如何授予使用USB Manager打开USB设备的权限? openDevice()始终返回null [英] How to grant permission to open usb device with usb manager? openDevice() always returns null

问题描述

我想在以下代码中使用USB设备.它成功列出了USB设备并对其进行迭代.在以下代码中，对象设备"是我需要打开的USB设备.除OpenDevice()方法始终返回 null值！

I want to use a usb device in the following code. It successfully lists the usb devices and iterates over them. In the following code the object "device" is the usbdevice that i need to open. Everything seems Ok except the OpenDevice() method that always returns a null value!

[Activity(Label = "TestApp", MainLauncher = true, Icon = "@drawable/icon")]
[IntentFilter(new[] {UsbManager.ActionUsbDeviceAttached})]
[MetaData(UsbManager.ActionUsbDeviceAttached, Resource = "@xml/device_filter")]

public class MainActivity : Activity
{
    int count = 1;
   {
       base.OnCreate(bundle);

        // Set our view from the "main" layout resource
        SetContentView(Resource.Layout.Main);
        UsbManager manager = (UsbManager)GetSystemService(Context.UsbService);
        UsbDevice device = null;
        foreach (var dev in manager.DeviceList)
        {
            if (dev.Value.VendorId == 5401)
            {
                device = dev.Value;
            }
        }
        var connection = manager.OpenDevice(device);
        // Read some data! Most have just one port (port 0).
    }

device_filter.xml包含以下几行:

The device_filter.xml contains the following lines:

<?xml version="1.0" encoding="utf-8" ?>
<resources>
   <usb-device product-id="8704" vendor-id="5401" />
</resources>

当我尝试bool hasPermision = manager.HasPermission(device);我看到hasPermission是错误的.有人可以告诉我如何授予在xamarin中打开USB设备的权限吗? 感谢您的帮助.

When I tried bool hasPermision = manager.HasPermission(device); I saw that hasPermission is false. Could anybody tell me How can I grant permission for opening a usb device in xamarin? Thanks for any help.

推荐答案

最后，我尝试了一些建议后将其修复.我发现在清单中添加意图过滤器由于未知原因无法解决权限问题.听起来像Xamarin的错误.实话实说，Xamarin usb名称空间似乎太幼稚了，更好的是您不要浪费时间将其用于USB管理和连接.它还具有其他一些令人讨厌的限制.例如，请参见此处. (因此，我建议用Java编写低级的USB通信代码，并通过JNI将文件导入xamarin中，我感到很累，应该说这比第一次看起来要容易得多).

At last I fixed it after trying several suggestions. I found that adding the intent filter in manifest does not solve the permission issue for unknown reasons. It's sounds like a bug of the Xamarin. To tell the truth, It seems that Xamarin usb namespace is too naive, and its better you do not waste your time to use that for USB management and connection. It also has some other annoying limitations. For example look at here. (So I suggest to write low level usb communication codes in java and import the jar file in xamarin by JNI, I tired it and I should say It's a lot easier than it seemed at first time)

要授予打开USB设备的权限，必须使用grantPermission()方法.以下代码显示了如何使用该方法和BroadcastReceiver弹出一个对话框，要求用户允许使用USB.

To grant the permission of opening the usb device, you have to use the grantPermission() method. The following code shows how to use the method and BroadcastReceiver to pop up a dialog asking the user to let the usb usage.

 public class MainActivity : Activity
{
    private static String ACTION_USB_PERMISSION = "com.android.example.USB_PERMISSION";
    UsbDevice device; 
    protected override void OnCreate(Bundle bundle)
    {
        base.OnCreate(bundle);

        // Set our view from the "main" layout resource
        SetContentView(Resource.Layout.Main);
        UsbManager manager = (UsbManager)GetSystemService(Context.UsbService);

        UsbReciever usbReciever = new UsbReciever();
        PendingIntent mPermissionIntent = PendingIntent.GetBroadcast(this, 0, new Intent(
            ACTION_USB_PERMISSION), 0);
        IntentFilter filter = new IntentFilter(ACTION_USB_PERMISSION);
        RegisterReceiver(usbReciever, filter);

        foreach (var dev in manager.DeviceList)
        {
            if (dev.Value.VendorId == 8192)
            {
                device = dev.Value;
            }
        }
        manager.RequestPermission(device, mPermissionIntent);
        bool hasPermision = manager.HasPermission(device);

        UsbDeviceConnection connection = manager.OpenDevice(device);
        if (connection == null)
        {
            return;
        }
        Button button = FindViewById<Button>(Resource.Id.MyButton);
    }
    class UsbReciever : BroadcastReceiver
    {
        public override void OnReceive(Context context, Intent intent)
        {
            String action = intent.Action;
            if (ACTION_USB_PERMISSION.Equals(action))
            {
                lock (this)
                {
                    UsbDevice device = (UsbDevice)intent
                            .GetParcelableExtra(UsbManager.ExtraDevice);

                    if (intent.GetBooleanExtra(
                            UsbManager.ExtraPermissionGranted, false))
                    {
                        if (device != null)
                        {
                            // call method to set up device communication
                        }
                    }
                    else
                    {

                    }
                }
            }
        }
    }


}

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