android - 执行doInBackground()时发生错误-Android小部件

Question

我正在使用Async的气象应用程序。它非常适合MainActivity，现在我正尝试为其开发一个小部件，但出现异常。

与SO的其他答案一样，对此问题的普遍共识是停止在 doInBackground 中使用UI线程。所以我尽量减少它。

package ali.projecto;

import android.app.PendingIntent;
import android.appwidget.AppWidgetManager;
import android.appwidget.AppWidgetProvider;
import android.content.ComponentName;
import android.content.Context;
import android.content.Intent;
import android.location.Criteria;
import android.location.Location;
import android.location.LocationManager;
import android.os.AsyncTask;
import android.widget.RemoteViews;
import org.w3c.dom.Document;
import org.w3c.dom.Element;
import org.w3c.dom.Node;
import java.io.InputStream;
import java.net.URL;

import javax.xml.parsers.DocumentBuilder;
import javax.xml.parsers.DocumentBuilderFactory;

public class Widget extends AppWidgetProvider {
    String xtemp;
    Location loc;
    Context context;
    //======================================= OnUpdate Method
    public void onUpdate(Context context, AppWidgetManager appWidgetManager, int[] appWidgetIds) {
        try {
            RemoteViews remoteViews = new RemoteViews(context.getPackageName(), R.layout.widget);

            Intent intent = new Intent(context, Widget.class);
            intent.putExtra(AppWidgetManager.EXTRA_APPWIDGET_ID, appWidgetIds[0]);
            intent.setAction("update");

            PendingIntent pi = PendingIntent.getBroadcast(context, 0, intent, PendingIntent.FLAG_UPDATE_CURRENT);
            remoteViews.setOnClickPendingIntent(R.id.rButton, pi);

            new MyAsyncTask2().execute(context);

            appWidgetManager.updateAppWidget(appWidgetIds, remoteViews);
        }catch (Exception e){
            e.printStackTrace();
        }
    }
    //======================================= OnReceive Method
    @Override
    public void onReceive(Context context, Intent intent) {
        super.onReceive(context, intent);
        try {
        if (intent.getAction().equals("update")) {
            new MyAsyncTask2().execute();
        }
        } catch (Exception e){
            e.printStackTrace();
        }
    }
    //======================================= AsyncTask
    public class MyAsyncTask2 extends AsyncTask<Context, Void, String> {
        private RemoteViews views;
        private Context context;

        @Override
        protected void onPreExecute() {
            //getLocation();
        }
        @Override
        protected String doInBackground(Context... params) {
            context = params[0];
            return loadXML2();
        }
        @Override
        protected void onPostExecute(String result) {
            try {
                AppWidgetManager appWidgetManager = AppWidgetManager.getInstance(context);
                views = new RemoteViews(context.getPackageName(), R.layout.widget);
                if (result != null && result.length() >= 1) {
                    views.setTextViewText(R.id.widtemp, result);
                }
                appWidgetManager.updateAppWidget(new ComponentName(context, Widget.class), views);
            } catch (Exception e){
                e.printStackTrace();
            }
        }
    }
    //======================================= Load XML
    public String loadXML2() {
        try {
            //=============================== Getting Data
            URL xmlUrl = new URL("http://api.openweathermap.org/data/2.5/weather?q=dallas%20ga&units=metric&mode=xml&MYIDGOESHERE&units=metric&mode=xml");
            InputStream in = xmlUrl.openStream();
            Document doc = parse(in);
            doc.getDocumentElement().normalize();
            //================================ Getting Temperature
            Node nNode = doc.getElementsByTagName("temperature").item(0);
            Element eElement = (Element) nNode;
            double d = Math.round(Double.parseDouble(eElement.getAttribute("value")));
            int dx = (int) d;
            xtemp = Integer.toString(dx) + "°";
        } catch (Exception e) {
            e.printStackTrace();
        }
        return xtemp;
    }
    //======================================= Document Parsing
    public static Document parse (InputStream is) {
        Document ret = null;
        DocumentBuilderFactory domFactory;
        DocumentBuilder builder;

        try {
            domFactory = DocumentBuilderFactory.newInstance();
            domFactory.setValidating(false);
            domFactory.setNamespaceAware(false);
            builder = domFactory.newDocumentBuilder();

            ret = builder.parse(is);
        }
        catch (Exception ex) {
            System.err.println("unable to load XML: " + ex);
        }
        return ret;
    }
}

