java - 绑定(bind)服务出错

Question

我只是在玩绑定(bind)服务的示例教程。运行时出现空指针异常错误。

FATAL EXCEPTION: main
                                                                                   Process: com.boundservice.boundservice, PID: 12342
                                                                                   java.lang.NullPointerException: Attempt to invoke virtual method 'java.lang.String com.boundservice.boundservice.MyService.getCurrentTime()' on a null object reference
                                                                                       at com.boundservice.boundservice.MainActivity$1.onClick(MainActivity.java:36)
                                                                                       at android.view.View.performClick(View.java:5637)
                                                                                       at android.view.View$PerformClick.run(View.java:22429)
                                                                                       at android.os.Handler.handleCallback(Handler.java:751)
                                                                                       at android.os.Handler.dispatchMessage(Handler.java:95)
                                                                                       at android.os.Looper.loop(Looper.java:154)
                                                                                       at android.app.ActivityThread.main(ActivityThread.java:6121)
                                                                                       at java.lang.reflect.Method.invoke(Native Method)
                                                                                       at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:889)
                                                                                       at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:779)

下面是我的代码:

Activity :

package com.boundservice.boundservice;

import android.app.Service;
import android.content.ComponentName;
import android.content.Context;
import android.content.Intent;
import android.content.ServiceConnection;
import android.os.IBinder;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.util.Log;
import android.view.View;
import android.widget.Button;
import android.widget.TextView;
import android.widget.Toast;

public class MainActivity extends AppCompatActivity {

    MyService myService;
    boolean isBound  = false;
    TextView myTextView;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        myTextView = (TextView)findViewById(R.id.myTextView);

        Intent intent = new Intent(this, MyService.class);                //Start Service
        bindService(intent, myConnection, Context.BIND_AUTO_CREATE);


        final Button button = (Button) findViewById(R.id.button);
        button.setOnClickListener(new View.OnClickListener() {
            public void onClick(View v) {
                String currentTime = myService.getCurrentTime();
                TextView myTextView = (TextView)findViewById(R.id.myTextView);
                myTextView.setText(currentTime);
            }
        });

    }


    private ServiceConnection myConnection = new ServiceConnection() {   //To see whether service is connected or not, if yes it will return true
        @Override
        public void onServiceConnected(ComponentName componentName, IBinder service) {
            MyService.MyLocalBinder binder = (MyService.MyLocalBinder) service;
            myService = binder.getService();
            isBound = true;
            Log.d("Service", "Service is successfully bound");
        }

        @Override
        public void onServiceDisconnected(ComponentName componentName) {
            isBound = false;
        }
    };




}

服务:

package com.boundservice.boundservice;

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

import java.text.SimpleDateFormat;
import java.util.Date;
import java.util.Locale;

public class MyService extends Service {

    public IBinder myBinder = new MyLocalBinder();   //Declare an object of local class

    public MyService() {
    }

    @Override
    public IBinder onBind(Intent intent) {           //Auto generated method
       return null;
    }

    public String getCurrentTime() {                 //Simple method to fetch date
        SimpleDateFormat dateformat = new SimpleDateFormat("HH:mm:ss MM/dd/yyyy", Locale.US);
        Date date = new Date();
        String datestring = dateformat.format(date);
        Log.d("Service", "Date is : " + datestring);
        return (dateformat.format(new Date()));
    }

    public class MyLocalBinder extends Binder {      //Create a local class that will reference this service which in return will be used to access from Activity

        MyService getService() {
            return MyService.this;
        }

    }
}

不知道为什么会这样。我是否需要使用处理程序来更新我的 TextView 或不需要。我觉得它没有启动服务并绑定(bind)它。

Answer 1

我认为您错误地覆盖了 onBind() 方法:

@Override
public IBinder onBind(Intent intent) {
   return myBinder;
}