Question

我正在制作一个类似测验的应用。

当您选择答案并将其交给后台的下一个应该发送响应xml文件并转到下一个问题（活动）

这是调用后台任务并传递第二个活动的活动的代码

if(options == "0") ans.setText("Must select an answer");
        else {

           Intent intent =
                 new Intent(PM1_1Activity.this, PM1_2Activity.class);


           AsyncLoadXML carga = new AsyncLoadXML(PM1_1Activity.this);
           carga.execute();

           startActivity(intent);
           finish();

        }

这是创建后台任务的类的代码

    package com.asde.ipac;

import java.io.FileInputStream;
import java.io.FileNotFoundException;
import java.io.FileOutputStream;
import java.io.IOException;
import java.util.ArrayList;
import java.util.List;

import org.xmlpull.v1.XmlPullParser;
import org.xmlpull.v1.XmlSerializer;

import android.content.Context;
import android.os.AsyncTask;
import android.util.Xml;
import android.widget.Toast;

class AsyncLoadXML extends AsyncTask<Void, Integer, Boolean> {

   Context ctx;



   public AsyncLoadXML(Context c) {
      this.ctx = c;

   }

   @Override
   protected Boolean doInBackground(Void... params) {



      try {
         writeXML(ctx);
      } catch (IOException e) {

         e.printStackTrace();
      }

      return null;
   }


   public void writeXML(Context ctx) throws IOException{   
      FileOutputStream fout = null;

      try {
         fout = ctx.openFileOutput("answers.xml", Context.MODE_PRIVATE);
      } catch (FileNotFoundException e) {
         Toast.makeText(ctx, e.getMessage(), Toast.LENGTH_LONG).show();
      }

      XmlSerializer serializer = Xml.newSerializer();
      try {
         serializer.setOutput(fout, "UTF-8");
         serializer.startDocument(null, true);
         serializer.setFeature("http://xmlpull.org/v1/doc/features.html#indent-output", true);

         serializer.startTag(null, "questions");

         serializer.startTag(null, "question");
         serializer.attribute(null,"grupo" , "test");
         serializer.attribute(null,"grupo" , "test");
         serializer.text("A");
         serializer.endTag(null, "question");



         serializer.endTag(null, "questions");


         serializer.endDocument();
         serializer.flush();
         fout.close();

         Toast.makeText(ctx, "write done", Toast.LENGTH_LONG).show();
      } catch (Exception e) {
         Toast.makeText(ctx, e.getMessage(), Toast.LENGTH_LONG).show();
      }
   }



}

这是LogCat的输出

    09-15 14:34:04.151: E/AndroidRuntime(1225): FATAL EXCEPTION: AsyncTask #5
09-15 14:34:04.151: E/AndroidRuntime(1225): java.lang.RuntimeException: An error occured while executing doInBackground()
09-15 14:34:04.151: E/AndroidRuntime(1225):    at android.os.AsyncTask$3.done(AsyncTask.java:299)
09-15 14:34:04.151: E/AndroidRuntime(1225):    at java.util.concurrent.FutureTask.finishCompletion(FutureTask.java:352)
09-15 14:34:04.151: E/AndroidRuntime(1225):    at java.util.concurrent.FutureTask.setException(FutureTask.java:219)
09-15 14:34:04.151: E/AndroidRuntime(1225):    at java.util.concurrent.FutureTask.run(FutureTask.java:239)
09-15 14:34:04.151: E/AndroidRuntime(1225):    at android.os.AsyncTask$SerialExecutor$1.run(AsyncTask.java:230)
09-15 14:34:04.151: E/AndroidRuntime(1225):    at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1080)
09-15 14:34:04.151: E/AndroidRuntime(1225):    at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:573)
09-15 14:34:04.151: E/AndroidRuntime(1225):    at java.lang.Thread.run(Thread.java:841)
09-15 14:34:04.151: E/AndroidRuntime(1225): Caused by: java.lang.RuntimeException: Can't create handler inside thread that has not called Looper.prepare()
09-15 14:34:04.151: E/AndroidRuntime(1225):    at android.os.Handler.<init>(Handler.java:197)
09-15 14:34:04.151: E/AndroidRuntime(1225):    at android.os.Handler.<init>(Handler.java:111)
09-15 14:34:04.151: E/AndroidRuntime(1225):    at android.widget.Toast$TN.<init>(Toast.java:324)
09-15 14:34:04.151: E/AndroidRuntime(1225):    at android.widget.Toast.<init>(Toast.java:91)
09-15 14:34:04.151: E/AndroidRuntime(1225):    at android.widget.Toast.makeText(Toast.java:238)
09-15 14:34:04.151: E/AndroidRuntime(1225):    at com.asde.ipac.AsyncLoadXML.escribirXML(AsyncLoadXML.java:96)
09-15 14:34:04.151: E/AndroidRuntime(1225):    at com.asde.ipac.AsyncLoadXML.doInBackground(AsyncLoadXML.java:43)
09-15 14:34:04.151: E/AndroidRuntime(1225):    at com.asde.ipac.AsyncLoadXML.doInBackground(AsyncLoadXML.java:1)
09-15 14:34:04.151: E/AndroidRuntime(1225):    at android.os.AsyncTask$2.call(AsyncTask.java:287)
09-15 14:34:04.151: E/AndroidRuntime(1225):    at java.util.concurrent.FutureTask.run(FutureTask.java:234)
09-15 14:34:04.151: E/AndroidRuntime(1225):    ... 4 more

