android - 重启后 USB 附件无法通信

Question

我想弄清楚为什么我的应用程序在手机重启后没有开始与 USB 配件通信。如果我拔下电缆并将其重新插入，通信将恢复。该应用程序针对 Android API 19。

在安装应用程序时，我将它设置为始终是家庭应用程序，当我第一次将它连接到配件时，我选中该框以始终允许访问当前配件。

所以当我重新启动手机时，应用程序会自动打开，它会通过检查权限的步骤 (usbmanager.hasPermission) 并且它实际上已经获得了权限而没有出现任何警报，但是通信未在 OpenAccessory 方法中启动。

list :

        <intent-filter>
            <action android:name="android.hardware.usb.action.USB_ACCESSORY_ATTACHED" />
        </intent-filter>

        <meta-data
            android:name="android.hardware.usb.action.USB_ACCESSORY_ATTACHED"
            android:resource="@xml/accessory_filter"></meta-data>

通讯:

// Init USB Manager
usbmanager = (UsbManager) context.getSystemService(Context.USB_SERVICE);
mPermissionIntent = PendingIntent.getBroadcast(context, 0, new Intent(ACTION_USB_PERMISSION), 0);
IntentFilter filter = new IntentFilter(ACTION_USB_PERMISSION);
filter.addAction(UsbManager.ACTION_USB_ACCESSORY_DETACHED);
context.registerReceiver(mUsbReceiver, filter);

// Resume Accessory
if (usbmanager.hasPermission(accessory)) {
                OpenAccessory(accessory);
            }
            else
            {
                synchronized (mUsbReceiver) {
                    if (!mPermissionRequestPending) {
                        Toast.makeText(global_context, "Request USB Permission", Toast.LENGTH_SHORT).show();
                        usbmanager.requestPermission(accessory,
                                mPermissionIntent);
                        mPermissionRequestPending = true;
                    }
                }
            }

// Broadcast Receiver
private final BroadcastReceiver mUsbReceiver = new BroadcastReceiver()
    {
        @Override
        public void onReceive(Context context, Intent intent)
        {
            String action = intent.getAction();
            if (ACTION_USB_PERMISSION.equals(action))
            {
                synchronized (this)
                {
                    UsbAccessory accessory = (UsbAccessory) intent.getParcelableExtra(UsbManager.EXTRA_ACCESSORY);
                    if (intent.getBooleanExtra(UsbManager.EXTRA_PERMISSION_GRANTED, false))
                    {
                        Toast.makeText(global_context, "Allow USB Permission", Toast.LENGTH_SHORT).show();
                        OpenAccessory(accessory);
                    }
                    else
                    {
                        Toast.makeText(global_context, "Deny USB Permission", Toast.LENGTH_SHORT).show();
                        Log.d("LED", "permission denied for accessory "+ accessory);

                    }
                    mPermissionRequestPending = false;
                }
            }
            else if (UsbManager.ACTION_USB_ACCESSORY_DETACHED.equals(action))
            {
                DestroyAccessory(true);
                //CloseAccessory();
            }else
            {
                Log.d("LED", "....");
            }
        }
    };

// OpenAccessory
private void OpenAccessory(UsbAccessory accessory)
    {
        filedescriptor = usbmanager.openAccessory(accessory);
        if(filedescriptor != null){
            usbaccessory = accessory;

            FileDescriptor fd = filedescriptor.getFileDescriptor();

            inputstream = new FileInputStream(fd);
            outputstream = new FileOutputStream(fd);
            /*check if any of them are null*/
            if(inputstream == null || outputstream==null){
                return;
            }

            if(READ_ENABLE == false){
                READ_ENABLE = true;
                readThread = new read_thread(inputstream);
                readThread.start();
            }

            // Initialize the serial port here
            SerialComm.getInstance().initPort();
        }
    }

Answer 1

在 UsbManager 和 IntentFilter 中，您使用 ACTION_USB_ACCESSORY_DETACHED 和 ACTION_USB_ACCESSORY_ATTACHED 事件，它们在插入或拔出设备时触发.

如果这些事件/ Action 发生，代码将被执行，应用程序将运行

( https://developer.android.com/reference/android/hardware/usb/UsbManager.html )

现在的问题是，当应用程序在重启时启动时，这些事件/操作不会被触发，因此链接到它们的代码将不会被执行

要规避这一点并不容易，因为应用程序只能通过 ACTION_USB_ACCESSORY_ATTACHED Intent 获取 UsbAccessory 类的实例:

An instance of this class is sent to the application via the ACTION_USB_ACCESSORY_ATTACHED Intent. The application can then call openAccessory(UsbAccessory) to open a file descriptor for reading and writing data to and from the accessory.

来源:https://developer.android.com/reference/android/hardware/usb/UsbAccessory.html

如果应用程序没有实例，则应用程序无法使用类(附件)...