在 MonoDroid 中使用 xml / linq / 网络访问吗？

这是完整的活动代码：

using System;

using Android.App;
using Android.Content;
using Android.Runtime;
using Android.Views;
using Android.Widget;
using Android.OS;
using System.Xml.Linq;

namespace RssDownlowd
{
    [Activity(Label = "RssDownlowd", MainLauncher = true, Icon = "@drawable/icon")]
    public class Activity1 : Activity
    {
        EditText rssUriInput;
        Button button;
        TextView output;

        protected override void OnCreate(Bundle bundle)
        {
            base.OnCreate(bundle);

            SetContentView(Resource.Layout.RssDownload);

            rssUriInput = FindViewById<EditText>(Resource.Id.rssUriText);
            button = FindViewById<Button>(Resource.Id.downloadButton);
            output = FindViewById<TextView>(Resource.Id.outputTextView);

            button.Click += new EventHandler(button_Click);
        }

        void button_Click(object sender, EventArgs e)
        {
            output.Text += "user input: " + rssUriInput.Text + "\n";

            try
            {
                output.Text += "### document ###";
                output.Text += XDocument.Load(rssUriInput.Text).ToString();
                output.Text += "### document ###";
            }
            catch (Exception ex)
            {
                output.Text += "OOOPS something went wrong:\n" + ex.ToString();
            }
        }

    }
}

这里是完整的例外：

"System.ObjectDisposedException: The object was used after being disposed.

  at System.Net.WebConnection.BeginRead (System.Net.HttpWebRequest request, System.Byte[] buffer, Int32 offset, Int32 size, System.AsyncCallback cb, System.Object state) [0x00000] in <filename unknown>:0 

  at System.Net.WebConnectionStream.BeginRead (System.Byte[] buffer, Int32 offset, Int32 size, System.AsyncCallback cb, System.Object state) [0x00000] in <filename unknown>:0 

  at System.Net.WebConnectionStream.Read (System.Byte[] buffer, Int32 offset, Int32 size) [0x00000] in <filename unknown>:0 

  at System.Xml.XmlInputStream.Read (System.Byte[] buffer, Int32 offset, Int32 count) [0x00000] in <filename unknown>:0 

  at System.Xml.NonBlockingStreamReader.ReadBuffer () [0x00000] in <filename unknown>:0 

  at System.Xml.NonBlockingStreamReader.Read (System.Char[] dest_buffer, Int32 index, Int32 count) [0x00000] in <filename unknown>:0 

  at System.Xml.XmlStreamReader.Read (System.Char[] dest_buffer, Int32 index, Int32 count) [0x00000] in <filename unknown>:0 

  at Mono.Xml2.XmlTextReader.ReadTextReader (Int32 remained) [0x00000] in <filename unknown>:0 

  at Mono.Xml2.XmlTextReader.PeekChar () [0x00000] in <filename unknown>:0 

  at Mono.Xml2.XmlTextReader.ReadChar () [0x00000] in <filename unknown>:0 

  at Mono.Xml2.XmlTextReader.Expect (Int32 expected) [0x00000] in <filename unknown>:0 

  at Mono.Xml2.XmlTextReader.ReadEntityReference (Boolean ignoreEntityReferences) [0x00000] in <filename unknown>:0 

  at Mono.Xml2.XmlTextReader.ReadReference (Boolean ignoreEntityReferences) [0x00000] in <filename unknown>:0 

  at Mono.Xml2.XmlTextReader.ReadText (Boolean notWhitespace) [0x00000] in <filename unknown>:0 

  at Mono.Xml2.XmlTextReader.ReadContent () [0x00000] in <filename unknown>:0 

  at Mono.Xml2.XmlTextReader.Read () [0x00000] in <filename unknown>:0 

  at System.Xml.XmlTextReader.Read () [0x00000] in <filename unknown>:0 

  at Mono.Xml.XmlFilterReader.Read () [0x00000] in <filename unknown>:0 

  at System.Xml.Linq.XElement.LoadCore (System.Xml.XmlReader r, LoadOptions options) [0x00000] in <filename unknown>:0 

  at System.Xml.Linq.XNode.ReadFrom (System.Xml.XmlReader r, LoadOptions options) [0x00000] in <filename unknown>:0 

  at System.Xml.Linq.XContainer.ReadContentFrom (System.Xml.XmlReader reader, LoadOptions options) [0x00000] in <filename unknown>:0 

  at System.Xml.Linq.XElement.LoadCore (System.Xml.XmlReader r, LoadOptions options) [0x00000] in <filename unknown>:0 

  at System.Xml.Linq.XNode.ReadFrom (System.Xml.XmlReader r, LoadOptions options) [0x00000] in <filename unknown>:0 

  at System.Xml.Linq.XContainer.ReadContentFrom (System.Xml.XmlReader reader, LoadOptions options) [0x00000] in <filename unknown>:0 

  at System.Xml.Linq.XElement.LoadCore (System.Xml.XmlReader r, LoadOptions options) [0x00000] in <filename unknown>:0 

  at System.Xml.Linq.XNode.ReadFrom (System.Xml.XmlReader r, LoadOptions options) [0x00000] in <filename unknown>:0 

  at System.Xml.Linq.XContainer.ReadContentFrom (System.Xml.XmlReader reader, LoadOptions options) [0x00000] in <filename unknown>:0 

  at System.Xml.Linq.XElement.LoadCore (System.Xml.XmlReader r, LoadOptions options) [0x00000] in <filename unknown>:0 

  at System.Xml.Linq.XNode.ReadFrom (System.Xml.XmlReader r, LoadOptions options) [0x00000] in <filename unknown>:0 

  at System.Xml.Linq.XContainer.ReadContentFrom (System.Xml.XmlReader reader, LoadOptions options) [0x00000] in <filename unknown>:0 

  at System.Xml.Linq.XDocument.ReadContent (System.Xml.XmlReader reader, LoadOptions options) [0x00000] in <filename unknown>:0 

  at System.Xml.Linq.XDocument.LoadCore (System.Xml.XmlReader reader, LoadOptions options) [0x00000] in <filename unknown>:0 

  at System.Xml.Linq.XDocument.Load (System.String uri, LoadOptions options) [0x00000] in <filename unknown>:0 

  at System.Xml.Linq.XDocument.Load (System.String uri) [0x00000] in <filename unknown>:0 

  at RssDownlowd.Activity1.button_Click (System.Object sender, System.EventArgs e) [0x0004a] in C:\\Users\\khd483\\code\\HelloMonoDroid\\RssDownlowd\\Activity1.cs:47 "

Answer 1

奇怪的是，当我尝试你的代码时它工作得很好：

您是否在 Mono for Android 选项中的项目中启用了链接？

还可以考虑对 RSS 进行异步下载，因为它会阻塞 UI 线程，直到下载完成，从而导致应用无响应。