我是Android Studio编码方面的新手，一直在尝试为学校编写应用程序，并且正在尝试使用导航抽屉制作youtube流媒体应用程序。但是，每次我运行它时，都会收到消息：
我的应用程序不断停止
我该怎么解决？
这是主要活动：
package com.example.myapplication;
import android.content.Intent;
import android.os.Bundle;
import com.android.volley.Request;
import com.android.volley.RequestQueue;
import com.android.volley.Response;
import com.android.volley.VolleyError;
import com.android.volley.toolbox.StringRequest;
import com.android.volley.toolbox.Volley;
import com.example.myapplication.Adapter.MyCustomAdapter;
import com.example.myapplication.Model.VideoDetails;
import androidx.core.view.GravityCompat;
import androidx.navigation.NavController;
import androidx.navigation.Navigation;
import androidx.navigation.ui.AppBarConfiguration;
import androidx.navigation.ui.NavigationUI;
import com.example.myapplication.ui.gallery.GalleryFragment;
import com.google.android.material.navigation.NavigationView;
import com.google.android.youtube.player.YouTubePlayerView;
import androidx.drawerlayout.widget.DrawerLayout;
import androidx.appcompat.app.AppCompatActivity;
import androidx.appcompat.widget.Toolbar;
import androidx.recyclerview.widget.RecyclerView;
import android.provider.MediaStore;
import android.view.Menu;
import android.view.MenuItem;
import android.widget.ListView;
import android.widget.Toast;
import org.json.JSONArray;
import org.json.JSONException;
import org.json.JSONObject;
import java.util.ArrayList;
public class MainActivity extends AppCompatActivity implements NavigationView.OnNavigationItemSelectedListener {
YouTubePlayerView playerView;
private RecyclerView rvVideo;
String API_KEY = "xxxxxx";
String url = "https://www.googleapis.com/youtube/v3/search?part=snippet&maxResults=25&type=video&q=larva&key=xxxxxxxxx";
ListView listView;
MyCustomAdapter myCustomAdapter;
ArrayList<VideoDetails> videoDetailsArrayList;
private AppBarConfiguration mAppBarConfiguration;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
videoDetailsArrayList = new ArrayList<>();
myCustomAdapter = new MyCustomAdapter(MainActivity.this, videoDetailsArrayList);
rvVideo= findViewById(R.id.rv_video);
rvVideo.setHasFixedSize(true);
displayVideos();
Toolbar toolbar = findViewById(R.id.toolbar);
setSupportActionBar(toolbar);
DrawerLayout drawer = findViewById(R.id.drawer_layout);
NavigationView navigationView = (NavigationView) findViewById(R.id.nav_view);
navigationView.setNavigationItemSelectedListener(this);
mAppBarConfiguration = new AppBarConfiguration.Builder(
R.id.nav_home, R.id.nav_about)
.setDrawerLayout(drawer)
.build();
NavController navController = Navigation.findNavController(this, R.id.nav_host_fragment);
NavigationUI.setupActionBarWithNavController(this, navController, mAppBarConfiguration);
NavigationUI.setupWithNavController(navigationView, navController);
}
private boolean displayVideos() {
RequestQueue requestQueue = Volley.newRequestQueue(getApplicationContext());
StringRequest stringRequest = new StringRequest(Request.Method.GET, url, new Response.Listener<String>() {
@Override
public void onResponse(String response) {
try {
JSONObject jsonObject = new JSONObject(response);
JSONArray jsonArray = jsonObject.getJSONArray("items");
for (int i = 0; i < jsonArray.length(); i++) {
JSONObject jsonObject1 = jsonArray.getJSONObject(i);
JSONObject jsonVideoID = jsonObject1.getJSONObject("id");
JSONObject jsonObjectSnippet = jsonObject1.getJSONObject("snippet");
JSONObject jsonObjectDefault = jsonObjectSnippet.getJSONObject("thumbnails").getJSONObject("medium");
String video_id = jsonVideoID.getString("videoId");
VideoDetails vd = new VideoDetails();
vd.setVideoId(video_id);
vd.setTitle(jsonObjectSnippet.getString("title"));
vd.setDescription(jsonObjectSnippet.getString("description"));
vd.setUrl(jsonObjectDefault.getString("url"));
videoDetailsArrayList.add(vd);
}
listView.setAdapter(myCustomAdapter);
} catch (JSONException e) {
e.printStackTrace();
}
}
},new Response.ErrorListener(){
@Override
public void onErrorResponse (VolleyError error){
Toast.makeText(getApplicationContext(), error.getMessage(), Toast.LENGTH_LONG).show();
}
}
);
requestQueue.add(stringRequest);
return false;
}
@Override
public boolean onSupportNavigateUp () {
NavController navController = Navigation.findNavController(this, R.id.nav_host_fragment);
return NavigationUI.navigateUp(navController, mAppBarConfiguration)
|| super.onSupportNavigateUp();
}
@Override
public void onBackPressed() {
DrawerLayout drawer = (DrawerLayout) findViewById(R.id.drawer_layout);
if(drawer.isDrawerOpen(GravityCompat.START)){
drawer.closeDrawer(GravityCompat.START);
} else {
super.onBackPressed();
}
}
@Override
public boolean onCreateOptionsMenu(Menu menu) {
// Inflate the menu; this adds items to the action bar if it is present.
