activity_main.xml

MainActivity.java

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
     
       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
      
        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
       
         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));    }}