Recyclerview 在 activity 上正常工作，而 AsyncTask return 使用 Fragment 时为空值并崩溃

Question

以下所有代码都在 activity 上正常工作，但在尝试使用 Fragment 后，调试器显示它首先尝试调用 Fragment，然后尝试执行 AsyncTask class 不正确，它崩溃并且没有从 API 获得输入流值。我搜索了与我的问题相关的不同文章，但如果你愿意，我想在这里听取建议，这是我的代码如下：

activity_main.xml 文件代码行（其中包含片段将被添加或替换的容器）：

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:id="@+id/mainactivity_container"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:paddingBottom="@dimen/activity_vertical_margin"
    android:paddingLeft="@dimen/activity_horizontal_margin"
    android:paddingRight="@dimen/activity_horizontal_margin"
    android:paddingTop="@dimen/activity_vertical_margin"
    android:orientation="vertical"
        tools:context="com.example.prof_mohamedatef.tabletfragments.MainActivity">

</LinearLayout>

main_fragment.xml 文件代码行：

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
android:orientation="vertical"
android:layout_width="match_parent"
android:layout_height="match_parent">

<android.support.v7.widget.RecyclerView
    android:id="@+id/card_recycler_view"
    android:scrollbars="vertical"
    android:layout_width="match_parent"
    android:layout_height="match_parent"/>

</LinearLayout>

MainActivity java 文件中的activity Container 与MainFragment 布局之间的beginTransaction 如下：

package com.example.prof_mohamedatef.tabletfragments;

import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;

public class MainActivity extends AppCompatActivity {

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        MainFragment mainFragment=new MainFragment();
        getFragmentManager().beginTransaction()
                .add(R.id.mainactivity_container,mainFragment)
                .commit();
    }
}

MainFragment java 文件正在 activity 上膨胀：

package com.example.prof_mohamedatef.tabletfragments;

import android.os.AsyncTask;
import android.os.Bundle;
import android.support.annotation.Nullable;
import android.support.v7.widget.GridLayoutManager;
import android.support.v7.widget.RecyclerView;
import android.util.Log;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import org.json.JSONArray;
import org.json.JSONException;
import org.json.JSONObject;
import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.net.HttpURLConnection;
import java.net.URL;
import java.util.ArrayList;


/**
 * Created by Prof-Mohamed Atef on 9/8/2016.
 */
public class MainFragment extends android.app.Fragment{

private static final String TAG = "RecyclerViewFragment";

public MainFragment() {}

RecyclerView mRecyclerView;
public ImagesAdapter mAdapter;

ArrayList<MovieEntity> list = new ArrayList<MovieEntity>();

final String now = "http://api.themoviedb.org/3/movie/popular?api_key=868bebbf76a3831f11b3985c703cf959";

@Override
public void onCreate(@Nullable Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    update_START();
}

@Nullable
@Override
public View onCreateView(LayoutInflater inflater,
                         @Nullable ViewGroup container,
                         @Nullable Bundle savedInstanceState) {
    View rootView=inflater.inflate(R.layout.main_fragment,container,false);
    rootView.setTag(TAG);
    mRecyclerView = (RecyclerView)rootView.findViewById(R.id.card_recycler_view);
//    mRecyclerView.setHasFixedSize(true);
    RecyclerView.LayoutManager layoutManager = new GridLayoutManager(getActivity(), 2);
    mRecyclerView.setLayoutManager(layoutManager);
    mRecyclerView.setAdapter(mAdapter);
    return rootView;
}

private void update_START() {
    Fetch_Moview_data f_m_data = new Fetch_Moview_data();
    f_m_data.execute(now);
}

public String main_List = "results";
public String POSTER_PATH = "poster_path";
public String VIDEO_ID = "id";
public String TITLE = "title";
public String OVERVIEW = "overview";
public String RELEASE_DATE = "release_date";
public String POPULARITY = "popularity";
public String VOTE_AVERAGE_="vote_average";

public String POSTER_PATH_STRING;
public String VIDEO_ID_STRING;
public String TITLE_STRING;
public String OVERVIEW_STRING;
public String RELEASE_DATE_STRING;
public String POPULARITY_STRING;
public String VOTE_AVERAGE_STRING;

public JSONObject MoviesJson;
public JSONArray moviesDataArray;
public JSONObject oneMovieData;

public class Fetch_Moview_data extends AsyncTask<String, Void, ArrayList<MovieEntity>> {

    private final String LOG_TAG = Fetch_Moview_data.class.getSimpleName();

    private ArrayList<MovieEntity> getMovieDataFromJson(String MoviesJsonStr)
            throws JSONException {

