如何将参数传递给广播接收器的子类？ [英] How to pass a parameter to a subclass of BroadcastReceiver?

问题描述

我设法时pressed我耳机按键得到由我的应用程序认可，但其中一个按钮需要调用这是在MyCustomActivity的方法。问题是的onReceive的第一个参数是不能转换到活动并使用MyCustomActivity的的的内部类的荣获上下文Android中4.1 的将不起作用，除非它是静态的（其具有无法访问MyCustomActivity的方法的同样的问题。

I managed to get my headset buttons get recognized by my app when pressed, but one of the buttons needs to call a method that's in MyCustomActivity. The problem is onReceive's 1st parameter is a Context that cannot be cast to Activity and using a MyCustomActivity's inner class won't work in Android 4.1 unless it is static (which has the same problem of inability to access MyCustomActivity's method.

所以，剩下的唯一选择，我（以支持2.x和4.1）是传递活动作为参数的 RemoteControlReceiver 。

So the only option left for me (in order to support both 2.x and 4.1) is to pass the activity as a parameter to RemoteControlReceiver.

但我怎么做，当初始化它的唯一途径是通过：

But how do I do that, when the only way to instantiate it is via:

private ComponentName mRemoteControlReceiver = new ComponentName(this, RemoteControlReceiver.class);

不接受任何额外的参数？

Which doesn't accept any additional parameters?

不知道如何解决此限制？

Any idea how to work around this limitation?

注意：如果我尝试定义 RemoteControlReceiver 为具有一个参数的构造函数，我收到以下异常：

Note: If I try to define RemoteControlReceiver as having a constructor with a parameter, I receive the following exception:

E/AndroidRuntime(2836): java.lang.RuntimeException: Unable to instantiate receiver com.example.RemoteControlReceiver: java.lang.InstantiationException: can't instantiate class com.example.RemoteControlReceiver; no empty constructor

Caused by:
E/AndroidRuntime(2836): Caused by: java.lang.InstantiationException: can't instantiate class com.example.RemoteControlReceiver; no empty constructor
E/AndroidRuntime(2836):     at java.lang.Class.newInstanceImpl(Native Method)
E/AndroidRuntime(2836):     at java.lang.Class.newInstance(Class.java:1319)
E/AndroidRuntime(2836):     at android.app.ActivityThread.handleReceiver(ActivityThread.java:2205)

所以，很显然，这个新的registerMediaButtonEventReceiver要求（在Android的4.1引入的）期望一个空构造

请问有没有办法解决此问题？

Is there no way to work around this?

例如，是否有一种方式来获得实际RemoteControlReceiver对象的引用（通过 mAudioManager.registerMediaButtonEventReceiver间接实例化（））？所以，我可以用一个访问设置后RemoteControlReceiver的的数据成员的它已被实例化？

For example, is there a way to get a reference to the actual RemoteControlReceiver object (instantiated indirectly via mAudioManager.registerMediaButtonEventReceiver())? So that I can use an accessor to set a data-member of RemoteControlReceiver after it has been instantiated?

推荐答案

<一个href=\"http://developer.android.com/reference/android/media/AudioManager.html#registerMediaButtonEventReceiver%28android.content.ComponentName%29\">registerMediaButtonEventReceiver需要在应用程序清单中声明的​​广播接收器。这意味着接收机必须是一个独立的阶级，这意味着它什么都不知道关于你的当前活动或服务。

registerMediaButtonEventReceiver requires the BroadcastReceiver to be declared in the application manifest. This means that the receiver must be a standalone class, meaning it knows nothing about your current activity or service.

为了得到这个消息，您的活动或服务，您有多种选择：

In order to get this message to your activity or service, you have a number of options:

• 使用静态全局的活动或服务，这样的接收器可以将邮件转发给它。这通常不是一个好主意，因为它会导致泄漏，当你想以后改变code不是很适应。静是一般应​​避免。

• Use a static global for the activity or service so the receiver can forward the message to it. This is generally not a good idea as it leads to leaks and isn't very adaptable when you want to change the code later. Statics are generally to be avoided.

重新广播消息到具体的类别，这恰好是一个内部类，你要调用的活动或服务的。例如。在广播接收器的registerMediaButtonEventReceiver：

Re-broadcast the message to a specific class, which happens to be an inner class of the activity or service you want to invoke. E.g. in the BroadcastReceiver for registerMediaButtonEventReceiver:

// Standalone class, declared in the manifest
public class ButtonReceiver extends BroadcastReceiver {
    @Override
    public void onReceive(final Context context, final Intent intent) {
        Intent intent = new Intent();
        intent.setAction("com.foo.ACTION");

        // Rebroadcasts to your own receiver. 
        // This receiver is not exported; it'll only be received if the receiver is currently registered.
        context.sendBroadcast(intent); 
    }
}

而在你的活动：

    class MyActivity extends Activity {
        private BroadcastReceiver myReceiver = new BroadcastReceiver() {
            @Override
             public void onReceive(final Context context, final Intent intent) {
                MyActivity.this.onMessageReceived();
             }
        }
        @Override
        protected void onResume() {
            registerReceiver(myReceiver, new IntentFilter("com.foo.ACTION"));
        }

        @Override
        protected void onPause() {
            unregisterReceiver(myReceiver);
        }

        private void onMessageReceived() {
        }
    }

• 上述方法类似，它不一定必须是一个广播，也可以是传递到活性的意图，这取决于你的使用情况。要做到的，而不是使用sendBroadcast这个，你（如果你使用的服务或startService）使用startActivity。



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