单页背景（单页背景怎么弄）
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2022-05-28
Android 通过广播监听USB连接状态的改变
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, *
- *
- {@link #USB_CONNECTED} boolean indicating whether USB is connected or disconnected. *
- {@link #USB_CONFIGURED} boolean indicating whether USB is configured. currently zero if not configured, one for configured. *
- {@link #USB_FUNCTION_ADB} boolean extra indicating whether the adb function is enabled *
- {@link #USB_FUNCTION_RNDIS} boolean extra indicating whether the RNDIS ethernet function is enabled *
- {@link #USB_FUNCTION_MTP} boolean extra indicating whether the MTP function is enabled *
- {@link #USB_FUNCTION_PTP} boolean extra indicating whether the PTP function is enabled *
- {@link #USB_FUNCTION_PTP} boolean extra indicating whether the accessory function is enabled *
- {@link #USB_FUNCTION_AUDIO_SOURCE} boolean extra indicating whether the audio source function is enabled *
- {@link #USB_FUNCTION_MIDI} boolean extra indicating whether the MIDI function is enabled *
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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; @Override protected 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() { @Override public 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: /* *
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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。
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Android API
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