        MoviesJson = new JSONObject(MoviesJsonStr);
        moviesDataArray = MoviesJson.getJSONArray(main_List);

        list.clear();
        for (int i = 0; i < moviesDataArray.length(); i++) {

            // Get the JSON object representing a movie per each loop
            oneMovieData = moviesDataArray.getJSONObject(i);

            POSTER_PATH_STRING = oneMovieData.getString(POSTER_PATH);
            VIDEO_ID_STRING = oneMovieData.getString(VIDEO_ID);
            TITLE_STRING = oneMovieData.getString(TITLE);
            OVERVIEW_STRING = oneMovieData.getString(OVERVIEW);
            RELEASE_DATE_STRING = oneMovieData.getString(RELEASE_DATE);
            POPULARITY_STRING = oneMovieData.getString(POPULARITY);
            VOTE_AVERAGE_STRING=oneMovieData.getString(VOTE_AVERAGE_);

            mAdapter=null;
            MovieEntity entity = new MovieEntity(POSTER_PATH_STRING, VIDEO_ID_STRING, TITLE_STRING, OVERVIEW_STRING, RELEASE_DATE_STRING, POPULARITY_STRING,VOTE_AVERAGE_STRING);
            list.add(entity);
        }

        return list;
    }

    @Override
    protected ArrayList<MovieEntity> doInBackground(String... params) {

        String Movies_images_JsonSTR = null;

        HttpURLConnection urlConnection = null;
        BufferedReader reader = null;

        if (params.length == 0) {
            return null;
        }

        try {

            URL url = new URL(params[0]);
            urlConnection = (HttpURLConnection) url.openConnection();

            urlConnection.setRequestMethod("GET");
            urlConnection.connect();

            InputStream inputStream = urlConnection.getInputStream();
            StringBuffer buffer = new StringBuffer();
            if (inputStream == null) {
                Movies_images_JsonSTR = null;
            }

            reader = new BufferedReader(new InputStreamReader(inputStream));
            String line;
            while ((line = reader.readLine()) != null) {
                buffer.append(line + "\n");
            }
            if (buffer.length() == 0) {
                return null;
            }

            Movies_images_JsonSTR = buffer.toString();

            Log.v(LOG_TAG, "Movies JSON String: " + Movies_images_JsonSTR);
        } catch (IOException e) {
            Log.e(LOG_TAG, "Error here Exactly ", e);

            return null;
        } finally {
            if (urlConnection != null) {
                urlConnection.disconnect();
            }
            if (reader != null) {
                try {
                    reader.close();
                } catch (final IOException e) {
                    Log.e(LOG_TAG, "Error closing stream", e);
                }
            }else {
                Log.v(LOG_TAG, "Reader = null ( No Input Stream ) ");
            }
        }
        try {
            return getMovieDataFromJson(Movies_images_JsonSTR);
        } catch (JSONException e) {
            Log.e(LOG_TAG, "didn't got Movies Data from getJsonData method", e);
            e.printStackTrace();
        }
        return null;
    }

    @Override
    protected void onPostExecute(ArrayList<MovieEntity> result) {
        mAdapter=null;
        list=result;
        mAdapter = new ImagesAdapter(getContext(), result);
        mRecyclerView.setAdapter(mAdapter);
    }
}
}

编辑问题不在AsyncTask本身，但是它并没有从网上获取电影数据API，而是问题与这里使用的Fragment有关，调试器没有识别类型的异常，但我可以确定它没有连接到服务器，因此，返回的 InputStream、StringBuffer 和 JsonString 是空值。

当在我的 activity class 文件的 onCreate 方法上初始化 recyclerview 时，相同的代码工作正常，但在片段上，应用程序崩溃而没有获得 Json 字符串从 API 请求的数组。它在异步任务中崩溃。任何关于问题出在哪里以及需要执行什么才能成功显示 recyclerview 的指示都将受到赞赏。提前致谢。