产生此错误的步骤:

创建小部件(它会更新并显示温度很好)。

单击小部件，它将停止处理此异常。

错误:

11-06 22:54:09.869 2505-3375/ali.projecto E/AndroidRuntime: FATAL EXCEPTION: AsyncTask #4
11-06 22:54:09.869 2505-3375/ali.projecto E/AndroidRuntime: Process: ali.projecto, PID: 2505
11-06 22:54:09.869 2505-3375/ali.projecto E/AndroidRuntime: java.lang.RuntimeException: An error occured while executing doInBackground()
11-06 22:54:09.869 2505-3375/ali.projecto E/AndroidRuntime:     at android.os.AsyncTask$3.done(AsyncTask.java:300)
11-06 22:54:09.869 2505-3375/ali.projecto E/AndroidRuntime:     at java.util.concurrent.FutureTask.finishCompletion(FutureTask.java:355)
11-06 22:54:09.869 2505-3375/ali.projecto E/AndroidRuntime:     at java.util.concurrent.FutureTask.setException(FutureTask.java:222)
11-06 22:54:09.869 2505-3375/ali.projecto E/AndroidRuntime:     at java.util.concurrent.FutureTask.run(FutureTask.java:242)
11-06 22:54:09.869 2505-3375/ali.projecto E/AndroidRuntime:     at android.os.AsyncTask$SerialExecutor$1.run(AsyncTask.java:231)
11-06 22:54:09.869 2505-3375/ali.projecto E/AndroidRuntime:     at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1112)
11-06 22:54:09.869 2505-3375/ali.projecto E/AndroidRuntime:     at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:587)
11-06 22:54:09.869 2505-3375/ali.projecto E/AndroidRuntime:     at java.lang.Thread.run(Thread.java:818)
11-06 22:54:09.869 2505-3375/ali.projecto E/AndroidRuntime:  Caused by: java.lang.ArrayIndexOutOfBoundsException: length=0; index=0
11-06 22:54:09.869 2505-3375/ali.projecto E/AndroidRuntime:     at ali.projecto.Widget$MyAsyncTask2.doInBackground(Widget.java:77)
11-06 22:54:09.869 2505-3375/ali.projecto E/AndroidRuntime:     at ali.projecto.Widget$MyAsyncTask2.doInBackground(Widget.java:67)
11-06 22:54:09.869 2505-3375/ali.projecto E/AndroidRuntime:     at android.os.AsyncTask$2.call(AsyncTask.java:288)
11-06 22:54:09.869 2505-3375/ali.projecto E/AndroidRuntime:     at java.util.concurrent.FutureTask.run(FutureTask.java:237)
11-06 22:54:09.869 2505-3375/ali.projecto E/AndroidRuntime:     at android.os.AsyncTask$SerialExecutor$1.run(AsyncTask.java:231) 
11-06 22:54:09.869 2505-3375/ali.projecto E/AndroidRuntime:     at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1112) 
11-06 22:54:09.869 2505-3375/ali.projecto E/AndroidRuntime:     at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:587) 
11-06 22:54:09.869 2505-3375/ali.projecto E/AndroidRuntime:     at java.lang.Thread.run(Thread.java:818) 

Answer 1

Caused by: java.lang.ArrayIndexOutOfBoundsException: length=0; index=0

数组为空。

此行可能导致错误:

context = params[0];

解决方案是在执行参数时将参数传递给异步任务。

new MyAsyncTask2().execute(my_parameter);