android - 从 fragment 的 onCreateView 调用 AsyncTask 方法失败

Question

我一直在尝试实现 fragment 布局，并且在我使用异步任务的 fragment 类之一中。到目前为止，我无法从 fragment 的 oncreateView 调用 asynctask 方法。当我运行该应用程序时出现错误“不幸的是该应用程序已停止”

这是我的 fragment 代码

package com.example.mohamed.myapplication;

import java.io.File;
import java.io.IOException;

import org.jsoup.Connection;
import org.jsoup.Jsoup;
import org.jsoup.nodes.Attributes;
import org.jsoup.nodes.Document;
import org.jsoup.nodes.Element;
import org.jsoup.select.Elements;

import android.app.ActionBar;
import android.app.Activity;
import android.app.Fragment;
import android.app.FragmentManager;
import android.app.FragmentTransaction;
import android.app.ProgressDialog;
import android.content.Context;
import android.os.AsyncTask;
import android.os.Bundle;
import android.support.v13.app.FragmentPagerAdapter;
import android.support.v4.view.ViewPager;
import android.util.Log;
import android.view.LayoutInflater;
import android.view.Menu;
import android.view.MenuItem;
import android.view.View;
import android.view.ViewGroup;
import android.widget.TextView;
import android.widget.Toast;
import android.widget.ListView;


import java.util.Locale;
import java.util.regex.Matcher;
import java.util.regex.Pattern;


public class FirstFragment extends Fragment {

    // URL Address
    String url = "http://www.androidbegin.com";
    ProgressDialog mProgressDialog;
    AsyncTask aTask;

    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container,
                         Bundle savedInstanceState) {

        new Title().execute();

        View rootView = inflater.inflate(R.layout.first_frag, container, false);
        return rootView;

    }


    // Title AsyncTask
    private class Title extends AsyncTask<Void, Void, Void> {
        String title;

//      Context mcontext;
//      public Title(Context c){
//          mcontext=c;
//      }
        @Override
        protected void onPreExecute() {
            super.onPreExecute();
//              mProgressDialog = new ProgressDialog(mcontext);
//              mProgressDialog.setTitle("Android Basic JSoup Tutorial");
//              mProgressDialog.setMessage("Loading...");
//              mProgressDialog.setIndeterminate(false);
//              mProgressDialog.show();
        }

        @Override
        protected Void doInBackground(Void... params) {
            try {
                // Connect to the web site
                Document document = Jsoup.connect(url).get();
                // Get the html document title
                title = document.title();
            } catch (IOException e) {
                e.printStackTrace();
            }
            return null;
        }

        @Override
        protected void onPostExecute(Void result) {
            // Set title into TextView
            TextView txttitle = (TextView) getView().findViewById(R.id.First);
            txttitle.setText(title);
            mProgressDialog.dismiss();
        }
    }

    public static FirstFragment newInstance(String text) {

        FirstFragment f = new FirstFragment();
        Bundle b = new Bundle();
        b.putString("msg", text);

        f.setArguments(b);

        return f;

    }

}

那么，调用 asynctask 的正确方法是什么？

这是我的日志

12-01 14:44:40.052    1093-1093/com.example.mohamed.myapplication D/dalvikvm﹕ GC_FOR_ALLOC freed 49K, 3% free 3755K/3868K, paused 2ms, total 4ms
12-01 14:44:40.056    1093-1093/com.example.mohamed.myapplication D/dalvikvm﹕ GC_FOR_ALLOC freed 3K, 3% free 3973K/4092K, paused 2ms, total 2ms
12-01 14:44:40.064    1093-1093/com.example.mohamed.myapplication I/dalvikvm-heap﹕ Grow heap (frag case) to 6.356MB for 2536932-byte allocation
12-01 14:44:40.072    1093-1103/com.example.mohamed.myapplication D/dalvikvm﹕ GC_FOR_ALLOC freed <1K, 2% free 6450K/6572K, paused 5ms, total 5ms
12-01 14:44:40.180    1093-1093/com.example.mohamed.myapplication D/libEGL﹕ loaded /system/lib/egl/libEGL_genymotion.so
12-01 14:44:40.180    1093-1093/com.example.mohamed.myapplication D/﹕ HostConnection::get() New Host Connection established 0xb8a8f1c0, tid 1093
12-01 14:44:40.184    1093-1093/com.example.mohamed.myapplication D/libEGL﹕ loaded /system/lib/egl/libGLESv1_CM_genymotion.so
12-01 14:44:40.184    1093-1093/com.example.mohamed.myapplication D/libEGL﹕ loaded /system/lib/egl/libGLESv2_genymotion.so
12-01 14:44:40.224    1093-1093/com.example.mohamed.myapplication W/EGL_genymotion﹕ eglSurfaceAttrib not implemented
12-01 14:44:40.224    1093-1093/com.example.mohamed.myapplication E/OpenGLRenderer﹕ Getting MAX_TEXTURE_SIZE from GradienCache
12-01 14:44:40.228    1093-1093/com.example.mohamed.myapplication E/OpenGLRenderer﹕ MAX_TEXTURE_SIZE: 8192
12-01 14:44:40.232    1093-1093/com.example.mohamed.myapplication E/OpenGLRenderer﹕ Getting MAX_TEXTURE_SIZE from Caches::initConstraints()
12-01 14:44:40.232    1093-1093/com.example.mohamed.myapplication E/OpenGLRenderer﹕ MAX_TEXTURE_SIZE: 8192
12-01 14:44:40.236    1093-1093/com.example.mohamed.myapplication D/OpenGLRenderer﹕ Enabling debug mode 0

Answer 1

您试图在创建 View 之前在 onCreateView 中使用 AsyncTask。

尝试在onActivityCreated中调用AsyncTask:

@Override
public void onActivityCreated(Bundle savedInstanceState) {
   super.onActivityCreated(savedInstanceState);
   new Title().execute();
}