第二次编辑

E/dalvikvm: **Could not find class 'android.util.ArrayMap'**, referenced from method com.android.tools.fd.runtime.MonkeyPatcher.monkeyPatchExistingResources
09-09 21:04:48.351 26794-26794/com.example.prof_mohamedatef.tabletfragments W/dalvikvm: VFY: unable to resolve check-cast 2079 (Landroid/util/ArrayMap;) in Lcom/android/tools/fd/runtime/MonkeyPatcher;
09-09 21:04:48.351 26794-26794/com.example.prof_mohamedatef.tabletfragments D/dalvikvm: VFY: replacing opcode 0x1f at 0x0258
09-09 21:04:48.361 26794-26794/com.example.prof_mohamedatef.tabletfragments E/dalvikvm: Could not find class 'android.util.ArrayMap', referenced from method com.android.tools.fd.runtime.MonkeyPatcher.pruneResourceCacheandroid.app.Fragment.setAllowEnterTransitionOverlap, referenced from method com.example.prof_mohamedatef.tabletfragments.MainFragment.access$super
09-09 21:04:49.061 26794-26794/com.example.prof_mohamedatef.tabletfragments W/dalvikvm: VFY: unable to resolve virtual method 377: Landroid/app/Fragment;.setAllowEnterTransitionOverlap (Z)V
09-09 21:04:49.061 26794-26794/com.example.prof_mohamedatef.tabletfragments D/dalvikvm: VFY: replacing opcode 0x6f at 0x03d8
09-09 21:04:49.061 26794-26794/com.example.prof_mohamedatef.tabletfragments I/dalvikvm: **Could not find method android.app.Fragment.onInflate**, referenced from method com.example.prof_mohamedatef.tabletfragments.MainFragment.access$super
09-09 21:04:49.061 26794-26794/com.example.prof_mohamedatef.tabletfragments W/dalvikvm: VFY: unable to resolve virtual method 358: Landroid/app/Fragment;.onInflate (Landroid/content/Context;Landroid/util/AttributeSet;Landroid/os/Bundle;)V
09-09 21:04:49.061 26794-26794/com.example.prof_mohamedatef.tabletfragments D/dalvikvm: VFY: replacing opcode 0x6f at 0x0468
09-09 21:04:49.061 26794-26794/com.example.prof_mohamedatef.tabletfragments I/dalvikvm: Could not find method android.app.Fragment.getEnterTransition, referenced from method com.example.prof_mohamedatef.tabletfragments.MainFragment.access$super
09-09 21:04:49.061 26794-26794/com.example.prof_mohamedatef.tabletfragments W/dalvikvm: VFY: unable to resolve virtual method 311: Landroid/app/Fragment;.getEnterTransition ()Landroid/transition/Transition;
09-09 21:04:49.061 26794-26794/com.example.prof_mohamedatef.tabletfragments D/dalvikvm: VFY: replacing opcode 0x6f at 0x0499
09-09 21:04:49.071 26794-26794/com.example.prof_mohamedatef.tabletfragments E/dalvikvm: **Could not find class 'android.transition.Transition', referenced from method** com.example.prof_mohamedatef.tabletfragments.MainFragment.access$super
09-09 21:04:49.071 26794-26794/com.example.prof_mohamedatef.tabletfragments W/dalvikvm: VFY: unable to resolve check-cast 2075 (Landroid/transition/Transition;) in Lcom/example/prof_mohamedatef/tabletfragments/MainFragment;
09-09 21:04:49.071 26794-26794/com.example.prof_mohamedatef.tabletfragments D/dalvikvm: VFY: replacing opcode 0x1f at 0x04b5
09-09 21:04:49.071 26794-26794/com.example.prof_mohamedatef.tabletfragments I/dalvikvm: Could not find method **android.app.Fragment.getAllowEnterTransitionOverlap**, referenced from method com.example.prof_mohamedatef.tabletfragments.MainFragment.access$super
09-09 21:04:49.071 26794-26794/com.example.prof_mohamedatef.tabletfragments W/dalvikvm: VFY: unable to resolve virtual method 306: Landroid/app/Fragment;.getAllowEnterTransitionOverlap ()Z
09-09 21:04:49.071 26794-26794/com.example.prof_mohamedatef.tabletfragments D/dalvikvm: VFY: replacing opcode 0x6f at 0x04c9

