应用程序在模拟器上运行，在设备上崩溃

Question

我遇到了一个奇怪的问题。我正在编写应用程序，它使用来自 Web 的 XML。在模拟器上一切正常，但在手机上它崩溃（点击按钮后关闭，没有任何警报）。

代码如下：

using System;

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

namespace KursyWalut
{
 [Activity (Label = "KursyWalut", MainLauncher = true, Icon = "@drawable/icon")]
 public class MainActivity : Activity
 {
   protected override void OnCreate (Bundle bundle)
   {
     base.OnCreate (bundle);

        // Set our view from the "main" layout resource
        SetContentView (Resource.Layout.Popularne);

        // Get our button from the layout resource,
        // and attach an event to it
        Button button = FindViewById<Button> (Resource.Id.przycisk);
        TextView data = FindViewById<TextView> (Resource.Id.data);
        TextView kurs = FindViewById<TextView> (Resource.Id.kurs);
        RadioGroup radioGroup = FindViewById<RadioGroup> (Resource.Id.radioGroup);
        RadioButton dolar = FindViewById <RadioButton> (Resource.Id.rbDolar);
        RadioButton euro = FindViewById <RadioButton> (Resource.Id.rbEuro);
        RadioButton frank = FindViewById <RadioButton> (Resource.Id.rbFrank);
        int checkedRadioButton;

        XmlDocument dokument = new XmlDocument ();

        //  --------------------------------------------------------------------------
        button.Click += delegate {
            try{
                dokument.Load("http://nbp.pl/kursy/xml/LastA.xml");
            }
            catch(Exception ex){
                Toast.MakeText(this,"Brak połaczenia z Internetem!",ToastLength.Long);
            }
            data.Text = "Data: " + getDocumentDate(dokument);

            checkedRadioButton = radioGroup.CheckedRadioButtonId;
            switch(checkedRadioButton){

            case Resource.Id.rbDolar:
                kurs.Text = "Kurs USD: " + getRate(dokument,"USD");
                break;

            case Resource.Id.rbEuro:
                kurs.Text = "Kurs EUR: " + getRate(dokument,"EUR");
                break;

            case Resource.Id.rbFrank:
                kurs.Text = "Kurs CHF: " + getRate(dokument,"CHF");
                break;
            }
        };
    }
    String getDocumentDate(XmlDocument xml){
        return xml.SelectSingleNode("/tabela_kursow/data_publikacji").InnerText;
    }

    String getRate(XmlDocument xml, String currency){
        foreach (XmlNode xmlNode in xml.DocumentElement) {

            if (xmlNode.Name == "pozycja") {
                if (xmlNode.SelectSingleNode ("kod_waluty").InnerText == currency)
                    return xmlNode.SelectSingleNode ("kurs_sredni").InnerText;      
            }
        }
        return "Nie znaleziono kursu";
    }
  }
}

Answer 1

好吧，我想我找到了。您当前正在阅读按钮中的文档。单击。您应该尝试在后台线程中执行此操作。以 Task Parallel Library 为例：

        XmlDocument dokument = new XmlDocument ();

        Task task = Task.Factory.StartNew(() =>
        {
            try
            {
                dokument.Load("http://nbp.pl/kursy/xml/LastA.xml");
            }
            catch (Exception ex)
            {
                Toast.MakeText(this, "Brak połaczenia z Internetem!", ToastLength.Long);
            }
        });

Answer 2

首先，如果dokument.Load() 中出现异常，它将通过catch 处理程序，并且您的代码将继续运行，即使文档未加载也是如此。您可能应该将您的 catch 处理程序更改为：

try
{
    // read xml into string
    var xml = new System.Net.WebClient()
        .DownloadString("http://nbp.pl/kursy/xml/LastA.xml");
    dokument.LoadXml(xml);
}
catch (Exception ex)
{
    Toast
        .MakeText(this, "Brak połaczenia z Internetem! " + ex, ToastLength.Long)
        .Show();
    return;
}

请注意，我在MakeText() 的末尾添加了.Show()。否则，您将看不到实际的 Toast。我还添加了实际的异常。

我感觉您在加载文档时遇到了异常。一旦你确定了原因，其余的应该更容易弄清楚。