后已创建活动的BroadcastReceiver火灾 [英] BroadcastReceiver fires after the activity is already created

问题描述

我想用一个BroadcastReceiver获得许可与USB设备进行通信。我想实现它是在Android网站 HTTP做了同样的方式：// developer.android.com/guide/topics/usb/host.html
这一切的作品，那种。
但广播接收器是在创建的主要活动后才fireing。我这就意味着能够与设备进行通信仅关闭后，应用程序，然后再次打开它（当我不注销的BroadcastReceiver，当我这样做，我不能在所有通信）。
可能是什么原因？
我的code是这样的：

I want to use a BroadcastReceiver to get permission to communicate with a USB device. I am trying to implement it the same way it is done on android website http://developer.android.com/guide/topics/usb/host.html It all works, kind of. But the broadcastReceiver is fireing only after the main activity is created. Which means I am able to communicate with the device only after close the app and open it again (when I don't unregister the broadcastReceiver, when I do I can't communicate at all). What can be the reason? My code is like this:

私人最终的BroadcastReceiver mUsbReceiver =新的广播接收器（）
    {

private final BroadcastReceiver mUsbReceiver = new BroadcastReceiver() {

    public void onReceive(Context context, Intent intent) 
    {
        String action = intent.getAction();

        if (ACTION_USB_PERMISSION.equals(action)) 
        {
            synchronized (this) 
            {
                device = (UsbDevice) intent.getParcelableExtra(UsbManager.EXTRA_DEVICE);
                if (intent.getBooleanExtra(UsbManager.EXTRA_PERMISSION_GRANTED, false)) 
                {
                    if(device != null)
                    {

           //things I do when the permission is granted             

                    }

                } 
                else 
                {
                    devMessage = "permission denied for device ";
                }
            }
        }
    }
};

在code，其中我注册它的一部分：

The part of the code where I register it:

公共无效的onCreate（捆绑savedInstanceState）
        {
        super.onCreate（savedInstanceState）;
        的setContentView（R.layout.main）;

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

    mUsbManager = (UsbManager) getSystemService(Context.USB_SERVICE);       

    mPermissionIntent = PendingIntent.getBroadcast(this, 0, new Intent(ACTION_USB_PERMISSION), 0);
    filter = new IntentFilter(ACTION_USB_PERMISSION);
    registerReceiver(mUsbReceiver, filter);

    HashMap<String, UsbDevice> deviceList = mUsbManager.getDeviceList();
    Iterator<UsbDevice> deviceIterator = deviceList.values().iterator();
        while(deviceIterator.hasNext())
        {
            device = deviceIterator.next();
            mUsbManager.requestPermission(device, mPermissionIntent);             
        }

            // ...      

    if(device!=null)
    {
      // ...
    }
    else
    {
      // ...
    }
    tv.setText(devMessage);
    }

有谁知道为什么会这样，我可能是做错了？

Does anyone know why is this happening, what I might be doing wrong?

推荐答案

您要注册的广播接收器在你的活动。这意味着，您在运行活动之前，你不能接收广播。

You're registering your broadcast receiver in you activity. That means that before you run that activity, you cannot receive broadcasts.

您或许应该看看你的Andr​​oidManifest.xml中注册reciever标签。
这是接收器标签中的文档。这可以让你无需启动你的活动注册接收器。

You should probably look at registering a reciever-tag in in you AndroidManifest.xml. This is the docs for the receiver-tag. This allows you to register receivers without starting your activity.

这部分是很重要的：

在＆lt;用途＆gt;元素适用于所有应用程序组件，包括广播接收器自身的启用属性。在＆lt;用途＆gt;和＆lt;接收器GT;属性必须要启用的广播接收机都为真。如果任何一个为假，它被禁用;它不能被实例化。

The <application> element has its own enabled attribute that applies to all application components, including broadcast receivers. The <application> and <receiver> attributes must both be "true" for the broadcast receiver to be enabled. If either is "false", it is disabled; it cannot be instantiated.

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