Android bindService抛出NullPointerException

为了在Android中构建我的第一个bindService，我学习了好几本教程，但我一直得到同样的NullPointerException，我不明白。我的最后一个例子很简单

MyActivity.java：

package de.123team.myapplication;

import android.app.Activity; import android.content.ComponentName; import android.content.Intent; import android.content.ServiceConnection; import android.os.Bundle; import android.os.IBinder; import android.view.Menu; import android.view.MenuItem; import android.widget.TextView;

public class MyActivity extends Activity {

    // Connection
    MySumService mService;
    boolean mBound;

    ServiceConnection mConnection = new ServiceConnection() {

        @Override
        public void onServiceDisconnected(ComponentName name) {
            mBound = false;
            //mService = null;
        }

        @Override
        public void onServiceConnected(ComponentName name, IBinder service) {
            mBound = true;
            MySumService.LocalBinder binder = (MySumService.LocalBinder)service;
            mService = binder.getService();
        }

    };


    @Override
    protected void onStart() {
        super.onStart();
    }


    @Override
    protected void onStop() {
        super.onStop();

        if (mBound) {
            mService.unbindService(mConnection);
            mBound = false;
        }
    }


    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_my);


        TextView tvResult = (TextView)findViewById(R.id.tvResult);
        //tvResult.setText("Test123");

        Intent i = new Intent(this, MySumService.class);
        bindService(i, mConnection, BIND_AUTO_CREATE); 

        int r = mService.sum(1, 2);
        tvResult.setText(new String().valueOf(r));
    } }

MySumService.java：

package de.123team.myapplication;

import android.app.Service;
import android.content.Intent;
import android.os.Binder;
import android.os.IBinder;

public class MySumService extends Service {


    private IBinder mBinder = new LocalBinder();


    @Override
    public IBinder onBind(Intent intent) {
        // TODO: Return the communication channel to the service.
        return mBinder;
    }


    public int sum(int a, int b) {
        return 666;
    }


    public class LocalBinder extends Binder {
        public MySumService getService() {
            return MySumService.this;
        }
    }


}

AndroidManifest.xml

<?xml version="1.0" encoding="utf-8"?> <manifest xmlns:android="http://schemas.android.com/apk/res/android"
    package="de.proteam.myapplication" >

    <application
        android:allowBackup="true"
        android:icon="@drawable/ic_launcher"
        android:label="@string/app_name"
        android:theme="@style/AppTheme" >

        <activity
            android:name=".MyActivity"
            android:label="@string/app_name" >
            <intent-filter>
                <action android:name="android.intent.action.MAIN" />

                <category android:name="android.intent.category.LAUNCHER" />
            </intent-filter>
        </activity>

        <service
            android:name=".MySumService"
            android:enabled="true"
            android:exported="true" >
        </service>

    </application> </manifest> 

---

请检查活动生命周期。onCreate方法在onStart方法之前调用。您正在onStart中初始化mService对象，并在onCreate中使用它

参考：

在onCreate as mService中，未初始化mService，根据java中对象的默认值，它为null，引发null指针异常

---

理想情况下，您应该从onServiceConnected回调调用sum方法。

这里，您在调用bindservice（）函数后立即调用sum方法

移动到代码行下面

int r = mService.sum(1, 2);
tvResult.setText(new String().valueOf(r));

要使用如下所示的OnServiceConnectiond（）函数

@Override
    public void onServiceConnected(ComponentName name, IBinder service) {
        mBound = true;
        MySumService.LocalBinder binder = (MySumService.LocalBinder)service;
        mService = binder.getService();

        int r = mService.sum(1, 2);
        tvResult.setText(new String().valueOf(r));
    }

---

它将确保您的服务绑定到您的活动。

MyActivity.java:86行？您的清单文件在哪里？您不能调用mService.sum（1，2）；在onCreate中，mService尚未分配。您是对的。我将行从onStart移到onCreate，但结果是一样的。请不要使用>符号，而只是缩进4个空格以显示代码块。格式的详细信息可以在FAQ中找到：就像我在上面的评论中提到的一样-我解决了这个问题，但结果是一样的。

@Override
    public void onServiceConnected(ComponentName name, IBinder service) {
        mBound = true;
        MySumService.LocalBinder binder = (MySumService.LocalBinder)service;
        mService = binder.getService();

        int r = mService.sum(1, 2);
        tvResult.setText(new String().valueOf(r));
    }