我正在尝试通过带有 4.2(果冻 bean )的 android 设备“nexus 7”通过 USB 与我的 freeduino 板进行通信，该板类似于 arduino uno。

几个月后，我使用开发人员指南与设备进行通信，但没有结果。我想我错过了一些细节。我试图简单地显示我的 freeduino 板的供应商 ID。我的 list 文件如下所示。

    package="com.example.usb_host_final_try"
    android:versionCode="1"
    android:versionName="1.0" >

    
        android:minSdkVersion="8"
        android:targetSdkVersion="17" />

    <ứng>
        android:allowBackup="đúng"
        android:icon="@drawable/ic_launcher"
        android:label="@string/tên_ứng_dụng"
        android:theme="@style/AppTheme" >
        
            android:name="com.example.usb_host_final_try.MainActivity"
            android:label="@string/tên_ứng_dụng" >
            
                

                
            
            
        
    

    
        android:resource="@xml/device_filter" />
        
    

我在 res/xml 目录中创建了一个文件 device_filter。看起来像这样

我的 MainActivity.java 有以下代码。

package com.example.usb_host_final_try;

import java.util.HashMap;

import android.hardware.usb.UsbDevice;
import android.hardware.usb.UsbManager;
import android.os.Build;
import android.os.Bundle;
import android.annotation.TargetApi;
import android.app.Activity;
import android.content.Context;
import android.content.Intent;
import android.view.Menu;
import android.widget.TextView;

public class MainActivity extends Activity {

    @TargetApi(Build.VERSION_CODES.HONEYCOMB_MR1)
    @Ghi đè
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        Intent intent = new Intent();
        UsbManager manager = (UsbManager) getSystemService(Context.USB_SERVICE);
        HashMap deviceList = manager.getDeviceList();
        UsbDevice device = deviceList.get("deviceName");
        int vid=device.getVendorId();
        TextView tv = (TextView) findViewById(R.id.textview);
        tv.setText(Integer.toString(vid));
    }

请帮帮我，我从过去几个月开始就搞砸了。我试过这样做，但它也不起作用。

liên kết

liên kết

Stack overfolow question

stack overflow question

我已经尝试了所有这些，但仍然无法成功。我还尝试使用 if else 循环来查看枚举是否有效，如果没有设备将文本设置为未找到的设备，则将文本设置为供应商 ID。在模拟器上显示没有找到设备，但在我的平板电脑上我连接了它强制关闭的设备，否则它仍然显示没有找到任何设备，没有任何连接。

堆栈跟踪在这里..