不，我做错了。 OnPostExecute方法是强制性的吗？

非常感谢

Answer 1

问题是您尝试在doInBackground()中显示Toasts，而此方法中禁止UI操作。

您应该做的是在此方法中进行所有处理，返回处理结果，然后在onPostExecute()处理它并在必要时显示Toasts。

修改

类似的东西：更改writeXML的返回值：

public String writeXML(Context ctx) throws IOException{ FileOutputStream fout = null; try { fout = ctx.openFileOutput("answers.xml", Context.MODE_PRIVATE); } catch (FileNotFoundException e) { return e.getMessage(); } XmlSerializer serializer = Xml.newSerializer(); try { serializer.setOutput(fout, "UTF-8"); serializer.startDocument(null, true); serializer.setFeature("http://xmlpull.org/v1/doc/features.html#indent-output", true); serializer.startTag(null, "questions"); serializer.startTag(null, "question"); serializer.attribute(null,"grupo" , "test"); serializer.attribute(null,"grupo" , "test"); serializer.text("A"); serializer.endTag(null, "question"); serializer.endTag(null, "questions"); serializer.endDocument(); serializer.flush(); fout.close(); return "write done"; } catch (Exception e) { return e.getMessage(); } }

同时更改doInBackground的返回值:(您还必须更改AsyncTask声明：class AsyncLoadXML extends AsyncTask<Void, Integer, String>）

@Override protected String doInBackground(Void... params) { String result = ""; try { result = writeXML(ctx); } catch (IOException e) { e.printStackTrace(); } return result; }

并添加onPostExecute方法：

protected void onPostExecute(String result) { if(!result.equals("")) Toast.makeText(getApplicationContext(), result, Toast.LENGTH_LONG).show(); }

Answer 2

查看您的日志：

Can't create handler inside thread that has not called Looper.prepare()

将Looper.prepare();添加到运行Handler的线程

或

通过处理程序与Thread UI一起使用迭代，例如：

private Handler mHandler = null;
protected static final int TOAST = 1;

private Handler mHandler = new Handler() {
    @Override
    public void handleMessage(Message msg) {
        String txt;
        switch (msg.what) {
        case TOAST:
            txt = msg.obj.toString();
            Toast.makeText(ctx, txt, Toast.LENGTH_LONG).show();
            break;          
        default:
            super.handleMessage(msg);
        }           



    }
};

现在您可以使用处理程序显示您的祝酒词：

mHandler.sendMessage(mHandler.obtainMessage(TOAST, "write done"));

或

就像jbihan所说，把你的逻辑放在onPostExecute()

下显示Toast的地方

因为在doInBackground下的Toast下丢失了您的错误

AsyncTask存在XML文件创建问题

2 个答案: