如何让android app等待通话结束？

import android.content.Context;
import android.telephony.PhoneStateListener;
import android.telephony.TelephonyManager;
import android.util.Log;

public class CallStateListener extends PhoneStateListener {
    private static final String TAG = "CallStateListener";
    private Context context;

    public CallStateListener(Context context) {
        this.context = context;
    }

    @Override
    public void onCallStateChanged(int state, String incomingNumber) {
        super.onCallStateChanged(state, incomingNumber);

        switch (state) {
            case TelephonyManager.CALL_STATE_IDLE:
                // 通话结束
                Log.d(TAG, "Call ended");
                // 执行其他操作
                break;
            case TelephonyManager.CALL_STATE_OFFHOOK:
                // 通话中
                Log.d(TAG, "Call in progress");
                break;
            case TelephonyManager.CALL_STATE_RINGING:
                // 有来电
                Log.d(TAG, "Incoming call");
                break;
        }
    }
}

TelephonyManager telephonyManager = (TelephonyManager) getSystemService(Context.TELEPHONY_SERVICE);
CallStateListener callStateListener = new CallStateListener(this);
telephonyManager.listen(callStateListener, PhoneStateListener.LISTEN_CALL_STATE);

// 启动通话
// ...