Android的USB枚举(Android usb enumeration)

2019-07-29 21:00发布

站内文章 / 前沿技术
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我写这我试图枚举与平板电脑连接的设备一个Android USB主机应用程序。 我跟随在开发者网站在Android USB主机文档中的代码。

我的代码如下

AndroidUSBActivity 

public class AndroidUSBActivity extends Activity {
/** Called when the activity is first created. */
@Override
public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.main);

    USBClass usb = new USBClass();
    ArrayList<String> deviceList = usb.GetUSBDevices(getBaseContext());
    final CharSequence[] items = deviceList.toArray(new CharSequence[deviceList.size()]);

    AlertDialog.Builder builder = new AlertDialog.Builder(this);
    builder.setTitle("Select a Reader");
    builder.setSingleChoiceItems(items, -1, new DialogInterface.OnClickListener() {
        public void onClick(DialogInterface dialog, int item) {
            String selectedDevice = (String) items[item];
            dialog.dismiss();

            TextView DeivceName = (TextView)findViewById(R.id.textView1);
            DeivceName.setText(selectedDevice);
        }
    });
    AlertDialog alert = builder.create();
    alert.show();
}
}

USBClass 

public class USBClass {


private static UsbManager mManager = null;
private static HashMap<String, UsbDevice> mdevices;
private static PendingIntent mPermissionIntent;
private static final String ACTION_USB_PERMISSION =
        "com.android.example.USB_PERMISSION";
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) {
                UsbDevice device = (UsbDevice)intent.getParcelableExtra(UsbManager.EXTRA_DEVICE);
                if (intent.getBooleanExtra(UsbManager.EXTRA_PERMISSION_GRANTED, false)) {
                    if(device != null){
                        //call method to set up device communication 
                        Log.i("usb", "permission granted for device " + device);
                    }
                } 
                else {
                    Log.i("usb", "permission denied for device " + device);
                }
            }
        }
    }
};   


public ArrayList<String> GetUSBDevices(Context context){
    mManager = (UsbManager) context.getSystemService(Context.USB_SERVICE);
    mdevices = new HashMap<String, UsbDevice>();
    ArrayList<String> deviceList = new ArrayList<String>();
    mPermissionIntent = PendingIntent.getBroadcast(context, 0, new Intent("com.android.example.USB_PERMISSION"), 0);
    IntentFilter filter = new IntentFilter(ACTION_USB_PERMISSION);
    context.registerReceiver(mUsbReceiver, filter);


    // check for existing devices
    for (UsbDevice device :  mManager.getDeviceList().values()) {
        String deviceName = null;
        UsbDeviceConnection connection = null;
        if(device.getVendorId() == 0x0123){
            mManager.requestPermission(device, mPermissionIntent);
            connection = mManager.openDevice(device);
            byte rawBuf[] = new byte[255];
            int len = connection.controlTransfer(0x80, 0x06, 0x0302, 0x0409, rawBuf, 0x00FF, 60);
            rawBuf = Arrays.copyOfRange(rawBuf, 2, len);
            deviceName = new String(rawBuf);
            deviceList.add(deviceName);
            mdevices.put(deviceName, device);
        }

