Question

您好我正在学习如何在Android中使用服务和通知，当我尝试启动服务时，我正面临NullPointerException。我写了一个小应用程序，其中有一个按钮和2个EditTextes（标题和内容）。当我单击按钮时，我检索EditTextes中的值，然后启动一个创建通知的新服务。我的代码分为两部分。这是我的代码。这个介绍了该应用程序的主要活动：

@Override
public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.main);

    Button button = (Button) findViewById(R.id.serviceButton);

    final Context ctx = getApplicationContext();

    button.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View v) {
            final Intent i = new Intent(ctx, NotificationService.class);


            Toast.makeText(ctx, "Clicking ...", Toast.LENGTH_SHORT).show();

            EditText title = (EditText) findViewById(R.id.notif_title);
            EditText content = (EditText) findViewById(R.id.notif_content);

            Bundle bundle = new Bundle();
            bundle.putCharSequence("NOTIF_TITLE", title.getText());
            bundle.putCharSequence("NOTIF_CONTENT", content.getText());
            i.putExtras(bundle);

            startService(i);

        }
    });
}

这个描述了将启动通知的服务：

public class NotificationService extends IntentService {

public NotificationService(String name) {
    super(name);
}

@Override
protected void onHandleIntent(Intent intent) {

    Context ctx = getApplicationContext();
    Toast.makeText(ctx, "NotificationService", Toast.LENGTH_LONG).show();

    String ns = Context.NOTIFICATION_SERVICE;
    NotificationManager notificationManager = (NotificationManager) getSystemService(ns);


    Bundle b = intent.getExtras();

    String title = b.getString("NOTIF_TITLE");
    String content = b.getString("NOTIF_CONTENT");
    Intent i = new Intent(this, NotificationService.class);
    PendingIntent pendingIntent = PendingIntent.getActivity(ctx, 0, i,
            Intent.FLAG_ACTIVITY_NEW_TASK);

    int icon = R.drawable.ic_launcher;
    long when = System.currentTimeMillis();
    Notification notification = new Notification(icon,
            "New notification arrives", when);

    notification.setLatestEventInfo(ctx, title, content, pendingIntent);

    notificationManager.notify(
            NOTIFICATIONS.HELLO_NOTIFICATION.ordinal(), notification);
}

}

当我点击按钮时，我有这个例外：

    FATAL EXCEPTION: main
 java.lang.NullPointerException 
at  android.content.ContextWrapper.startService(ContextWrapper.java:336)
at com.androidprojects.AndroidActivity$1.onClick(AndroidActivity.java:67)
at android.view.View.performClick(View.java:2485)
at android.view.View$PerformClick.run(View.java:9080)
at android.os.Handler.handleCallback(Handler.java:587)
at android.os.Handler.dispatchMessage(Handler.java:92)
at android.os.Looper.loop(Looper.java:123)
at android.app.ActivityThread.main(ActivityThread.java:3683)
at java.lang.reflect.Method.invokeNative(Native Method)
at java.lang.reflect.Method.invoke(Method.java:507)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:839)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:597)
at dalvik.system.NativeStart.main(Native Method)

FATAL EXCEPTION: main
java.lang.NullPointerException
at android.content.ContextWrapper.startService(ContextWrapper.java:336)
at com.androidprojects.AndroidActivity$1.onClick(AndroidActivity.java:62)
at android.view.View.performClick(View.java:2485)
at android.view.View$PerformClick.run(View.java:9080)
at android.os.Handler.handleCallback(Handler.java:587)
at android.os.Handler.dispatchMessage(Handler.java:92)
at android.os.Looper.loop(Looper.java:123)
at android.app.ActivityThread.main(ActivityThread.java:3683)
at java.lang.reflect.Method.invokeNative(Native Method)
at java.lang.reflect.Method.invoke(Method.java:507)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:839)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:597)
at dalvik.system.NativeStart.main(Native Method)

修改：我对我的代码进行了更正，删除了new NotificationService，但我仍然得到NullPointerException

Answer 1

您不通过将其对象作为new启动来运行您的服务。只需按以下方式运行您的服务：

startService(i);

有关详情，请参阅this

Answer 2

我终于纠正了我的问题。在我做了Terrance，@ waqas，@ akki建议的纠正后，我又有了一个例外：InstantiationException。问题发生在我的NotificationService课程中。扩展IntentService以定义新服务时，必须定义默认构造函数，但此构造函数不接受参数，我们必须在其中调用super(name)。
我刚刚在NotificationService类的构造函数中删除了参数，一切正常。谢谢你的帮助!!

Answer 3

我认为akki是正确的 http://mobile.tutsplus.com/tutorials/android/android-fundamentals-intentservice-basics/ 所以只需删除NotificationService的实例化。只需调用就可以在链接的第三步中看到你的意图。

所以像这样的东西


button.setOnClickListener(new View.OnClickListener() {      
        @Override      
        public void onClick(View v) {      
            startService(i);

            Toast.makeText(ctx, "Clicking ...", Toast.LENGTH_SHORT).show();      

            EditText title = (EditText) findViewById(R.id.notif_title);      
            EditText content = (EditText) findViewById(R.id.notif_content);      

            Bundle bundle = new Bundle();      
            bundle.putCharSequence("NOTIF_TITLE", title.getText());      
            bundle.putCharSequence("NOTIF_CONTENT", content.getText());      
            i.putExtras(bundle);      

            notificationService.startService(i);      

        }      
    });

启动服务时出现NullPointerException

3 个答案: