【android系统问题】呼叫状态变化

测试。做一个Receiver监听手机通话状态。发现这样个问题。

package com.duduli.call;

import android.content.BroadcastReceiver;
import android.content.Context;
import android.content.Intent;
import android.content.pm.PackageStats;
import android.os.Bundle;
import android.telephony.PhoneStateListener;
import android.telephony.SmsManager;
import android.telephony.TelephonyManager;

public class CallComingReceiver extends BroadcastReceiver {
	
	@Override
	public void onReceive(Context context, Intent intent) {
		// TODO Auto-generated method stub
		TelephonyManager tm = (TelephonyManager) context.getSystemService(Context.TELEPHONY_SERVICE);
//		System.out.println("a");
		tm.listen(MyPhoneState.getInstance(), PhoneStateListener.LISTEN_CALL_STATE);
//		System.out.println("b");
		
//		
//		Bundle b = intent.getExtras();
//		String phoneNr= b.getString("incoming_number");
//		if(phoneNr != null){
//			System.out.println(phoneNr);
//		}
//		System.out.println(tm.getLine1Number());
		
	}

	
	
}

package com.duduli.call;

import android.telephony.PhoneStateListener;
import android.telephony.TelephonyManager;


public class MyPhoneState extends PhoneStateListener{
	private int last_state = TelephonyManager.CALL_STATE_IDLE;
	private MyPhoneState(){}
	private static MyPhoneState mps = null;
	public static MyPhoneState getInstance(){
		if(mps == null){
			mps = new MyPhoneState();
		}
		return mps;
	}
	
	@Override
	public void onCallStateChanged(int state, String incomingNumber) {
		// TODO Auto-generated method stub
//		super.onCallStateChanged(state, incomingNumber);
		
		
		switch (state) {
		case TelephonyManager.CALL_STATE_IDLE:
//			System.out.println("空闲时间");
//			System.out.println("CALL_STATE_IDLE");
			last_state = TelephonyManager.CALL_STATE_IDLE;
			break;
		case TelephonyManager.CALL_STATE_OFFHOOK:
//			System.out.println("CALL_STATE_OFFHOOK");
			break;
		case TelephonyManager.CALL_STATE_RINGING:
			if(last_state == TelephonyManager.CALL_STATE_IDLE){
				System.out.println("发送邮件0------？");
				last_state = TelephonyManager.CALL_STATE_RINGING;
			}
//			System.out.println("来电了");
//			System.out.println("CALL_STATE_RINGING");
			break;
		default:
			break;
		}
	}
	
}; 

不知怎么回事，我这边调试的结果，总会这样。
第一次呼入会出现一个“来电了”。
但是挂断之后就会出现两个“空闲时间”
再次呼入又会出现两个“来电了”
……以后的都是出现两次状态。
我都把实现都弄成了单例了还是出现问题，都不知道在哪里的问题。 

有没有大神给指点下。