     }
    context.unregisterReceiver(mUsbReceiver);
    return deviceList;
}
}

logcat的 

06-13 10:13:54.556: D/dalvikvm(2219): Late-enabling CheckJNI
06-13 10:13:54.586: I/System.out(2219): Sending WAIT chunk
06-13 10:13:54.586: W/ActivityThread(2219): Application bri.sample is waiting for the debugger on port 8100...
06-13 10:13:54.596: I/dalvikvm(2219): Debugger is active
06-13 10:13:54.786: I/System.out(2219): Debugger has connected
06-13 10:13:54.786: I/System.out(2219): waiting for debugger to settle...
06-13 10:13:54.986: I/System.out(2219): waiting for debugger to settle...
06-13 10:13:55.186: I/System.out(2219): waiting for debugger to settle...
06-13 10:13:55.406: I/System.out(2219): waiting for debugger to settle...
06-13 10:13:55.596: I/System.out(2219): waiting for debugger to settle...
06-13 10:13:55.796: I/System.out(2219): waiting for debugger to settle...
06-13 10:13:55.996: I/System.out(2219): waiting for debugger to settle...
06-13 10:13:56.206: I/System.out(2219): waiting for debugger to settle...
06-13 10:13:56.406: I/System.out(2219): waiting for debugger to settle...
06-13 10:13:56.645: I/System.out(2219): waiting for debugger to settle...
06-13 10:13:56.846: I/System.out(2219): debugger has settled (1337)
06-13 10:13:57.116: E/UsbManager(2219): exception in UsbManager.openDevice
06-13 10:13:57.116: E/UsbManager(2219): java.lang.SecurityException: User has not given  permission to device   UsbDevice[mName=/dev/bus/usb/001/004,mVendorId=1254,mProductId=20758,mClass=0,mSubclass=0,mProtocol=0,mInterfaces=[Landroid.hardware.usb.UsbInterface;@41679100]
06-13 10:13:57.116: E/UsbManager(2219):     at android.os.Parcel.readException(Parcel.java:1327)
06-13 10:13:57.116: E/UsbManager(2219):     at android.os.Parcel.readException(Parcel.java:1281)
06-13 10:13:57.116: E/UsbManager(2219):     at android.hardware.usb.IUsbManager$Stub$Proxy.openDevice(IUsbManager.java:340)
06-13 10:13:57.116: E/UsbManager(2219):     at android.hardware.usb.UsbManager.openDevice(UsbManager.java:250)
06-13 10:13:57.116: E/UsbManager(2219):     at  bri.sample.USBClass.GetUSBDevices(USBClass.java:66)
06-13 10:13:57.116: E/UsbManager(2219):     at bri.sample.AndroidUSBActivity.onCreate(AndroidUSBActivity.java:19)
06-13 10:13:57.116: E/UsbManager(2219):     at android.app.Activity.performCreate(Activity.java:4465)
06-13 10:13:57.116: E/UsbManager(2219):     at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1049)
06-13 10:13:57.116: E/UsbManager(2219):     at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1920)
06-13 10:13:57.116: E/UsbManager(2219):     at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:1981)
06-13 10:13:57.116: E/UsbManager(2219):     at android.app.ActivityThread.access$600(ActivityThread.java:123)
06-13 10:13:57.116: E/UsbManager(2219):     at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1147)
06-13 10:13:57.116: E/UsbManager(2219):     at android.os.Handler.dispatchMessage(Handler.java:99)
06-13 10:13:57.116: E/UsbManager(2219):     at android.os.Looper.loop(Looper.java:137)
06-13 10:13:57.116: E/UsbManager(2219):     at android.app.ActivityThread.main(ActivityThread.java:4424)
06-13 10:13:57.116: E/UsbManager(2219):     at java.lang.reflect.Method.invokeNative(Native Method)
06-13 10:13:57.116: E/UsbManager(2219):     at java.lang.reflect.Method.invoke(Method.java:511)
06-13 10:13:57.116: E/UsbManager(2219):     at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:784)
06-13 10:13:57.116: E/UsbManager(2219):     at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:551)
06-13 10:13:57.116: E/UsbManager(2219):     at dalvik.system.NativeStart.main(Native Method)
06-13 10:13:57.566: D/dalvikvm(2219): threadid=1: still suspended after undo (sc=1 dc=1)
06-13 10:14:04.266: D/AndroidRuntime(2219): Shutting down VM
06-13 10:14:04.266: W/dalvikvm(2219): threadid=1: thread exiting with uncaught exception (group=0x40a531f8)
06-13 10:14:04.296: E/AndroidRuntime(2219): FATAL EXCEPTION: main
06-13 10:14:04.296: E/AndroidRuntime(2219): java.lang.RuntimeException: Unable to start activity ComponentInfo{bri.sample/bri.sample.AndroidUSBActivity}: java.lang.NullPointerException
06-13 10:14:04.296: E/AndroidRuntime(2219):     at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1956)
06-13 10:14:04.296: E/AndroidRuntime(2219):     at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:1981)
06-13 10:14:04.296: E/AndroidRuntime(2219):     at android.app.ActivityThread.access$600(ActivityThread.java:123)
06-13 10:14:04.296: E/AndroidRuntime(2219):     at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1147)
06-13 10:14:04.296: E/AndroidRuntime(2219):     at android.os.Handler.dispatchMessage(Handler.java:99)
06-13 10:14:04.296: E/AndroidRuntime(2219):     at android.os.Looper.loop(Looper.java:137)
06-13 10:14:04.296: E/AndroidRuntime(2219):     at android.app.ActivityThread.main(ActivityThread.java:4424)
06-13 10:14:04.296: E/AndroidRuntime(2219):     at java.lang.reflect.Method.invokeNative(Native Method)
06-13 10:14:04.296: E/AndroidRuntime(2219):     at java.lang.reflect.Method.invoke(Method.java:511)
06-13 10:14:04.296: E/AndroidRuntime(2219):     at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:784)
06-13 10:14:04.296: E/AndroidRuntime(2219):     at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:551)
06-13 10:14:04.296: E/AndroidRuntime(2219):     at dalvik.system.NativeStart.main(Native Method)
06-13 10:14:04.296: E/AndroidRuntime(2219): Caused by: java.lang.NullPointerException
06-13 10:14:04.296: E/AndroidRuntime(2219):     at bri.sample.USBClass.GetUSBDevices(USBClass.java:68)
06-13 10:14:04.296: E/AndroidRuntime(2219):     at bri.sample.AndroidUSBActivity.onCreate(AndroidUSBActivity.java:19)
06-13 10:14:04.296: E/AndroidRuntime(2219):     at android.app.Activity.performCreate(Activity.java:4465)
06-13 10:14:04.296: E/AndroidRuntime(2219):     at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1049)
06-13 10:14:04.296: E/AndroidRuntime(2219):     at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1920)
06-13 10:14:04.296: E/AndroidRuntime(2219):     ... 11 more

问题

我在插入的设备，然后我安装应用程序。 当应用程序启动第一次 ，它就会崩溃。

Answer 1:

在危机来临，当你试图与接入设备

connection = mManager.openDevice(device);

它崩溃，因为它是抛出SecurityException因为你还没有获得许可的用户使用该设备。 它看起来像你试图从用户获得许可，在该行此前 

mManager.requestPermission(device, mPermissionIntent);

但是，你要明白，在调用requestPermission()是异步的。 它不与权限立即返回。 它所做的是，它显示一个对话框，用户并询问用户是否他将权限授予您的应用程序。 一旦用户授予或拒绝权限对话框驳回， PendingIntent ，你传递给requestPermission()用于广播的意图表示被授予（或不）的权限。 你需要在注册监听这个BroadcastReceiver和当onReceive()方法被调用，您可以再检查额外的接收Intent ，并决定如何处理。 只有当用户授权您可以在移动上调用openDevice()

这听起来有点复杂，但是这是它的工作方式。

基本上，你需要调用

mManager.requestPermission(device, mPermissionIntent);

然后等到权限已被授予您尝试访问该设备前。



文章来源: Android usb enumeration
标签： android permissions usb broadcastreceiver android-pendingintent
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