usb-host一步一步学（一）安卓在usb-host模式下列出当前连接的usb设备

在本次尝试中，我的安卓手机（HTC One X） 通过OTG线作为usb主机模式列出当前插入的usb设备，版本要求minSDKVersion=“12”。

没有外设的情况下，结果如下图所示：

通过OTG线插入读卡器设备后，结果如下：

为了指定应用程序以usb-host模式运行，在AndroidManifest.xml文件中需要添加<uses-feature android:name="android.hardware.usb.host">并且修改安卓的minSDKVersion="12"

主要代码如下：

<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
    package="com.example.androidusbhost"
    android:versionCode="1"
    android:versionName="1.0" >

    <uses-feature android:name="android.hardware.usb.host" />
    <uses-sdk
        android:minSdkVersion="12"
        android:targetSdkVersion="18" />

    <application
        android:allowBackup="true"
        android:icon="@drawable/ic_launcher"
        android:label="@string/app_name"
        android:theme="@style/AppTheme" >
        <activity
            android:name="com.example.androidusbhost.MainActivity"
            android:label="@string/app_name" >
            <intent-filter>
                <action android:name="android.intent.action.MAIN" />

                <category android:name="android.intent.category.LAUNCHER" />
            </intent-filter>
        </activity>
    </application>
</manifest>

主要的java代码如下：

package com.example.androidusbhost;

import java.util.HashMap;
import java.util.Iterator;

import android.hardware.usb.UsbConstants;
import android.hardware.usb.UsbDevice;
import android.hardware.usb.UsbManager;
import android.os.Bundle;
import android.view.View;
import android.view.View.OnClickListener;
import android.widget.Button;
import android.widget.TextView;
import android.app.Activity;
import android.content.Context;

public class MainActivity extends Activity {

 Button btnCheck;
 TextView textInfo;

 @Override
 protected void onCreate(Bundle savedInstanceState) {
  super.onCreate(savedInstanceState);
  setContentView(R.layout.activity_main);
  btnCheck = (Button) findViewById(R.id.check);
  textInfo = (TextView) findViewById(R.id.info);
  btnCheck.setOnClickListener(new OnClickListener() {

   @Override
   public void onClick(View arg0) {
    checkInfo();
   }
  });
 }

 private void checkInfo() {
  UsbManager manager = (UsbManager) getSystemService(Context.USB_SERVICE);
  HashMap<String, UsbDevice> deviceList = manager.getDeviceList();
  Iterator<UsbDevice> deviceIterator = deviceList.values().iterator();
  
  String i = "";
  while (deviceIterator.hasNext()) {
   UsbDevice device = deviceIterator.next();
   i += "
" +
    "DeviceID: " + device.getDeviceId() + "
" +
    "DeviceName: " + device.getDeviceName() + "
" +
    "DeviceClass: " + device.getDeviceClass() + " - " 
     + translateDeviceClass(device.getDeviceClass()) + "
" +
    "DeviceSubClass: " + device.getDeviceSubclass() + "
" +
    "VendorID: " + device.getVendorId() + "
" +
    "ProductID: " + device.getProductId() + "
";
  }
  
  textInfo.setText(i);
 }
 
 private String translateDeviceClass(int deviceClass){
  switch(deviceClass){
  case UsbConstants.USB_CLASS_APP_SPEC: 
   return "Application specific USB class";
  case UsbConstants.USB_CLASS_AUDIO: 
   return "USB class for audio devices";
  case UsbConstants.USB_CLASS_CDC_DATA: 
   return "USB class for CDC devices (communications device class)";
  case UsbConstants.USB_CLASS_COMM: 
   return "USB class for communication devices";
  case UsbConstants.USB_CLASS_CONTENT_SEC: 
   return "USB class for content security devices";
  case UsbConstants.USB_CLASS_CSCID: 
   return "USB class for content smart card devices";
  case UsbConstants.USB_CLASS_HID: 
   return "USB class for human interface devices (for example, mice and keyboards)";
  case UsbConstants.USB_CLASS_HUB: 
   return "USB class for USB hubs";
  case UsbConstants.USB_CLASS_MASS_STORAGE: 
   return "USB class for mass storage devices";
  case UsbConstants.USB_CLASS_MISC: 
   return "USB class for wireless miscellaneous devices";
  case UsbConstants.USB_CLASS_PER_INTERFACE: 
   return "USB class indicating that the class is determined on a per-interface basis";
  case UsbConstants.USB_CLASS_PHYSICA: 
   return "USB class for physical devices";
  case UsbConstants.USB_CLASS_PRINTER: 
   return "USB class for printers";
  case UsbConstants.USB_CLASS_STILL_IMAGE: 
   return "USB class for still image devices (digital cameras)";
  case UsbConstants.USB_CLASS_VENDOR_SPEC: 
   return "Vendor specific USB class";
  case UsbConstants.USB_CLASS_VIDEO: 
   return "USB class for video devices";
  case UsbConstants.USB_CLASS_WIRELESS_CONTROLLER: 
   return "USB class for wireless controller devices";
  default: return "Unknown USB class!";
  
  }
 }
}

布局文件主要代码：

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:paddingBottom="@dimen/activity_vertical_margin"
    android:paddingLeft="@dimen/activity_horizontal_margin"
    android:paddingRight="@dimen/activity_horizontal_margin"
    android:paddingTop="@dimen/activity_vertical_margin"
    android:orientation="vertical"
    tools:context=".MainActivity" >

    <TextView
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_gravity="center_horizontal"
        android:autoLink="web"
        android:text="http://android-er.blogspot.com/"
        android:textStyle="bold" />
    <Button
        android:id="@+id/check"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:text="Check USB devices" />
    <TextView
        android:id="@+id/info"
        android:layout_width="match_parent"
        android:layout_height="wrap_content" />

</LinearLayout>