getMenuInflater().inflate(R.menu.main, menu);
return true;
}
@Override
public boolean onOptionsItemSelected(MenuItem item) {
// Handle action bar item clicks here. The action bar will
// automatically handle clicks on the Home/Up button, so long
// as you specify a parent activity in AndroidManifest.xml.
int id = item.getItemId();
//noinspection SimplifiableIfStatement
if (id == R.id.action_settings) {
return true;
}
return super.onOptionsItemSelected(item);
}
@SuppressWarnings("StatementWithEmptyBody")
@Override
public boolean onNavigationItemSelected(MenuItem item) {
// Handle navigation view item clicks here.
int id = item.getItemId();
if (id == R.id.nav_gallery) {
Intent intentku= new Intent(MainActivity.this, GalleryFragment.class);
startActivity(intentku);
}
DrawerLayout drawer = (DrawerLayout) findViewById(R.id.drawer_layout);
drawer.closeDrawer(GravityCompat.START);
return true;
}
}
这是清单：
<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
package="com.example.myapplication">
<uses-permission android:name="android.permission.INTERNET" />
<application
android:allowBackup="true"
android:icon="@mipmap/ic_launcher"
android:label="@string/app_name"
android:roundIcon="@mipmap/ic_launcher_round"
android:supportsRtl="true"
android:theme="@style/AppTheme">
<activity android:name=".VideoPlayActivity"></activity>
<activity
android:name=".MainActivity"
android:label="@string/app_name"
android:theme="@style/AppTheme.NoActionBar">
<intent-filter>
<action android:name="android.intent.action.MAIN" />
<category android:name="android.intent.category.LAUNCHER" />
</intent-filter>
</activity>
</application>
</manifest>
这是logcat错误：
Process: com.example.myapplication, PID: 25434
java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.myapplication/com.example.myapplication.MainActivity}: java.lang.NullPointerException: Attempt to invoke virtual method 'void androidx.recyclerview.widget.RecyclerView.setHasFixedSize(boolean)' on a null object reference
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2817)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2892)
at android.app.ActivityThread.-wrap11(Unknown Source:0)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1593)
at android.os.Handler.dispatchMessage(Handler.java:105)
at android.os.Looper.loop(Looper.java:164)
at android.app.ActivityThread.main(ActivityThread.java:6541)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.Zygote$MethodAndArgsCaller.run(Zygote.java:240)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:767)
Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'void androidx.recyclerview.widget.RecyclerView.setHasFixedSize(boolean)' on a null object reference
at com.example.myapplication.MainActivity.onCreate(MainActivity.java:66)
at android.app.Activity.performCreate(Activity.java:6975)
at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1213)
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2770)
这是我的activity_main.xml
<?xml version="1.0" encoding="utf-8"?>
<androidx.drawerlayout.widget.DrawerLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:app="http://schemas.android.com/apk/res-auto"
xmlns:tools="http://schemas.android.com/tools"
android:id="@+id/drawer_layout"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:fitsSystemWindows="true"
tools:openDrawer="start">
<include
layout="@layout/app_bar_main"
android:layout_width="match_parent"
android:layout_height="match_parent" />
<com.google.android.material.navigation.NavigationView
android:id="@+id/nav_view"
android:layout_width="wrap_content"
android:layout_height="match_parent"
android:layout_gravity="start"
android:fitsSystemWindows="true"
app:headerLayout="@layout/nav_header_main"
app:menu="@menu/activity_main_drawer" />
</androidx.drawerlayout.widget.DrawerLayout>
这是HomeFragment：
package com.example.myapplication.ui.home;
import android.os.Bundle;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.TextView;
import androidx.annotation.Nullable;
import androidx.annotation.NonNull;
import androidx.fragment.app.Fragment;
import androidx.lifecycle.Observer;
import androidx.lifecycle.ViewModelProviders;
import com.example.myapplication.R;
public class HomeFragment extends Fragment {
private HomeViewModel homeViewModel;
public View onCreateView(@NonNull LayoutInflater inflater,
ViewGroup container, Bundle savedInstanceState) {
homeViewModel =
ViewModelProviders.of(this).get(HomeViewModel.class);
View root = inflater.inflate(R.layout.fragment_home, container, false);
final TextView textView = root.findViewById(R.id.text_home);
homeViewModel.getText().observe(this, new Observer<String>() {
@Override
public void onChanged(@Nullable String s) {
textView.setText(s);
}
});
return root;
}
}
这是片段home.xml：
<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:app="http://schemas.android.com/apk/res-auto"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent"
>
<TextView
android:id="@+id/text_home"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:layout_marginStart="8dp"
android:layout_marginTop="8dp"
android:layout_marginEnd="8dp"
android:textAlignment="center"
android:textSize="20sp"
app:layout_constraintEnd_toEndOf="parent"
app:layout_constraintStart_toStartOf="parent"
app:layout_constraintTop_toTopOf="parent"/>
<androidx.recyclerview.widget.RecyclerView
android:id="@+id/rv_video"
android:layout_width="match_parent"
android:layout_height="match_parent"
tools:listitem="@layout/item_video" />
</RelativeLayout>
答案 0 :(得分：0)
您正在尝试从活动中访问recyclerview的地方，其中片段中没有recyclerview。
因此在片段的oncreateview方法中添加与不在活动中的片段相关的代码。