Question

当我尝试在主活动类上调用任何服务方法时，我收到错误。

错误日志

java.lang.NullPointerException: Attempt to invoke virtual method 'java.lang.String in.ac.iitkgp.alpha.dbService.getUser()' on a null object reference
                                                                    at in.ac.iitkgp.alpha.MainScreen.onCreateOptionsMenu(MainScreen.java:95)
                                                                    at android.app.Activity.onCreatePanelMenu(Activity.java:2846)
                                                                    at android.support.v4.app.FragmentActivity.onCreatePanelMenu(FragmentActivity.java:341)
                                                                    at android.support.v7.view.WindowCallbackWrapper.onCreatePanelMenu(WindowCallbackWrapper.java:85)
                                                                    at android.support.v7.app.AppCompatDelegateImplBase$AppCompatWindowCallbackBase.onCreatePanelMenu(AppCompatDelegateImplBase.java:258)
                                                                    at android.support.v7.view.WindowCallbackWrapper.onCreatePanelMenu(WindowCallbackWrapper.java:85)
                                                                    at android.support.v7.app.ToolbarActionBar.populateOptionsMenu(ToolbarActionBar.java:454)
                                                                    at android.support.v7.app.ToolbarActionBar$1.run(ToolbarActionBar.java:61)
                                                                    at android.os.Handler.handleCallback(Handler.java:739)
                                                                    at android.os.Handler.dispatchMessage(Handler.java:95)
                                                                    at android.os.Looper.loop(Looper.java:148)
                                                                    at android.app.ActivityThread.main(ActivityThread.java:5417)
                                                                    at java.lang.reflect.Method.invoke(Native Method)
                                                                    at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:726)
                                                                    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:616)

我有两个活动，第一个活动将输入传递给服务并使用startService（intent）启动它;并调用下一个活动。然后，下一个活动绑定到服务并读取输入数据并更改UI上的TextView。我需要通过服务传递它，因为在许多活动中需要输入。

服务类

public class dbService extends Service {

private final IBinder Mybinder = new dbBinder();
public String user;
public dbService() {
}

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

public final String getUser(){
   return user;
}


public class dbBinder extends Binder{
    dbService getService(){
        return dbService.this;
    }
}

@Override
public int onStartCommand(Intent intent, int flags, int startId) {
    user = intent.getStringExtra("User");
    return START_NOT_STICKY;
}
}

第一项活动的片段

Intent intent = new Intent(this,MainScreen.class);
    Intent service = new Intent(this,dbService.class);
    String usr = user.getText().toString();
    service.putExtra("User",usr);
    startService(service);
    startActivity(intent);

第二项活动的片段

dbService Myservice;
boolean bound  = false;
private ServiceConnection connection = new ServiceConnection() {
    @Override
    public void onServiceConnected(ComponentName name, IBinder service) {
        dbBinder binder = (dbBinder) service;
        Myservice = binder.getService();
        bound = true;
    }

    @Override
    public void onServiceDisconnected(ComponentName name) {
        bound = false;
    }
};

@Override
protected void onCreate(Bundle savedInstanceState) {
.
.
.
Intent i = new Intent(this,dbService.class);
    bindService(i,connection, Context.BIND_AUTO_CREATE);
    TextView user = (TextView) findViewById(R.id.user);
    user.setText(Myservice.getUser());
}

仅从第二个活动访问服务方法会导致应用崩溃。其他一切似乎都很好。对不起，如果这是一个愚蠢的问题。我是java和android app开发的新手。提前致谢

Answer 1

将以下代码放在onServiceConnected：

中

TextView user = (TextView) findViewById(R.id.user); user.setText(Myservice.getUser());`

除非服务已连接，否则您无法访问服务对象方法。

android服务方法调用调用null引用错误

1 个答案: