Android Question How to detect the SD card or usb unmounted/mounted, and get the path

package com.example.usbtest;
import android.content.BroadcastReceiver;
import android.content.Context;
import android.content.Intent;
import android.content.IntentFilter;
import android.os.Message;
import android.util.Log;

public class UsbStatesReceiver extends BroadcastReceiver  {
    MainActivity execactivity;

    public static final int USB_STATE_MSG = 0x00020;
    public static final int USB_STATE_ON = 0x00021;
    public static final int USB_STATE_OFF = 0x00022;
    public IntentFilter filter = new IntentFilter();
 
    public UsbStatesReceiver(Context context){
        execactivity = (MainActivity)context;
        filter.addAction(Intent.ACTION_MEDIA_CHECKING);
        filter.addAction(Intent.ACTION_MEDIA_MOUNTED);
        filter.addAction(Intent.ACTION_MEDIA_EJECT);
        filter.addAction(Intent.ACTION_MEDIA_REMOVED);
        filter.addDataScheme("file");  
    }

    public Intent registerReceiver() {
        return execactivity.registerReceiver(this, filter);
    }

    public void unregisterReceiver() {
        execactivity.unregisterReceiver(this);
    }

    @Override
    public void onReceive(Context context, Intent intent) {
        // TODO Auto-generated method stub
        if(execactivity.mhandler == null){
            return;
        }
     
        Message msg = new Message();
       msg.what = USB_STATE_MSG;
       
       if( intent.getAction().equals(Intent.ACTION_MEDIA_MOUNTED ) ||
              intent.getAction().equals(Intent.ACTION_MEDIA_CHECKING)){
           msg.arg1 = USB_STATE_ON;
           msg.obj=intent.getData().getPath();
         
         
       }else{
           msg.arg1 = USB_STATE_OFF;
       }
       execactivity.mhandler.sendMessage(msg);

    };
 
}

package com.example.usbtest;

import android.os.Bundle;
import android.os.Handler;
import android.os.Message;
import android.app.Activity;
import android.view.Menu;
import android.widget.TextView;

public class MainActivity extends Activity {

    MyHandler mhandler;
    UsbStatesReceiver usbstates;
    TextView Usb;
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
     
        mhandler = new MyHandler();
        usbstates = new UsbStatesReceiver(this);
        Usb = (TextView)findViewById(R.id.usbstates);
    }

 
 
    @Override
    protected void onStart() {
        // TODO Auto-generated method stub
        super.onStart();
        usbstates.registerReceiver();
    }



    @Override
    protected void onStop() {
        // TODO Auto-generated method stub
        super.onStop();
        usbstates.unregisterReceiver();
    }



    @Override
    public boolean onCreateOptionsMenu(Menu menu) {
        // Inflate the menu; this adds items to the action bar if it is present.
        getMenuInflater().inflate(R.menu.activity_main, menu);
        return true;
    }

    class MyHandler extends Handler{
        public MyHandler(){};
     
        @Override
        public void handleMessage(Message msg) {

            super.handleMessage(msg);
            System.out.println("=============mainactivity handler");


            if(msg.arg1 == 0x00021)    Usb.setText("Usb is mounted"+msg.obj.toString());
            else if(msg.arg1 == 0x00022)  Usb.setText("Usb is out");
        }
    }
}