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 += "\n" +
"DeviceID: " + device.getDeviceId() + "\n" +
"DeviceName: " + device.getDeviceName() + "\n" +
"DeviceClass: " + device.getDeviceClass() + " - "
+ translateDeviceClass(device.getDeviceClass()) + "\n" +
"DeviceSubClass: " + device.getDeviceSubclass() + "\n" +
"VendorID: " + device.getVendorId() + "\n" +
"ProductID: " + device.getProductId() + "\n";
}

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>