一、原理讲解
Android通过广播监听USB连接状态的改变的动作在UsbManager.java文件里，为ACTION_USB_STATE。然而在UsbManager中，该常量的注释中包含{@hide}，该注释是控制该API是否开放用的。未开发的API意味着google可以随时调整该API的定义或实现方式，而不用保证向下兼容。
所以尽量避免调用未开发的API，因为一旦系统升级导致其实现方式改变，程序很有可能就直接崩溃了。
注意：
目前仍未发现 ACTION_USB_ACCESSORY_XXX 这种广播插拔手机与电脑之间的USB线：ACTION_USB_STATE（主要参数是 Boolean connected）插拔U盘发送的是OTG广播：ACTION_USB_DEVICE_XXX，XXX代表了ATTACH 或 DETACH，这种情况是手机是主，u盘是从，手机给U盘供电。
二、代码如下
1、MyUsbManager.java
package com.example.testapp;public class MyUsbManager {/*** Broadcast Action: A sticky broadcast for USB state change events when in device mode.* This is a sticky broadcast for clients that includes USB connected/disconnected state,* <ul>* <li> {@link #USB_CONNECTED} boolean indicating whether USB is connected or disconnected.* <li> {@link #USB_CONFIGURED} boolean indicating whether USB is configured. currently zero if not configured, one for configured.* <li> {@link #USB_FUNCTION_ADB} boolean extra indicating whether the adb function is enabled* <li> {@link #USB_FUNCTION_RNDIS} boolean extra indicating whether the RNDIS ethernet function is enabled* <li> {@link #USB_FUNCTION_MTP} boolean extra indicating whether the MTP function is enabled* <li> {@link #USB_FUNCTION_PTP} boolean extra indicating whether the PTP function is enabled* <li> {@link #USB_FUNCTION_PTP} boolean extra indicating whether the accessory function is enabled* <li> {@link #USB_FUNCTION_AUDIO_SOURCE} boolean extra indicating whether the audio source function is enabled* <li> {@link #USB_FUNCTION_MIDI} boolean extra indicating whether the MIDI function is enabled* </ul>*/public static final String ACTION_USB_STATE = "android.hardware.usb.action.USB_STATE";/*** Boolean extra indicating whether USB is connected or disconnected.* Used in extras for the {@link #ACTION_USB_STATE} broadcast.*/public static final String USB_CONNECTED = "connected";/*** Boolean extra indicating whether USB is configured.* Used in extras for the {@link #ACTION_USB_STATE} broadcast.*/public static final String USB_CONFIGURED = "configured";/*** Boolean extra indicating whether confidential user data, such as photos, should be* made available on the USB connection. This variable will only be set when the user* has explicitly asked for this data to be unlocked.* Used in extras for the {@link #ACTION_USB_STATE} broadcast.*/public static final String USB_DATA_UNLOCKED = "unlocked";/*** A placeholder indicating that no USB function is being specified.* Used to distinguish between selecting no function vs. the default function in {@link #setCurrentFunction(String)}.*/public static final String USB_FUNCTION_NONE = "none";/*** Name of the adb USB function.* Used in extras for the {@link #ACTION_USB_STATE} broadcast*/public static final String USB_FUNCTION_ADB = "adb";/*** Name of the RNDIS ethernet USB function.* Used in extras for the {@link #ACTION_USB_STATE} broadcast*/public static final String USB_FUNCTION_RNDIS = "rndis";/*** Name of the MTP USB function.* Used in extras for the {@link #ACTION_USB_STATE} broadcast*/public static final String USB_FUNCTION_MTP = "mtp";/*** Name of the PTP USB function.* Used in extras for the {@link #ACTION_USB_STATE} broadcast*/public static final String USB_FUNCTION_PTP = "ptp";/*** Name of the audio source USB function.* Used in extras for the {@link #ACTION_USB_STATE} broadcast*/public static final String USB_FUNCTION_AUDIO_SOURCE = "audio_source";/*** Name of the MIDI USB function.* Used in extras for the {@link #ACTION_USB_STATE} broadcast*/public static final String USB_FUNCTION_MIDI = "midi";}
2、UsbActivity.java
package com.example.testapp;import android.app.Activity;import android.content.BroadcastReceiver;import android.content.Context;import android.content.Intent;import android.content.IntentFilter;import android.content.pm.PackageManager;import android.hardware.usb.UsbAccessory;import android.hardware.usb.UsbDevice;import android.hardware.usb.UsbManager;import android.os.Bundle;import android.widget.LinearLayout;import android.widget.ScrollView;import android.widget.TextView;public class UsbActivity extends Activity {private TextView textView;private UsbManager usbManager;private BroadcastReceiver receiver;private IntentFilter intentFilter;@Overrideprotected void onCreate(Bundle savedInstanceState) {super.onCreate(savedInstanceState);ScrollView scrollView = new ScrollView(this);LinearLayout linearLayout = new LinearLayout(this);linearLayout.setOrientation(LinearLayout.VERTICAL);textView = new TextView(this);scrollView.addView(linearLayout);linearLayout.addView(textView);setContentView(scrollView);usbManager = (UsbManager) getSystemService(Context.USB_SERVICE);receiver = new BroadcastReceiver() {@Overridepublic void onReceive(Context context, Intent intent) {String action = intent.getAction();addText("action : " + action);if(intent.hasExtra(UsbManager.EXTRA_PERMISSION_GRANTED)) {boolean permissionGranted = intent.getBooleanExtra(UsbManager.EXTRA_PERMISSION_GRANTED, false);addText("permissionGranted : " + permissionGranted);}switch(action) {case UsbManager.ACTION_USB_ACCESSORY_ATTACHED:case UsbManager.ACTION_USB_ACCESSORY_DETACHED://Name of extra for ACTION_USB_ACCESSORY_ATTACHED and ACTION_USB_ACCESSORY_DETACHED broadcasts containing the UsbAccessory object for the accessory.UsbAccessory accessory = intent.getParcelableExtra(UsbManager.EXTRA_ACCESSORY);addText(accessory.toString());break;case UsbManager.ACTION_USB_DEVICE_ATTACHED:case UsbManager.ACTION_USB_DEVICE_DETACHED://Name of extra for ACTION_USB_DEVICE_ATTACHED and ACTION_USB_DEVICE_DETACHED broadcasts containing the UsbDevice object for the device.UsbDevice device = intent.getParcelableExtra(UsbManager.EXTRA_DEVICE);addText(device.toString());break;case MyUsbManager.ACTION_USB_STATE:/** <li> {@link #USB_CONNECTED} boolean indicating whether USB is connected or disconnected.* <li> {@link #USB_CONFIGURED} boolean indicating whether USB is configured.* currently zero if not configured, one for configured.* <li> {@link #USB_FUNCTION_ADB} boolean extra indicating whether the* adb function is enabled* <li> {@link #USB_FUNCTION_RNDIS} boolean extra indicating whether the* RNDIS ethernet function is enabled* <li> {@link #USB_FUNCTION_MTP} boolean extra indicating whether the* MTP function is enabled* <li> {@link #USB_FUNCTION_PTP} boolean extra indicating whether the* PTP function is enabled* <li> {@link #USB_FUNCTION_PTP} boolean extra indicating whether the* accessory function is enabled* <li> {@link #USB_FUNCTION_AUDIO_SOURCE} boolean extra indicating whether the* audio source function is enabled* <li> {@link #USB_FUNCTION_MIDI} boolean extra indicating whether the* MIDI function is enabled* </ul>*/boolean connected = intent.getBooleanExtra(MyUsbManager.USB_CONNECTED, false);addText("connected : " + connected);boolean configured = intent.getBooleanExtra(MyUsbManager.USB_CONFIGURED, false);addText("configured : " + configured);boolean function_adb = intent.getBooleanExtra(MyUsbManager.USB_FUNCTION_ADB, false);addText("function_adb : " + function_adb);boolean function_rndis = intent.getBooleanExtra(MyUsbManager.USB_FUNCTION_RNDIS, false);addText("function_rndis : " + function_rndis);boolean function_mtp = intent.getBooleanExtra(MyUsbManager.USB_FUNCTION_MTP, false);addText("function_mtp : " + function_mtp);boolean function_ptp = intent.getBooleanExtra(MyUsbManager.USB_FUNCTION_PTP, false);addText("usb_function_ptp : " + function_ptp);boolean function_audio_source = intent.getBooleanExtra(MyUsbManager.USB_FUNCTION_AUDIO_SOURCE, false);addText("function_audio_source : " + function_audio_source);boolean function_midi = intent.getBooleanExtra(MyUsbManager.USB_FUNCTION_MIDI, false);addText("function_midi : " + function_midi);break;}}};intentFilter = new IntentFilter();intentFilter.addAction(UsbManager.ACTION_USB_ACCESSORY_ATTACHED);intentFilter.addAction(UsbManager.ACTION_USB_ACCESSORY_DETACHED);intentFilter.addAction(UsbManager.ACTION_USB_DEVICE_ATTACHED);intentFilter.addAction(UsbManager.ACTION_USB_DEVICE_DETACHED);intentFilter.addAction(MyUsbManager.ACTION_USB_STATE);registerReceiver(receiver, intentFilter);boolean hasUsbHost = getPackageManager().hasSystemFeature(PackageManager.FEATURE_USB_HOST);boolean hasUsbAccessory = getPackageManager().hasSystemFeature(PackageManager.FEATURE_USB_ACCESSORY);addText("hasUsbHost : " + hasUsbHost);addText("hasUsbAccessory : " + hasUsbAccessory);}@Overrideprotected void onDestroy() {unregisterReceiver(receiver);super.onDestroy();}private void addText(String str) {textView.setText(textView.getText().toString() + str + "\n");}}
三、运行截图
四、ACTION_USB_DEVICE_ATTACHED 和 ACTION_USB_DEVICE_DETACHED的缺点
广播是去监测U盘插入和拔出的，也就意味着，你只要一插入或者一拔出U盘，就是收到这两个广播。它不会管你的设备有没有准备好，有没有mounted或者unmounted。
因此就需要引入一个新的广播 android.os.storage.extra.VOLUME_STATE。
这个广播就是用来监听Volume状态的。当外置Usb设备在Mounted或者UnMounted的时候则就可以用来做监听 int 类型的 VolumeInfo.EXTRA_VOLUME_STATE。
注意：android.os.storage.extra.VOLUME_STATE 一定要声明读写权限，否则是收不到的。
<uses-permission android:name="android.permission.READ_EXTERNAL_STORAGE" /><uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE" />
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