某些呼叫到来时，TelephonyManager.CALL_STATE_RINGING会多次呼叫

Question

public void onReceive(Context context, Intent intent) {
    TelephonyManager tm = (TelephonyManager) context
            .getSystemService(Context.TELEPHONY_SERVICE);
    tm.listen(new PhoneStateListener() {
        public void onCallStateChanged(int state, String incomingNumber) {
            super.onCallStateChanged(state, incomingNumber);
            if (TelephonyManager.CALL_STATE_RINGING == state) {
                // phone ringing
                Log.d("ervin", incomingNumber);
                phone = incomingNumber;

                StringBuilder sb = new StringBuilder();
                sb.append("phone").append("&").append("com.android.phone").append("&").append(phone);
                service.writeData(sb.toString());
            }else if(TelephonyManager.CALL_STATE_IDLE== state){ 
                StringBuilder sb = new StringBuilder();
                sb.append("endphone").append("&").append("com.android.phone").append("&").append(phone);
                service.writeData(sb.toString());
            }
        }
    }, PhoneStateListener.LISTEN_CALL_STATE); //listener
}

这是我的接收器代码收听来电和呼叫结束。 当呼叫到来时，TelephonyManager.CALL_STATE_RINGING将多次调用，而我的Log.d（）将多次打印。

我的问题是我怎样才能使TelephonyManager.CALL_STATE_RINGING状态在呼叫来电时调用一次