注意那些粗体行，这是什么意思，这是我可以从 logCat 中的这次崩溃中得到的唯一参考。并且没有其他异常类型。

第三次编辑

09-11 14:25:14.968 3547-3714/com.example.prof_mohamedatef.tabletfragments E/AndroidRuntime: FATAL EXCEPTION: AsyncTask #1
                                                                                        Process: com.example.prof_mohamedatef.tabletfragments, PID: 3547
                                                                                        java.lang.RuntimeException: An error occurred while executing doInBackground()
                                                                                            at android.os.AsyncTask.done(AsyncTask.java:309)
                                                                                            at java.util.concurrent.FutureTask.finishCompletion(FutureTask.java:354)
                                                                                            at java.util.concurrent.FutureTask.setException(FutureTask.java:223)
                                                                                            at java.util.concurrent.FutureTask.run(FutureTask.java:242)
                                                                                            at android.os.AsyncTask$SerialExecutor.run(AsyncTask.java:234)
                                                                                            at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1113)
                                                                                            at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:588)
                                                                                            at java.lang.Thread.run(Thread.java:818)
                                                                                         Caused by: java.lang.SecurityException: Permission denied (missing INTERNET permission?)
                                                                                            at java.net.InetAddress.lookupHostByName(InetAddress.java:464)
                                                                                            at java.net.InetAddress.getAllByNameImpl(InetAddress.java:252)
                                                                                            at java.net.InetAddress.getAllByName(InetAddress.java:215)
                                                                                            at com.android.okhttp.internal.Network.resolveInetAddresses(Network.java:29)
                                                                                            at com.android.okhttp.internal.http.RouteSelector.resetNextInetSocketAddress(RouteSelector.java:188)
                                                                                            at com.android.okhttp.internal.http.RouteSelector.nextProxy(RouteSelector.java:157)
                                                                                            at com.android.okhttp.internal.http.RouteSelector.next(RouteSelector.java:100)
                                                                                            at com.android.okhttp.internal.http.HttpEngine.createNextConnection(HttpEngine.java:357)
                                                                                            at com.android.okhttp.internal.http.HttpEngine.nextConnection(HttpEngine.java:340)
                                                                                            at com.android.okhttp.internal.http.HttpEngine.connect(HttpEngine.java:330)
                                                                                            at com.android.okhttp.internal.http.HttpEngine.sendRequest(HttpEngine.java:248)
                                                                                            at com.android.okhttp.internal.huc.HttpURLConnectionImpl.execute(HttpURLConnectionImpl.java:433)
                                                                                            at com.android.okhttp.internal.huc.HttpURLConnectionImpl.connect(HttpURLConnectionImpl.java:114)
                                                                                            at com.example.prof_mohamedatef.tabletfragments.MainFragment$Fetch_Movies_data.doInBackground(MainFragment.java:175)
                                                                                            at com.example.prof_mohamedatef.tabletfragments.MainFragment$Fetch_Movies_data.doInBackground(MainFragment.java:125)
                                                                                            at android.os.AsyncTask.call(AsyncTask.java:295)
                                                                                            at java.util.concurrent.FutureTask.run(FutureTask.java:237)
                                                                                            at android.os.AsyncTask$SerialExecutor.run(AsyncTask.java:234) 
                                                                                            at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1113) 
                                                                                            at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:588) 
                                                                                            at java.lang.Thread.run(Thread.java:818) 
                                                                                         Caused by: android.system.GaiException: android_getaddrinfo failed: EAI_NODATA (No address associated with hostname)
                                                                                            at libcore.io.Posix.android_getaddrinfo(Native Method)
                                                                                            at libcore.io.ForwardingOs.android_getaddrinfo(ForwardingOs.java:55)
                                                                                            at java.net.InetAddress.lookupHostByName(InetAddress.java:451)
                                                                                            at java.net.InetAddress.getAllByNameImpl(InetAddress.java:252) 
                                                                                            at java.net.InetAddress.getAllByName(InetAddress.java:215) 
                                                                                            at com.android.okhttp.internal.Network.resolveInetAddresses(Network.java:29) 
                                                                                            at com.android.okhttp.internal.http.RouteSelector.resetNextInetSocketAddress(RouteSelector.java:188) 
                                                                                            at com.android.okhttp.internal.http.RouteSelector.nextProxy(RouteSelector.java:157) 
                                                                                            at com.android.okhttp.internal.http.RouteSelector.next(RouteSelector.java:100) 
                                                                                            at com.android.okhttp.internal.http.HttpEngine.createNextConnection(HttpEngine.java:357) 
                                                                                            at com.android.okhttp.internal.http.HttpEngine.nextConnection(HttpEngine.java:340) 
                                                                                            at com.android.okhttp.internal.http.HttpEngine.connect(HttpEngine.java:330) 
                                                                                            at com.android.okhttp.internal.http.HttpEngine.sendRequest(HttpEngine.java:248) 
                                                                                            at com.android.okhttp.internal.huc.HttpURLConnectionImpl.execute(HttpURLConnectionImpl.java:433) 
                                                                                            at com.android.okhttp.internal.huc.HttpURLConnectionImpl.connect(HttpURLConnectionImpl.java:114) 
                                                                                            at com.example.prof_mohamedatef.tabletfragments.MainFragment$Fetch_Movies_data.doInBackground(MainFragment.java:175) 
                                                                                            at com.example.prof_mohamedatef.tabletfragments.MainFragment$Fetch_Movies_data.doInBackground(MainFragment.java:125) 
                                                                                            at android.os.AsyncTask.call(AsyncTask.java:295) 
                                                                                            at java.util.concurrent.FutureTask.run(FutureTask.java:237) 
                                                                                            at android.os.AsyncTask$SerialExecutor.run(AsyncTask.java:234) 
                                                                                            at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1113) 
                                                                                            at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:588) 
                                                                                            at java.lang.Thread.run(Thread.java:818) 
                                                                                         Caused by: android.system.ErrnoException: android_getaddrinfo failed: EACCES (Permission denied)
                                                                                            at libcore.io.Posix.android_getaddrinfo(Native Method) 
                                                                                            at libcore.io.ForwardingOs.android_getaddrinfo(ForwardingOs.java:55) 
                                                                                            at java.net.InetAddress.lookupHostByName(InetAddress.java:451) 
                                                                                            at java.net.InetAddress.getAllByNameImpl(InetAddress.java:252) 
                                                                                            at java.net.InetAddress.getAllByName(InetAddress.java:215) 
                                                                                            at com.android.okhttp.internal.Network.resolveInetAddresses(Network.java:29) 
                                                                                            at com.android.okhttp.internal.http.RouteSelector.resetNextInetSocketAddress(RouteSelector.java:188) 
                                                                                            at com.android.okhttp.internal.http.RouteSelector.nextProxy(RouteSelector.java:157) 
                                                                                            at com.android.okhttp.internal.http.RouteSelector.next(RouteSelector.java:100) 
                                                                                            at com.android.okhttp.internal.http.HttpEngine.createNextConnection(HttpEngine.java:357) 
                                                                                            at com.android.okhttp.internal.http.HttpEngine.nextConnection(HttpEngine.java:340) 
                                                                                            at com.android.okhttp.internal.http.HttpEngine.connect(HttpEngine.java:330) 
                                                                                            at com.android.okhttp.internal.http.HttpEngine.sendRequest(HttpEngine.java:248) 
                                                                                            at com.android.okhttp.internal.huc.HttpURLConnectionImpl.execute(HttpURLConnectionImpl.java:433) 
                                                                                            at com.android.okhttp.internal.huc.HttpURLConnectionImpl.connect(HttpURLConnectionImpl.java:114) 
                                                                                            at com.example.prof_mohamedatef.tabletfragments.MainFragment$Fetch_Movies_data.doInBackground(MainFragment.java:175) 
                                                                                            at com.example.prof_mohamedatef.tabletfragments.MainFragment$Fetch_Movies_data.doInBackground(MainFragment.java:125) 
                                                                                            at android.os.AsyncTask.call(AsyncTask.java:295) 
                                                                                            at java.util.concurrent.FutureTask.run(FutureTask.java:237) 
                                                                                            at android.os.AsyncTask$SerialExecutor.run(AsyncTask.java:234) 
                                                                                            at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1113) 
                                                                                            at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:588) 
                                                                                            at java.lang.Thread.run(Thread.java:818)

解决方法正是在这行错误中：

Caused by: java.lang.SecurityException: Permission denied (missing INTERNET permission?)

Answer 1

错误非常简单： Could not find class 'android.util.ArrayMap 表示编译器找不到它需要的 android classes。这不是您推理或代码中的错误，而是设置问题。仔细检查：

你的SDK路径是正确的
您的库和 SDK 级别已更新（在 SDK 管理器中）
在应用程序的 build.gradle 上，您的 defaultConfig 目标和编译至少 API 级别 20。
如果您使用的是 appcompat 库，请将所有缺失的 class 中的导入从 import android.util.ArrayMap; 更改为 import android.support.v4.util.ArrayMap;。

让我知道它是否有效

Answer 2

我的清单中缺少互联网许可，只需添加：

<uses-permission android:name="android.permission.INTERNET" />

然后一切都会正常工作

Recyclerview 在 activity 上正常工作，而 AsyncTask return 使用 Fragment 时为空值并崩溃

Recyclerview working correctly on activity while AsyncTask return null value when using Fragment and crash

android

android-asynctask

android-fragments

android-fragmentactivity