<?xml version="1.0" encoding="utf-8"?>

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"

    android:layout_width="match_parent"

    android:layout_height="match_parent"

    android:gravity="center"

    android:orientation="vertical">

    <TextView

        android:id="@+id/msgTextView"

        android:layout_width="wrap_content"

        android:layout_height="wrap_content"

        android:text="Message Stub"

        android:textColor="@android:color/holo_red_light" />

    <Button

        android:id="@+id/retrievePrinterButton"

        android:layout_width="wrap_content"

        android:layout_height="wrap_content"

        android:text="检索打印机" />

    <Button

        android:id="@+id/requestPermissionButton"

        android:layout_width="wrap_content"

        android:layout_height="wrap_content"

        android:text="请求权限" />

</LinearLayout>

package com.raycloud.wolf.usbmanagertest;

import android.app.PendingIntent;

import android.content.BroadcastReceiver;

import android.content.Context;

import android.content.Intent;

import android.content.IntentFilter;

import android.hardware.usb.UsbConstants;

import android.hardware.usb.UsbDevice;

import android.hardware.usb.UsbManager;

import android.support.v7.app.AppCompatActivity;

import android.os.Bundle;

import android.view.View;

import android.widget.TextView;

import android.widget.Toast;

import java.util.HashMap;

import java.util.HashSet;

import java.util.Iterator;

public class MainActivity extends AppCompatActivity {

    private TextView msgTextView;

    private UsbManager usbManager;

    private HashSet<UsbDevice> printerSet = new HashSet();

    private BroadcastReceiver usbBroadcastReceiver = new BroadcastReceiver() {

        @Override

        public void onReceive(Context context, Intent intent) {

            String action = intent.getAction();

            if (action.equals(UsbManager.ACTION_USB_DEVICE_ATTACHED)) {

                Toast.makeText(context, "接入了一个USB设备", Toast.LENGTH_SHORT).show();

                retrievePrinter();

            } else if (action.equals(UsbManager.ACTION_USB_DEVICE_DETACHED)) {

                Toast.makeText(context, "移除了一个USB设备", Toast.LENGTH_SHORT).show();

                retrievePrinter();

            } else {

                if (intent.getBooleanExtra(UsbManager.EXTRA_PERMISSION_GRANTED, false))

                    Toast.makeText(context, "已授予打印机USB权限", Toast.LENGTH_SHORT).show();

                else

                    Toast.makeText(context, "未授予打印机USB权限", Toast.LENGTH_SHORT).show();

            }

        }

    };

    //    private final String tag = "MainActivity";

    private static final String ACTION_USB_PERMISSION_GRANTED = "com.raycloud.wolf.usbmanagertest.action.USB_PERMISSION_GRANTED";

    @Override

    protected void onCreate(Bundle savedInstanceState) {

        super.onCreate(savedInstanceState);

        setContentView(R.layout.activity_main);

        msgTextView = findViewById(R.id.msgTextView);

        findViewById(R.id.retrievePrinterButton).setOnClickListener(new View.OnClickListener() {

            @Override

            public void onClick(View v) {

                retrievePrinter();

            }

        });

        findViewById(R.id.requestPermissionButton).setOnClickListener(new View.OnClickListener() {

            @Override

            public void onClick(View v) {

                Iterator<UsbDevice> iterator = printerSet.iterator();

                while (iterator.hasNext()) {

                    UsbDevice usbDevice = iterator.next();

                    if (!usbManager.hasPermission(usbDevice))

                        usbManager.requestPermission(usbDevice, PendingIntent.getBroadcast(MainActivity.this, 0, new Intent(ACTION_USB_PERMISSION_GRANTED), 0));

                    Toast.makeText(MainActivity.this, "打印机已具备USB权限", Toast.LENGTH_SHORT).show();

                }

            }

        });

        usbManager = (UsbManager) getSystemService(USB_SERVICE);

        IntentFilter intentFilter = new IntentFilter();

        intentFilter.addAction(UsbManager.ACTION_USB_DEVICE_ATTACHED);

        intentFilter.addAction(UsbManager.ACTION_USB_DEVICE_DETACHED);

        intentFilter.addAction(ACTION_USB_PERMISSION_GRANTED);

        registerReceiver(usbBroadcastReceiver, intentFilter);

    }

    @Override

    protected void onDestroy() {

        super.onDestroy();

        unregisterReceiver(usbBroadcastReceiver);

    }

    private void retrievePrinter() {

        HashMap deviceList = usbManager.getDeviceList();

        Iterator<UsbDevice> iterator = deviceList.values().iterator();

        int numberOfPrinters = 0;

        while (iterator.hasNext()) {

            UsbDevice usbDevice = iterator.next();

            int interfaceCount = usbDevice.getInterfaceCount();

            for (int i = 0; i != interfaceCount; ++i) {

                if (usbDevice.getInterface(i).getInterfaceClass() == UsbConstants.USB_CLASS_PRINTER) {

                    ++numberOfPrinters;

                    printerSet.add(usbDevice);

                }

            }

        }

        msgTextView.setText(String.format("检索到%d台打印机", numberOfPrinters));

    }

}