Android如何在程序中加入USB设备连接状态的检测

Android可以通过注册BroadcastReceiver来实现USB设备连接状态的检测。具体步骤如下：

1. 在AndroidManifest.xml中添加以下权限：

<uses-permission android:name="android.permission.USB_PERMISSION" />

2. 在Activity中注册BroadcastReceiver：

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) {
                UsbDevice device = (UsbDevice)intent.getParcelableExtra(UsbManager.EXTRA_DEVICE);

                if (intent.getBooleanExtra(UsbManager.EXTRA_PERMISSION_GRANTED, false)) {
                    if(device != null){
                        // USB设备已授权
                    }
                }
                else {
                    // USB设备未授权
                }
            }
        }
        else if (UsbManager.ACTION_USB_DEVICE_ATTACHED.equals(action)) {
            // USB设备已连接
        }
        else if (UsbManager.ACTION_USB_DEVICE_DETACHED.equals(action)) {
            // USB设备已断开
        }
    }
};

private void registerReceiver() {
    IntentFilter filter = new IntentFilter();
    filter.addAction(ACTION_USB_PERMISSION);
    filter.addAction(UsbManager.ACTION_USB_DEVICE_ATTACHED);
    filter.addAction(UsbManager.ACTION_USB_DEVICE_DETACHED);
    registerReceiver(mUsbReceiver, filter);
}

private void unregisterReceiver() {
    unregisterReceiver(mUsbReceiver);
}

3. 在Activity的onCreate方法中注册BroadcastReceiver：

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);

    registerReceiver();
}

4. 在Activity的onDestroy方法中取消注册BroadcastReceiver：

@Override
protected void onDestroy() {
    super.onDestroy();

    unregisterReceiver();
}

这样，在USB设备连接状态发生变化时，就会通过BroadcastReceiver接收到相关的广播，从而进行相应的处理。