使用LocalBroadcastManager时出现NullPointerException

Question

我正在尝试将LocalBroadcastManager与我的自定义意图一起使用.似乎它对意图非常挑剔,如果我以这种方式发送意图:

在Myintents.java中,我声明了

public static final String LOCATION_UPDATE = "com.example.myapp.location_update";

稍后在广播发送者中我做:

Intent intent = new Intent(MyIntents.LOCATION_UPDATE);
localBroadcastManager.sendBroadcast(intent);

然后我得到这个例外:

05-05 02:23:29.914: E/AndroidRuntime(6952): FATAL EXCEPTION: main 
05-05 02:23:29.914: E/AndroidRuntime(6952): java.lang.NullPointerException 
05-05 02:23:29.914: E/AndroidRuntime(6952): at android.support.v4.content.LocalBroadcastManager.executePendingBroadcasts(LocalBroadcastManager.java:297) 
05-05 02:23:29.914: E/AndroidRuntime(6952): at android.support.v4.content.LocalBroadcastManager.access$000(LocalBroadcastManager.java:46)  
05-05 02:23:29.914: E/AndroidRuntime(6952): at android.support.v4.content.LocalBroadcastManager$1.handleMessage(LocalBroadcastManager.java:116) 
05-05 02:23:29.914: E/AndroidRuntime(6952): at android.os.Handler.dispatchMessage(Handler.java:99)

但是,如果我使用显式字符串

Intent intent = new Intent("my-intent");

一切正常.

怎么了？为什么我不能在另一个类中定义意图名称？

Answer 1

我刚刚遇到过这个.NPE是注册侦听器(读取:接收方)的结果,因为您正在触发的事件(MyIntents.LOCATION_UPDATE)尚未由托管它的组件实例化.

检查您要响应此广播的内容是否已在实际位置(可能是托管活动/片段)实例化.

Answer 2

在我的情况下,(我有同样的错误)我忘了创建扩展BroadcastReceiver的类的实例.(并覆盖onReceive()方法)

    private MeasurementUpdateReceiver   m_MeasurementUpdateReceiver;

// Listens to local broadcasts done by the MeasurementService
private class MeasurementUpdateReceiver extends BroadcastReceiver {
    @Override
    public void onReceive(Context context, Intent intent) {
        // Intent already filtered by the LocalBroadcastManager in onResume()
        String data = intent.getStringExtra("data"));
        Toast.makeText(getApplicationContext(), "Received data " + data, Toast.LENGTH_LONG).show();
    }
}

将此类的空引用传递给LocalBroadcastManager:

LocalBroadcastManager.getInstance(this).registerReceiver(m_MeasurementUpdateReceiver, new IntentFilter("measurementupdate"));

在尝试调用类的onReceive()方法之前没有问题.我忘了的是:

m_MeasurementUpdateReceiver = new MeasurementUpdateReceiver();

我希望这可以帮助其他人面对这个错误.