Question

我一直在尝试实现片段布局，并且在其中一个片段类中我正在使用asynctask。到目前为止，我无法从片段的oncreateView调用asynctask方法。当我运行应用程序时给出错误'不幸的是应用程序已停止'

这是我的片段代码

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logcat

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

您在创建视图之前尝试在AsyncTask中使用onCreateView。

尝试在onActivityCreated中调用AsyncTask：

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

Answer 2

我认为问题出在这一行：

TextView txttitle = (TextView) getView().findViewById(R.id.First);

删除该行，并在onCreateView：

中添加此行

txttitle = (TextView) rootview.findViewById(R.id.First);

使txttitle成为全局变量。

之后，执行AsyncTask

中的onActivityCreated

Answer 3

您的代码中存在竞争条件。在您返回Title之前，您从onCreateView()方法开始rootView。因此，如果AsyncTask执行并在之前完成，Fragment成功进入运行状态，则getView()中的onPostExecute()将无法获取任何内容}}。此外，代码无法在对话框启动时显示，因此您可以在尝试访问NullPointerException时获得mProgressDialog。

顺便说一下，你的logat是不完整的：它缺少实际的崩溃堆栈跟踪。寻找它，它会告诉你你的异常发生的确切位置。

从片段onCreateView调用AsyncTask方法失败

3 个答案: