以下所有代码都在一个活动上正常工作，但在尝试使用Fragment之后，调试器首先尝试调用Fragments，然后尝试不正确地执行AsyncTask类，这会崩溃并且没有得到输入来自API的流值 . 我搜索了与我的问题相关的不同文章，但如果你愿意，我想在这里提出建议，这里的代码如下：
activity_main.xml文件代码行（包含将添加或替换片段的容器）：
<?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，其活动与Container之间的BeginTransaction与MainFragment布局如下：
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文件在活动上膨胀：
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);
}
}
}
Edit 问题是从在线API获取电影数据，但问题与此处使用的片段有关，调试器没有连接到服务器，因此，返回的InputStream，StringBuffer和JsonString是空值 .
在我的活动类文件的onCreate方法上初始化了recyclerview时，相同的代码正常工作，但是在片段上，应用程序崩溃而没有从API请求的Json字符串数组 . 它在异步任务中崩溃 . 任何关于问题所在的指针以及为了成功显示recyclelerview而需要执行的操作都是值得赞赏的 . 提前致谢 .
second edit
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
注意那些粗体格式的行，它意味着什么，这是我可以从logCat中的崩溃中获得的唯一引用 . 并且没有其他异常类型 .
Third Edit
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$3.done(AsyncTask.java:309)
at java.util.concurrent.FutureTask.finishCompletion(FutureTask.java:354)
at java.util.concurrent.FutureTask.setException(FutureTask.java:223)
at java.util.concurrent.FutureTask.run(FutureTask.java:242)
at android.os.AsyncTask$SerialExecutor$1.run(AsyncTask.java:234)
at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1113)
at java.util.concurrent.ThreadPoolExecutor$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$1.resolveInetAddresses(Network.java:29)
at com.android.okhttp.internal.http.RouteSelector.resetNextInetSocketAddress(RouteSelector.java:188)
at com.android.okhttp.internal.http.RouteSelector.nextProxy(RouteSelector.java:157)
at com.android.okhttp.internal.http.RouteSelector.next(RouteSelector.java:100)
at com.android.okhttp.internal.http.HttpEngine.createNextConnection(HttpEngine.java:357)
at com.android.okhttp.internal.http.HttpEngine.nextConnection(HttpEngine.java:340)
at com.android.okhttp.internal.http.HttpEngine.connect(HttpEngine.java:330)
at com.android.okhttp.internal.http.HttpEngine.sendRequest(HttpEngine.java:248)
at com.android.okhttp.internal.huc.HttpURLConnectionImpl.execute(HttpURLConnectionImpl.java:433)
at com.android.okhttp.internal.huc.HttpURLConnectionImpl.connect(HttpURLConnectionImpl.java:114)
at com.example.prof_mohamedatef.tabletfragments.MainFragment$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$2.call(AsyncTask.java:295)
at java.util.concurrent.FutureTask.run(FutureTask.java:237)
at android.os.AsyncTask$SerialExecutor$1.run(AsyncTask.java:234)
at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1113)
at java.util.concurrent.ThreadPoolExecutor$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$1.resolveInetAddresses(Network.java:29)
at com.android.okhttp.internal.http.RouteSelector.resetNextInetSocketAddress(RouteSelector.java:188)
at com.android.okhttp.internal.http.RouteSelector.nextProxy(RouteSelector.java:157)
at com.android.okhttp.internal.http.RouteSelector.next(RouteSelector.java:100)
at com.android.okhttp.internal.http.HttpEngine.createNextConnection(HttpEngine.java:357)
at com.android.okhttp.internal.http.HttpEngine.nextConnection(HttpEngine.java:340)
at com.android.okhttp.internal.http.HttpEngine.connect(HttpEngine.java:330)
at com.android.okhttp.internal.http.HttpEngine.sendRequest(HttpEngine.java:248)
at com.android.okhttp.internal.huc.HttpURLConnectionImpl.execute(HttpURLConnectionImpl.java:433)
at com.android.okhttp.internal.huc.HttpURLConnectionImpl.connect(HttpURLConnectionImpl.java:114)
at com.example.prof_mohamedatef.tabletfragments.MainFragment$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$2.call(AsyncTask.java:295)
at java.util.concurrent.FutureTask.run(FutureTask.java:237)
at android.os.AsyncTask$SerialExecutor$1.run(AsyncTask.java:234)
at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1113)
at java.util.concurrent.ThreadPoolExecutor$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$1.resolveInetAddresses(Network.java:29)
at com.android.okhttp.internal.http.RouteSelector.resetNextInetSocketAddress(RouteSelector.java:188)
at com.android.okhttp.internal.http.RouteSelector.nextProxy(RouteSelector.java:157)
at com.android.okhttp.internal.http.RouteSelector.next(RouteSelector.java:100)
at com.android.okhttp.internal.http.HttpEngine.createNextConnection(HttpEngine.java:357)
at com.android.okhttp.internal.http.HttpEngine.nextConnection(HttpEngine.java:340)
at com.android.okhttp.internal.http.HttpEngine.connect(HttpEngine.java:330)
at com.android.okhttp.internal.http.HttpEngine.sendRequest(HttpEngine.java:248)
at com.android.okhttp.internal.huc.HttpURLConnectionImpl.execute(HttpURLConnectionImpl.java:433)
at com.android.okhttp.internal.huc.HttpURLConnectionImpl.connect(HttpURLConnectionImpl.java:114)
at com.example.prof_mohamedatef.tabletfragments.MainFragment$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$2.call(AsyncTask.java:295)
at java.util.concurrent.FutureTask.run(FutureTask.java:237)
at android.os.AsyncTask$SerialExecutor$1.run(AsyncTask.java:234)
at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1113)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:588)
at java.lang.Thread.run(Thread.java:818)
The Solution Exactely in this line of error :
Caused by: java.lang.SecurityException: Permission denied (missing INTERNET permission?)
2 回答
错误非常简单： Could not find class 'android.util.ArrayMap 意味着编译器找不到它需要的android类 . 这不是您推理或代码中的错误，而是设置问题 . 仔细检查：
您的SDK路径正确无误
您的库和SDK级别已更新（在SDK Manager中）
在应用程序的build.gradle上，您的defaultConfig正在进行目标并至少编译API级别20 .
如果您使用的是appcompat库，请在所有缺失的类中将导入从
import android.util.ArrayMap;更改为import android.support.v4.util.ArrayMap;.让我知道它是否有效
我错过了我的清单中的Internet权限，只需添加：
一切都会正常工作