java - Android USB 权限、onPause、onResume - 不幸的是，系统 UI 已停止”

Question

我正在使用 Android Studio 0.5.2 开发 Android 应用程序。

我的应用程序正在运行一个 USB 主机，该主机似乎运行正常 - 除非应用程序启动时已连接设备(并且尚未授予权限)。

通常，连接 USB 时(应用程序运行时)会发生什么:

• “onResume”被调用 - 这会检测设备并请求许可。创建意图过滤器来捕获 USB 连接、分离或授予权限的时间

• 显示权限请求，选择“确定”

• 再次调用“onResume”。该函数的第一行是“super.onResume()”

• 一旦我跨过 super.onResume，就会显示“不幸的是，系统 UI 已停止”消息，并且 Android UI 崩溃

• 我的应用程序继续正常工作

如果我在应用程序已运行时连接设备，则不会出现问题 - 仅当启动时连接 USB 时才会出现此问题。

任何有关可能导致此问题的原因或如何进一步缩小问题范围的见解将不胜感激。我在下面附上了值得注意的代码。我通常不是 Java 开发人员，因此我怀疑问题与暂停/恢复行为、接收器、意图过滤器或权限有关。

// *************************************************************
// ************************* USB Stuff *************************
// *************************************************************
boolean resumePermissionBlocked = false;
PendingIntent pendingIntent = null;
BroadcastReceiver receiver = new BroadcastReceiver() {
    public void onReceive(Context context, Intent intent) {
        // Get the information about what action caused this event
        try {
            String action = intent.getAction();
            Log.i(TAG, "$EC: action:" + action);

            if ("com.android.example.USB_PERMISSION".equals(action)) {
                UsbDevice device = intent.getParcelableExtra(UsbManager.EXTRA_DEVICE);

                if (intent.getBooleanExtra(UsbManager.EXTRA_PERMISSION_GRANTED, false)) {
                    if (device != null) {


                        if (device.getProductId() == 0xAAAA) {
                            if (device.getVendorId() == 0xBBBB) {
                                // see if we have permission
                                UsbManager openManager = (UsbManager) context.getSystemService(Context.USB_SERVICE);

                                // send a message to the worker thread to begin opening a connection to this device
                                ThreadMsg msg = new ThreadMsg();
                                msg.request = MsgRequest.openConnection;
                                msg.objectA = device;
                                msg.objectB = openManager;
                                sendMessageToWorker(msg);

                            }
                        }
                    }
                } else {
                    if (device != null)
                        Log("USB Permission denied", TextFormat.StrongWarning_withTime);
                }
            }
            if (UsbManager.ACTION_USB_DEVICE_ATTACHED.equals(action)) {
                UsbDevice device = intent.getParcelableExtra(UsbManager.EXTRA_DEVICE);
                if (device == null) return;
                if (device.getProductId() == 0x003C) {
                    if (device.getVendorId() == 0x04D8) {
                        // see if we have permission
                        UsbManager openManager = (UsbManager) context.getSystemService(Context.USB_SERVICE);
                        if (!openManager.hasPermission(device)) {
                            resumePermissionBlocked = true; // block the resume function from trying to re-ask for permission
                            openManager.requestPermission(device, mPermissionIntent);
                            return;
                        }
                        ThreadMsg msg = new ThreadMsg();
                        msg.request = MsgRequest.openConnection;
                        msg.objectA = device;
                        msg.objectB = openManager;
                        sendMessageToBootloader(msg);
                    }
                }
            } else if (UsbManager.ACTION_USB_DEVICE_DETACHED.equals(action)) {
                // If it was a USB device detach event, then get the USB device
                // that caused the event from the intent.
                UsbDevice device = intent.getParcelableExtra(UsbManager.EXTRA_DEVICE);

                ThreadMsg msg = new ThreadMsg();
                msg.request = MsgRequest.closeConnection;
                msg.objectA = device;
                sendMessageToBootloader(msg);
            }
        } catch (Exception e) {
            Log.i(TAG, "onResume catch: " + e.toString());
        }
    }

};

boolean receiverHasBeenRegistered = false;

PendingIntent mPermissionIntent;
@Override
public void onResume(){
    try {

        super.onResume();

        if (resumePermissionBlocked) {
            // this was resumed from a permission request - don't try to connect to the device now, leave it for the USB_PERMISSION_GRANTED intent
            resumePermissionBlocked = false;    // clear the flag
        } else {
            UsbManager manager = (UsbManager) getSystemService(Context.USB_SERVICE);
            HashMap<String, UsbDevice> deviceList = manager.getDeviceList();
            if (deviceList != null) {
                Iterator<UsbDevice> deviceIterator = deviceList.values().iterator();
                Log.i(TAG, "$EC: Begin iteration");

                while (deviceIterator.hasNext()) {
                    // Is this the device we are after?
                    UsbDevice device = deviceIterator.next();
                    if (device == null) return;
                    if (device.getProductId() == 0xAAAA) {
                        if (device.getVendorId() == 0xBBBB) {
                            // see if we have permission
                            UsbManager openManager = (UsbManager) this.getSystemService(Context.USB_SERVICE);
                            if (!openManager.hasPermission(device)) {
                                resumePermissionBlocked = true;         // block the subsequent call to this (between the application resuming and permission being granted)
                                openManager.requestPermission(device, mPermissionIntent);
                                return;
                            }
                            ThreadMsg msg = new ThreadMsg();
                            msg.request = MsgRequest.openConnection;
                            msg.objectA = device;
                            msg.objectB = openManager;
                            sendMessageToWorker(msg);
                        }
                    }
                }
            }
        }
    } catch (Exception e)
    {
        Log.i(TAG, "onResume catch: " + e.toString());
    }

    if (!receiverHasBeenRegistered) {
        // this line is for permissions
        mPermissionIntent = PendingIntent.getBroadcast(this, 0, new Intent("com.android.example.USB_PERMISSION"), 0);

        //Create a new filter to detect USB device events
        IntentFilter filter = new IntentFilter();
        filter.addAction(UsbManager.ACTION_USB_DEVICE_ATTACHED);
        filter.addAction(UsbManager.ACTION_USB_DEVICE_DETACHED);
        filter.addAction("com.android.example.USB_PERMISSION");
        registerReceiver(receiver, filter);
        pendingIntent = PendingIntent.getBroadcast(this, 0, new Intent(getPackageName() + ".USB_PERMISSION"), 0);
        receiverHasBeenRegistered = true;
    }
}

@Override
public void onPause() {
    /* unregister any receivers that we have */
    try {
        if (receiver != null && receiverHasBeenRegistered) {
            unregisterReceiver(receiver);
            receiverHasBeenRegistered = false;
        }
    } catch (Exception e) {
        // if this happens, then the receiver was probably never registered in the first place
        Log.i(TAG, "onPause catch: " + e.toString());
    }
    super.onPause();
}

Answer 1

1. 在 onResume 方法末尾尝试 super.onResume
2. 提醒用户在应用程序启动时连接 USB 设备(主要 Activity 的onCreate)如果设备未连接，则发出警报消息并完成/关闭主要 Activity
3. 在 list 文件中添加意图过滤器，允许应用在连接设备时自动启动
4. 当 UI 停止消息出现时， try catch 异常 printstacktrack显示并进一步调试异常。
5. 确保遵循 Android 文档中的步骤 https://developer.android.com/guide/topics/connectivity/usb/host.html