重新启动后USB附件无法通信 [英] USB Accessory not communicating after restart

问题描述

我试图弄清楚为什么手机重启后我的应用程序无法开始与USB附件通信.如果拔下电缆，然后重新插入，通信将继续.该应用程序针对Android API 19.

I'm trying to figure out why my application does not start communicating with the USB accessory after the phone restarts. If I unplug the cable and plug it back in, the communication resumes. The application is targeted at Android API 19.

在安装应用程序时，我将其设置为始终为Home应用程序，当我首次将其连接到附件时，请选中该框以始终允许访问当前附件.

At the app install I set it to always be the Home app and when I first connect it to the accessory I check the box to always permit the access to the current accessory.

因此，当我重新启动手机时，该应用程序会自动打开，它会执行检查权限(usbmanager.hasPermission)的步骤，并且实际上具有该权限，而不会出现任何警报，但是通讯不是在方法.

So when I restart the phone, the app opens up automatically, it goes through the steps of checking for permission (usbmanager.hasPermission) and it actually has the permission without any alert appearing, but the communication is not starting in OpenAccessory method.

清单:

        <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();
        }
    }

推荐答案

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

in UsbManager and IntentFilter you use ACTION_USB_ACCESSORY_DETACHED and ACTION_USB_ACCESSORY_ATTACHED events that are triggered when plugging or unplugging the device.

如果发生这些事件/操作，则代码将被执行并且应用可以正常工作

if these events /actions occur the code is executed and the app works

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

现在的问题是，在重新启动应用程序时启动这些事件/操作不会触发，因此链接到它们的代码将不会执行

the problem is now that when the app is started at reboot these events /actions are not triggered and so the code that is linked to them will not be executed

绕开它并不容易，因为应用程序仅通过ACTION_USB_ACCESSORY_ATTACHED意图获得UsbAccessory类的实例:

it is not easy to circumvent this because an application gets an instance of the UsbAccessory class only via the ACTION_USB_ACCESSORY_ATTACHED intent :

此类的实例通过以下方式发送到应用程序: ACTION_USB_ACCESSORY_ATTACHED目的.然后，应用程序可以调用 openAccessory(UsbAccessory)打开文件描述符以进行读取和 在附件中写入数据.

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.

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

如果应用没有类，则该应用将无法使用该类(附件)...

it is not possible for the app to use a class ( the accessory ) if it has no instance of it ...

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