如何与USB设备通信？

Question

我试图建立作为主机的USB通信。我正在按照这里的例子http://developer.android.com/guide/topics/usb/host.html，但我无法得到这个工作。这里是我的代码：

private static final String ACTION_USB_PERMISSION = "com.multitools.andres.LCView"; 
    UsbDevice device; 
    //Pide permisos al usuario para comunicacion con el dispositivo USB 
    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) { 
        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 
         } 
        } 
        else { 
         Log.d(TAG, "permission denied for device " + device); 
        } 
       } 
      } 
     } 
    }; 

    @Override 
    public void onCreate(Bundle savedInstanceState) { 
     super.onCreate(savedInstanceState); 
     if(DEBUG) Log.i(TAG, "onCreate() -> MainMenu"); 

     actionBar = getActionBar();      //obtengo el ActionBar 
     actionBar.setDisplayHomeAsUpEnabled(true);  //el icono de la aplicacion funciona como boton HOME 
     //Menu 
     setListAdapter(new ArrayAdapter<String>(MainMenu.this, android.R.layout.simple_list_item_1, MenuNames)); 

     //USB 
     if(DEBUG) Log.i(TAG, "Setting UsbManager -> MainMenu"); 
     UsbManager mUsbManager = (UsbManager) getSystemService(Context.USB_SERVICE); 
     PendingIntent mPermissionIntent; 

     if(DEBUG) Log.i(TAG, "Setting PermissionIntent -> MainMenu"); 
     mPermissionIntent = PendingIntent.getBroadcast(this, 0, new Intent(ACTION_USB_PERMISSION), 0); 
     if(DEBUG) Log.i(TAG, "Setting IntentFilter -> MainMenu"); 
     IntentFilter filter = new IntentFilter(ACTION_USB_PERMISSION); 
     if(DEBUG) Log.i(TAG, "Setting registerReceiver -> MainMenu"); 
     registerReceiver(mUsbReceiver, filter); 
     if(DEBUG) Log.i(TAG, "Setting requestPermission -> MainMenu"); 
     mUsbManager.requestPermission(device, mPermissionIntent); 

    } 

我得到了部队关闭对话框，当我取消对该行mUsbManager.requestPermission(device, mPermissionIntent);如果我评论它，我不亲近力，但它不工作。我认为这个问题是：

private static final String ACTION_USB_PERMISSION = "com.multitools.andres.LCView"; 

在谷歌的例子是为：

private static final String ACTION_USB_PERMISSION = "com.android.example.USB_PERMISSION"; 

