如何与USB设备进行通信？ [英] How to communicate with a USB device?

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问题描述

我试图建立USB通信的主机。我下面的例子在这里<一href="http://developer.android.com/guide/topics/usb/host.html">http://developer.android.com/guide/topics/usb/host.html但我不能得到这个工作。这是我的code：

I am trying to establish USB communication as host. I am following the examples here http://developer.android.com/guide/topics/usb/host.html but I cannot get this working. Here is my code:

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);

    }

我得到的部队关闭对话框时，我去掉注释 mUsbManager.requestPermission（设备，mPermissionIntent）; 如果我评论的话，我没有得到强制关闭，但它不工作。我认为这个问题是：

I get the Force Close dialog when I uncomment the line mUsbManager.requestPermission(device, mPermissionIntent); If I comment it, I don't get the force close but it doesnt work. I think the problem is in:

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

在谷歌的例子是如下：

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

但我不知道究竟我要放在那里，我无法找到任何解释。我已经把存在或者是我的错误？这里是LogCat中我得到当我启动我的应用程序：

But I dont know what exactly I have to put there and i could not find any explanation about that. What i have to put there or where is my error ? Here is the LogCat i am getting when i start my application:

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'

谢谢您：）

推荐答案

这串仅仅是一个标志，所以你承认，当你调用返回的意图 registerReceiver（mUsbReceiver，过滤器）; 。这是没有问题的。

That string is just a marker so you recognize the intent that is returned when you call registerReceiver(mUsbReceiver, filter);. That isn't the problem.

我认为这个问题是在这里：

I think the problem is here:

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

这行应该让你的USB管理器，但据我记得不是所有的手机都支持Android USB附件API。这条线可能只是分配空到 mUsbManager 然后使你 NullPointerException异常时，你就可以调用一个方法，在code进一步下跌。尝试检查，如果这不是空拨打电话就可以了。

This line is supposed to get you your USB Manager, but as far as I recall not all phones have to support the Android USB Accessory API. This line is probably just assigning null to mUsbManager which then causes you NullPointerException when you call a method on it further down in the code. Trying checking if that isn't null before making a call on it.

有关详细信息，结帐以下链接：

For more info, checkout these links:

  1. <一个href="http://developer.android.com/guide/topics/usb/index.html">http://developer.android.com/guide/topics/usb/index.html
  2. <一个href="http://developer.android.com/guide/topics/usb/accessory.html">http://developer.android.com/guide/topics/usb/accessory.html
  1. http://developer.android.com/guide/topics/usb/index.html
  2. http://developer.android.com/guide/topics/usb/accessory.html

编辑：

我想我看到的是什么问题了。你说得对，它不是USB管理。这是UsbDevice对象（设备）。它永远不会在你的code初始化的任何地方。在这一行：

I think I see what the issue is now. You're right, it's not the USB Manager. It's the UsbDevice object (device). It is never initialized anywhere in your code. In this line : 

mUsbManager.requestPermission(device, mPermissionIntent);

你基本上发射了一个意向询问用户是否也没关系，为您与由UsbDevice对象设备 psented设备重新$ P $工作。然而，当这个电话被炒鱿鱼设备尚未初始化（因此具有空的默认值）。所以，当你试图请求允许你最终得到的 NullPointerException异常，而不是预期的结果。为了解决这个问题，你需要找出你要连接并将其分配给设备的设备。你看在这里 ，在设备枚举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的设备的名称，是你找回USB管理后做出如下要求：

you're basically firing off an intent to ask the user if it's okay for you to work with the device represented by the UsbDevice object device. However when this call gets fired device has not yet been initialized (and therefore has the default value of null). So when you try to request permission you end up getting a NullPointerException instead of the expected result. To fix this you need to figure out which device you want to connect to and assign it to device. Look in here, under "Enumerating devices" to figure out different ways to do that. One way, if you know the name of the device you want to connect to, is to make the following calls after you retrieve the Usb Manager:

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

（很明显，你将取代＆LT; D​​EVICENAME＆GT; 与设备的实际名称

这篇关于如何与USB设备进行通信？的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！

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