01-05 09:10:35.364: W/Trace(1658): Unexpected value from nativeGetEnabledTags: 0 01-05 09:10:35.364: W/Trace(1658): Unexpected value from nativeGetEnabledTags: 0 01-05 09:10:35.464: W/Trace(1658): Unexpected value from nativeGetEnabledTags: 0 01-05 09:10:35.464: W/Trace(1658): Unexpected value from nativeGetEnabledTags: 0 01-05 09:10:35.624: D/AndroidRuntime(1658): Shutting down VM 01-05 09:10:35.624: W/dalvikvm(1658): threadid=1: thread exiting with uncaught exception (group=0x40a70930) 01-05 09:10:35.644: E/AndroidRuntime(1658): FATAL EXCEPTION: main 01-05 09:10:35.644: E/AndroidRuntime(1658): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.usb_host_final_try/com.example.usb_host_final_try.MainActivity}: java.lang.NullPointerException 01-05 09:10:35.644: E/AndroidRuntime(1658): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2180) 01-05 09:10:35.644: E/AndroidRuntime(1658): at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2230) 01-05 09:10:35.644: E/AndroidRuntime(1658): at android.app.ActivityThread.access$600(ActivityThread.java:141) 01-05 09:10:35.644: E/AndroidRuntime(1658): at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1234) 01-05 09:10:35.644: E/AndroidRuntime(1658): at android.os.Handler.dispatchMessage(Handler.java:99) 01-05 09:10:35.644: E/AndroidRuntime(1658): at android.os.Looper.loop(Looper.java:137) 01-05 09:10:35.644: E/AndroidRuntime(1658): at android.app.ActivityThread.main(ActivityThread.java:5039) 01-05 09:10:35.644: E/AndroidRuntime(1658): at java.lang.reflect.Method.invokeNative(Native Method) 01-05 09:10:35.644: E/AndroidRuntime(1658): at java.lang.reflect.Method.invoke(Method.java:511) 01-05 09:10:35.644: E/AndroidRuntime(1658): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:793) 01-05 09:10:35.644: E/AndroidRuntime(1658): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:560) 01-05 09:10:35.644: E/AndroidRuntime(1658): at dalvik.system.NativeStart.main(Native Method) 01-05 09:10:35.644: E/AndroidRuntime(1658): Caused by: java.lang.NullPointerException 01-05 09:10:35.644: E/AndroidRuntime(1658): at com.example.usb_host_final_try.MainActivity.onCreate(MainActivity.java:35) 01-05 09:10:35.644: E/AndroidRuntime(1658): at android.app.Activity.performCreate(Activity.java:5104) 01-05 09:10:35.644: E/AndroidRuntime(1658): at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1080) 01-05 09:10:35.644: E/AndroidRuntime(1658): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2144) 01-05 09:10:35.644: E/AndroidRuntime(1658): ... 11 more 01-05 09:10:46.074: W/Trace(1712): Unexpected value from nativeGetEnabledTags: 0 01-05 09:10:46.074: W/Trace(1712): Unexpected value from nativeGetEnabledTags: 0 01-05 09:10:46.754: D/AndroidRuntime(1712): Shutting down VM 01-05 09:10:46.754: W/dalvikvm(1712): threadid=1: thread exiting with uncaught exception (group=0x40a70930) 01-05 09:10:46.766: E/AndroidRuntime(1712): FATAL EXCEPTION: main 01-05 09:10:46.766: E/AndroidRuntime(1712): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.usb_host_final_try/com.example.usb_host_final_try.MainActivity}: java.lang.NullPointerException 01-05 09:10:46.766: E/AndroidRuntime(1712): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2180) 01-05 09:10:46.766: E/AndroidRuntime(1712): at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2230) 01-05 09:10:46.766: E/AndroidRuntime(1712): at android.app.ActivityThread.access$600(ActivityThread.java:141) 01-05 09:10:46.766: E/AndroidRuntime(1712): at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1234) 01-05 09:10:46.766: E/AndroidRuntime(1712): at android.os.Handler.dispatchMessage(Handler.java:99) 01-05 09:10:46.766: E/AndroidRuntime(1712): at android.os.Looper.loop(Looper.java:137) 01-05 09:10:46.766: E/AndroidRuntime(1712): at android.app.ActivityThread.main(ActivityThread.java:5039) 01-05 09:10:46.766: E/AndroidRuntime(1712): at java.lang.reflect.Method.invokeNative(Native Method) 01-05 09:10:46.766: E/AndroidRuntime(1712): at java.lang.reflect.Method.invoke(Method.java:511) 01-05 09:10:46.766: E/AndroidRuntime(1712): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:793) 01-05 09:10:46.766: E/AndroidRuntime(1712): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:560) 01-05 09:10:46.766: E/AndroidRuntime(1712): at dalvik.system.NativeStart.main(Native Method) 01-05 09:10:46.766: E/AndroidRuntime(1712): Caused by: java.lang.NullPointerException 01-05 09:10:46.766: E/AndroidRuntime(1712): at com.example.usb_host_final_try.MainActivity.onCreate(MainActivity.java:35) 01-05 09:10:46.766: E/AndroidRuntime(1712): at android.app.Activity.performCreate(Activity.java:5104) 01-05 09:10:46.766: E/AndroidRuntime(1712): at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1080) 01-05 09:10:46.766: E/AndroidRuntime(1712): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2144) 01-05 09:10:46.766: E/AndroidRuntime(1712): ... 11 more 01-05 09:10:49.104: I/Process(1712): Sending signal. PID: 1712 SIG: 9

1 Câu trả lời

biên tập :如果在 XML 中定义，则实际上不需要权限，因此以下答案不适用。问题是 NPE - 代码中不存在这样的设备“deviceName”。

您似乎没有获得使用 USB 附件的权限，如 here in the docs 所述在 this answer .

Trong của bạn onCreate() :

UsbManager mUsbManager = (UsbManager) getSystemService(Context.USB_SERVICE);
private static final String ACTION_USB_PERMISSION =
    "com.android.example.USB_PERMISSION";
...
mPermissionIntent = PendingIntent.getBroadcast(this, 0, new Intent(ACTION_USB_PERMISSION), 0);
IntentFilter filter = new IntentFilter(ACTION_USB_PERMISSION);
registerReceiver(mUsbReceiver, filter);

Trong của bạn Activity :

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) {
                UsbAccessory accessory = (UsbAccessory) intent.getParcelableExtra(UsbManager.EXTRA_ACCESSORY);

                if (intent.getBooleanExtra(UsbManager.EXTRA_PERMISSION_GRANTED, false)) {
                    if(accessory != null){
                        //call method to set up accessory communication
                    }
                }
                else {
                    Log.d(TAG, "permission denied for accessory " + accessory);
                }
            }
        }
    }
};

要显示对话框以获取权限:

UsbAccessory accessory;
...
mUsbManager.requestPermission(accessory, mPermissionIntent);

关于android - 适用于安卓的 USB 主机，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/14168947/