我正在尝试为Android应用程序创建远程服务。我或多或少已经从Android Developers网站复制了代码，出于我的目的对其进行了重新设计。但是，当我进入bindService步骤时，我在android.content.Context.getPackageName（）上得到了NullPointerException。我究竟做错了什么？
我已经在应用程序的早期版本中使用了进程内服务，但是对于我想要的应用程序来说，这还不够。除了必要的代码更改之外，两者之间的服务本身保持不变。我已经查看了此处的所有结果，但它们要么无关，要么无济于事。
我试过将调用从onCreate移动到onStart。没有不同。 BinderActivity的onCreate从未执行。我尝试使用startService而不是bindService，但是它给了我同样的错误。我检查过这个，意图和mConnection都是非空的（它们是）。我知道该服务尚未启动，但是我正在使用Context.BIND_AUTO_CREATE（如果没有启动，应该启动它）。由于没有为问题挥舞死鸡，我不确定在这里还有什么可做的。
我的主要活动：
package com.example.trainchecker;
import android.content.Intent;
import android.os.Bundle;
import com.google.android.material.floatingactionbutton.FloatingActionButton;
import androidx.appcompat.app.AppCompatActivity;
import androidx.appcompat.widget.Toolbar;
import androidx.recyclerview.widget.LinearLayoutManager;
import androidx.recyclerview.widget.RecyclerView;
import android.content.Context;
import android.os.Message;
import android.os.Messenger;
import java.io.*;
import java.util.ArrayList;
import android.widget.TextView;
public class MainActivity extends AppCompatActivity {
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
BinderActivity ba = new BinderActivity();
ba.BindService();
}
}
这是BinderActivity，应该在其中发生魔术。相反，该错误会：
package com.example.trainchecker;
import android.app.Activity;
import android.content.ComponentName;
import android.content.Context;
import android.content.Intent;
import android.content.ServiceConnection;
import android.os.IBinder;
import android.os.RemoteException;
import android.util.Log;
import android.os.Message;
import android.os.Handler;
import android.os.Messenger;
public class BinderActivity extends Activity {
public Messenger ms = null;
private MainActivity ma;
class IncomingHandler extends Handler{
@Override
public void handleMessage(Message msg){
super.handleMessage(msg);
}
}
final Messenger mm = new Messenger(new IncomingHandler());
private ServiceConnection mConnection = new ServiceConnection() {
public void onServiceConnected(ComponentName className, IBinder service) {
Log.d("MCon","Sentinel Online");
ms = new Messenger(service);
try {
Message msg = Message.obtain(null,TCService.MSG_REGISTER_CLIENT);
msg.replyTo = mm;
ms.send(msg);
} catch (RemoteException e){ e.printStackTrace();}
}
public void onServiceDisconnected(ComponentName className) {
Log.d("MCon","Sentinel Offline");
try {
Message msg = Message.obtain(null,2);
msg.replyTo = mm;
ms.send(msg);
} catch (RemoteException e){ e.printStackTrace();}
}
};
public void BindService() {
bindService(new Intent(this, TCService.class), mConnection, Context.BIND_AUTO_CREATE);
}
}
最后，服务本身。那里不多，但是是我的：
package com.example.trainchecker;
import android.app.NotificationChannel;
import android.app.NotificationManager;
import android.app.Service;
import android.content.Context;
import android.content.Intent;
import android.os.Handler;
import android.os.IBinder;
import android.util.Log;
import java.util.ArrayList;
import android.os.Message;
import android.os.Messenger;
public class TCService extends Service {
ArrayList<Messenger> mc = new ArrayList<>();
@Override
public IBinder onBind(Intent i) {
Log.d("TCS", "Binding Now");
return mm.getBinder();
}
static final int MSG_REGISTER_CLIENT = 1;
class IncomingHandler extends Handler {
@Override
public void handleMessage(Message msg) {
switch (msg.what) {
case 1:
mc.add(msg.replyTo);
break;
case 2:
mc.remove(msg.replyTo);
break;
default:
super.handleMessage(msg);
}
}
}
final Messenger mm = new Messenger(new IncomingHandler());
}
这是整个错误：
09-15 11:39:04.518 15448-15448/com.example.trainchecker E/AndroidRuntime: FATAL EXCEPTION: main
Process: com.example.trainchecker, PID: 15448
java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.trainchecker/com.example.trainchecker.MainActivity}: java.lang.NullPointerException: Attempt to invoke virtual method 'java.lang.String android.content.Context.getPackageName()' on a null object reference
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2416)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2476)
at android.app.ActivityThread.access$900(ActivityThread.java:150)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1344)
at android.os.Handler.dispatchMessage(Handler.java:102)
at android.os.Looper.loop(Looper.java:171)
at android.app.ActivityThread.main(ActivityThread.java:5417)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:726)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:616)
Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'java.lang.String android.content.Context.getPackageName()' on a null object reference
at android.content.ContextWrapper.getPackageName(ContextWrapper.java:133)
at android.content.ComponentName.<init>(ComponentName.java:128)
at android.content.Intent.<init>(Intent.java:4468)
at com.example.trainchecker.BinderActivity.BindService(BinderActivity.java:58)
at com.example.trainchecker.MainActivity.onCreate(MainActivity.java:65)
at android.app.Activity.performCreate(Activity.java:6285)
at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1108)
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2369)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2476)
at android.app.ActivityThread.access$900(ActivityThread.java:150)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1344)
at android.os.Handler.dispatchMessage(Handler.java:102)
at android.os.Looper.loop(Looper.java:171)
at android.app.ActivityThread.main(ActivityThread.java:5417)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:726)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:616)
最佳答案
以编程方式实例化Activity实例不会触发生命周期，因此您的上下文在那里无效。将其传递给您的BindService（）调用。从技术上讲，您的BinderActivity不需要存在，可以存在于MainAcitivity或服务中。