Android-Service抛出NullException

Question

我的代码是这样的：

public class BillingService extends Service implements ServiceConnection {
...
    @Override
    public void onStart(Intent intent, int startId) {
        handleCommand(intent, startId); // line 361
    }

    /**
     * The {@link BillingReceiver} sends messages to this service using intents.
     * Each intent has an action and some extra arguments specific to that action.
     * @param intent the intent containing one of the supported actions
     * @param startId an identifier for the invocation instance of this service
     */
    public void handleCommand(Intent intent, int startId) {
        String action = intent.getAction();
        if (Debug.Yes) {
            Log.i(TAG, "handleCommand() action: " + action);
        }
        if (Consts.ACTION_CONFIRM_NOTIFICATION.equals(action)) {
            String[] notifyIds = intent.getStringArrayExtra(Consts.NOTIFICATION_ID);
            confirmNotifications(startId, notifyIds);
        } else if (Consts.ACTION_GET_PURCHASE_INFORMATION.equals(action)) {
            String notifyId = intent.getStringExtra(Consts.NOTIFICATION_ID);
            getPurchaseInformation(startId, new String[] { notifyId });
        } else if (Consts.ACTION_PURCHASE_STATE_CHANGED.equals(action)) {
            String signedData = intent.getStringExtra(Consts.INAPP_SIGNED_DATA);
            String signature = intent.getStringExtra(Consts.INAPP_SIGNATURE);
            purchaseStateChanged(startId, signedData, signature);
        } else if (Consts.ACTION_RESPONSE_CODE.equals(action)) {
            long requestId = intent.getLongExtra(Consts.INAPP_REQUEST_ID, -1);
            int responseCodeIndex = intent.getIntExtra(Consts.INAPP_RESPONSE_CODE,
                    ResponseCode.RESULT_ERROR.ordinal());
            ResponseCode responseCode = ResponseCode.valueOf(responseCodeIndex);
            checkResponseCode(requestId, responseCode);
        }
    }

Answer 1

(1)程序崩溃在361行，也就是intent的参数是null。原因是这个intent参数是通过startService(Intent)方法所传递过来的，但是如果Service在你的进程退出后有可能被系统自动重启，这个时候intent就会是null。

(2)官方对参数intent参数的解释：The Intent supplied to startService(Intent), as given. This may be null if the service is being restarted after its process has gone away, and it had previously returned anything except START_STICKY_COMPATIBILITY.

(3)方法onStart()已经deprecated，在Android 2.0之后被onStartCommand所取代。onStartCommand为了backwards compatibility，默认实现是去call onStart方法，并且会在最后返回START_STICKY or START_STICKY_COMPATIBILITY.

（4）所以你可以选择使用标准的onStartCommand来操作.良好的编程习惯为自己的intent加上null check来避免NullPointerException。