但我不知道到底是什么我已经把那里，我无法找到任何解释。我必须放在那里或我的错误在哪里？这里是logcat的时候我开始我的应用程序我得到：

04-17 00:57:50.944: I/dalvikvm(1362): threadid=3: reacting to signal 3 
04-17 00:57:51.331: I/dalvikvm(1362): Wrote stack traces to '/data/anr/traces.txt' 
04-17 00:57:51.981: I/(1362): onCreate() -> MainMenu 
04-17 00:57:52.013: I/dalvikvm(1362): threadid=3: reacting to signal 3 
04-17 00:57:52.151: I/dalvikvm(1362): Wrote stack traces to '/data/anr/traces.txt' 
04-17 00:57:52.570: I/dalvikvm(1362): threadid=3: reacting to signal 3 
04-17 00:57:52.731: I/dalvikvm(1362): Wrote stack traces to '/data/anr/traces.txt' 
04-17 00:57:53.122: I/dalvikvm(1362): threadid=3: reacting to signal 3 
04-17 00:57:53.231: I/dalvikvm(1362): Wrote stack traces to '/data/anr/traces.txt' 
04-17 00:57:53.390: I/(1362): Setting UsbManager -> MainMenu 
04-17 00:57:53.451: I/(1362): Setting PermissionIntent -> MainMenu 
04-17 00:57:53.470: I/(1362): Setting IntentFilter -> MainMenu 
04-17 00:57:53.470: I/(1362): Setting registerReceiver -> MainMenu 
04-17 00:57:53.511: I/(1362): Setting requestPermission -> MainMenu 
04-17 00:57:53.660: I/dalvikvm(1362): threadid=3: reacting to signal 3 
04-17 00:57:53.791: I/dalvikvm(1362): Wrote stack traces to '/data/anr/traces.txt' 
04-17 00:57:54.311: I/dalvikvm(1362): threadid=3: reacting to signal 3 
04-17 00:57:54.401: I/dalvikvm(1362): Wrote stack traces to '/data/anr/traces.txt' 
04-17 00:57:54.531: I/(1362): onCreateOptionsMenu() -> MainMenu 
04-17 00:57:54.683: I/dalvikvm(1362): threadid=3: reacting to signal 3 
04-17 00:57:54.772: I/dalvikvm(1362): Wrote stack traces to '/data/anr/traces.txt' 
04-17 00:57:55.186: I/dalvikvm(1362): threadid=3: reacting to signal 3 
04-17 00:57:55.291: I/dalvikvm(1362): Wrote stack traces to '/data/anr/traces.txt' 
04-17 00:57:55.661: I/dalvikvm(1362): threadid=3: reacting to signal 3 
04-17 00:57:55.751: I/dalvikvm(1362): Wrote stack traces to '/data/anr/traces.txt' 
04-17 00:57:55.791: D/gralloc_goldfish(1362): Emulator without GPU emulation detected. 
04-17 01:11:47.323: I/dalvikvm(1459): threadid=3: reacting to signal 3 
04-17 01:11:47.720: I/dalvikvm(1459): Wrote stack traces to '/data/anr/traces.txt' 
04-17 01:11:48.124: I/dalvikvm(1459): threadid=3: reacting to signal 3 
04-17 01:11:48.291: I/dalvikvm(1459): Wrote stack traces to '/data/anr/traces.txt' 
04-17 01:11:48.452: I/(1459): onCreate() -> MainMenu 
04-17 01:11:48.691: I/dalvikvm(1459): threadid=3: reacting to signal 3 
04-17 01:11:48.813: I/dalvikvm(1459): Wrote stack traces to '/data/anr/traces.txt' 
04-17 01:11:49.172: I/dalvikvm(1459): threadid=3: reacting to signal 3 
04-17 01:11:49.321: I/dalvikvm(1459): Wrote stack traces to '/data/anr/traces.txt' 
04-17 01:11:49.653: I/dalvikvm(1459): threadid=3: reacting to signal 3 
04-17 01:11:49.821: I/dalvikvm(1459): Wrote stack traces to '/data/anr/traces.txt' 
04-17 01:11:49.901: I/(1459): Setting UsbManager -> MainMenu 
04-17 01:11:49.931: I/(1459): Setting PermissionIntent -> MainMenu 
04-17 01:11:50.021: I/(1459): Setting IntentFilter -> MainMenu 
04-17 01:11:50.031: I/(1459): Setting registerReceiver -> MainMenu 
04-17 01:11:50.051: I/(1459): Setting requestPermission -> MainMenu 
04-17 01:11:50.071: D/AndroidRuntime(1459): Shutting down VM 
04-17 01:11:50.133: W/dalvikvm(1459): threadid=1: thread exiting with uncaught exception (group=0x409c01f8) 
04-17 01:11:50.231: I/dalvikvm(1459): threadid=3: reacting to signal 3 
04-17 01:11:50.331: I/dalvikvm(1459): Wrote stack traces to '/data/anr/traces.txt' 
04-17 01:11:50.401: E/AndroidRuntime(1459): FATAL EXCEPTION: main 
04-17 01:11:50.401: E/AndroidRuntime(1459): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.multitools.andres/com.multitools.andres.MainMenu}: java.lang.NullPointerException 
04-17 01:11:50.401: E/AndroidRuntime(1459):  at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1956) 
04-17 01:11:50.401: E/AndroidRuntime(1459):  at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:1981) 
04-17 01:11:50.401: E/AndroidRuntime(1459):  at android.app.ActivityThread.access$600(ActivityThread.java:123) 
04-17 01:11:50.401: E/AndroidRuntime(1459):  at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1147) 
04-17 01:11:50.401: E/AndroidRuntime(1459):  at android.os.Handler.dispatchMessage(Handler.java:99) 
04-17 01:11:50.401: E/AndroidRuntime(1459):  at android.os.Looper.loop(Looper.java:137) 
04-17 01:11:50.401: E/AndroidRuntime(1459):  at android.app.ActivityThread.main(ActivityThread.java:4424) 
04-17 01:11:50.401: E/AndroidRuntime(1459):  at java.lang.reflect.Method.invokeNative(Native Method) 
04-17 01:11:50.401: E/AndroidRuntime(1459):  at java.lang.reflect.Method.invoke(Method.java:511) 
04-17 01:11:50.401: E/AndroidRuntime(1459):  at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:784) 
04-17 01:11:50.401: E/AndroidRuntime(1459):  at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:551) 
04-17 01:11:50.401: E/AndroidRuntime(1459):  at dalvik.system.NativeStart.main(Native Method) 
04-17 01:11:50.401: E/AndroidRuntime(1459): Caused by: java.lang.NullPointerException 
04-17 01:11:50.401: E/AndroidRuntime(1459):  at android.os.Parcel.readException(Parcel.java:1333) 
04-17 01:11:50.401: E/AndroidRuntime(1459):  at android.os.Parcel.readException(Parcel.java:1281) 
04-17 01:11:50.401: E/AndroidRuntime(1459):  at android.hardware.usb.IUsbManager$Stub$Proxy.requestDevicePermission(IUsbManager.java:535) 
04-17 01:11:50.401: E/AndroidRuntime(1459):  at android.hardware.usb.UsbManager.requestPermission(UsbManager.java:361) 
04-17 01:11:50.401: E/AndroidRuntime(1459):  at com.multitools.andres.MainMenu.onCreate(MainMenu.java:80) 
04-17 01:11:50.401: E/AndroidRuntime(1459):  at android.app.Activity.performCreate(Activity.java:4465) 
04-17 01:11:50.401: E/AndroidRuntime(1459):  at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1049) 
04-17 01:11:50.401: E/AndroidRuntime(1459):  at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1920) 
04-17 01:11:50.401: E/AndroidRuntime(1459):  ... 11 more 
04-17 01:11:50.751: I/dalvikvm(1459): threadid=3: reacting to signal 3 
04-17 01:11:50.851: I/dalvikvm(1459): Wrote stack traces to '/data/anr/traces.txt' 
04-17 01:11:51.331: I/dalvikvm(1459): threadid=3: reacting to signal 3 
04-17 01:11:51.403: I/dalvikvm(1459): Wrote stack traces to '/data/anr/traces.txt' 
04-17 01:11:51.774: I/dalvikvm(1459): threadid=3: reacting to signal 3 
04-17 01:11:51.961: I/dalvikvm(1459): Wrote stack traces to '/data/anr/traces.txt' 

谢谢你:)

Answer 1

该字符串只是一个标记，以便你认识到，当你调用registerReceiver(mUsbReceiver, filter);时，返回的意图。这不是问题。

我认为这个问题是在这里：

UsbManager mUsbManager = (UsbManager) getSystemService(Context.USB_SERVICE); 

这条线应该接受您的USB经理，但据我记得不是所有手机都支持Android USB附件API。此行可能只是将null分配给mUsbManager，然后当您在代码中进一步调用方法时，会导致您NullPointerException。在打电话之前试着检查是否不是null。

欲了解更多信息，结帐以下链接：

1. http://developer.android.com/guide/topics/usb/index.html
2. http://developer.android.com/guide/topics/usb/accessory.html

编辑：

我想我看到现在的问题是什么。你是对的，这不是USB管理器。这是UsbDevice对象（device）。它永远不会在代码中的任何地方初始化。在这一行：

mUsbManager.requestPermission(device, mPermissionIntent); 

你基本上发射过的意图，询问用户是否也没关系让你由UsbDevice对象device表示的设备正常工作。但是，当此呼叫被触发时，device尚未初始化（因此其默认值为null）。因此，当您尝试请求权限时，您最终得到的是NullPointerException而不是预期的结果。要解决此问题，您需要确定要连接的设备并将其分配给device。查看here，在“枚举设备”下找出不同的方法来做到这一点。一种方法，如果你知道你要连接到该设备的名称，是您检索USB管理后做出以下电话：

HashMap<String, UsbDevice> deviceList = mUsbManager.getDeviceList(); 
device = deviceList.get("<deviceName>"); 

（很明显，你会用的实际名称替换<deviceName> 。设备

Answer 2

minSdkVersion必须> = 12

要启用USB主机API的支持，你应该添加一个名为文件 android.hardware.usb.host.xml并包含以下行：

<permissions> 
<feature name="android.hardware.usb.host"/>